Buffer Tube dimensions - Short Stroke

[gsmopar]

While researching my short stroking problem, I stumbled upon these videos. 

http://www.youtube.com/watch?v=ygdiqV5ppkw

http://www.youtube.com/watch?v=W8i_lXMhgV0

http://www.youtube.com/watch?v=HW2Hs8MmqpY

 

Questions:

1.  What is the correct internal depth dimension for a Carbine LR308 tube?  Mine is a little over 6.75 inches. 

2.  How much (estimate) room do you have between the bolt face and bolt catch with the charging handle pulled all the way back?  I would have to use a feeler gauge to measure mine as it appears to be minimal.

 

 

[shibiwan]

That looks like a standard carbine tube. You should be using an LR308-Carbine length buffer+spring. The 308 buffers are shorter than the regular length AR15 carbine buffers.

 

Does the bolt lock back properly on an empty mag?

[gsmopar]

I'm using a Heavy Buffer CAR-10 with spring, and no the bolt doesn't lock back.

[shibiwan]

Looks like something isn't right. Have you tried to pull the bolt all the way back without the buffer spring - just to verify that it isn't the spring that is binding.

[gsmopar]

I'll go try that now.  Give me a second.

[gsmopar]

With the spring removed, I have between 1/16 an 1/18 inch between the bolt face and bolt catch. 

 

edit:  I meant between 1/16 and 1/32

Edited February 2, 2014 by gsmopar

[shibiwan]

2-4mm (1/16"-5/32") is about normal. It's likely the spring then. It's binding when the buffer is fully compressed. Gotta go get one that has less coils.... You could clip 1-2 complete coils from the rear end of the spring to see if it helps.

Edited February 2, 2014 by shibiwan

[98Z5V]

Internal depth on the receiver extension should be 7", unless it's an Armalite AR-10 carbine receiver extension.  The AR-15 stuff is all 7" internal depth.

 

Get another receiver extension, brother.  That one's too short. <thumbsup>

[washguy]

What 98Z sez :) Wash

[survivalshop]

Is the receiver extension a Commercial or Milspec ? 

 

Have you tried a DPMS 308 carbine spring ?

Edited February 3, 2014 by survivalshop

[gsmopar]

Is the receiver extension a Commercial or Milspec ? 

 

Have you tried a DPMS 308 carbine spring ?

 

Commercial and yes on the DPMS spring.  The DPMS is actually longer than the Heavybuffer spring. 

 

How much space do some of your rifles have from the bolt face to the bolt catch with the charging handle pulled all the way back.  I'm tempted to run by a gun store today and look at some other guns.  I have no where near as much space as the guy in the videos in the 1st post. 

[survivalshop]

I have two receiver extensions in front of me , one was supposed to be a Milspec , it has the correct out side diameter of 1.15" but has the slant at the back like a Commercial extension & its showing  6 15/16" where the buffer retaining pin sits.

The other Commercial one is exactly 7" inside depth & it has the Commercial out side diameter of 1.17" . You may well have a bad or out of spec extension .

The Milspec one I have, worked with out any problems, yours seems a little short & that will definitely cause problems.

 

My DPMS 308 Carbine spring is 11 1/4 " long & has 29 coils in it . 

Edited February 3, 2014 by survivalshop

[washguy]

Hi GSM I just checked a couple of my 308 car's....while holding the charging handle back ive got about a 1/4 inch between bolt face and catch. your tube is too short..or you got the wrong spring.buffer in there. The only screwup ive ever had was a 6.8 that wouldnt cycle correctly....after rebuilding and swapping parts....it came down to an out of spec cheapie buffer tube that wasnt machined correctly on the inside ....drove me crazy for a bit :) Wash

Edited February 3, 2014 by washguy

[gsmopar]

Thanks guys!

 

I checked the stock buffer next to my Heavybuffer and the Heavybuffer is longer. 

