Cutting chamber in a new barrel - send a dummy round?

[Creedmore]

I've just about gathered all the groceries for my .260AI build, and wondering about chamber dimensions.

It's a chicken and egg kind of thing - I can't make a 260AI dummy round to send to my gunsmith until I can fireform brass. So, looking for advice on what instructions to give him. I want to shoot 120 Nosler BTs - 140gr Berger VLDs. Don't want to get short-throated, but then again, don't want a mile of freebore.

Suggestions?
Thanks,
-Gene

 

[Kodiak]

Will your rifle be a single-shot or a bolt-action repeater? If a repeater, your g'smith may already have the chambering reamer and it is wise to instruct him to not cut the throat any longer than your magazine length. Some reamer companys make their chambering reamer without a throat taper, then the g'smith can use a throater to cut the overall length not to exceed magazine length. I've had a few factory rifles throated to let me set the bullet out and still not exceed the magazine length.

You may not know what bullet you will end up using and not all bullets have the same nose shape. Don't over-cut the throat!

Jim

All the best,

 

[joelkdouglas]

Gene,

I would call Pacific Tool and Gauge, http://www.pacifictoolandgauge.com/products.htm, and talk to Dave Kiff. Tell Dave what chamber and bullet you'd like to use, and ask him the reamer and freebore he recommends. Buy the reamer and send it with the parts to your smith.

Maybe you don't want a reamer, but I normally buy the reamer, and it will get you what you're after...

v/r
Joel

 

[SJB358]

CM, can you load a 140 Berger into a 260 case at mag length and have your smith cut the chamber so you'd be .005 or .010" off the rifling to start. Great question though, as I haven't ever had this issue yet. I also wonder if it wouldn't be smart to have a little shorter round to begin with in order to allow you to chase the lands a little as the rifle is shot.

 

[IdahoCTD]

I'd use a long action and seat it as long as you can. That will maximize the velocity and case capacity. It will take a while to burn the lands in a .260AI and if I planned to shoot it that much I'd nitride it.

 

[SJB358]

Great info Nathan. Learning has occurred!

 

[Creedmore]

CM, can you load a 140 Berger into a 260 case at mag length and have your smith cut the chamber so you'd be .005 or .010" off the rifling to start.

I was wondering about this very thing. It will be on a Rem700 long action, so magazine maximum shouldn't be a problem.

Isn't there a rule of thumb about minimum bullet seating depth? The bullet should be seated into the case mouth at least as deep as the caliber: in this case bullet seated no less than 0.264?



Nathan, can you elaborate on the nitride? That's a new one to me, I'm curious. Also -- one of those brakes I ordered will be on this rifle, I'll be sure and post pics when she's done. :wink:

-Gene

 

[nvbroncrider]

That is correct. I had some issues on my 6.5X55 by seating them too long. I had to seat the 125PT real short cause of the length of the bullet no where near the lands. Seating them at 3.1" and could seat them out to 3.2+" before I touch the rifling. I think to make them shoot I need to bring them in to somewhere around 3.025". The new 129 LRAB should really shine.

 

[IdahoCTD]

Typically you seat the bullet where the bearing surface/boattail junction is at the shoulder/neck junction of the case. Nitriding is a surface hardening used to increase barrel life. It seems to vary but most people get about 50% more barrel life. The down side is the barrel cant be set back or rechambered.