New Barrel Puzzling Developments???

[RonAKA]

Ron, I think you may have been onto something when you said the bullet was leaving the case before engaging the lands.
Maybe try crimping a few rounds to try and boost shot start pressure, or use a longer bullet that will hit rifling before leaving the case. I would be willing to bet the second option would give better results, and the first may help as well. I doubt either will hurt, and it may even help to solve the problem.

Yes, it would seem that the 107 SMK which were just bought to play around with at the range, were a bad choice. I didn't realize that they had such a short bearing surface. In my other 264WM I have shot 87 grain Speers that look like they barely poke out of the neck, with no case denting issues. However they have the powder compressed to get all the 4831 you can get in there, and have clocked them at over 3800 fps. So probably the pressure is well up there. Probably the secret is early pressure, and those low conservative loads just did not open the necks up to seal. Plan to play around with some more of the SMK's and push the load to max to see what that does.

 

[AckleymanII]

First, it is blow by, low pressure did not seal the necks

Second, federal brass is soft, get yourself some winchester and start over, execially if you like measuring the expansion, I dont use that method myself.

Powders like IMR 4350 should work well with the 107's. I suspect that you have pushed the shoulder back in the process of necking down the brass, just a guess.

 

[jo191145]

Its definately blow by folks. If there was an obstruction in the chamber to cause that they indeed would'nt eject or chamber for that matter. To cause a dent like that in the extraction cycle you'd need a hammer.

Whenever doing wildcatting no matter how small a variation between parent cartridges its wise to create a false shoulder. That helps greatly eliminate problems like this. Especially in chambers of unknown headspace.

Unless the powder used is totally incorrect for the application(still no knowledge or comment) your dealing with hardened necks. My quess would be the headspace is a little long compared to your brass also.
Flattened primers can tell of high pressure but they also warn of excessive headspace.

Long freebore in and of itself does not cause this problem. Most factory 204 Rugers for instance have enough freebore that many bullets have left the case before contacting the lands. Yet they obturate just fine if the brass is soft enough. Jamming definately can help the problem but it also helps to mask the problem
Odd fact: All Viht powders (133, 135, 530, 140 tested) will fail to obturate 204R brass long before other appropriate powders. Smooth power curve maybe?????

Quick fix is anneal and switch to a longer bullet that can be jammed real hard. Revisit powder choice also?
Once the brass is fully formed to your chamber you can try jumping short bullets.

Safety wise it could'nt hurt to have a chamber cast done to know exactly what neck your dealing with.

Lastly I've never had a problem blowing out lube dents. These are much more severe than any lube dent I've seen.
I'd chuck em. They'll probably exhibit excessive runout and premature failure. Just a quess.

 

[RonAKA]

I loaded up some rounds with more powder to a grain or so over the Hodgdon max. No hint of the cartridge dents. And I fired the rounds that had the dents in them. Those that predicted the dents would form out, win the lottery. Except for a dark spot in the brass, the cases fully formed back out to normal. I did anneal them before loading them this time.

So, yes I would say these rounds were underloaded. Pay attention to those minimum loads, and even when you do, you can still get into trouble.