Bolt nose clearance

[Lucky Shooter]

I'm getting ready to chamber a barrel for a BAT SV action and have
a BAT tenon drawing that specifies dimensions which will produce
a bolt face to barrel clearance of .007" +/- .003".

Is .003" clearance considered to be enough ? I like the idea of maximum
chamber support of the case but realize that tightness is often a problem.

At what point does this clearance become too close ?

Would appreciate more thinking on this.

A. Weldy

 

[Walt Krafft]

Shoot to the 0.007.

 

[LVLAaron]

The way you wrote it, the clearance is .004 to .010 - I aim for 5-8 thou.

 

[Alex Wheeler]

You want more clearence than you will bump the shoulders. Sometimes I bump a little over .003. You dont want the bolt to ever touch the cone with a case in the chamber. Case web height determines how much clearence you can get away with safely. I get nervous with less than .015 of solid web in the chamber.

 

[LVLAaron]

Based on the BAT's I have, if you get the clearance where the print says the case will be supported all the way to the extractor groove

 

[gunsandgunsmithing]

I use .004-.008 now. Unsupported case is the main reason but the size of that gap also meters the volume and the size of the brass bits that can come passed it in a rupture, too. Of course, with enough pressure, nothing is gonna hold, much less meter anything. I read this years ago in an article with Mike Walker, the designer of the Remington 3 Rings of Steel. At the time, he recommended .003-.005 at all surfaces between the bolt and bbl of a Remington and he cited the metering of gas and particle size as reasoning. Of course, I'm not sure how many actions that Remington has ever made that met his stated clearances but that doesn't change the point. I will say that I've seen firsthand that his system works in a catastrophic over pressure event...but everything has limits. I agree to a point with Alex about it being more than shoulder bump, at least the logic...but the case simply can't ignite until the fp is already pushing the bolt rearward and case forward, even ever so slightly and fast.

 

[jackieschmidt]

The only actions I can remember where the bolt nose clearance was super critical were the Stiller Drop Ports in PPC ,He used a Remington style extractor, and the counterbore was pretty deep. You could easily uncover the case web if not adhering to his .003 to .005 nose to barrel clearance.

I give all of my Farley, Bat Neuvo, and Bat M .005 to .008..

 

[Lucky Shooter]

The only actions I can remember where the bolt nose clearance was super critical were the Stiller Drop Ports in PPC ,He used a Remington style extractor, and the counterbore was pretty deep. You could easily uncover the case web if not adhering to his .003 to .005 nose to barrel clearance.

I give all of my Farley, Bat Neuvo, and Bat M .005 to .008..

 

[Lucky Shooter]

Thanks for the replies.

It appears BAT's dimensions are pretty much in line with what you use.

A. Weldy