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Help me understand this ruptured case


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13 hours ago, chevrofreak said:

You have a sharp ridge at the mouth of your chamber that is shaving lead from your bullets and brass from your cases, which appears to be causing your rounds not to fully chamber.  

This seems most likely close inspection of ramp and chamber see what is damaging the rounds.

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Glock mag lowers have this issue. The round had a bit of travel with no guidance to get to the chamber. I had the same issues (bullet dents, setback, etc.) until I installed the Taccom feed ramp. It makes a huge difference.

 

If you have one, look at a Colt mag lower. There is a ramp that feeds the round from the magazine to the chamber. No such animal in a Glock mag lower.

 

JP seems to have dealt with this in their Glock mag lowers, but no others I know of have. It may work, but the round is bouncing off the back of the barrel  as often as not. 

 

The Taccom feedramp is cheap and works (at least it worked for my NFA lower).

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So that isnt normal? Ok, I'll call PSA. Could anyone post a pic of a GOOD feed ramp/chamber?
Normally I'd fire up the dremel to ease that transition, but anything removed will also remove chamber support. Seems like material needs to be added in this case.
For what it's worth, I was able to get a super slow mo video:



Sent from my SM-N960U using Tapatalk

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Agree with others, that corner is most likely what is causing your issue.  Looks like my Kimber 1911 barrel when I started shooting SS many moons ago.  It was doing same thing.  After I smoothed that corner out, it fed like a champ.  Making that transition smooth should not remove anything from the chamber support, or very minimal if any.  

 

Will be interesting to see what PSA says.  

Edited by GregJ
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Two thoughts after watching your video.

1- after chambering the round, slowly pull bolt back, take a black marker and put a mark where the ejector is.  Then line up the round with the bolt, to ensure the marks on the bullet/case are lined up with the sharp edge on the chamber.

2- I guess that bolt bounce back is normal for a blow back.   

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39 minutes ago, obsessiveshooter said:

So that isnt normal? Ok, I'll call PSA. Could anyone post a pic of a GOOD feed ramp/chamber?
Normally I'd fire up the dremel to ease that transition, but anything removed will also remove chamber support. Seems like material needs to be added in this case.
For what it's worth, I was able to get a super slow mo video:

 


Sent from my SM-N960U using Tapatalk
 

 

 

42C497A0-BD0D-4373-AE93-D8CEB69FD15D.jpeg

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On 12/29/2019 at 8:05 PM, Bwilmot said:

Psa pcc barrels are notoriously short chambered. Try plunk testing your ammo.  Might have to get the chamber reamed to be able to accept the ammo your using.  

My PSA PCC barrel was tight too, had to have a gun smith open the chamber up a hair. Been 100% since then.

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I had a similar thing happening to my rifle. I would occasionally get a failure where the hammer dropped "early" with the bolt in a position that the hammer could not fully strike the firing pin. It turns out that things were getting delayed by the bullet getting hung up temporarily on the sharp corner of the chamber (and also some sharp edges on the bolt face and extractor). This only happened once every 300-400 rounds until I tried a new brand of bullets where the alloy was a bit softer and more prone to cause the delay.

 

The fix was to soften the edge around the chamber and do some smoothing of the edges on the bolt face and extractor. I have one rifle with a feed ramp barrel like HoMiE and one without and they both run equally well. FWIW I use Berry's 115 grain TP bullets. The non-ramped rifle has run for >7000 rounds with only one malfunction. And that was likely do to an issue with a Goliath mag extension, ammo OAL and desert dirt.. YMMV

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That type of half-assed ramp causes more issues than it solves.  A simple chamfering to the entire chamber opening does less damage to ammo, but is still not as good as a true ramped barrel like the one pictured above.  

 

If 100% feeding is a must, then you want a Shooting Innovations ramped barrel and matching bolt. 

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3 hours ago, GregJ said:

thoughts after watching your video.

 

2- I guess that bolt bounce back is normal for a blow back.   

Seems excessive(To me at least), I thought that floating weight in the buffer was suppose to act like a dead blow hammer to prevent bounce back?

 

Wonder what type of buffer the OP has?

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Good on you for getting such good pictures for everyone to evaluate. It has been noted but I suggest light polishing the chamber edge all the way around, not just at the bottom, rounds can also bounce up and want to catch on the upper lip. Were not talking about removing much material here just a little radius and polish. This type of thing also comes up in other applications like mag fed shotguns so pretty much any new platform I am always looking at chamber edges, use the finger nail test, if its sharp enough to scratch finger nail, it will catch rounds. Also up to you if you want to fiddle with it or see what PSA wants to do.

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I sent PSA a very detailed email about the issue, along with my order # and relevant info. Instead of an actual response, I got an email asking for my relevant info and order number so I could send it back. I think I'm going to just modify it myself instead of possibly being without the gun for weeks.

Thanks everyone for the super helpful info! I feel like I know where to start to fix it.

Sent from my SM-N960U using Tapatalk

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  • 3 weeks later...

UPDATE

I polished the feed ramp and eased the transition from feed ramp to chamber.  This took care of ALL the issues and it feeds without damaging brass or denting the bullets.  It now runs perfect and I can move on to tuning the felt recoil.  

If anyone else has this issue with their PSA barrel, I highly recommend doing the same thing yourself instead of sending it back to PSA.  

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