SR-25 build - My first .308

[ninjajimmy]

So i got very lucky and scored a pre-ban Knights SR-25 receiver set yesterday. Trying to read up and learn all I can so I make the right decisions off the bat. After hours of research this is where i'm at.

 

Upper:
Barrel: 16" Rainier Arms Select Mid-length (DMPS pattern)
Gas Block: Troy Low-Profile .750 or CMMG Micro Gas block
Brake: AAC 51T Blackout 7.62
BCG: DMPS 308 (on sale at $190)
Rail: Knights rail 
Charging handle: stock Knights for now, BCM eventually


Lower:
Stock: B5 Sopmod or similar
Buffer tube: AR15 mil spec buffer tube
Buffer: CAR-10 from HeavyBuffers.com
Spring:308 Carbine spring from HeavyBuffers.com
LPK: Armalite AR10 LPK
Misc. KNS Non Rotating Pins

Grip: Magpul

 

Now I really wanted to replicate a SR-25 ECC. The problem is I can't find one manufacturer that makes a 16" barrel with a rifle length gas system. This would be used with a URX 3.1 SR-25 rail. Seeing as it looks like i'll need to go with a 16" mid length system the 3.1 rail just won't look right with the gas block hidden IMO. 

 

I was pretty set on a KAC rail, but i'm up for other suggestions as well. Looking for pretty long...12.5 to 14". I just don't know what will work on the KAC upper receiver.

 

Any ideas?

Edited June 25, 2014 by ninjajimmy

[blue109]

Fulton armory makes your barrel.

[edgecrusher]

Fulton armory sells a 16" rifle length ultralight profile barrel, you'll just have to contact them to find out when they expect it in.

Everything else looks good.... except stay away from any and all cmmg stuff. They just aren't consistent in their quality.

Unless you are a gambling man....

[ninjajimmy]

The only reason I was considering the CMMG gas block was it was labeled as fitting under the URX rails.  If I can get a rifle length 16" barrel I won't have to worry about that. I've emailed Fulton Armory about a 16" rifle length DPMS pattern barrel so now that's a waiting game. I don't want to order the rail until I can confirm the barrel, but the KAC rails are so hard to find in stock I might just have to.

 

Pic for the help :)

 

[FaRKle!]

Good to see you've found this place (I replied to your post on M4C).

What trigger are you planning on getting? I recommend that you pass on the KNS FCG pins. They're simply un-needed.

Unless you're a smaller dude (<5'5") I'm going to recommend you go with an AR-10 buffer system again. There's simply no good reason to go with the LR308 format with HeavyBuffer's CAR-10 if you're building from the ground up. Those LR308 heavy buffers were meant for people who already have a LR308 format rifle and either don't know how to, don't have the tools to, or don't want to pay somebody else to convert to AR-10 pattern. Plus, if you look at the prices of the Heavy Buffers' buffers, the 6.5oz CAR-10XH costs $125 while the 6.5oz HSS AR-15/AR-10 buffer is only $75.

The problem is I can't find one manufacturer that makes a 16" barrel with a rifle length gas system.

CMMG makes a 16" rifle-gassed .308 barrel. It's also melonited.

 

The only reason I was considering the CMMG gas block was it was labeled as fitting under the URX rails.

The URX 3.1 isn't picky. The Troy or other low-profile gas blocks will work just fine.

 

the KAC rails are so hard to find in stock I might just have to.

www.boltcarrier.com says they'll be getting the SR-25 URX 3.1 back in stock in a few days.

Edited June 25, 2014 by FaRKle!

[darb]

So i got very lucky and scored a pre-ban Knights SR-25 receiver set yesterday. Trying to read up and learn all I can so I make the right decisions off the bat. After hours of research this is where i'm at.

