seating depth; jam/jump vs. base

[zini72]

Hi folks, sorry if this has already been asked, searched but didn't find it already out there.

I have a 7mm SAUM that I bought for the action, wanting the action to build a 1K gun. Thought I'd play around with the factory rifle while waiting for new parts to come in. When loading the Berger 180 Gr. VLD to just touch the lands, the base of the bullet is just below the bottom of the shoulder,into the body of the case). I told my smith about it, and asked where to seat the sample round for the reamer. He said it didn't matter. I usually only neck size the top 3/4 of my necks & assumed that ideal seating depth would be touching the lands,or possibly jumping a little) and keeping the base of the bullet inside the neck or atleast the area just above the boat tail in the neck sized area,allowing the boat tail to 'hang' down into the top part of the shoulder? Thoughts are greatly appreciated.

 

[fdshuster]

zini72: When I spec reamer throat dimensions, and include a 'dummy' round, sent to Dave Kiff/ Pacific), my first bullet of choice will be seated so the full diameter is at the bottom of the case neck. If it is a boatail, the heel will be extending into the shoulder area, and a request will be that the bullet ogive touch the 1.5 degree leade angle. So, seating with a .020' jump will put the full diameter approx. .020' below the neck, but that will 'move forward' after the first 80 to 100 rds. are fired. Recently spe'ed out a 223 reamer, with a tight, no-turn neck and .072' of freebore allowing proper seating depth for all bullets from the 55 V-Max to the 80 gr. Sierra MK. Don't mean to dis-agree with any gunsmiths, or anyone else out there), but when I'm spending the big $$$$ for a custom barrel and all the related expense, I'll be the one to decide on chamber neck dia. and throat depth, the main reason I provide the chambering reamer to the gunsmith. Works for me.

 

[Chuckhunter]

zini72, I have to agree with Frank on this one. It matters! Since you specifically mentioned Berger Bullets, I would call their new Tech Support line and put the question to Kevin Thomas, this kind of question is exactly, one of the things he was hired for. I can only tell you from some small experiments that my partner and I have tried, that a bullet with a dinged up or damaged base will affect your bullets flight a whole lot more than a deformed tip. That is why when ordering a reamer, I always want the pressure ring of the bullet in the case neck. Thats the beauty of getting a custom chamber, it fits the specific bullet or bullets that you want to shoot. There are a lot of Benchresters and Long Range Shooters on this site with a whole lot of reloading savy and I hope some more will jump in and either confirm or correct my information. Kevin Thomas has fired thousands of rounds in Sierra's test tunnel and I'm sure with his experience, his answer will give you a more detailed explanation of why the pressure ring should be in the neck.