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30BR Trim Too what?

I'm 1.508, I didn't choose that number it just worked out that way on the rcbs power trimmer, I have thought about 1.500, but!
 
I have had 2 30br's built from different gunsmiths. Both were said to be built on a "typical Robinette reamer" and with one I have to trim to 1.51 and the other I do not need to trim at all if I don't want to. What I am saying is that just because it was said to have been chambered with a Robinette reamer doesn't necessarily mean that the neck length is always ordered to a certain standard. You need to find out what the length of your chamber is before you make the decision on what to trim to if you want to be safe.
 
With all the variances in play, the best way to find out your trim length is to expand up a case (they'll end up about 1.535-ish), neck turn it to under the chamber neck dimension, then try the case in the chamber. If the bolt doesn't close, trim the case a few thou and try it again. Repeat until the bolt closes...now you know exactly how long your specific chamber is and you can trim to a proper length. Check this with the firing pin assy removed from the bolt. Otherwise, the cocking effort can mask the 'feel' of the neck hitting the end of the chamber. Likewise for checking that the shoulder is bumped back far enough.

On a reamer I haven't used on a chamber before, I do the above but first trim the neck very, very short so I know the bolt will close with the shoulder of the case 'as is'....just to make sure it's not the shoulder that's keeping the bolt from closing. If it is the shoulder, adjust the die so the shoulder is bumped back far enough to allow the case to chamber. Then proceed as outlined.

I worked with one 30BR that the print was for an 1.520 chamber length and the gun was tossing flyers out of the group. Measuring the cases, they were from 1.510 to 1.512. With a sized case with the primer removed, the bolt would not close on a 1.512 long case w/o some effort. Bingo....flyer problem solved. 8) Since the shooter had a pretty good 'jam seat' on the bullets, the additional effort from the neck hitting the end of the chamber wasn't noticeable.

Check everything. ;)

I know there are other ways to do it, but this method always works. And you only sacrifice two cases to do this.

Good shootin'. -Al
 
Invest $7 in a reusable Sinclair chamber length gauge and get the length of your (emphasis on the word "your") chamber.
 
Well since I had everything ready for expanding, a redding 6mm to 30 cal one pass deal, and I was turning brass today I had my K&M tool set to cut and now I find out I didn't have to trim brass after two bumps, at 1.522 fits fine in both guns, one Shilen, and one Krieger, dam all that time for nothing, guess I should have asked before starting. THANKS!
 
I should have added to my original post : Check this with the firing pin assy removed from the bolt. Otherwise, the cocking effort can mask the 'feel' of the neck hitting the end of the chamber. Likewise for checking that the shoulder is bumped back far enough.

I've editted my original post to add this. -Al
 

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