F T/R Competition New Barrel Chamber?

[DropinLead]

Looking for some guidance or best practice for a competition chamber set up. Seems a bit of chicken and egg going on but I am sure I am missing something.

I am getting my new barrel on Wed. I plan on getting new rifle set up and working out a load for 300yd F-class. The gun smith wanted me to provide the round I would use so he can closely size the chamber to the round. Sounds good except I have not worked up a load, I needed the barrel first. Different powders/bullets take different seating depths and what not, it takes experimenting.

When you all get new barrels and have not worked up a load yet for what ever reason, switching classes, switching calibers or what not, what does one do?
*Do you just get a SAMI spec chamber work out a load and then get another barrel?
*Do you just get a SAMI spec chamber or chamber for your case but with a but a few hundredths less jump?
*Do you select a bullet and powder and then research and guesstimate ?
*Some other option I have not thought of yet?

 

[gstaylorg]

Couple of possibilities given your situation. First, you can spend some time here or Accurate Shooter (or similar) asking/looking for reamer specs someone else has already used successfully with whatever caliber/bullet you plan on shooting. Your smith should be able to figure out how to proceed once he has the caliber, neck, and freebore dimensions you want. Alternatively, I would call Dave Kiff at Pacific Tool and Gauge with the exact barrel specs, along with specific details on what bullets I was planning to shoot. He likely already has designed a reamer optimized for whatever you're planning to load/shoot. Once the barrel is finished, you optimize the load to it once you have the rifle in hand. Unless you're wanting to experiment with a very unusual caliber or chamber dimensions, there's no need to reinvent the wheel. Chances are extremely good that a reamer that will work well with your chosen bullet(s) has already been developed and used by someone else.

 

[DropinLead]

Yep pretty much what I figured, research select and go from there. Pretty sure the gun Smith uses the pacific tool reamers for match 308. I know he has two with different freebore. I'll bring him a dummy round seated CBTO of 2.225. The powder I want to play with apparently likes a tad shallower seating depth due to rapid pressure build. I can still work out loads with Varget and 4064 at that seating depth. Yep using the SMk168 I know you all hate. Got 2000 of them.

Thanks for validating what I thought, look what others do then duplicate it to start with that. Can always get a different barrel in 12 months.

Thanks!

 

[BERTMAN77MK2]

Some benchrest shooters use the same reamer for the chamber and a blank Die
to achieve the best results.

 

[damoncali]

There is a very good chance that one of the reamer makers makes what you want already, especially if it's a .308. No need for a custom grind. The big choices are:

1) Neck clearance. Buy some brass and measure the neck thickness. Assume you'll turn off a thou or two (or don't). Add whatever neck clearance you want - for example: if the (6mm) brass comes with a thickness of .0135" , assume you'll turn it to .012" and you might want a .005" clearance. 2 x .012 + .243 + .005 = .272 neck.

1) Freebore. You'll want more for heavy bullets, less for light bullets. Ask the reamer maker what's recommended for the bullets you have in mind.

 

[gstaylorg]

FWIW - below is a link to a similar thread that has several reamer prints posted for you to look over. Based on your desire to use 168 SMKs, something like the Bisley reamer would be a very good choice. All my .308s were cut using the PTG .308 Win FTR reamer (.342nk, .085 FB, 1deg30), which is very similar to the Bisley. This is GAP's standard .308 reamer and works very well with a variety of bullets ranging from 155s to 190s. All of my GAP rifles with this chamber have shot very well with factory 168 and 175 match loads. You should be able to do a lot better with handloads.

FWIW, I'm currently shooting Berger 185 Juggernauts at ~2780 fps in a rifle with these chamber specs, so you'd have a pretty wide choice of bullet weights (lengths) with which to work in a similar chamber. Even though the .085 freebore isn't optimal for a bullet as long as the 185 (PTG makes a reamer specifically designed for those with a .168 FB), so far they have worked extremely well and I'm very happy with the results. Hope this info helps.

What Reamer for F-class .308

 

[DropinLead]

Doesn't the gun smith cut the chamber so the ogive is .01 or so off the lands if you have a round? I can't work out what the .085 fb translates to in terms of jump to the lands. What is the chamber length from cartridge bottom to the lands? My fn for example was 2.867.

 

[damoncali]

What you care about is the distance from the case mouth to the leade. You just have to have enough room for the bullet to fit without seating it too far into the case. Some people don't want the bearing surface to hit the neck/shoulder junction due to donuts, for example. If you have too much room (too long a throat), you'll be jumping, but there are worse things in life. It really is as easy as saying "I need a .308 reamer for a no turn neck throated for 185's." You'll have to adjust your seating a little no matter what. The throat length just gets you in the ballpark for the bullet you want. This has already been figured out for most common cartridges. Ask the experts - the reamer makers. They'll tell you if you need a .085 or a .070 or a .120 or whatever. No dummy round necessary.