CRASH! What went wrong?

ironmonster · April 9, 2015

So I took my new Aero precision rig to the range today, Fired 40 flawless rounds through it and was feeling pretty good.

Got it home and opened her up to do a wipe down and WTF! The BCG was crashing into the buffer boss/tube. Id say at this point this buffer tube (which of course is a $150 PWS "enhanced" buffer tube) and the receiver are married for life. Taking them apart I think will do some damage to both.

Anyway WHY??

As mentioned it is a Aero upper, Aero BGC PWS Enhanced AR-15 buffer tube (which measures 7" deep) I am using a Tubb's flat coil spring and a DPMS 2.5" buffer

When I push the BCG into the buffer with the spring and buffer in place it goes all the way back to the sectional change in the carrier and hits

I have a second rifle set up almost exactly the same (same spring, buffer, upper and BCG but using a UBR/rifle buffer tube and it shows marks where the carrier touched, but did not do the damage this one did.

ironmonster · April 9, 2015

This is the spring and buffer

http://www.midwayusa.com/product/988692/tubb-speedlock-systems-flat-wire-buffer-spring-ar-10-chrome-silicon

http://www.midwayusa.com/product/232006/dpms-buffer-lr-308-carbine

AngelDeVille · April 9, 2015

Buffer detent hole in the receiver is set too far back.

ironmonster · April 9, 2015

I dont think so, It sure does not look like its set back

washguy · April 9, 2015

Buffer detent hole in the receiver is set too far back.

Yep it is! here's a quote from a post here a while back answering this problem

"Your issue is a result of the buffer retainer hole being too far rearward. When the upper is closed on the lower the back of the BCG is supposed to push the buffer off of the retaining pin. When the firearm cycles with the upper on, the buffer should never touch the buffer retainer. You can visually inspect this two ways, the first is to separate the upper and lower. You should be able to see the buffer protruding beyond the rear of the receiver (towards the fire control area) where the receiver extension threads into. The second way is to look for the rear of the bcg pushing the buffer off of the buffer retainer when closing the upper on the lower. A light helps with this.

If you really want to try fixing this yourself you'll need to try to extend the buffer retainer hole more towards the fire control pocket and then use a shim to keep the buffer retainer towards the front of the receiver. The hole is 1/4". ... end of quote a Tubbs cws will solve it for ya

but your $hit is beat up :) Wash

Edited April 9, 2015 by washguy

Robocop1051 · April 9, 2015

You need to increase the mass behind the the BCG. That's the easiest fix.

Personally, I'd just add the Tubb CWS. It's a cheap & easy installation.

That'll decrease the gap and reduce the damage to your receiver.

Robocop1051 · April 9, 2015

That'll decrease the gap and reduce the damage to your receiver.

Edit:

That SHOULD decrease the gap and reduce the damage to your receiver.

ironmonster · April 9, 2015

Im down for the Tubb CWS. I'll order a couple up.

BUT what would be wrong with putting a flat spacer in the bottom of the buffer tube behind the spring that limited the travel of the buffer to just short of coming in contact with the buffer tube boss?

ironmonster · April 9, 2015

It seems to me that if the buffer was just a wee bit longer so the bumper hit before the carrier did, which is how I thought it worked anway

98Z5V · April 9, 2015

Tubb CWS will add 0.080" to the length of the BCG. If your buffer face isn't chewed up, that's not the problem, though. Post a pic of the buffer face for confirmation.

Stack a couple quarters in the receiver extension, then insert spring, buffer, etc. See if that solves it. If you can't lock the BCG back by hand, then remove one of them. See if it works.

2nd time I've seen this with the PWS extension, in just a couple days here.

ironmonster · April 9, 2015

The buffer looks fine, no damage there. Its the front ears on the carrier that come in contact with the buffer boss while the buffer is a the bottom of the tube under full tention

MikedaddyH · April 9, 2015

Accidents happen ! That's how our kids got here. Once again "Trick parts" are causing problems.

Isn't the gap in front of the buffer ??

Would welding a couple washers to the BCG fix it ?

98Z5V · April 9, 2015

The buffer looks fine, no damage there. Its the front ears on the carrier that come in contact with the buffer boss while the buffer is a the bottom of the tube under full tention

Then the machined hole for the buffer retainer is in the correct position. Look elsewhere for the problem/solution, and don't waste anymore time on that recommendation. if that hole was out of place, it would fuk your buffer all up around the edges, like this pic below.

MGI-buffer-tube-detent-pin-hole-buffer.j

The Tubb CWS will not cure the problem you're seeing here. Your receiver extension is too deep, your buffer is too short, or you have the wrong spring in there.

Stacking quarters will tell you if you can fix it.

Edited April 9, 2015 by 98Z5V

98Z5V · April 9, 2015

That buffer detent hole isn't the issue here, or you would see this type of damage.

FaRKle! · April 9, 2015

^Heh, I spy one of my lowers there ;)

How deep is the travel from the end of the receiver extension (internally) to the edge of the lower where the marks are? Also, got a pic of your carrier? I'm curious if the shoulder extends further back than most other .308 carriers.

Toolndie7 · April 9, 2015

Stacking quarters will tell you if you can fix it.

THIS. hell if it works leave em in there <laughs>

your problem has absolutely nothing to do with the retaining pin. BCG is blowing back too far when cycled.

EDIT: are you missing this by any chance?

Edited April 9, 2015 by Toolndie7

washguy · April 9, 2015

Yep..I didnt pay attention too close at first read....98Z is right....if the buffer face edges arnt tore up its not the problem with the buffer retainer pin.... for folks on new builds...one should pay close attention and make sure the carrier comes into contact with buffer as you close up the rifle....moving the buffer back off the pin...its only thousandths we are talking bout :) Wash

FaRKle! · April 9, 2015

EDIT: are you missing this by any chance?

I'm not sure they have the dead blow buffer in there anymore... When I last looked at my .308 EBT it didn't look like it had one..

ironmonster · April 9, 2015

I dont think it does, But I could machine up a chunk of UHMW and push it to the back of the buffer tube, figure out how thick it had to be for the buffer bumper to hit it rather than never come in contact with the back of the tube which is happening now.