Things did not go as planned - Newbie needs advice

[Im4Rights]

Hello 308AR gurus!

I am one of those AR-15 builders who thought he could just slap together a bunch of parts, and viola, I'd have a big brother for my AR-15s.  Of course, I found out the hard way that is not the case.  So, I've been looking over a lot of the info on this forum, and I think I've got my failure to cycle problem narrowed down.  "Project 1" was built and failed to cycle, so I thought I better seek some advice to fix "Project 1" before I finish "Project 2."  I appreciate any advice you may provide. On to the specifics.

Project 1 - AP M5 upper/lower - A2 stock with std spring and 5.3 oz rifle buffer - 24" SS Bull bbl (AP/ELD?), with rifle length gas system (tube = 15.125), .935 journal, and .072 gas port (per my digital caliper) - Dwell time = 11 3/16 by tape measure.

Symptoms:  Does not cycle, hard to extract by hand after firing, and carbon shadow not very well aligned with gas port.

Proposed actions:  From what I've read this gas port is too small (even if properly aligned), I think it needs to be .089ish.  I need to align the non-adjustable gas block better, and hand cycle the bolt several hundred times.  I'm also going to soak the BCG in Mobil 1 in my hot garage for a good long while.  Do I have that right?  Any other suggestions?

Project 2 - I want to start with proper gas port size before proceeding.  16" mid-length with 11.75" gas tube, .750 journal, .063 gas port, with 6 7/16 dwell time.  I'll be running a non-adjustable gas block, carbine buffer with std spring and 3.8 oz. buffer.  Any thoughts?

Many thanks,

--Tom

"The Second Protects the Rest!"

[dpete]

22 minutes ago, Im4Rights said:

Project 2 - I want to start with proper gas port size before proceeding.  16" mid-length with 11.75" gas tube, .750 journal, .063 gas port, with 6 7/16 dwell time.  I'll be running a non-adjustable gas block, carbine buffer with std spring and 3.8 oz. buffer.  Any thoughts?

Many thanks,

--Tom

"The Second Protects the Rest!"

ANY 308 AR needs a 5.3-5.4 oz buffer.   DO NOT put a 3.8 oz buffer in it, you are more than likely asking for issues later on. 

Get this:  https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201

It comes from Armalite and they make it correct every time, but right now shows as out of stock.  Find their phone # on their website and call them and talk to a real person.  They can usually hook you up with those parts no matter what the stock level says on the site.

[Im4Rights]

Thank you for the info.  I was shocked to see this buffer come out of an AP complete 308 lower purchased through Brownell's, but figured they know what they're doing.🤔

[dpete]

 

2 hours ago, Im4Rights said:

 but figured they know what they're doing.🤔

With 308 ARs even the best manufacturers....not so much.  Armalite is the original, everyone else does whatever they please with it.  There is no Mil-Spec in the 308.

[98Z5V]

9 hours ago, Im4Rights said:

Symptoms:  Does not cycle, hard to extract by hand after firing,

Project 2 - I want to start with proper gas port size before proceeding.  16" mid-length with 11.75" gas tube, .750 journal, .063 gas port, with 6 7/16 dwell time.  I'll be running a non-adjustable gas block, carbine buffer with std spring and 3.8 oz. buffer.  Any thoughts?

 

Did you use headspace gauges and check this chamber before firing it?  What ammo are you using?  Headspace check is the NUMBER ONE THING that needs to be done on any large-frame AR build.  Numero Uno.

Second statement - an 18" midlenth gas gun with your barrel specifics needs 0.080"~0.085" gas port diameter, and I recommend the 0.085" end of that spectrum, to make it function correctly.  That's WITH a proper recoil system.  For a 16" barrel, 2" less dwell time, you will need 0.090"~0.095"  - and I recommend the higher side of that range.  Start smaller, try 0.090".  Don't be surprised if it has to go up a little bit.  0.63" is nowhere close to what it needs to be, nowhere.

Fix your recoil system first.  Play with the barrel gas port later - or at the same time.  Start 0.090" after you have the correct recoil system parts installed.

[Im4Rights]

Thank you!  Re: headspace, I didn't use gauges. I removed firing pin, and it went into battery with the BCG lining up properly with the rear of the upper.  I will check with gauges before proceeding.

