This is why you headspace a barrel, because manufacturers apparently have different idea of what safe conditions are in a rifle and because some of them bore feed ramps more aggressively than they should. That is my opinion, here are the facts.
First of all, here is a comparison of chamber seating with several 9mm barrel mfg:
The best case support (works great):
OK case support (but no bulging or rupture):
Deep feed ramp that led to case bulging:
My equally deep feed ramp that led to case bulging and rupture:
Because 1/4" of the case wall is already exposed, even the slightest mischamber caused by dirt in the chamber or slightly larger rounds can cause unsafe conditions resulting in case ruptures. Also, any weaker brass will bulge at the least and rupture at the worst.
This is where another warning comes into play when you purchase ammo (or choose brass) for use in a 9mm AR: Tula and some of the chinese mfg's have weaker brass than say, Winchester, Remington, or Federal. These are Tula cases that were fired through a 9mm AR pattern rifle with a dedicated CMMG lower, CMMG 9mm ramped bolt, and my ADCO barrel pictured above:
After inspection and a "gentle" test fire, we fired a few more shots off and got this case rupture along with a cracked upper that caused the bolt to fly off track, sheer the buffer retaining pin, and snap the bolt catch:
Even after being confronted with this information, the mfg states that the barrel is in spec and that this is how all of his barrels are made. He fired six rounds through the barrel of various high end mfg's and did not have any problems.
MY case ruptures occurred after roughly 200 rounds had been fired through the gun so there was dirt and heat compounding the poorly designed feed ramps and barrel. The mfg has offered to refund my money and that is all. He maintains that the barrel is cut to spec and that the design of the barrel did not lead to the case ruptures. I had the barrel checked by a local gun smith who confirmed that the feed ramps exposed too much of the case wall and that he would not use such a barrel, considering it unsafe and suggested sending it back to the mfg.
First of all, here is a comparison of chamber seating with several 9mm barrel mfg:
The best case support (works great):
OK case support (but no bulging or rupture):
Deep feed ramp that led to case bulging:
My equally deep feed ramp that led to case bulging and rupture:
Because 1/4" of the case wall is already exposed, even the slightest mischamber caused by dirt in the chamber or slightly larger rounds can cause unsafe conditions resulting in case ruptures. Also, any weaker brass will bulge at the least and rupture at the worst.
This is where another warning comes into play when you purchase ammo (or choose brass) for use in a 9mm AR: Tula and some of the chinese mfg's have weaker brass than say, Winchester, Remington, or Federal. These are Tula cases that were fired through a 9mm AR pattern rifle with a dedicated CMMG lower, CMMG 9mm ramped bolt, and my ADCO barrel pictured above:
After inspection and a "gentle" test fire, we fired a few more shots off and got this case rupture along with a cracked upper that caused the bolt to fly off track, sheer the buffer retaining pin, and snap the bolt catch:
Even after being confronted with this information, the mfg states that the barrel is in spec and that this is how all of his barrels are made. He fired six rounds through the barrel of various high end mfg's and did not have any problems.
MY case ruptures occurred after roughly 200 rounds had been fired through the gun so there was dirt and heat compounding the poorly designed feed ramps and barrel. The mfg has offered to refund my money and that is all. He maintains that the barrel is cut to spec and that the design of the barrel did not lead to the case ruptures. I had the barrel checked by a local gun smith who confirmed that the feed ramps exposed too much of the case wall and that he would not use such a barrel, considering it unsafe and suggested sending it back to the mfg.
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