Home Forums Hunting & Shooting Ask The Gunwriters Tight Chamber

Yep, turn and ream are different.
Let us know how this all ends up, Forty. I think you're on the path to happiness.

Do you have a good way to check headspace on your fired rounds to compare to your chamber? You do not want to bump the shoulder until you know where you happen to be. I fell into bumping until mine chambered and extracted easy. Remember that when you bump you are also sizing the base a little more. Problem is you may start having case head separation from bumping too much. Have your gunsmith make a gizzy (headspace gauge) using the chambering reamer. Have him take a barrel cutoff and run the reamer until the shoulder is cut in the gizzy. Put your fired, unsized, and primer less brass in it and measure. You can then measure and adjust your die to bump no more than .002". Using your figures it should not be a neck diameter problem. Have you measured the base of your brass yet?

Butch, I have an order in to Brownell's for a bump gauge and comparator insert setup, so with that I should be able to measure the shoulder bump and keep it at .002 so I am not working the brass too much. I like your idea of having my gunsmith make a gizzy so I may contact him to see what that would cost. Would probably be the most precise way to do what I'm trying to do. My batch of new, unfired Lapua brass measures .466 at the base. After firing, unsized brass also measures .466. The reamer measures .467 at the base. So I think, as Dave Skinner said, and it sounds like you agree, my chamber should be a good fit with the Lapua brass I'm using. Minimum clearances but that should help brass life as long as I don't overdo it on the resizing. Thanks for your suggestions.

Dave Skinner asked me to post a follow up when I got this issue sorted out, so here's the follow up. I have been doing more loading and shooting, and I believe my concerns were unfounded. Yes the chamber is on the tight side with Lapua brass, particularly in the neck, but not excessively tight. I think I'm getting a good bullet release. I've decided to order a Ti Nitride bushing for the Redding die a little smaller than what I'm currently using. My .251 is only giving me a thousandth or two of constriction so I ordered a .249 to provide just a little more neck tension. I've got my body die set to bump the shoulder back .002. Cases feed without issue. Decided to try H4831 with the 75 grain ELD-M bullets and a trip to the range on Saturday gave me several 5 shot groups around 0.6 to 0.7 inch at 100, and that's good enough for me. I'm using CCI-200 primers, and I think on my next loads I will try CCI-250s just to see if it makes any difference. One more note, I changed scopes from an old Leupold 16X to a Meopta 4.5-14X. The Meopta is very clear and was very easy to sight in; no Leupold dance. The turrets are much more low profile than the Leupold and that solved an issue with ejected rounds bouncing back into the ejector port. Very happy with the rifle and the scope at this point.

Actually you only need .002 for release. That means you have to cast your chamber and measure the neck. You will be turning the necks so that with a seated bullet it comes out to spec IN ALL DIRECTIONS. You are safer going .004 on that size which to me always seemed to work just as well.

You are not going to have a great deal of neck tension. Figure on firing single shot as you don't want bullets moving in the magazine.

You then can seat where you want, or seat with the rifle. That means the bullet is in contact with the lead and is pushed into the case when the bolt closes. With that throw your data away and start over from the bottom.

I contact seat in my 284. I ended up a full 2.5 grains less of H4831sc than book max. Note that when you chamber you have to fire the round because the bullet will stay with the barrel. Otherwise you have to elevate the muzzle, remove the case and tap he bullet with a rod.


Now I don't mean you just put the bullet in and jam it home. In my 284 it's .005 beyond contact.

Thanks for the info Armednfree.. I've measured base-to-ogive and I'm aiming for about .02 of jump to the lands. Those long 75 grain bullets at that seating depth don't come close to fitting in the magazine. One of the drawbacks of using a model 788. I don't mind loading one at a time though. I don't think I want to try seating with the rifle, although it's an interesting idea. It's going to be a coyote and prairie dog rifle (prairie dogs it will be accompanied by a .223 and be used more sparingly for longer range shots).

What I told you was all bench rest stuff. The accuracy requirements you need are not nearly that high. I'm talking about shaving .1 off a group, that doesn't mean anything in your objective.