• Heavybuffer:  Shorter spring, longer buffer
• DPMS:  Short Buffer, longer spring

If I use the Heavybuffer Spring with the DPMS Buffer I have about 1/4 inch between the bolt face and bolt catch.  I'm thinking about trying this combo to see if it fixes my cycling issues.  If it works I'll replace the tube and probably look at one of the nicer butt stocks that comes with a tube.  Thoughts?

• Heavybuffer and Heavybuffer Spring = Short Stoke
• DPMS Buffer and DPMS Spring = Short Stroke
• Heavybuffer Spring and DPMS Buffer = ?

Heavy Buffer with no spring:

Edited February 3, 2014 by gsmopar

[shibiwan]

Are you sure you got the correct heavybuffer buffer? There are two lengths - standard CAR and DPMS-LR308 CAR length

[gsmopar]

Are you sure you got the correct heavybuffer buffer? There are two lengths - standard CAR and DPMS-LR308 CAR length

 

I would have the wrong one then.  Where on the site do you see the DPMS?  I only see 2 for the 308:  http://heavybuffers.com/ar10carbine.html

 

 

A CAR-10 buffer will allow you to use any AR15 collapsing stock (Magpul/LMT/VLTOR/Ace/etc) on your AR10, SR25, LMT, POF or DPMS-pattern .308 rifle. Standard carbine length stocks cannot be used on these rifles with regular carbine buffers. This is strictly a 'Drop-In' part, no gunsmithing or modifications are required.

 

His table lists the one I have for DPMS:

 

Edited February 3, 2014 by gsmopar

[gsmopar]

PS:  I stayed home from work today (sick).  I don't want you guys thinking that I actually spend all day on the internet on a regular basis.  Funny how I feel like crap and didn't go to work, but I'm considering heading up the street to the range to see if my rifle will cycle.  >:D

[washguy]

So are you using slash's modified spring with his buffer like it sez in the chart? :) Wash

[gsmopar]

So are you using slash's modified spring with his buffer like it sez in the chart? :) Wash

 

Yes.  His spring and buffer, but I think the real problem is my tube. 

 

This is the Tube:  http://www.midwayusa.com/product/238414/dpms-buttstock-assembly-6-position-collapsible-lr-308-carbine-synthetic-black

Edited February 3, 2014 by gsmopar

[survivalshop]

That should be the right one. Could be just a bad part (receiver extension )

 

How long is the Slash spring & how long is the other DPMS spring ?

[gsmopar]

That should be the right one. Could be just a bad part (receiver extension )

 

How long is the Slash spring & how long is the other DPMS spring ?

 

 

DPMS:

  Spring = 11 1/4, 29 coils

  Buffer = 2 1/2

Heavybuffers:

    Spring = 10 1/2, 28 coils

    Buffer =  2 9/16

[98Z5V]

GS, in relation to bolt travel, and how much of a gap you should have between the bolt face and bolt stop - there's no set in stone dimension for that, but there are some practical answers/info on it.

 

Take a look at the blowback-operated pistol calibers, when running through the AR platform -  there are special, longer buffers out there to limit the bcg/bolt travel.  Blowbacks have so much bolt travel that they'll break bolt stops - too much over travel.  That's the reason for the longer buffers - limit bcg travel in order to prevent broken parts.

 

In a nutshell - the less overtravel you have, the easier it is on parts.  As long as it travels enough to lock the bolt back.  The more overtravel, the harder it's gonna be on parts.  Doesn't necessarily mean you'll start snapping parts, but the parts in your rifle will suffer from fatigue or breakage long before an identical rifle with less bolt travel - this "assumes" that both rifles function fine, too.

 

P.S.  On a blowback pistol cal AR, if you don't run the special longer buffers, stack $1.75 in quarters inside the back of the receiver extension before you put the spring in there.  That stacked thickness is the equivalent distance of overtravel that the pistol cal blowbacks have.

[washguy]

Like I said before...you can have a mismachined tube....try that spring buffer combo that gives you some space just to see if it locks back on a single round. :) Wash