Ar15 failure to extract

[[email protected]]

I recently did an ar build and I can't seem to get it to cycle properly. It is chambered in 5.56 and is a m4 carbine. Tht problem that I am having is after I fire the spent case stays in the chamber. It then tries to chamber another round. After I clear the jam the case will easily pull from the chamber. I have noticed that a section of the case rim gets torn from the case by the extractor. I have cleaned the chamber and even tried a different bolt carrier group. Any suggestions are welcomed.

 

[PBR Streetgang]

Headspacing problem? saw you tried another bolt do you have access to go / no go gauges?

tried different mags?

 

[ApacheCoTodd]

If you've successfully extracted a case manually - show us some photos all the way around it.

Does a spent case come out easily when cooled a bit?

 

[TurtlePhish]

Could be overgassed or something... try a heavier buffer?

 

[dprice3844444]

http://www.brownells.com/.aspx/pid=24635/Product/AR-15-M16-EXTRACTOR-UPGRADE-KIT

here ya go,this is the first thing that should be put on all buiilds

 

[Upstater]

You can't hardly beat that for 12 dollars and change, I'm going to get one of those kits for my bushmaster right now.

 

[243winxb]

If handloads, high pressure may stick the fired brass in the chamber. It will rip off the rim.

 

[MrCleanOK]

If you are consistently ripping off parts of the rim, extractor tension is not your problem. It sounds like your rifle is over-gassed. I would try using an auto bolt carrier if you are using a semi carrier, and using a heavier buffer. Both of those changes will slow the action down a little, and may give the pressure in the chamber enough time to drop for reliable extraction. If heaver components in the reciprocating masses won't solve your problems, I would take it to a gunsmith to have the gas port measured, and if it is truly oversized, replace your barrel.

 

[rcmodel]

˄˄˄˄
What he said.

That right there is your problem.
NOT a weak or damaged extractor or spring or rubber extractor buffer.

If it's tearing the rim off, the bolt is unlocking before chamber pressure has dropped enough to allow extraction of the still expanded case.

rc

 

[[email protected]]

The first bolt I tried the headspace was checked. It was a little on the tight side but according to the department armorer who checked it, it was within spec. My first guess was the rifle was over gassed. The chamber looks smooth the best that I can tell. I am using reloads, but the load I am using was developed using this rifle and my DPMS and it is a couple grains below the max charge. Before settleing on this load I ran 3 full 30 round mags throught this rifle without any problems. When I started having problems I tried a different load that I have ran over 800 rounds through my DPMS. I had the same problem with this load which is a different powder, but also below max. The load has plenty of power to cycle the action and the avg velocity in in the upper 2800fps using 55 grain fmj (16 inch barrel). Today I measured some cases both fired and resized. The cases I used for the test run of this load I FL resized the cases on a single stage press, but the "production" run was loaded on my LNL AP press. I resized and then trimed. After I measured how much the shoulder was set back after resizing, the average setback was more on the single stage than on the AP press. I did check the function of the rounds while loading and the bolt closes completly. Also the second load I tried the cases were FL resized in the single stage press, but the had the same problem. While I was measuring the cases I notice that the cases fired in my DPMS was longer (same head stamp brass from same lot of ammo) when measuring from the case head to the shoulder using a hornady compatior.

 

[dj_28]

My guess is that while the DPMS will shoot a load that is close to the max. powder charge and the other will not is do to the chamber more so than the gas system. The reason the case fired though the DPMS are longer after fired is it has a slightly longer chamber allowing the case to stretch. The other has a tighter chamber and the hotter load is causing to much pressure in the chamber for reliable extraction. Try a lighter load in that gun and see if it will extract. If so, then you can try slowing the bolt down to get better extration by allowing alittle more pressure to disapate before the bolt unlocks and starts the extraction process.

Just my thoughts on the matter, but I'm not an AR man so I might be way off base here. But from what you have told that would be where I started.

Hope this helps

DJ