AR .260 feed/eject prob. sighting in

[VTmtn.man]

So I bought all the parts (prior to 6mo. ago) and recently finished the build. I used 60 rounds of Rem factory ammo to try to get things tuned and initially thought I had it as brass was ejecting. This wasn't the case after a while as shells were not feeding or brass getting stuck on the way out. Also couldn't group hand feeding it one at a time at 100 yd. I'm now out of factory ammo.

First build of this kind. Instead of messing with the gas block w/ factory ammo any suggestions on hand loads - rifle build issues?

 

[taliv]

Can you be a lot more specific about the malfunctions? Was it always the same thing? Does the bolt lock to the rear on the last round in the mag? What magazine are you using? When it fails are there two rounds in the action? One spent? One live? One of each?

Can you tell if anything moved? Like the gas block

Are the rounds keyholing in the target or round. What size groups?

 

[VTmtn.man]

Started off with 20 rd. P-mag and got it to cycle on its own so I thought the gas block was good.

Went back to the range with a 5 round DPMS mag and same scenario cycled well at 50 yds, thought I would have the SWFA scope sighted in roughly in a few shots

Groups initially at 50 yds were within an inch of quickly fired shots used for rough estimates of cranking the dials on the scope to center it

Went back to 100 yds thinking that I should at least see holes on a sheet of computer paper dot in the center and that's when the thing started not to function.

Same thing didn't happen ea. time after the initial 5-8 rounds... A round would always fire, most of the time the bolt would not eject the spent case at all and the bolt would stay closed on the spent brass in the chamber, a few times the brass would get jammed on the way out. All of the holes that did hip paper from 50 to 100 yds were perfect passes no tears or oblongs.

I do not think that any mechanical changes occurred with the rifle, gas block moving etc.

 

[rcmodel]

I do not think that any mechanical changes occurred with the rifle, gas block moving etc.

Well, it sounds to me like something sure did.

Lack of lube as it got dirty with initial firing?
Or the gas block alignment started creeping off the gas port as recoil did it's magic.

One, or a tother, or both I think.

rc

 

[C-grunt]

What kind of gas block is on the rifle? Pinned or screw set?

 

[VTmtn.man]

DPMS gas block... I had a 'guy' who knew an "experienced AR guy" do the actual barrel wrench tightening and gas block. I'm trying to fix things as I don't want to deal with these guys again.

Pictured is the identical gas block just taken out of its packing from DPMS, bought for the next build. I assume it is a screw tighten gas block. Please educate me/us...

 

[rcmodel]

Yes it's a screw-on.

Look on the bottom and see if there are not two set-screws holding it on the barrel??

A pinned version would have taper pins through the side holding it to the barrel.

They are either right, or wrong, and can't move out of alignment with the gas port.

Your set-screw version can if the screws were not tight, and or/or whoever put it on didn't drill dimples in the barrel where the set-screws bear to keep it from moving.

rc

 

[VTmtn.man]

RC, thanks for the pointers.

The set screws are tight

Do you think the internals could be that messed up w/ gunk after 30-45 rounds & hand fed 45-60?

 

[adelbridge]

Are you using soft points? I have seen the lead tip get shaved off and jam up the breech and prevent the bolt from fully closing and screw up ejection. Head spacing would be erratic with lead chunks and cause groups to open and you might begin to see signs of too much head space- bulged primers and head stamp smudged out. Load up a round and let the bolt slam shut with the bolt release. Manually eject it and inspect ejected round. get a light and shine it in the chamber to see what is going on. Who's barrel in on there? M4 feed cuts? What receiver? Chamber brush it and try FMJ or polymer tips.

 

[redneck2]

Sounds like the same thing I had happen with my SOCOM. Tried different hand loads, etc. After a while, we just lubed it really well with teflon lube. Runs smooth now.

 

[taliv]

Take some brake cleaner and hold the upper with the muzzle pointed downward toward a bucket. Squirt the brake cleaner into the gas tube. You should see a heavy flow comin out the muzzle.


Check the gas key on the carrier to make sure it's not loose or obstructed

 

[MrCleanOK]

I agree with Taliv. If the rifle initially cycled, and then gradually started to malfunction with stovepipes and empty casings in the chamber then you're looking at one or both of two problems:

1. Dirty, dry rifle slowing the movement of the bolt carrier enough to cause malfunctions.

2. Defect somewhere in the gas system.

Can you tell us how you lubricate your rifle? That will help us rule cause #1 out or in.

Follow taliv's recommendations for trouble shooting the gas system. It's not at all uncommon for set screwed gas blocks to move under recoil if they aren't installed correctly, same for gas keys loosening.