Coned bolt nose to barrel clearance

CYanchycki

CYanchycki

Club Coordinator
Okay I am by no means a machinist. I pay to have my barrels chambered. I was in a conversation and it came up about that clearance.

I run BAT actions. From what I heard today, if I heard right 5-7 thou the typical?

We know the less the clearance the potential of the nose rubbing the barrel. To much and un
suppported case head. I guess that
Could be relative to the headspace?

The main question is, has anyone ever noticed any difference in rifle performance between say having 7thou clearance versus say 2 thou or 10 thou?

I hope this makes sense what I am asking?

Calvin
 
The two reasons you stated are the only considerations concerning coned bolt to barrel.clearance.

Too little little clearance, there is the possibility of the bolt nose contacting the barrel, or getting bound up by some small piece of debris.

Too much, you uncover the web of the case and risk a ruptured case head. I have personally seen this on a6PPC.

If you fool with enough actions, you will notice that because they vary in the amount of bolt face-recess, some can get away with more clearance without uncovering the web. Early Farleys had a particularly deep recess, so about .008 was max. The Stiller Drop Ports, while not a coned bolt, were EXTREMELY critic in that area of nose to barrel clearance. In truth, you only had a few thousandths to play with with the 6PPC case.

As to the accuracy question, as long as the bolt does not get interfered with, the actual number is a moot point......until you blow the head of of a case.

As to the headspace reference, you can have perfect headspace and still have too much or too little bolt to barrel clearance as they are too separate measurements.
 
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CYanchycki said:
We are aware of the recommendation for clearance, we are more interested in my last question re rifle performance/accuracy.

Calvin
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Calvin, as I said. As long as it has clearance, and not so much as the web of the case is compromised, it has no affect on accuracy.
 
Thanks

Jackie.

Appreciate your input.... nice to here from one willing to share and not hold it dear to their heart.

Calvin
 
Calvin,
I have had one instance were the bolt clearance was to tight but the bolt still closed fine. After about 100 rds and nothing working for groups I began inspecting and everything looked good until I noticed a faint imprint of the bolt nose in the closed position on the barrel. Sent it back and had a few thou more relief put on it and it started to behave better. I do not remember what the measurement was but I thought it was in the .002- .003 range.
John
 
There is a wealth of information here and Jackie is one who has shared allot. This also reminds me of cutting my barrel threads to screw on with somewhat of a real snug hand fit. Until Jackie as well as others here have shared that it might not actually be the best or even the right approach.
 
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Excessive clearance

Here is the aftermath of way to much 4198 and excessive bolt nose clearance.
Joe
 

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I err on the side of a little more clearance rather than less. As much as we like to think all custom actions are perfect and in alignment but some aren't. So I want a little wiggle room and some space for debris. Everything has a natural resting place. I've learned if you try and manipulate location with tight tolerances you introduce variables that are difficult to diagnosis.
This is more important on factory actions. I fit the counterbores on Remington's to .730" with .010" end play
 
A pal of mine had a new barrel on his Kodiak actioned HBR rig that was tossing shots. Not much...about a bullet's worth. At the end of the first days shooting, he removed the f-pin assy and was double checking his seating depth. As he opened the stripped bolt, there was a barely audible 'click'. I put some black Magic Marker on the extractor front edge and you could clearly see where the forward edge of the extractor was rubbing on the barrel coned area.

With another .005 off the coned area, it went from tossing a shot to shooting dots. -Al
 
John Pierce had me “glue” a spot of lead on the bolt cone with a spot of grease, close the bolt of it, and when it measured .004 he said perfect.
 
Along with clearance and unsupported case, another aspect of this clearance is that it meters both gas and debris in the event of a ruptured case, that can escape the gap. Add enough pressure and this too can certainly be defeated but I read this years ago in regard to the Remington 3 rings of steel. I feel it holds mostly holds true on any action design. The biggest area for error is the angle. If I'm off a tad, I'd rather err toward the bolt clearance being less, closer to the bolt nose.(inner)
 
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NezRongero said:
One layer of blue tape is go, two layers is no go. Right or wrong?
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I too use tape Nez.....

I bought Plasti-Gage of all sizes, I've tried lead shot and lead wire in greaze, I stuck a liddle Chinee in there and had him hold him hands apart belly belly carefully.

Compared to tape all these methods suck.

My tapes (I gotta lotta tapes) measure from prox .0025 to prox .004 with my current 'blue' at flat .003 But I don 't care. I measure all tapes before/after and in any case I'm looking for gross measurements so no biggie.

I also gotta lotta scissors. Wipe the end with degreaser, iron the tape on, trim with scissors/razor knife and gooda'go

Incidentally, of my barrels done by pros.... maybe 20 barrels, 6 gunsmiths..... most of them measure 'wayy biggie clearances like around 10thou VS the oft-touted <.005 and a couple are so sloppy I sometimes find kittens snuggled all up in there, have to gouge 'em out.... but they shoot like a house afire (these are coned bolts)

I don't really dink with Rem700 stuff these days what with Kelbly's making the perfect 700 action with all the bugs worked out ...... Ryan Pierce's iteration of a Kelbly is flat out hands-down the best value in the market. I can't afford Remingtons.
 
It's not impossible for somebody unfamiliar with coned bolts to err on the side of generous (AKA known as WTF) clearances.

This is from an incorrectly fitted barrel from a Barnard action.
 

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John Kielly said:
.......

This is from an incorrectly fitted barrel from a Barnard action.
Click to expand...

Note "incorrectly fitted"

I'm not disagreeing that the preponderance of folks on this planet will eff-up a wetdream. Nor that most people blunder through life applying a muddled system of trial-and-error VS actually UNDERSTANDING the parameters....

I'm saying that of work done by competent people, "looser" is better than "tighter". Just like barrel threads.
 
Interesting topic indeed for myself having absolutely no knowledge of how to go about working with a cone bolt. And the fine line there appears to be to either get right or possibly wrong.
 
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