Test fire ammo was 150 Grain Soft Point Federal Power-Shok.  However, I want to make sure it will cycle mil-spec 7.62 NATO, so future tests will use that ammo.

So, two questions - 1. What port size do you recommend for the 24 in bbl?, and 2. What carbine recoil system do you recommend?

Again, many thanks!

[Im4Rights]

Thank you!  Re: headspace, I didn't use gauges. I removed firing pin, and it went into battery over a round with the BCG lining up properly with the rear of the upper.  I will check with gauges before proceeding.

Test fire ammo was 150 Grain Soft Point Federal Power-Shok.  However, I want to make sure it will cycle mil-spec 7.62 NATO, so future tests will use that ammo.

So, two questions - 1. What port size do you recommend for the 24 in bbl?, and 2. What carbine recoil system do you recommend?

Again, many thanks!

[jtallen83]

Welcome from Iowa!

The Armalite buffer kit is the best route, IMHO. As stated above, you need a 5.4ish oz buffer. I tend to use new Armalite or Tubbs flat wire springs just because I've never seen or heard of a problem with them. @98Z5V knows the math on those port sizes, I would guess you need to go up a bit  with the 24 inch but real curious to see what the math would say.

[Im4Rights]

Thank you!  I'll see what i can find.

[shooterrex]

If the web says out of stock call them.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201

[Rsquared]

Welcome aboard from Maryland.

I can't add to anything that hasn't already been pointed out, except to not run the soft points. AR's tend to not like them for the most part.

Like others have said. Go with the Armalite carbine buffer kit and just be done with it. It just works.

And I ain't saying that just cause I'm the Armalite guy.

[Im4Rights]

Armalite buffer kit on order along with Go/No Go set and variety of drill bits.  Stay tuned for updates on these two projects.

[Im4Rights]

Armalite buffer kit is scheduled to arrive tomorrow.  I conducted headspace check with Go/No-Go gauges on both projects and got the expected results.  Bolts closed on "Go" and did not close on "No-Go."  I opened up the gas port on the 24" bbl to 0.089 and the 16" bbl to 0.093.  After installing the buffer kit on the carbine project, I will take both rifles to the range to see if they run.  Stay tuned for results.  Thanks to all who have offered advise!

[98Z5V]

  Good work.

[Im4Rights]

Update -  I took Project 1 and Project 2 to the range yesterday.  Project 1 (24" barrel) improved a bit, but not enough to cycle rounds.  I have opened the gas port from 0.089" to 0.093".  If that doesn't do the trick, I'm wondering if the buffer spring might be too strong? Anyway, I'll give it another try and report back.  Project 2 (16" bbl) performed well as far as cycling, but neither project locked back with or without magazine. Both BCGs and buffer tubes are in alignment with no damage to the lower receivers at the buffer tube.  Not sure if this is a common problem among home builds, and  I'm not super concerned about locking back; hell, standard AK-47's don't lock back, so there's that.  I just want to make sure these guns go bang and shove another round in the chamber until there are no more rounds to feed.  Manually depressing the bolt catch does lock the bcg to the rear on both guns.  Regards, --Tom

[98Z5V]

55 minutes ago, Im4Rights said:

Manually depressing the bolt catch does lock the bcg to the rear on both guns.

This means the recoil systems clear, on both guns.

Go over the details again, each gun specifically, now in the thread.  Get the current infor on each gun, in it's on paragraph - list all the current specs and details, as well as what each one is doing.  Let's work on each gun individually. 

Recoil system details, complete, each gun.  Gas system complete, each gun - all info in a paragrah for each gun, both gas and recoil.  For gas system info, gas port diameter, gas block journal diameter, type of gas system (either midlentgth or rifle)l pic of each gas tube's protrusion into the upper receiver, in relation to the cam pin cutout in the upper receiver.

[Matt.Cross]

Obligatory "run it soaking wet in oil" post.

[Im4Rights]

@98Z5V has a good idea, I'm going to focus on one gun at a time.  Get Project 1 running right, then Project 2.  So, here are the details on Project 1.

