Bolt fit/clearance in counterbore of barrel

[carlsbad]

Standard bolt nose clearance on a Rem 700 is about .010". The counterbore in the barrel tenon is generally cut at .706 and the diameter of the bolt nose is about .695.

I bought a slightly used barrel with a chamber installed. However, the counterbore is .722.

What are people's thoughts on the extra clearance? In the event of a major malfunction (blocked barrel or case separation) this would allow lots more gas to escape.

The caliber is a fairly high power short semi-magnum.

--Jerry

 

[carlsbad]

Well, Lots of reads and no concerns. The guy that sold it to me got back to me that he likes it that way to make sure the bolt won't touch the barrel.

I'm just an engineer by trade and always ask why they designed it that way. Looks like it isn't an issue.

--Jerry

 

[DOGCAPPER]

Check the chamber using a no go gage.

 

[Minesweeper3433]

If the bolt is .695 and the tennon . 706 than wouldn't you actually have a clearance of only .0055 since this is a diameter?

 

[carlsbad]

I'll be setting the headspace. You can't swap barrels without adjusting the headspace. (except for a thread I read on BAT actions which I found amazing).

Yes, radial clearance is .05 if you assume it is centered. I generally talk diametrical clearance since that is what we measure.

Thanks guys.

 

[boltfluter]

Jerry,

By chance does the bolt have an m16 extractor. If so the clearance is probably needed to pop over the rim.
Either way you should be fine IMHO.

Regards, Paul

www.boltfluting.com

 

[Dusty Stevens]

Good call paul. Back in the old days when we used real m16 extractors you had to have way more than that unless you ground the nub off and tapered it to a point which made it weaker. Did it both ways and preferred to leave it whole so big clearance was the norm. Its not designed to hold in gas its designed to provide one more ring of steel for catastrophic blow ups. Gas will flow thru it if theres .001 clearance. Its only there as an additional safety measure and as long as its there its good to go

 

[carlsbad]

Thanks guys. Good call on the extractor. Applies to Sako type extractors too. I'll have to confirm clearance on the Weatherby project I'm working also as Weatherby uses a similar extractor.

--Jerry

 

[Minesweeper3433]

You can also cut a clearance for the M16 and sako extractors as a last step. After having your chamber and recess and tenon done torque on the barrel to the specs you use make an index mark and recenter back in lathe off recess. Shift the barrel to be off center by they clearance you need and make an appropriate clearance cut in the 1/4 rotation of the extractor in relationship to the breech. If done right you can have your three rings of steel supporting your extractor but still be able to have it snap over the rim of a cartridge before rotating into the support area outside of your cut. I am sorry if I didn't explain this too well.

 

[Bugholes]

There's no good reason to keep bolt nose to counterbore fit tight. I use a .720 counterbore and wouldn't care if it was .750 wide. There's so many variables regarding concentricity ( stacking tolerances) that having a tight fit here is only a detriment. I do .010 forward of the bolt nose and a minimum of .720 on he counterbore width. Counterbore are crap collectors and they need to be measured as such

 

[X Ring Accuracy]

There's no good reason to keep bolt nose to counterbore fit tight. I use a .720 counterbore and wouldn't care if it was .750 wide. There's so many variables regarding concentricity ( stacking tolerances) that having a tight fit here is only a detriment. I do .010 forward of the bolt nose and a minimum of .720 on he counterbore width. Counterbore are crap collectors and they need to be measured as such

Amen

 

[STS]

Yep. I do .010 all around. Keeps me out of trouble.

 

[Roeder]

Jerry,

By chance does the bolt have an m16 extractor. If so the clearance is probably needed to pop over the rim.
Either way you should be fine IMHO.

Regards, Paul

www.boltfluting.com

When Jerry Stiller started using an m16 extractor on his Predator / Tac30 actions he changed the drawing dimension from .720 to .740. It works just as well to leave the recess smaller and machine extra clearance on the extractor side. Either method works equally well. Here is his drawing: http://viperactions.com/files/predator_tenon.pdf