Gunsmithing Bolt Cone to Cone Breech Clearance, How Much?

[Dennis_in_VA]

I'm getting ready to put a barrel on a Bat MB and I'm ready to put the tool to the steel.

My question for those of you more experienced than myself is:

How much clearance between the bolt and the breech is necessary and how do you
go about checking this to make sure that you have what you <span style="font-style: italic">THINK</span> you have?

How much is too much or too little gap?

Thanks in advance for your input.

 

[Bluejazz]

Re: Bolt Cone to Cone Breech Clearance, How Much?

Just watched a gunsmithing video by Gordy Gritter, who is a top notch gunsmith here in the midwest.
he sets it at 6-7 thousands clearance, and measures it by seating the bolt in the action, without the bolt guts, and puts a dial caliper against it and measures the bolt movement(wiggle) back and forth.

 

[Dennis_in_VA]

Re: Bolt Cone to Cone Breech Clearance, How Much?

Well Bluejazz, I watched the very same video and I can tell ya this.

That .006" clearance that he SAID he had was BS.... he could have had a MILE and still would have shown .006 or .007 or what ever. I took my brand new Bat MB which is basically the same action he had and guess what? My receiver had exactly .006" of bolt handle travel WITHOUT a barrel. Makes ya kinda thing twice about what these guys are puttin out there for those of us that are just getting into the Gun Plumbing hobby.

A .006" feeler gauge will just fit in the gap with the bolt lugs all the way to the rear.


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[lfagan]

Re: Bolt Cone to Cone Breech Clearance, How Much?

Well I just did this operation on a Model 70 and I set the clearance at .005". I cut the cone until the stripped bolt would just "go" against the cone and then cut my clearance. I checked my work with a dial indicator on the back of the bolt....
Len

 

[AKA-Spook]

Re: Bolt Cone to Cone Breech Clearance, How Much?

.010 . I measure the outside edge of the cone from the face of the receiver,without firing pin assembly in the bolt,action hung vertically in a vice.
The clearance of the bolt to the receiver (side to side) never mattered much by virtue of the bolt's purchase on case in the chamber actually locating the bolt in the center of the action( in theory)..... if I've done everything correctly.

In this instance clearance is clearance and what you're actually gauging is the case protrusion at the breech.

I disassembled a rifle with a coned bolt once and found it didnt have a coned breech at all...from the factory in Europe ...Talk about clearance!

 

[wnroscoe]

Re: Bolt Cone to Cone Breech Clearance, How Much?

Dennis,

I use .005" clearance on most of my builds, cone breech or recessed bolt nose, BR or field rifle. There are drawings available for the BAT Receivers and I'd try to obtain one Tuesday from BAT if I were you. First, strip the bolt to a bare bolt body. Now, with a set of depth mics measure the headspace of your receiver, receiver face to bolt face if no recoil lug is being used, record this measurement. This is typically the tenon length I use unless the drawing calls for something different.

Now, after threading and fitting cut the cone breech, I believe 27 degrees on a BAT but don’t quote me. Typically, the cone runs out to just short of the breech OD. When you’re about 75% complete with the cone stop. Screw the receiver on with the bolt in and closed. The cone and bolt lug faces will intersect and stop the receiver short leaving a gap between the receivers face and barrel shoulder. Measure the gap with a set of feeler gauges and record the measurement. This is the amount of material to be removed for a zero clearance fit. Check your self several times while using this method as you go and the fit will be dead nuts perfect. Deduct your clearance of .005" + .001" for the crush and it'll GTG. Prior to chambering, make sure your dry fit is dead nuts and you have at least .005" forward and rearward movement of the bolt while it's closed. Any less and you could have problems when the receiver heats up in the sun.

Look me up if you hit a snag.

 

[Bluejazz]

Re: Bolt Cone to Cone Breech Clearance, How Much?

Dennis,
Just trying to help. Sorry I bothered to post.

 

[Dennis_in_VA]

Re: Bolt Cone to Cone Breech Clearance, How Much?

Hey Bluejazz, I was not blasting you.

I was just relating what I had observed versus what the "Pro" was showing in the Video.

I appreciate ALL of the help here.

This Forum is a treasure trove of real world information just for the asking.

I'm sorry if you thought I was aiming at you.

 

[Dennis_in_VA]

Re: Bolt Cone to Cone Breech Clearance, How Much?

That Bat MB I have has a recessed area of about 1" before the threads even start.

Therefore I cannot cut the tenon long and check the gap between the shoulder and the face of the receiver.

Here is a practice stub I did the other day. I had .020" clearance.

I checked it by sticking a piece of lead wire on the bolt cone and closing the bolt on it.

I have received enough input here that I have came up with a solution.

I will however give Bat a call and get a copy of their drawing for this model.

Thanks to all that have responded.

I will post up when I get it screwed together.

 

[wnroscoe]

Re: Bolt Cone to Cone Breech Clearance, How Much?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dennis_in_VA</div><div class="ubbcode-body">That Bat MB I have has a recessed area of about 1" before the threads even start.</div></div>

A 1" relief groove is a lot, do you have a picture?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dennis_VA</div><div class="ubbcode-body"> I cannot cut the tenon long and check the gap between the shoulder and the face of the receiver.</div></div>

Not what I said to do. Go back and re-read my post very carefully. I've chambered several BATS, I wasn’t guessing.

 

[Dennis_in_VA]

Re: Bolt Cone to Cone Breech Clearance, How Much?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dennis_in_VA</div><div class="ubbcode-body">That Bat MB I have has a recessed area of about 1" before the threads even start.</div></div>

A 1" relief groove is a lot, do you have a picture?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Dennis_VA</div><div class="ubbcode-body"> I cannot cut the tenon long and check the gap between the shoulder and the face of the receiver.</div></div>

Not what I said to do. Go back and re-read my post very carefully. I've chambered several BATS, I wasn’t guessing.
</div></div>

I was not insinuating that <span style="font-style: italic">you</span> were guessing. I was referring to the videos that I have watched. Those "Pro's".

 

[WRM]

Re: Bolt Cone to Cone Breech Clearance, How Much?

I'm with Roscoe....

You can still do it that way with that "counterbore" - thread and fit up the tenon/counterbore without the bolt (fit the barrel OD/face to the action), then use the bolt to fit your cone (fit the barrel face to the bolt). Separate operations.

At least that's the way that I see it....

Bill

 

[Dennis_in_VA]

Re: Bolt Cone to Cone Breech Clearance, How Much?

OK, I got a print from Bat today. The headspace dimension that I got from my action was 1.073". So I was spot on there. As indicated by the dimensions on the print there should be .013" bolt to barrel gap ( 1.073-1.060=.013).

 

[wnroscoe]

Re: Bolt Cone to Cone Breech Clearance, How Much?

The Headspace is 1.073" / 1.075" I'd opt 1.073" or headspace to fit.

Threaded Extension Length and diameter is 1.060" and that’s what I'd cut it for. <span style="text-decoration: underline"><span style="font-weight: bold">I'd still cut the breech cone to fit the bolt cone -.005" clearance </span></span>

The .013" difference isn’t clearance between the bolt cone and breech cone. The bolt face is recessed enough to allow minimal clearance at the breech and bolt cone.

Chamber only after the cone, fit and polish is complete. Polish to your liking with 240, 320, 400 grit paper.