 

Upper:

Barrel: 16" Rainier Arms Select Mid-length (DMPS pattern)

Gas Block: Troy Low-Profile .750 or CMMG Micro Gas block

Brake: AAC 51T Blackout 7.62

BCG: DMPS 308 (on sale at $190)

Rail: Knights rail 

Charging handle: stock Knights for now, BCM eventually

Lower:

Stock: B5 Sopmod or similar

Buffer tube: AR15 mil spec buffer tube

Buffer: CAR-10 from HeavyBuffers.com

Spring:308 Carbine spring from HeavyBuffers.com

LPK: Armalite AR10 LPK

Misc. KNS Non Rotating Pins

Grip: Magpul

 

Now I really wanted to replicate a SR-25 ECC. The problem is I can't find one manufacturer that makes a 16" barrel with a rifle length gas system. This would be used with a URX 3.1 SR-25 rail. Seeing as it looks like i'll need to go with a 16" mid length system the 3.1 rail just won't look right with the gas block hidden IMO. 

 

I was pretty set on a KAC rail, but i'm up for other suggestions as well. Looking for pretty long...12.5 to 14". I just don't know what will work on the KAC upper receiver.

 

Any ideas?

You may consider going with an adjustable gas block as that will reduce recoil which helps stay on target and reduces wear and tear on your bcg,ship the kns pins not needed, IMO. Also you may want to consider a two stage trigger. I have a giessle ssa and gs2 they are very smooth. good luck with your build

[ninjajimmy]

Good to see you've found this place (I replied to your post on M4C).

What trigger are you planning on getting? I recommend that you pass on the KNS FCG pins. They're simply un-needed.

Unless you're a smaller dude (<5'5") I'm going to recommend you go with an AR-10 buffer system again. There's simply no good reason to go with the LR308 format with HeavyBuffer's CAR-10 if you're building from the ground up. Those LR308 heavy buffers were meant for people who already have a LR308 format rifle and either don't know how to, don't have the tools to, or don't want to pay somebody else to convert to AR-10 pattern. Plus, if you look at the prices of the Heavy Buffers' buffers, the 6.5oz CAR-10XH costs $125 while the 6.5oz HSS AR-15/AR-10 buffer is only $75.

CMMG makes a 16" rifle-gassed .308 barrel. It's also melonited.

 

The URX 3.1 isn't picky. The Troy or other low-profile gas blocks will work just fine.

 

www.boltcarrier.com says they'll be getting the SR-25 URX 3.1 back in stock in a few days.

 

Ok...buffer setup. You are saying go with:

 

HSS 6.5oz Buffer $75 on here:

http://www.heavybuffers.com/ar15carbine.html

 

VLTOR A5 buffer tube here:

http://www.bravocompanyusa.com/Vltor-A5-Receiver-Extension-Tube-p/vltor%20re-a5.htm

 

For springs, do I go with the Armalite Rifle 308 spring or the Wolf XP Rifle AR15 spring. Am I understanding correctly that the spring has to be a rifle length due to the slightly longer buffer tube? 

http://www.heavybuffers.com/springs.html

 

Will I still be able to use my standard SOPMOD or Magpul stocks from my AR15s with this setup? 

 

Gonna skip the KNS pins as recommended.

 

I just ordered the KAC URX 3.1 from Ayan as well as the KAC URX panel kit and a KAC Combat Trigger Guard. I'll have to send the upper assembly to him to install as i'm not dropping $300 on the URX wrench (even if I could find it). 

 

I'm holding out on the gas block till I decide on the barrel so I get the correct size. Any idea of which gas block size I need with the CMMG? I've heard bad things about the CMMG barrels. Is this still true? Hopefully Fulton gets the Criterion 16" rifle length barrel in and I can go with that. 

 

You may consider going with an adjustable gas block as that will reduce recoil which helps stay on target and reduces wear and tear on your bcg,ship the kns pins not needed, IMO. Also you may want to consider a two stage trigger. I have a giessle ssa and gs2 they are very smooth. good luck with your build

 

 

I'm grabbing the Armalite AR10 LPK kit. It's $95. For an extra $55 I can get the one with the two stage tactical trigger. Worth it or should I just go with the standard for now and grab a better trigger later on?

Edited June 26, 2014 by ninjajimmy

[FaRKle!]

