Need minimum/max case mouth to chamber.

[Tycer]

Howdy,

What do you'uns use as a case mouth to chamber minimum and maximum?

I need to outside trim the first .100 a couple of thousandths as the case is touching the chamber on a .358 bullet (not on the .357), but I want to try a batch of .359s and .361s to see how they fly...

[victorcharlie]

Howdy, I'm not sure I fully understand the question, but when I trim I trim to minimum specs listed in the reloading manual.  I assume your talking about case mouth to throat, or the fact that the case length is exceeding chamber dimensions?

In the past, I've had a plaster cast made of the chamber.  Then, once the chamber dimensions are known, overall length, and neck thickness can be adjusted accordingly.

What cartridge and gun are you working with?

[Tycer]

Win 94, .357 Trapper.

I've cast the chamber and designed a bullet to fit - seated to just touch the rifling and using dan Wesson .360 brass to gain extra case bearing. The throat begins to neck to .378 the last tenth of the .360 case.

I've been shooting Brp and Cast Performance 180's in both .357 and .358. The rifling is.3575 -.3580, so I would like to experiment with .359, .360 & .361 diameters for accuracy.

The DW .360 brass is .010 - .012 thick.
.357 + .010 +.010 =.377. If I smoke the case and chamber a .357 round, very little soot is removed. .358 leaves a bright ring all the way around with some pressure felt on chambering. No extraction problems, even with some hotter loads.

My thought is: if I am snug with a .358, the base of the bullet is being formed a tad smaller before it even reaches the rifling. I don't thing I should even bother loading the larger rounds before turning the outside of the cases for clearance.

I'm thinking .0095 for the .358, .009 for the .359, etc. In other words, zero clearance.

My question is: do I need more clearance?

Thanks to you'uns from WNC,

Tycer

[Tycer]

Sans answer, I tried both and began seeing leading 400fps earlier on the untrimmed cases.