Project 1 – Aero Precision M5 upper/lower - Leapers LR 308 A2 stock kit with 5.3 oz rifle buffer - 24" SS Bull bbl (AP/ELD?), with rifle length gas system (tube = 15.125), .935 journal, and .093 gas port (currently) - Dwell time = 11 3/16 by tape measure.

Current symptoms:  Does not lock back with or without magazine and does not strip and feed a new round from the magazine.  It ejects cartridges reliably.  The bcg can be locked to the rear manually, and does strip a round off the magazine when the bolt catch is released, or when charged with the charging handle. BCG was well lubed. The BCG and buffer tube are in alignment given no signs of damage at the receiver/buffer tube junction.

My analysis (for what it's worth):  Not enough gas to get the bcg far enough back to both eject the previous round and feed the new round.  Either the .093 gas port is still too small, or the buffer spring is too stiff (assuming 5.3 oz buffer is correct), or the gas block is misaligned.  Given, it seems more difficult to pull the charging handle back than it should be, I'm of the opinion the spring is too stiff.  I have ordered an Armalite rifle buffer spring and will try that with the current gas port size.  If that doesn't do the trick, then I'll go to 0.96 gas port size and try again.  I do not want to over-gas the gun and have it beat itself up, but it may be necessary to go larger.

Ammo used is PPU M80 NATO 145 gr pill @ 2835 fps per manufacturer.

A few pictures.  That's oil on the buffer.  Let me know if you need additional information

Your thoughts are most welcome and appreciated.

Thanks!

--Tom

[edgecrusher]

I think you’ll find round count will help here. These take quite a few to break in and properly run. 100 rounds or more, way more metal to mesh together and wear in. Think of bedding rings on a piston.

 

for what it’s worth, soft points can have some serious issues loading from a magazine in any AR. Big or small. Feed ramps do a number on them and they deform pretty badly. Manually load a round if you’re  using it for hunting to keep the projectile in tip top shape. ( with bolt locked back drop it in and release the bolt)

[Im4Rights]

👍

[Im4Rights]

Project 1 Update:  Amazingly, my analysis was correct, the spring was the problem.  After installing an Armalite rifle buffer spring, the rifle is now cycling like a champ and locking back on an empty mag (two different makes).  Interestingly, the Armalite spring was longer than the Leapers spring, but it was not as stiff.  The rifle is definitely "Minute of Deer" at 100 yards, but I wasn't really trying for group size, more trying to test cycling and lock back.  Eventually, my goal with this rifle is to hit a man-sized target consistently at 1000 yards, but a lot of practice needs to occur before I'll achieve that goal, if I'm even able to with my old eyes. 🤔  Here's a picture of the final product.  Again, thanks to all for your suggestions.  Now, on to Project 2.

Edited August 20, 2022 by Im4Rights

[98Z5V]

4 hours ago, Im4Rights said:

Project 1 Update:  Amazingly, my analysis was correct, the spring was the problem.  After installing an Armalite rifle buffer spring, the rifle is now cycling like a champ and locking back on an empty mag (two different makes).  Interestingly, the Armalite spring was longer than the Leapers spring, but it was not as stiff.  The rifle is definitely "Minute of Deer" at 100 yards, but I wasn't really trying for group size, more trying to test cycling and lock back.  Eventually, my goal with this rifle is to hit a man-sized target consistently at 1000 yards, but a lot of practice needs to occur before I'll achieve that goal, if I'm even able to with my old eyes. 🤔  Here's a picture of the final product.  Again, thanks to all for your suggestions.  Now, on to Project 2.

Great update, and well done on the gun.  Fine work. 

[Armed Eye Doc]

Ditto to what 98 said.  Nice job with researching the issue and fixing the problem.  Enjoy the rifle.  Stick around and give us updates on the 1000 yard quest.

[shooterrex]

Good to hear.

[Im4Rights]

19 hours ago, 98Z5V said:

Great update, and well done on the gun.  Fine work. 

Thank you!

17 hours ago, Armed Eye Doc said:

Ditto to what 98 said.  Nice job with researching the issue and fixing the problem.  Enjoy the rifle.  Stick around and give us updates on the 1000 yard quest.

Will do!

14 hours ago, shooterrex said:

Good to hear.

Amen!  I was worried there for a minute. 👍