Ok...buffer setup. You are saying go with:

 

HSS 6.5oz Buffer $75 on here:

http://www.heavybuffers.com/ar15carbine.html

 

VLTOR A5 buffer tube here:

http://www.bravocompanyusa.com/Vltor-A5-Receiver-Extension-Tube-p/vltor%20re-a5.htm

 

For springs, do I go with the Armalite Rifle 308 spring or the Wolf XP Rifle AR15 spring. Am I understanding correctly that the spring has to be a rifle length due to the slightly longer buffer tube? 

http://www.heavybuffers.com/springs.html

For buffers I'd start out with an H3 weight buffer. Damage Industries has them for $28 right now with 30% off code "SUMMER30". If you decide you want an even softer shooting gun after trying the H3 you can try Heavy Buffers' HSS (6.5oz) or PWS' H4 (6.9oz) buffers. Both cost less than the CAR-10 heavy buffer.

For the action spring you'll need the Armalite AR-10 spring. The nice thing about the AR-10 pattern is that the action spring is the same whether you use an A2 style stock or adjustable stock receiver extension. AR-15 action springs are not compatible with .308 ARs.

Will I still be able to use my standard SOPMOD or Magpul stocks from my AR15s with this setup?

With the 6-position VLTOR A5 receiver extension your SOPMOD stock will work just fine. Some Magpul stocks are large enough to close on the 7-position A5 receiver extension (STR, ACS, and ACS-L).

 

I just ordered the KAC URX 3.1 from Ayan as well as the KAC URX panel kit and a KAC Combat Trigger Guard. I'll have to send the upper assembly to him to install as i'm not dropping $300 on the URX wrench (even if I could find it).

Ayan is a great dude!

I'm holding out on the gas block till I decide on the barrel so I get the correct size. Any idea of which gas block size I need with the CMMG? I've heard bad things about the CMMG barrels. Is this still true? Hopefully Fulton gets the Criterion 16" rifle length barrel in and I can go with that.

That CMMG barrel has a .750" diameter. I haven't heard anything bad about CMMG's .308 barrels. I know Shibiwan has one.

 

 

I'm grabbing the Armalite AR10 LPK kit. It's $95. For an extra $55 I can get the one with the two stage tactical trigger. Worth it or should I just go with the standard for now and grab a better trigger later on?

We like Geissele around here ;). You can get a G2S for $132 at Exile Machine.

[Robocop1051]

Fukc CMMG and all the parts that come from their shop. They are cheap sweatshop parts with no QC.

[ninjajimmy]

For buffers I'd start out with an H3 weight buffer. Damage Industries has them for $28 right now with 30% off code "SUMMER30". If you decide you want an even softer shooting gun after trying the H3 you can try Heavy Buffers' HSS (6.5oz) or PWS' H4 (6.9oz) buffers. Both cost less than the CAR-10 heavy buffer.

For the action spring you'll need the Armalite AR-10 spring. The nice thing about the AR-10 pattern is that the action spring is the same whether you use an A2 style stock or adjustable stock receiver extension. AR-15 action springs are not compatible with .308 ARs.

With the 6-position VLTOR A5 receiver extension your SOPMOD stock will work just fine. Some Magpul stocks are large enough to close on the 7-position A5 receiver extension (STR, ACS, and ACS-L).

 

Ayan is a great dude!

That CMMG barrel has a .750" diameter. I haven't heard anything bad about CMMG's .308 barrels. I know Shibiwan has one.

 

We like Geissele around here ;). You can get a G2S for $132 at Exile Machine.

 

Dude, thanks for all the info. It's much appreciated. I just ordered:

 

Damage Industries H3 buffer

Armalite AR-10B LPK

Armalite EA1095 AR-10 Operating Spring

VLTOR RE-10 buffer tube

 

A Geissele will have to come later, once I actually get this running.

 

I'll have to do more research on the barrels (CMMG and Fulton). Definitely want to go with a rifle length 16" and options are very limited. I'd prefer the Fulton, but it depends on when I could get one.

