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thermobollocks

What is my major malfunction?

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I think I've managed to put together some data regarding a gremlin in my rifle that's been driving me up the wall. Yesterday, I was dead set that it must've been a crimp issue related to the unramped Midway brand barrel being none-too-gentle during feeding, but now I think that was a fool's errand (mostly because crimping the absolute hell out of my ammo didn't fix it). One of my squaddies mentioned my malfs happened on full 33rd mags rather than halfway shot ones, so I decided to test that hypothesis. I also tested a couple of different OALs, and between 1.10" and 1.135" OAL, longer seemed to work better just a smidge, but I really think it's much more down to the mag thing.

 

After catching nominal results on video, I was able to get some off-nominal runs on video and on still camera.

 

 

The very first shot shows this characteristic hitch that I'm also able to repeat. A couple of rounds function correctly, then I get this characteristic jamming: https://imgur.com/a/bPL7b

 

I'll have total crap results and rack out a set back round that's jammed up hard for about the first ten rounds of the mag, then around the 20 round out of 33 remaining mark, things clear up considerably.

 

I'm hoping someone's having an "aha, he's having what I had" moment. The pictures and repeatability lead me to think my mag is filthy and needs cleaning/lube, it doesn't have enough spring to get the round where it needs to be in time, or I need an even bigger mag with even more spring. Thoughts?

 

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Fastest test fix, clean your mag and check for obstruction. Try thumbing you rounds out to check the mag.

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Does the second photo show a spent round (brass only) or is a bullet jamming into the back of the barrel?

 

I was having a similar problem.  I purchased a magazine extension around Thanksgiving that for the first several months ran 100%.  Then out of the blue it would not feed.  Rounds were hitting the back of the barrel and not feeding into the chamber

 

Discussion can be found on this thread:  

 

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44 minutes ago, Flatland Shooter said:

Does the second photo show a spent round (brass only) or is a bullet jamming into the back of the barrel?

 

I was having a similar problem.  I purchased a magazine extension around Thanksgiving that for the first several months ran 100%.  Then out of the blue it would not feed.  Rounds were hitting the back of the barrel and not feeding into the chamber

 

Discussion can be found on this thread:  

 

 

It's a bullet squished back into the case upon feeding. The important thing for me was that the case head wasn't making it directly to the bolt face, which makes me suspect sluggish or otherwise jacked up feeding. The mags didn't feel tremendously off, but I also don't have a particularly good frame of reference for how a fully loaded 33rder is supposed to feel. There was no maraca effect.

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Factory ammo ran well when the rifle was brand new, but I haven't tested recently. Surprisingly enough, it ate steel and aluminum case just fine.

 

Also, the feed ramp everyone's recommending will only band-aid the problem if the case rim isn't making it underneath the extractor during the feeding cycle.

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I don't think the case cams up under the bolt face as it might with a 2011 pistol, say. Rather, the bolt simply closes over it.

Take the bolt apart and clean it. Try cycling ammo by hand from a known to be good magazine and make sure you can pull the bolt all the way back.

Did you, by chance, happen to install a too heavy buffer spring? This can be problematic with very light loads.

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2 hours ago, thermobollocks said:

Factory ammo ran well when the rifle was brand new, but I haven't tested recently. Surprisingly enough, it ate steel and aluminum case just fine.

 

Also, the feed ramp everyone's recommending will only band-aid the problem if the case rim isn't making it underneath the extractor during the feeding cycle.

 

The rim will make it under the extractor once the round stops nosediving into the bottom of the barrel extension.  That's what's causing the setback.

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11 hours ago, MikieM said:

I don't think the case cams up under the bolt face as it might with a 2011 pistol, say. Rather, the bolt simply closes over it.

Take the bolt apart and clean it. Try cycling ammo by hand from a known to be good magazine and make sure you can pull the bolt all the way back.

Did you, by chance, happen to install a too heavy buffer spring? This can be problematic with very light loads.

 

That's something else I'll have to play with -- I did switch from Silhouette to Titegroup. I guess another buffer spring in the buffer spring drawer won't hurt.

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On 3/18/2018 at 7:59 PM, thermobollocks said:

 

It's a bullet squished back into the case upon feeding. The important thing for me was that the case head wasn't making it directly to the bolt face, which makes me suspect sluggish or otherwise jacked up feeding. The mags didn't feel tremendously off, but I also don't have a particularly good frame of reference for how a fully loaded 33rder is supposed to feel. There was no maraca effect.

This is usually caused by a buffer speed issue.  Mine was too light. The usual successful buffer & bolt combo seems to be around 18-20 ounces.  Plenty of threads about PCC bolt & buffer weight combinations.

I would first test with factory ammo to remove one variable from the equation.

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Suppose I should come back and eat my words. Man ammo (6.0 gr Silhouette + 115 gr plated RN as opposed to 4.2 gr Titegroup) and the Taccom feed ramp took care of the issue. I don't entirely understand why, since cycling it dry, it seemed worse.

 

Now I just have to create more issues for myself by experimenting with different buffers and springs to avoid learning recoil control minimize dot movement :D

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2 hours ago, thermobollocks said:

Suppose I should come back and eat my words. Man ammo (6.0 gr Silhouette + 115 gr plated RN as opposed to 4.2 gr Titegroup) and the Taccom feed ramp took care of the issue. I don't entirely understand why, since cycling it dry, it seemed worse.

 

Now I just have to create more issues for myself by experimenting with different buffers and springs to avoid learning recoil control minimize dot movement :D

Glad you’ve got it figured out.  PCC is both a blessing and a curse for those of us who like to tinker!

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