I am chambering a barrel in 6.5/284 for a friend for a varmint rifle on a Montana S.A. 1999 Action.At the present moment the go gauge is .002" shy of touching the bolt face when the action is hand tight on the barrel.I normally tighten about 1/8 " past hand tight ( on the circumference of the barrel).If this were a standard hunting rifle I would probably go another thousandth deeper with the reamer
but this fellow wants utmost accuracy and minimum chamber.My question is should I stop here or go for another
.001" in depth? Thanks in advance. Frank.

Frank, welcome back!





I don't know the experienced gunsmith answer, but my engineer's answer is that another 1/8 inch of circumference will give you exactly .002 inches of travel if it wasn't blocked by the Mauser-type mating face of the MRC. Thus you should have between zero and .001 clearance after you tighten it.



I'd screw it down as is, but I'm not a gunsmith!

The accuracy potential will be realized when the shooter resizes the cases the proper amount in dies that match the chamber. I like to make chambers about .004 to .005 DEEPER than the "go" gage. That allows me to use Redding's Special Shellholders to get just the right amount of "bump". And the dies should reduce the shoulder and base diameters just enough to get the case back into the chamber. Accuracy in rifles requires attention to many details, not just weighing powder to the .1 grain or shooting custom bullets.
Opinion by Jay

Depends.

Are you fitting the barrel shank with equal contact on both the front of the receiver ring and the inner shoulder???? Or do you have some clearance at the inner shoulder, with most of the torque taken at the front of the receiver ring? First way, can't get a lot of draw. Second way, can get up to 0.003" or so draw.

Check the inner shoulder on the MRC action, to be sure it is "true" both in surface finish and at 90 degrees to the action centerline.

Most of us allow about 0.002" for "crush" or "draw" between the hand tight position and the fully torqued position. On actions without an inner shoulder, like a M700 Rem, you can draw up 0.003" or more. You need a good barrel vise and action wrench to properly torque the barrel.

"Nother" thing: Brass. Most brass is shorter than the "go" gauge. So, be sure to check the dimensions with new unfired brass. For a "snug" chamber, like a varminter, I like about 0.002" clear over the brass when the barrel is torqued. Benchrest chambers, tighter.

Brass again: In the 6.5x284, Lapua is the best, Norma is OK, don't know about Hornady (have not used any). Do not use Winchester 284 Win brass necked down, quality is not there. And, check your chamber reamer drawings vs. the brass dimensions, especially the diameters. Lapua and Norma is larger than Winchester, so if your reamer was ground for a snug chamber using Winchester brass, you will have problems with Lapua or Norma brass.

Do a search on Headspace here in the gunsmithing section. Several months ago I posted photos showing headspace measurment with a dial indicator and there was a lot of discussion about minimum chambers.

Most rifles, I chamber so the bolt will not close on the go gauge when the barrel is torqued. But, not for the big bore DGR's, here one wants to be able to chamber any and all brass obtained world wide, so I chamber DGR's so the bolt will just close on the go gauge.

And, be sure to lube the barrel threads, the barrel shoulder, and the face of the barrel where it contacts the inner ring. I use an extreme pressure bearing grease. Very important if this is a stainless barrel in a stainless receiver. Be sure all chips are cleaned out of the threads.