Edited June 26, 2014 by ninjajimmy

[98Z5V]

I'll have to do more research on the barrels (CMMG and Fulton). Definitely want to go with a rifle length 16" and options are very limited. I'd prefer the Fulton, but it depends on when I could get one.

 

Don't overlook Rainier Arms. 

[shibiwan]

No complaints over my CMMG barrel. Still shooting better than I can. :D

 

That's a nice receiver set...hoping I can achieve that type/levelof quality on our own billet stuff.

Edited June 26, 2014 by shibiwan

[ninjajimmy]

I originally was going with a 16" Rainier Select barrel, but they don't offer it in a rifle length gas system. Black Hole Weaponry does an 18" rifle length barrel that would be fine if it came down to it, but it would be a 10-12 week wait according to their website. I'm trying to replicate this overall look with the 16" barrel. The more I think about it, the more I realize it would be just as cool with an 18" barrel as long as it's a rifle length gas system.

 

Edited June 26, 2014 by ninjajimmy

[FaRKle!]

That's a nice receiver set...hoping I can achieve that type/levelof quality on our own billet stuff.

Agreed. Half the reason I bought my MWS was so that it would be compatible with a Knight's upper in the future if I can get my hands on one!

[shibiwan]

Go 18"... or 20" IMO. Better overall dynamics from a barrel standpoint.

[ninjajimmy]

I'd be happy with 18"...any other brands with rifle length gas that you can think of?

 

On tacticalammunition.com I can customize the barrel and it works out to $265. Never heard of them though.

 

http://www.tacticalammunition.com/308-Win-Black-Hole-Weaponry-Rifle-Barrel-TA88-0373-TA88-0373.htm

Edited June 26, 2014 by ninjajimmy

[FaRKle!]

Go 18"... or 20" IMO. Better overall dynamics from a barrel standpoint.

I guess it depends on if he wants something than handles well (16") unsupported or a bench rest rifle (18" or 20"). I assumed the former since the ECC is what it's modeled after.

[ninjajimmy]

I'd prefer the 16" rifle length barrel as I like the overall look slightly more and it should handle better, but if I can't find a good one, an 18" rifle length will do.

[shibiwan]

I guess it depends on if he wants something than handles well (16") unsupported or a bench rest rifle (18" or 20"). I assumed the former since the ECC is what it's modeled after.

 

Just personal opinion. If I need the mobility, I'd be carrying something else, like a 300 BLK or a 5.56... I like my 18" 308 and I feel it's a good balance between something that can reach out a little farther and something that can handle well enough in tighter situations if need be. :D

[survivalshop]

Good to see you've found this place (I replied to your post on M4C).

What trigger are you planning on getting? I recommend that you pass on the KNS FCG pins. They're simply un-needed.

Unless you're a smaller dude (<5'5") I'm going to recommend you go with an AR-10 buffer system again. There's simply no good reason to go with the LR308 format with HeavyBuffer's CAR-10 if you're building from the ground up. Those LR308 heavy buffers were meant for people who already have a LR308 format rifle and either don't know how to, don't have the tools to, or don't want to pay somebody else to convert to AR-10 pattern. Plus, if you look at the prices of the Heavy Buffers' buffers, the 6.5oz CAR-10XH costs $125 while the 6.5oz HSS AR-15/AR-10 buffer is only $75.

CMMG makes a 16" rifle-gassed .308 barrel. It's also melonited.

 

The URX 3.1 isn't picky. The Troy or other low-profile gas blocks will work just fine.

 

www.boltcarrier.com says they'll be getting the SR-25 URX 3.1 back in stock in a few days.

 

  There is nothing wrong , IMO , with the STD DPMS buffer system , there has to be a tens of thousands of them out there working just fine, I have two builds with DPMS components  . Sure you can say this or that works better & some may clear up function problems , but there also may be more to it than just changing components.

