DPMS AP4 pulling the rim of the brass?

[1Sg (ret)]

My ap4 has the stock barrel.The brass i use is Win.It sometimes pulls through the rim of the brass.Could this be a weak buffer spring?could my buffer be too light?I have put a g David Tubb spring in it.It is the standard carbine length.If i change the barrel would a mid length set up help?Any help in this matter would be greatly appreciated.Thanks ahead of time.

 

[Casey Simpson]

Re: DPMS AP4 pulling the rim of the brass?

Polish the chamber.

 

[DP425]

Re: DPMS AP4 pulling the rim of the brass?

AP4 is a non-chrome lined chamber/bore and thus you may have some problems with corrosion, build-up, or just a generally rough chamber; all of which could be causing your problem.

Or you could be starting extraction while the case is still under pressure.

 

[1Sg (ret)]

Re: DPMS AP4 pulling the rim of the brass?

Thansks for the replys

 

[Tbag]

Re: DPMS AP4 pulling the rim of the brass?

If you put a Tubbs spring in it I doubt if it is weak, especially if it's one of his flat wire springs. Did it work fine prior to the spring swap? Shooting any corrosive ammo by chance, maybe some foreign stuff?

I too would start with polishing the chamber really well.

 

[1Sg (ret)]

Re: DPMS AP4 pulling the rim of the brass?

Ive had the rifle a couple of years and just started to notice the problem.i have shot port, Radway green,Austrialian,fed ggm brass ,and Win brass.i will polish the chamber and check it out.

 

[sinister]

Re: DPMS AP4 pulling the rim of the brass?

DPMS uses a short M4-style and length gas tube on their carbine (it was their attempt to get a 7.62 autoloader on to the market while the getting was good). It's no wonder you're getting ripped rims.

A longer gas tube (like the Armalite "Mid-length") will help, but even then I use a Tubb Carrier Weight and Slash Xtra-Heavy buffer.

 

[Adam B]

Re: DPMS AP4 pulling the rim of the brass?

try an adjustable gas block to cut off some of the gas

 

[1Sg (ret)]

Re: DPMS AP4 pulling the rim of the brass?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">DPMS uses a short M4-style and length gas tube on their carbine (it was their attempt to get a 7.62 autoloader on to the market while the getting was good). It's no wonder you're getting ripped rims.

A longer gas tube (like the Armalite "Mid-length") will help, but even then I use a Tubb Carrier Weight and Slash Xtra-Heavy buffer.</div></div> Thanks for the ideas i will try those out.

 

[CDAT]

Re: DPMS AP4 pulling the rim of the brass?

1SG (Ret), FYI and consideration, I had the same issue, extractor ripping case rims off, with my DPMS LR 308. However, it would only do it with reloads, never with new US made or US MilSup ammo. I installed an adj gas block and started using a small base resizing die on the cases I reload and shoot in the LR 308, After that the problem went away with one exception. When using Federal small based sized cases it would still sometimes rip a rim off. I have been told that Federal brass is soft (could be an issue with your brass/ammo also)and I may not be getting a true SB sized case when I process it. The alleged brass softness may have been affecting the rate and amount of case spring back, causing the case to remain sealed to the chamber longer after firing. Now I only use small based sized LC and Win Brass when reloading for this rifle. I was also told, when I purchased the rifle, that DPMS 308 chambers are on the small end of the tolerance scale.

CDAT

 

[matthew314]

Re: DPMS AP4 pulling the rim of the brass?

+1 on the gas block I had the same problem. After installing the jp adjustable gas block it went away.

 

[Unknown]

Re: DPMS AP4 pulling the rim of the brass?

I had a DPMS rifle that had a short throat in it. The extractor would often rip through the rim of a fired case stuck in the chamber. If I extracted unfired rounds, you could clearly see the lands engraved onto the bullet. Rounds that did fire showed excessive pressure signs.

So I sent the rifle back to DPMS. They kept it for about a week, said then checked it, and test fired it, but said they didn't do anything to it. After I got it back, all the problems were gone.

I suspect that they didn't want to admit to quality control issues, and just touched up the throat a bit. It was like they used a reamer with a worn throat section in it the first time, and when I sent it back, they touched up the throat to fix the issue.

I was surprised that the extractor held so tightly that when the bolt came back it had enough force to rip a chunk out of the case rim. Once the cases weren't stuck in the short throat any more, all the extraction issues, and the lands engraving onto the bullet were over with.

 

[2M10]

Re: DPMS AP4 pulling the rim of the brass?

Same here. I had an SASS that wouldn't close on a Clymer GO gauge. A very small adjustment with a finsih reamer had it running just fine.

 

[bustin]

Re: DPMS AP4 pulling the rim of the brass?

sleeving the gas port in the gas block usually works better than an adj GB, seems like the round port works better than a big set screw closing off the gas from one side.
Take the gas block off, flip it upside down and take the rear set screw out, tap the port going into the gas tube 8-24 and put a brass set screw in it, then drill a hole through that set screw,
.0625 if a carbine gas .086 if a mid gas. reinstall the gas block.