Mid length build problems

[bubbas4570]

So my youngest decided to put together an AR15,  and we are having some (anticipated) operating problems.

When we put the parts into the lower, I just had him use the whole buffer assembly from my 308AR carbine that was in the parts bin. Now it will cycle on first shot, strip next round in magazine,  but only put a small indent on the primer (second round). The bolt seems to be all the way forward and locked in to battery, but I am thinking there is something wrong with the buffer weight and timing of the system.

Parts list:

PSA 16 " mid length upper w/bolt

Aero stripped lower

APF 308AR carbine buttstock/buffer assembly

mixed stuff for lower internals

 

Here is some more information to help or muddy the situation....his mid length upper works fine on my A2 rifle buffer lower, and my rifle length gas system works fine on his carbine lower.

I am leaning towards getting a correct AR15 carbine buffer weight and spring and running that in his mid length.....that should fix the problem?

Or am I missing something completely off of what I am looking at here?

[bubbas4570]

And I just thought of something, with an extremely tight hold into the shoulder pocket, it did work for a couple of rounds, then I relaxed slightly and malfunction immediately.

[Robocop1051]

Get more weight in the buffer, and/or a better spring. 

[bubbas4570]

I would have thought that a 308AR buffer would be heavier than an 223.....

[Robocop1051]

1 hour ago, bubbas4570 said:

I would have thought that a 308AR buffer would be heavier than an 223.....

Kinda. The .308 buffer is normally the same weight as an AR-15 H3 buffer, at about 5.4oz

My personal buffer is 10oz tungsten. 

I also suggest using the Armalite AR-10 specific buffer spring, or CS Flat Wire spring. The former being slightly less expensive than he latter. 

[Robocop1051]

Give that BCG a good soak in some decent lube too. 

[Robocop1051]

i don’t know APF either... so I can’t give you a review of heir quality. 

Personally, I’d go with the Vltor A5 receiver extension (buffer tube) and either a Slash tungsten buffer and CS spring or a JP SCS system. 

The .308 is an amazing beast. If you’re willing to throw $$$ at it, the issues dissolve rapidly. Lol

[bubbas4570]

Robo.....

It is just the little brother that we built...223 not 308, I just used a 308 buffer system in the 223.

[bubbas4570]

I have had zero problems with my APF  stuff, they were a DPMS supplier for years before they went their own way.

 

And the one time I tried a heavy buffer, it made things worse for me.

[washguy]

Bubba    The ar15 and ar308's buffer system are not interchangeable......the only common part on a ar15 and ar 308 is the buffer tube....you need an ar15 spring and ar15 buffer...both the spring and buffer in the 308 is totally different from an ar15

"I just had him use the whole buffer assembly from my 308AR carbine that was in the parts bin"   that wont work        Wash

[bubbas4570]

Wash, figured that was our problem....hence the "anticipated" part of the opening statement of my post.

And guys.....yup I did learn sumpin from hanging out here....the bolt was dripping wet with Weapon Shield CLP before the test run.  It was not a NIB upper, and I think the previous owner had problems......bolt was a dry as a popcorn fart when the kid brought it home. I didn't say anything, but made sure there was copiuos amounts of love juice in there when testing. Bolt carrier showed wear marks from being run dry by previous owner.....more wear than should be for only "100 or so" rounds through it....and dry to boot, no lube on fingers hardly when taking it apart at first.

[98Z5V]

7 hours ago, bubbas4570 said:

Robo.....

It is just the little brother that we built...223 not 308, I just used a 308 buffer system in the 223.

 

6 hours ago, washguy said:

Bubba    The ar15 and ar308's buffer system are not interchangeable.....

He caught it. 

I saw that in your first post, but the answer is already there. 

 

Quote

So my youngest decided to put together an AR15,  and we are having some (anticipated) operating problems.

When we put the parts into the lower, I just had him use the whole buffer assembly from my 308AR carbine that was in the parts bin.

Edited October 8, 2017 by 98Z5V
pic

[98Z5V]

Check the back of your lower receiver - the 5.56 BCG body hit the lower receiver upon recoil, because the buffer was too short.  There will be signs of the hit. 

[bubbas4570]

12 minutes ago, 98Z5V said:

Check the back of your lower receiver - the 5.56 BCG body hit the lower receiver upon recoil, because the buffer was too short.  There will be signs of the hit. 

Will do....

[98Z5V]

2 minutes ago, bubbas4570 said:

Will do....

With only a couple rounds down the pipe, it won't be major. Nothing to worry about, or fix. Impact indentations will be there, but they won't affect rifle function in the future.  Paint 'em up with some Birchwood Casey flat black. 

[Robocop1051]

Every tool kit should have a Super Black pen in it.