  I see no scientific data on how the AR 10 buffer system is the best  , except some saying it is what you need for your rifle to work . We need to be careful on what some think is std for an 308 AR system to work properly .I have seen plenty of rifles that come in with this or that thats supposed to be the $hit & find that replacing said superior parts with STD operating parts , that they all of a sudden work flawlessly. 

  Not saying different parts won't work or are not better , but sometimes it is better to start out with components that were R&D'ed to work in that system & go from there. 

  If I'm making & selling something , I will be inclined to say my stuff is better than someone else's & it may be , but not for every system & may not be even needed.

 Seems a lot of people are looking for the softest feeling 308 AR they can put together . The problem there is you may end up causing function problems that would not be there if you would have just kept to the OEM parts. Its a freeking 308 & its going to have some recoil impulse.  

[edgecrusher]

Which isn't all that bad in the first place

[shibiwan]

Soft 308-AR? Even with an extra heavy buffer, mine leaves light shoulder bruising. Am I the only one?

Edited June 26, 2014 by shibiwan

[blue109]

I think he's just saying that if you are building from scratch, you can get a heavy AR10 buffer setup cheaper than a similar weight DPMS308 buffer setup.

I just use rifle length...so I win. ;)

[FaRKle!]

There is nothing wrong , IMO , with the STD DPMS buffer system , there has to be a tens of thousands of them out there working just fine, I have two builds with DPMS components  . Sure you can say this or that works better & some may clear up function problems , but there also may be more to it than just changing components.

  I see no scientific data on how the AR 10 buffer system is the best  , except some saying it is what you need for your rifle to work . We need to be careful on what some think is std for an 308 AR system to work properly .I have seen plenty of rifles that come in with this or that thats supposed to be the $hit & find that replacing said superior parts with STD operating parts , that they all of a sudden work flawlessly. 

  Not saying different parts won't work or are not better , but sometimes it is better to start out with components that were R&D'ed to work in that system & go from there. 

  If I'm making & selling something , I will be inclined to say my stuff is better than someone else's & it may be , but not for every system & may not be even needed.

The AR-10 system wasn't just whipped up out of thin air. Mr. Stoner worked with Knight's to fine tune the SR-25 into what he intended the platform to be. If you search around, you can find out Knight's results of testing LR308 vs AR-10 buffer systems. They did make SR-25 carbines at one point with an LR308 buffer system, but said that their testing showed reduced operating margin for the action spring, and thus stuck with the AR-10 pattern since the gun needs to work in the widest range of conditions.

I'm sure LMT also did their homework when testing the MWS buffer system for maximum reliability. It also uses the AR-10 pattern with H3 buffer. When the two most widely adopted AR-platform .308 rifles (SR-25 and MWS) by modern militaries worldwide use AR-10 buffer systems, that says something.

Edited June 26, 2014 by FaRKle!

[survivalshop]

The SR -25 uses a different spring  & buffer than the AR 10 , here's a comparison.

 

 

October 19, 1999

TECHNICAL NOTE 6: TECHNICAL INFORMATION CONCERNING AR-10B SERIES RIFLES

The purpose of this technical summary is to answer repeated questions concerning ArmaLite AR-10B series rifles, with an emphasis on differences between the AR-10B series, the M-16 series service rifle, and the SR-25 rifle produced by Knight's Armament Company (KAC).

GENERAL:  ArmaLite's priorities during development of the AR-10 were technical excellence first, and interchangeability with the KAC SR-25 and the M-16 following.  Because of the small number of early AR-10s produced between the late 1950s and early 1960s, no effort was made to maintain interchangeability with them, and no testing has yet been conducted to determine which parts interchange.

The design of the SR-25 emphasized interchangeability with the M-16 considerably more than ArmaLite has with the AR-10.  While both approaches are sound, the difference in priority has resulted in a number of technical advantages in the ArmaLite AR10 design.

For brevity, the new ArmaLite rifles are collectively referred to as AR-10s.  Four models of the AR-10B series exist:

AR-10B:  The base model of the new ArmaLite line.  It is patterned after early 1960 era rifles, and is produced largely for nostalgic reasons.  The charging handle looks like an upside down trigger and is located at the front of the carrying handle.  It special brown furniture and a rear sight elevation window at the rear of the carry handle.

