BAT MB Barrel Fitting

[critter_bill]

I have recently received two BAT MB actions from Bruce. I've been waiting for Krieger barrels from Dwight Scott for about 5 months now. If I had one in hand, I could answer my own question. I don't, so I will ask here.

The MB action uses the model M footprint with a 1 inch counterbore forward of the action threads which offers increased bedding and the shorter bolt of the model B. The model MB also has an integral recoil which the model B lacked.

My question is for anyone who has chambered barrels for the BAT model MB: How much, if any, chamfer do you cut on the barrel in the area which would, without relief, contact the radius or chamfer at the base of the action's counterbore? Dwight described cutting a small relief to avoid headspace problems but did not give an actual number normally found on drawings, eg 45° x .1.

I know that Dwight's barrels will be correct. What I am looking for is how much relief to apply to two existing BAT B barrels so I can use the barrels on my BAT MB actions. I just don't want to wait 5 or 6 months to have a small chamfer cut on my barrels when I can have it done locally in one day by a competent machinist.

Believe me, this is not a slam on Dwight Scott. I have used Dwight for barrel work since 1993. He is just swamped with work. It was a sad day for regular Joes like me when Tony Boyer found out about Dwight and within a short time, a 2-3 week turnaround became a 5 to 6 month turnaround.

Thanks for any advice/help. critter_bill

 

[tightneck]

Well I've never had one of the recessed BAT's in hand, so I am only guessing. If there is a radius between the inner wall of the counterbore and the shoulder abutment, then it would depend on the OD of the barrel shank. A skinny enough shank would require no chamfer, but a thicker one may. Are you sure Dwight wasn't refering to a relief being cut where the barrel tenon meets the barrel shoulder? This is common practice on most barreling jobs...

 

[critter_bill]

Hi Tightneck,

Thanks for taking the time to answer. I'm sure that Dwight was referring to the OD because the recess,or c'bore) is Ø1.27 and I usually use Ø1.20 barrels. I have a great shooting 308 Hart and a Krieger 6BR currently threaded for my B actions. I would like to use the 308 especially on the MB. I honestly can't see much of a chamfer at the bottom of the recess although I understand that is common machining practice to create a stronger junction than a sharp edge provides.

Just got the answer from Mr. Thom:

Bill

The bore on the MB is 1.270, we use an insert with a .015 radius when boring this area, so the maximum barrel diameter would be 1.240 without causing a headspace issue.

Regards,
Bruce Thom


Thanks again and happy shooting.

critter bill