Please check my calculations

[Dave in WI]

Ok, finally going to chamber my first barrel. Rem 700 action. Please check my measurements for me. Dimensions were measured with the recoil lug to be used and are assuming .005 clearance on bolt to shank.
Thank you

 

[DaveTooley]

I know this violates the "three rings of steel" rule somewhat but I never fit the CB diameter that close. A minimum of .010" on every side and the nose. If the bolt nose touches anywhere it can cause wild undiagnosable accuracy issues.

 

[BoydAllen]

One of the very best 700 smiths, Bob Brackney uses the fit of the diameter of the bolt nose in the recess like a front sleeve. Based on a long ago conversation about those clearances, he uses .001 total clearance on the diameter and .007 in front of the bolt nose to the bottom of the barrel recess, (after truing the nose of the bolt). Sleeved versions of his actions have won against the best shooting custom actions. I agree about contact with the front of the bolt, but not with the sides of the nose. He combines this fit at the nose with close clearance sleeving at the back of the bolt under the action's rear bridge.

 

[Dave in WI]

Thanks for the replies. So I should figure .954 for shank length and .800 CB depth leaving .010 clearance? Also, should I add another .002 to both for crush fit?
edit to add: my bolt nose diameter is .691"

 

[jkohler]

cut your tennon to .954 that's .010 clearance then cut your C.B to .154 you should have .010 automatically. Maybe set your headspace .001 deeper

 

[Dave in WI]

Thanks for the replies. Barrel dialed in on the lathe waiting for me to grow a pair...

 

[jkohler]

Go slow and calm down you'll be fine.

 

[carlsbad]

Wait!!! that .810 CB depth is gonna be a bit deep. You'd probably figure out it looks wrong long before you get to .810 but you might go well past the right depth first. Try .964-.810 = .154 depth. that sound a bit better? That will give you the same clearance on your bolt nose that you choose to use on your lugs to tenon clearance.

 

[mram10]

Jerry had a good catch there.
Dave, if you have any scrap, it’s a great idea to make a practice minus the reamer to fit your action. It will catch any mistakes. I was in your shoes 2 months ago and feel very comfortable now after lots of practice and 5 real builds. Best of luck

 

[STS]

Thanks for the replies. Barrel dialed in on the lathe waiting for me to grow a pair...

It's only steel, they make more of it every day. Go for it!!!!

 

[jkohler]

Jerry good catch had a brain fart. I was heading out the door for a work call out and not thinking.

 

[carlsbad]

The kind of thing you would likely have caught.

Remember, The approximate design is that the bolt face and face of lugs are about the same so the face of the bolt is approximately even with the tenon and the nose of the bolt is approximately .150. If you aren't getting numbers in this range, you've gotten something wrong.

Next error people make is applying the clearance twice. Once you've decided how much to keep the tenon clear of the bolt lugs (I use .007"), then if you want the same clearance on the bolt nose, you don't need to do anything except subtract the 2 numbers.

--Jerry

 

[STS]

Dave, just an additional comment or two. It's difficult to measure then come out with the exact dimensions that your measurements say you should have. Your depth mic isn't squashed down with a bunch of torque like the barrel will be. I use lead squirts out of my bullet dies to measure the actual clearance between the bolt and barrel after the barrel is tight. I find that the clearance usually closes up one to two thousands. Therefore I shoot for .008 and crush a lead squirt and mic the flattened strip of lead at about .0065 clearance or so. Point is you may want to shoot for a bit more than .005 end clearance. If you close up after the barrel is tight to .003 or .004 and get a brush bristle in there you may have a bit of a problem. You can use small diameter solder to check this also, just stick it to the nose of the bolt with a dab of grease and close the bolt. Pull the barrel and measure the strip with a mic. In addition it may be more intuitive for you to measure from action face (or recoil lug) to the lug face. That number minus .008 in my case is the tenon length. Then simply make your counterbore the same depth as your bolt nose length. That will give you the exact same clearance as the lug faces. No fancy and sometimes confusing calculations. Hopes this helps. STS