AR-10A2; virtually identical to the M16A2 service rifle, but caliber .308.

AR-l0A4:  A flexible combination of the AR-10A2 and the AR-10(T).  It is generally identical to the AR-10A2 except that the upper receiver and gas block are manufactured with the “Picatinny Rail” sight mounting surfaces of the AR-10(T).  Removable iron or telescopic sights are optional.

AR-10(T); target model featuring a 24 inch long, medium weight target barrel, tubular handguard, match trigger, and Picatinny Rail receiver and gas block. 

Each rifle is matched by a similar carbine: virtually identical save for a 16 inch long barrel.  The T carbine is equipped with a standard trigger rather than the match trigger of the AR-10(T) rifle.

BUTTSTOCK:  M-16A2 type shell.  A rounded buttplate is used to reduce sharp, uncomfortable edges.  A thicker, nylon trap door is used provide protruding checkering for good grip.  ArmaLite's feature olive green furniture (stocks, grips, and handguards) as a standard feature. Black furniture is available as an option.

BUFFER:  Similar to that of the M16 rifle, but dimensioned for the AR-10.  It is of aluminum construction containing the same weights and buffer disks used in the M-16.  The KMC buffer is a simple turned nylon plug.  The purpose of the weights is to reduce elastic rebound of the carrier from the barrel extension.

OPERATING SPRING:  32 coil 17-7 stainless steel versus the KMC 40 coil spring.  The shorter spring reduces slamming of the bolt carrier against the barrel extension.  The ArmaLite buffer places a slight preload on the spring, reducing the need for the longer spring.  The ArmaLite spring and buffer are usable in the KMC SR25.

UPPER RECEIVER:  Three versions are built: the AR-l0A4 version topped off with a Picatinny Rail (Weaver style) sight mounting surface, the AR-l0A2 version bearing an integral carrying handle, and a slightly modified AR-10A2 version made for the trigger-style charging handle of the AR-10B. ArmaLite produces a removable front sight and removable carrying handle for use on the Picatinny Rail surfaces. 

ArmaLite upper receivers are forged rather than extruded or cast, and include an integral case deflector.  ArmaLite’s uppers are available for the KMC Lower Receivers.  KMC use of an extrusion instead of a forging requires a flat-sided receiver form; the core of the ArmaLite upper receiver is generally cylindrical, and quite similar to that of the M-16.  No Forward Assist is provided.   It is not considered necessary given the more powerful operating spring used.

BARREL NUT:  Two barrel nuts are used on the ArmaLite rifles: a simple ring style on the target models, and a rather more complicated nut for the -A2 and -A4 models that adapts standard M16 handguards to the AR-10. 

The relatively complex -A2 barrel nut was designed to allow a spring loaded slip ring to be used to hold standard rifle handguards. This system is preferable to the early jam nut style handguard ring used on 1960 era AR-10s and on current SR-25s because the jam nut system loosen rapidly as the barrel expands during firing.   ArmaLite abandoned jam nut type handguard rings early in the AR-15 program.

The AR-10(T) barrel nut is a ring that bears internal threads matching those of the upper receiver, and an external diameter matched to the bushing of the handguard.  Because of the need to raise the gas tube, the gas tube holes of the ArmaLite nut are .010 farther from the boreline than those of the KMC part, but they remain interchangeable.

CARRIER:  The AR-10B carrier is virtually identical to that of the SR-25.  It is externally phosphated instead of chrome plated as with the SR-25, but is chrome plated in the gas expansion chamber like the carrier of the M-16.  The carrier key surface is .010 inch farther from the boreline than that of the KMC carrier, and .030 further to the rear for better gas transfer into the carrier.   Like the KMC carrier, the ArmaLite carrier will not allow a standard width hammer to enter the ArmaLite Carrier Assembly.  Initial testing has shown that the carrier and bolt group is interchangeable with the KMC components.

