Bolt not going back far enough to engage bolt face

Dan · May 9, 2019

Thanks for the information the correct measurements were as you said I will consult that chart I'm new to this sight seems to be pretty good thanks again

98Z5V · May 10, 2019

THE ARMALITE AR-10 CARBINE RECEIVER EXTENSIONS WILL BE 7 5/8" IN INTERNAL DEPTH, WITH ZERO VARIENCE. EVER. THAT NEVER CHANGES. IT'S NOT AN "AVERAGE" OR A "TOLERANCE."

Just thought I'd toss that out there. There is ZERO VARIENCE on an internal depth of a receiver extension on an AR-based rifle, no matter what the size. You're not working with "adjustable pushrods in a Harley" here.

*** That's not aimed at you Doc - that's aimed at the stupid comment above that stated:

Quote

That was the problem

you need the tube to be at least 7 3/4 to 8 inches I have a dons lower and a Omsk upper hope the fix will work for your set up

^^^ That statement is complete bullshiit, and a total fallacy.

Edited May 10, 2019 by 98Z5V

Armed Eye Doc · May 10, 2019

14 minutes ago, 98Z5V said:

That's not aimed at you Doc - that's aimed at the stupid comment above that stated

No issue, I went back to correct my post to avoid future confusion. That's what I get for posting that without verifying it first.

98Z5V · May 10, 2019

You're way good, Doc - WAY good. I'm going to address this right now, though, because I saw this bullshiit on another forum that I won't mention, from a guy that thought he was super-important on that forum, and thought he was a god on this platform ON that forum (because of the lack of knowledge on this platform, THERE, on that forum...)

On common AR platforms there are only THREE (3) receiver extension lengths, only. That does NOT COUNT Rock River Arms, and their LAR-8, and the previous Bushmaster BAR-10 that it was designed from. It does NOT include those guns - they are an anomoly - but a prevalent platform.

There are THREE (3) receiver extension lengths, period.

RIFLE RECEIVER EXTENSION = 9 11/16" internal depth. Period. There is no varience, there is no "give or take." It's fixed. People argue "A1 and A2!!!" They're fucking identical. Those that don't know that can research the differences between an A1 buttstock, and an A2 buttstock - and it's adaptors that are required to run that STOCK on the A1 rifle receiver extension - Yes, it's true - the difference it the buttstock and the adaptors required - NOT the extension. 9 11/16" internal depth, Rifle Receiver Extension. Period.

AR15 Carbine Receiver Extension = 7.000" internal depth. Done deal. There's a .gov TDP (Technical Data Package) on it. It's not a little short, or a little long. It's not 7.100" in internal depth. It's 7.000" internal depth. Armalite (original manufacturer of the system) actually lists it at 6 15/16" if I remember the data from @mrraley correctly. Maybe the TDP data was a fight with Armalite and Colt (previous holders of the TDP), but the truth is - that 1 /16" isn't affecting your AR15 Carbine at all.

Armalite AR-10 Carbine Receiver Extension = it's 7 5/8" internal depth, period. Nothing more, nothing less. It's not "between 7 3/4" and 8"..." That's bullshiit. It's 7 5/8" internal depth on the damn nose, every single time. There's no varience, or "tolerance" in that, in any way. It is designed at that internal depth in order to run a 3.250" buffer that weighs 5.4 oz, with a specific spring, to run a .308AR rifle.

VLTOR found a way to run THAT extension on the M16 for the US Marine Corps. They used the dimensions of the AR-10 Carbine Receiver Extension, with a "longer" AR15 Carbine Buffer (4.000" long) on a rifle-gas, 20" barreled M16A4, for the US Marine Corps. That made the 20" barreled M16A4 function properly, WITHOUT a rifle buttstock, and give the Marine Corps a collapsible buttstock for those rifles.

The internal depth on the VLTOR extension for that is exactly 7 5/8".

MagPul has come out with an extension, specifically listed for use with the KAC SR-25 and the KAC M110 - the don't list the internal depth, just the OAL on it, but the internal depth is 7 5/8". Period. It's this one:

https://www.magpul.com/products/magpul-enhanced-receiver-extension-sr25-m110

Anyone that wants to argue this logic can just bring it. You can't refute the proof, there's zero way to do that. You just cannot. If you want to argue that there's a "tolerance" or a "range" that the receiver extension can be manufactured to - you're wrong. There can be an OAL difference, but that doesn't matter. You cannot alter the internal depth of these receiver extensions, and have perfect function of them.

