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Old December 23, 2019, 12:01 AM   #140
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Join Date: March 2, 2014
Posts: 8,914
I was busy today too. I loaded up some 170 gr interlocks again using 1680; but gaining a bit more space in the case I ran my max charges 1 gr more than with the 180 hotcores. I saw no signs of any deformation or incipient over-pressure. However, just like the factory American whitetail, my groups while consistent were in the 1.75 to 2 MOA range @ 104 yds. The 180 hotcores sized to .357 I believe are engraving better to the grooves and lands than a .355 bullet and are inherently superior in accuracy potential IMO. It's interesting to see that mehavy's .356 sized bullet did not seem to differ much from the .355 in terms of accuracy potential.

My "gas leak" area in the former pictures I now think is nothing more than gas coming in from the cut-out in the bolt face wall for the extractor.

Another possibile issue that occurred to me is concentricity of the bullet to case, throat and bore. There isn't a whole lot of "stabilization room" between where the bullet exits the case and enters the bore. I wonder if it's possible that a .357 diameter bullet that starts out of concentricity might not get straightened in the throat and thus get forced into the bore out of concentricity--which in turn might ramp pressures up??

My modified case came in and the base of ogive on the interlock can be seated way beyond what will fit in magazine before it engages the grooves/lands.

P Flados--your wedging of the case mouth to the throat in front of the case step explanation is an interesting one and sounds like a way that pressures could ramp up. My failure cartridge was well within headspace tolerances and the diameter at the case mouth was maybe .001 more than a .355 cartridge, but it too was within tolerance for the diameter of case mouth.

The only other thing that strikes me as odd in my set-up is the carbine gas length system in a 20" barrel. I've never seen that before in a rifle length barrel and that amounts to 13" of dwell time in a cartridge generating 50,000 + psi

You are not the first. I have seen similar photos from Winchester factory 350 L ammo.
That I did not know. That's kind of scary when you say it's using factory ammo! BTW--I found references to the "overcrimped" factory 145 gr ammo allowing the brass to enter the throat. I don't think that's happening in my case since I put only a very light taper crimp and my OD at the mouth actually slightly exceeds the hornady factory stuff I have as a baseline.--but it's still interesting to check and I will see if I can.
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I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!

Last edited by stagpanther; December 23, 2019 at 12:48 AM.
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