FIRING PIN:  Similar to the KMC firing pin, but with several key improvements.  The firing pin tip bears a short cylindrical surface just behind the tip.  This allows the bolt to have a cylindrical section just behind the bolt face, reducing the possibility of sheared primer material jamming into the opening.  The KMC firing Pin and Bolt have tapered surfaces at this point.

The ArmaLite firing pin has a single flange, and a cylindrical section before it that mounts a firing pin spring.  The firing pin spring greatly reduces the light firing pin strike produced in M-16 type rifles when the bolt locks, and thus reduces the possibility of slam fire.  In addition, it positively prevents incorrect assembly of the bolt carrier assembly.  The KMC firing pin has two flanges which makes it possible to install the firing pin retainer in front of the second flange: the carrier assembly appears correctly assembled but the firing pin cannot strike the primer.

BOLT:  The Bolt is similar to that of the KMC model.  Like the KMC bolt, it bears tapered lugs with increased root width for added strength. Six locking and one Safety Lug (patent pending) are used.  This system provides greater strength than the seven conventional locking lugs of M16 type bolts.   The firing pin hole has been reduced in diameter to prevent primer material from extruding into the firing pin hole if cartridge pressures are high or if primer material is soft.

GAS RING:  A single three-turn McFarland gas ring is employed rather than the three piston rings of the early AR-10s and the SR-25.   This construction cannot suffer reduced gas energy due to alignment of the splits of the conventional rings.  The McFarland ring functions perfectly on the SR-25 bolt.

EXTRACTOR:  The extractor is patterned after that of the prototype ArmaLite AR-16 rifle.  It doesn’t interchange with either early AR-10 or SR-25 extractors.

EJECTION PORT COVER:  Generally identical to that of the M-16, but a half-inch longer to accommodate the 7.62mm cartridge.

EJECTION PORT COVER SPRING:  Due to the close fit of the ejection port cover to the upper receiver, insufficient space was available to accept a standard M-16 ejection port cover spring.  In addition, the wider ejection port would result in the short leg of the standard spring protruding into the ejection port, and could injure the fingers of a firer hand loading or clearing a cartridge or case.  A special spring was designed which fit the existing reinforcement ribs of the ejection port cover to solve the clearance problem, and with a shorter leg to prevent injury to the shooter.

GAS BLOCK:  Steel, bearing a short segment of Picatinny Rail mounting surface for sights or other accessories.  It may be loosened to zero the removable sights.  It is one, cross-slot longer than the KMC gas block to allow more secure attachment of hardware.

GAS TUBE:  .240 Longer than the M-16 gas tube used by KMC to allow use of standard handguards and the spring loaded slip ring of the AR-10A2 and -A4 (see above).

BARREL:  The AR-10(T) barrel is produced from a match grade, stainless steel barrel blank.  The standard AR-lOA2 and -A4 barrels are button rifled and chrome lined, with stainless barrels available as an option.   Target barrels are 24 inches long; standard barrels are 20 inches long.   Carbine length barrels are 16 inches long.  Replacement of the barrel requires special tools, and should be performed only by ArmaLite personnel or a qualified gunsmith.

RECOIL CHECK:  The AR-lOA2, A4, B, and all carbines, bear a three slot recoil check on the muzzle.  The recoil check is threaded and pinned into place, and the end of the pin is welded to the check to prevent its removal.

HANDGUARD:  The AR-10(T) employs a tubular fiberglass handguard assembly.  The A2 and A4 versions accept either M16Al or M16A2 style handguards. 

The AR-10(T) handguard is constructed differently from the KMC version.  The handguard-locating stud is pressed into a recess in the handguard bushing rather than riveted to the tube through the bushing. Instead of a bare fiberglass end, the ArmaLite handguard terminates in an aluminum sleeve that protects the fiberglass, reinforces it, and provides a mounting point for the sling swivel.

