Bolt to barrel clearances?

D

dmoran65

New member
With a cone bolt face (Defiance action) how much face to barrel clearance do you like to have for BR?
Same question again but for 700-Rem style?

Thanks for your input,
Donovan Moran
 
In Steve Acker's Video.... (Tell me if you get through it without sleeping) He states that you want .005 at the nose of the bolt to rear of barrel, .005 at the front of the lugs to rear of barrel, and .005 on the diameter around the bolt nose... then he only adds .005 to the Diameter, so he gets .0025 per side, I believe he is mistaken there. He originally stated he wanted .005 all the way around.

A long time back Phil Sauer told me .007 is optimal... That's what I shoot for. Remington, Panda, Viper etc.

Paul
 
You don't want to go over .010" as you run the risk of having the case head unsupported in front of the bolt head. Just about any bolt is going to have some case head protruding from the end of the chamber. The more of the web of the case is up inside the chamber the better, but that's pretty well limited by how the bolt head is made. Most of the coned bolts with Sako style extractors have the bolt face recessed somewhere around .125". Add .010" clearance and you'll have .135" of the case head unsupported by the chamber walls which isn't a problem. The more clearance you add past that gets more case head unsupported by the chamber. As long as the web of the case is inside the chamber, there isn't a problem.
 
Mike

I used to think as you but I've been chambering hundreds of barrels that have a considerable chamfer on the chamber. Like .060" in some cases. Most average around .180" of exposed case head. There has never been an issue. I learned the hard way that if the bolt nose touches anything it affects accuracy in a bad way. I'd rather err on .005" to much clearence as .001" to little.

Dave
 
Dave, I was at a match in Denton a few years ago and someone had chambered a barrel for a 30 BR on a Stiller drop port. The older style bolt that had the 14 degree cone on the end of the bolt, but instead of cutting the cone to the flat with the 14 degree cone, they had cut the cone on the barrel with a 30 degree cone. I think it was Dave Williams' rifle. The case head blew out the side caused from too much gap between the bolt head and the start of the chamber. I also cut a 60 degree bevel at the start of my Remington chambers, but try to cut as little a bevel as I can. Not enough clearance will cause problems.
 
Mike Bryant said:
Dave, I was at a match in Denton a few years ago and someone had chambered a barrel for a 30 BR on a Stiller drop port. The older style bolt that had the 14 degree cone on the end of the bolt, but instead of cutting the cone to the flat with the 14 degree cone, they had cut the cone on the barrel with a 30 degree cone. I think it was Dave Williams' rifle. The case head blew out the side caused from too much gap between the bolt head and the start of the chamber. I also cut a 60 degree bevel at the start of my Remington chambers, but try to cut as little a bevel as I can. Not enough clearance will cause problems.
Click to expand...

WoW...I can't image anyone chambering a barrel leaving any part of the case web outside of the chamber...I make sure that the only thing extending outside of the chamber is the extractor groove of the case...having a slight radius at the rear of the chamber to facilitate feeding can be as little as 1/32"...I usually do it with some 320 grit on a hard dowel then polish with some 600 and Cratex...bolt to barrel clearance is less important IMO than case web support...that being said they should never make contact, when locked up with round in the chamber...
 
eww1350 said:
WoW...I can't image anyone chambering a barrel leaving any part of the case web outside of the chamber...I make sure that the only thing extending outside of the chamber is the extractor groove of the case...h
Click to expand...

Maybe a terminological issue? The web is the strongest part of the case. Nothing wrong in having it unsupported, though as you get to the front of the web (case mouth side), you want support. Sometimes, with some cases & some bolts, you absolutely have to leave part of the web unsupported.

It also depends on the design of the case. Some, like RWS 7mm Mauser, have such a narrow extractor groove they're going to behave differently -- lots of extractors won't even pick them up. Others, like the Norma 6.5x54 M-S case have a web length of .14 inches. I kid you not. You'll spend some time uniforming the flash hole on one of these! Edit: why mess with these? For a 6 Ackley with RWS brass, and a 2-inch long PPC.

With some designs, the forward edge of the extractor groove is as far forward as the primer pocket. You just have to leave part of the web unsupported with that design.

I imagine Dave Tooley has recently been chambering a lot of .338 Lapuas & .338 Normas. Part of the Lapua re-design of the .416 Rigby case for the .338 Lapua had to do with strengthening the case head. Know nothing about the Norma.

I do know if I handed Dave one of those oddball 7mm Mauser's or 6.5x54 cases to chamber a rifle for, I'd get it back right either way...
 
Last edited:
Thanks all for the reply's !!!!!!!

More question:

- What kind of problem's/issues could arise from "not enough clearance" and/or actual contact?

- Had a barrel that basically had no clearance (very slight contact) and also it had a "carbon ring" build up. The barrel got shot a couple hundred rounds before these were discovered. In that time, accuracy was good, but the brass was getting hurt and early pressure signs in the charge ladders.
Would the hurt brass and early pressure signs be results of the lack of clearance? and if so, why?
(trying to de-siffer if the pressure issues were do to clearance issue or the carbon issue or both)
Since the issues, 0.006" clearance was machined and the carbon ring removed. No more issues to pressure and hurt brass.

Thanks for the input !!!!
Donovan Moran
 
Last edited:
Donovan,

If it's a cone bolt face how do you know it's touching? Either there's room or there isn't. I don't know how it could touch and you not know it. If it was a Rem style it could be touching on the sides. Either way it will cause inconsistant accuracy. This wouldn't have anything to do with pressure.

Dave
 
Dave -

Thanks for the reply (was hoping to read your input) !!!

It was a coned-bolt and we used grease to determine the amount of clearance. From which we determined it basically had no clearance with the barrel torqued on.
Your input to accuracy being inconsistent when in contact, makes very good sense....
The pressure issues not being related to the clearance, as you input, is what I figured but has had me "scratching my head" as to put all that blame on the carbon ring that was present, or if it could have been clearance related as well.

Again Thanks ...... and hope to hear more inputs!!!!
Donovan Moran
 
If it is a cone bolt;
-strip the bolt
-insert the bolt
-close the bolt
-if you can't feel some axial movement, the fit, for sure, is too tight.
-if you can move the bolt axially more than a few thousands, you need to relook the entire job!!!
 
JerrySharrett said:
If it is a cone bolt;
-strip the bolt
-insert the bolt
-close the bolt
-if you can't feel some axial movement, the fit, for sure, is too tight.
-if you can move the bolt axially more than a few thousands, you need to relook the entire job!!!
Click to expand...

Another way to get a near absolute measurement is to place a short piece of .015 lead wire in the face of the bolt and extending over the face of the cone and close the bolt. The wire will crush and you can get a micrometer measurement of the crushed wire.

David
 
You must log in or register to reply here.
Back
Top