Rebarreling 308 to 243AI as a switch barrel Savage

[CaptBeach]

Traded into a 243AI barrel for my rifle...plan is to have a switch barrel that will function with my CDI DBM bottom metal and mags...barrel is a nearly new (less than 40 rounds) stainless fluted 26" threaded 5/8 x 24 off of a Savage 12 LRPV that was re-threaded to small shank and rechamber'd to .243AI. Its a 1:8 twist and I plan on shooting 115 Moly DTAC and Bergers into the 3100+ fps range. I have a few questions that I've gotten mixed answers to in my searching...

1. Headspacing, I've got 308 go and no go gauges. Good enough?

2. Fire forming brass...I know the best way to accuracy is new .243 brass that's been fire formed in my chamber on a properly head spaced gun...but buying 5 same lot boxes of premium .243 will get some trigger time in and should be fairly accurate AND yield fire formed "to my chamber" cases. Some say Lapua cases are worth the $$$ are they? I'll be reloading this rifle only other than donating standard cases to brass.

3. Experiences of others out there who have been there...done that...

4. Bullets and brass...any preferences here

This is the donor rifle...

 

[CaptBeach]

So how should I go about head spacing this for the first time...I do not have access to a case fired from this barrel...I do have some new Federal 243 90 grain ammo

 

[284driver]

You should get a 243 a.I. go and no go gauges to set it with. don't skimp on this because you will be switching back and forth and you want to get it right every time.

 

[CaptBeach]

THAT is exactly what I'm going to do...

 

[Nomad47]

For a small shank barrel you can screw the barrel on until it JUST TOUCHES the 243/308 go gauge. Then turn the barrel .265" more as measured on the outside circumference of the barrel. This will move the barrel in .004" which is what Ackley prescribes. New brass should chamber with some effort. This will hold the brass against the bolt face for proper fireforming.

 

[firearmdoc1]

+1 for what Nomad said. A 308 go gauge will be used as a NO-GO gauge for the AI chamber, so you will only need to buy a 243AI go gauge.