LOWER RECEIVER:  The AR-10 lower receiver follows the familiar lines of the M16 much more than that of the SR-25.  The longer ArmaLite magazine catch button need not be mounted in a depression in the side of the receiver as is the M16 button used in the SR-25.  The AR-10B button can be operated without removing the hand from the grip.  The familiar fence protecting the M-16 magazine catch from accidental actuation has been built into the AR-10B. 

The AR-10B series Lower Receiver is not interchangeable with either the SR-25 receiver or those of the first generation AR-10 or AR-10A. ArmaLite Lower Receivers are NEVER sold separately.  All ArmaLite rifles are factory built.

TRIGGER MECHANISM: The AR-10(T) employs the ArmaLite two-stage match trigger as standard.  The B, 'A2, and 'A4 models employ the single stage trigger assemblies, but may be fitted with the two stage trigger mechanism as an option.

BOLT CATCH:  The SR-25 employs the M-16 bolt catch.  This device was designed to stop the small M-16 bolt carrier assembly, not heavier AR-10 bolt carrier assembly.  The AR-10 bolt catch is larger and stronger than that of the M-16/SR-25 to function with the heavier AR-10 components. It is designed to automatically catch the bolt when pressed upward by the bolt catch trip in the follower.

MAGAZINE CATCH BUTTON:  Identical to that of the M-16, except that it is somewhat longer to allow it to protrude from the side of the wide AR-10 lower receiver.

MAGAZINE CATCH:  An improved, machined catch with a longer engaging surface to capture the magazine better, elimination of a bevel to prevent excess upward movement of the magazine, and a longer shaft to span the wider receiver.

MAGAZINE:  The AR-10 magazine is based on the magazine of the M14 Rifle.  The M-14 magazine is well proven and available in large numbers.  It is both stronger and more reliable than that of early AR-10 and similar magazines.  It is made in 10 round capacity. 

The AR-10B magazine does not bear a latch plate on the rear surface like that of the M-14 magazine.  The lower receiver, however, has a clearance cut up the back of the magazine well to allow insertion of an M-14 magazine.  A 20 round M-14 magazine can therefore be modified to function perfectly in the AR-10.  This modification requires changes to the feed lips cutting a magazine catch opening cutting a slot down the back of the magazine replacement of the follower with a new follower addition of a bolt catch trip and spring a slight change in the follower spring.

The most unique aspect of the ArmaLite magazine is the follower.   A top surface similar to that of the M16 magazine has been combined with a form suited to the M-14 magazine box.  A patented spring-loaded plunger has been installed in the follower.  When the follower rises to the top of the magazine box, this plunger pops into the track at the rear of the magazine well and trips the bolt catch, thus holding the bolt carrier assembly to the rear.

The magazine will continue to function in the M-14 rifle, but will not trip the M-14 bolt catch unless the AR-10 follower is replaced with the M-14 follower.   The latch plate at the rear of the magazine (which engages the M-14 magazine catch) may be sufficiently weakened by removal of its upper half that it breaks off, rendering the magazine usable only in the AR-10.

USING M-14 RIFLE MAGAZINES:  The AR-10B magazine is based on the proven M-14/MlA rifle magazine.  A good quality metal 20 round M-14/MlA magazine can be altered to work perfectly in the AR-10B. U.S. GI and imported Chinese magazines are acceptable.  Commercial metal magazines with blue finish or pressed latch plates require replacement of the shell.  Fiberglass magazines (i.e. Thermold, etc.) are totally unsuitable for conversion.

ArmaLite sells 20 round magazines when available.  ArmaLite will provide converted magazines for a fee or on a 2-for-1-exchange basis. Magazine conversion kits allow a customer to convert all metal M14/M1A magazines and metric FAL magazines to AR-10B series magazines.

MAGAZINE INTERCHANGEABILITY:  10 round AR-10B magazines and converted 20 round M-14 magazines will not work in early AR-10/AR-10A rifles, or in the current SR-25 rifle.  Magazines for those rifles will not work in the new AR-10B series rifles.  Unless converted with the reversible magazine conversion kit, M-14/M1A magazines should not be used in the M-14 or M1A after modification.