I've personally had, in my own hands, a PSA PA-10 Carbine receiver extension that measured 8.000" internal depth. In my own hands. There were serious impact marks in the ears of the lower receiver. That was @sketch's own gun... We stacked quarters to make that fucker run for the weekend, and not smash his hardware anymore than it was already smashed.

You cannot, in any way, make any varience whatsoever, to the receiver extension internal depth. It's one of three, and no more. it's 9 11/16", or 7.000", or 7 5/8". Done.

RRA, you guys come up with your own stuff - that Bushmaster developed on the BAR-10. You guys are identical to the BAR-10.

Off this thing now... :soap:

Edited May 10, 2019 by 98Z5V

Dan · May 10, 2019

I guess I started this by Not tieing it down to the exact measurement I just did a quick measurement wasn't trying to prove any one wrong or wright just a place to start looking. I worked with artillery and small arms for years in the manufacture and inspection. I know there are tight tolerances on these arms as there is a tolerance applied to all manufacturing whether it be in ten thousands of an inch or in inches i will be more exact on my measurements from this point so I don't confuse people who aren't familiar with weapons and manufacturing.I do appreciate your reply as I know you are correct.i wasn't trying to be stupid just trying to help I will be more precise on my comments in the future.

Armed Eye Doc · May 10, 2019

4 minutes ago, Dan said:

I guess I started this by Not tieing it down to the exact measurement I just did a quick measurement wasn't trying to prove any one wrong or wright just a place to start looking. I worked with artillery and small arms for years in the manufacture and inspection. I know there are tight tolerances on these arms as there is a tolerance applied to all manufacturing whether it be in ten thousands of an inch or in inches i will be more exact on my measurements from this point so I don't confuse people who aren't familiar with weapons and manufacturing.I do appreciate your reply as I know you are correct.i wasn't trying to be stupid just trying to help I will be more precise on my comments in the future.

You're good. There are many threads on here that have had this problem. Some refuse to believe that 1/16 " would make a difference. There are manufacturers that don't think it matters. This has only gotten worse since more companies make cheaper guns. The budget is frequently cut in R&D.

@98Z5V and others have spent the last 10 years diagnosing this. We try to correct the misinformation so it doesn't continue to spread. As you saw, I made a mistake in measurements when I answered your post and was corrected as well. We are all here to learn and share the knowledge that we have.

Armed Eye Doc · May 10, 2019

@Dan start up an intro thread so we can hear about making big explosions.

mrraley · May 10, 2019

:popcorn:

RJC · December 31, 2020

I have a 308 and a 6.5 creedmoor. Same thing happened when I put the 6.5 together. I had my 308 to compare and found the spring that was sent with the 308 was 3" shorter but same spring so I cut the 6.5 spring off 3" and gun works perfectly.

98Z5V · January 1, 2021

3 hours ago, RJC said:

I have a 308 and a 6.5 creedmoor. Same thing happened when I put the 6.5 together. I had my 308 to compare and found the spring that was sent with the 308 was 3" shorter but same spring so I cut the 6.5 spring off 3" and gun works perfectly.

That's an ass-backwards way of solving the issue. There's no possible way that what you did solved your issue, if your issue was the same as the OPs issue.

Please explain, and give details. Pics will be appreciated.

392heminut · January 1, 2021

Yup, cutting coils works for lowriders, not so much for guns!

Rsquared · January 1, 2021

6 hours ago, 98Z5V said:

That's an ass-backwards way of solving the issue. There's no possible way that what you did solved your issue, if your issue was the same as the OPs issue.

Please explain, and give details. Pics will be appreciated.

Maybe he has an engineering background.

Albroswift · January 1, 2021

@boostless

Easy way to confirm is assemble without spring, put an empty mag in, pull the CH back. If it locks, it's the spring. Also with spring out good time to make sure the BCG is not contacting the "ears" of the receiver. Had the same thing (too long spring) with a Tubbs in a 7" tube. I went to the point of compressing the spring 100% on a dowel and measuring, 1/2" longer then the tail of the 2-1/2" buffer. Was what I thought to be the correct spring for that application, apparently not. You will likely have some growing pains with the short tube on a large frame, but it will work with the right port/ spring/ buffer combo. I ended up with a Sprinco orange spring and a 5.6 oz buffer. Also running a Seekins AGB and gas port dia .078. Runs like a top.