Short Stroking?

[PredatorDown]

I absolutely love this rifle when it functions correctly, but it seems that more and more it's not feeding reliably. It will either tilt the round up at a 45-degree angle and smash the bolt into it, or sometimes won't strip one from the magazine at all. It doesn't matter which side of the mag it is being pulled from. On the last round, the bolt will catch on the mag follower instead of the bolt catch.

I searched the forum and have put a bevel on the ejector as that seems to be the usual suspect, but am still having problems.

Specs are as follows:
Stag Arms lower
Vltor MUR upper
JP Enterprises 22" Supermatch barrel and bolt
Vltor A5 buffer system (tried with the H2 buffer it came with, no dice. Switched to their H0 buffer, same story)
Not sure on the gas block, had a local gun shop (that has since gone under) put it all together for me. It's not adjustable, so I'm thinking that will probably be the next step.
5rd and 10rd AR-Stoner mags
Shooting 123gr amax's, 30gr of BLC2, federal premium match primers, Hornady brass, COAL of 2.245.

I tried to take some slo-mo videos with my phone today to hopefully get a better idea of what it is doing, but it's still a little hard to tell because they aren't playing back smooth online (and it's not the best video to begin with).


Last round out of the mag:


Jamming the next round:

[dmsims21]

I can offer much advice, but you may want to include info on magazine and ammo.
I am sure others will ask for that info in order to help figure out the problem.

[PredatorDown]

Thanks, added to the original post

[CPT.CRAZY]

Its kind of hard to tell from the videos, but from the way it looks it might be a little over gassed.

[BjornF16]

Have you smoothed/polished the feed ramps?

Definitely not "short stroking"...or you'd have an empty chamber or the empty case you just fired still in the chamber.

See http://www.thetruthaboutguns.com/2011/06...-stroking/

[am4966]

When I had my first grendel when they first came out, I had feeding problems due to the Mags. Now if you've used that mag and never had a problem before then others will need to chime in.

[Butterbean]

If they're available, try swapping complete upper/lower with another AR. That should isolate the problem some. I seriously question the gas block alignment.

[cory]

Yea I'd say it's probably over gassed. Adjustable gas block will help.

[PredatorDown]

Polished the feed ramps today, still having the same problem. I'm almost certain it's a gas issue. I thought it was under-gassed because I would occasionally have an empty chamber with rounds still in the mag, and on the last round it has only ever caught on the follower instead of the bolt catch. I guess the next step is an adjustable gas block after payday.

[taggor]

Did you get the adj. gas block? If so how is it shooting now. I have a VLTOR A5 ext. as well and was curious of your results with the combo. I haven't shot mine yet and I have a couple of the different buffers in different weights.

[rasp65]

Did you take the sharp edges off the extractor as was discussed in the post below "Where were we".

[PredatorDown]

I finally got the problem figured out. Never again will I develop a load trusting the listed OAL in a reloading manual. I got the adjustable gas block, and had to open it up all the way and still wasn't seeing a difference. Ok, overpressure wasn't the issue.

I had never fired a factory round from the rifle, and finally decided it must be my handloads that were the problem. As it turns out, I had been seating the bullets too shallow (too long OAL) and was jamming it into the lands. I purchased the Hornady OAL gauge, set my bullets to the CORRECT (deeper than Hornady had listed in their manual) depth, and haven't had a problem since. I have now fired several hundred rounds without a failure to feed. I've been able to maintain 3/4 MOA, and am currently in the process of developing a load for it.

[dmsims21]

Booya. It is always awesome to figure something out.

[rasp65]

The OAL that reloading manuals provide is for the barrel that was used for their testing. It is always a good idea to measure for the maximum OAL and record it for future use in any rifle that you reload for. You can use the base line to measure throat erosion.