Chambering a barrel correctly

[xcalibor67]

Have been reading many many articles on this subject and have a few questions of my own...

Have read that the terminology for the phrase "Head Space" is the actual clearances in relation to the chamber and the case, and that "Head Clearance" is clearances in relation to the bolt face, case and chamber..Or least this is the way I understand their take on it. I have read where some say, don't worry about "Head Space" as its not important, only worry about Head Clearance.

I think I understand why they say this, but it is not a given when chambering a new barrel.. @ least using the savage type barrel nut.Here is an exaggerated example of why I say this..
Lets say I take a thread barrel and only ream the chamber 3/4 of the way. I can then screw the barrel in the action, use the Go-Gauge, and still set the
"Head Clearance" to specs....and Houston, we have a problem. To much unsupported case. What got me to thinking about this was, trying to find out the proper depth to ream a Barrel in 222Mag, How much case protrusion sticking out of the chamber, to be a finished chamber, ready to screw in the action using a barrel nut to set "Head Clearance"..Still have not found the answer im looking for, so if anyone knows please inform me.

 

[rcmodel]

You need to measure how deep the bolt face is.

In other words, how much case head is inside the bolt face before the bolt hits the barrel shank and the bolt won't close.

It's just a Little Chinese Algebra to cypher it out!

IMO: Headspace and Head Clearance are two different ways of saying the same thing.

rc

 

[Jim K]

xcalibor has hit on the problem when folks insist that excess headspace can be handled by just neck sizing cases. If the reason for the excess headspace is battering of the locking lugs and lug seats (the most common situation), neck sizing just lets the case protrude further and further out of the chamber until it lets go, wrecking the rifle and possibly the shooter. The head clearance can be OK, since the base of the case is up against the breech face, but with a lot of the back end of the case sticking out of the chamber, disaster, as they say, is being courted.

Jim

 

[xcalibor67]

TY, With the understanding of adding 8k for clearance, your talking of measuring from the very tip of the bolt, down to the actual bolt Face....
This is the way I was going to do, but then got to looking, seems the bolt tip may have been ground altered, for what reason god only knows,,Its used.
I understand the barrel makers have machines set up to finish ream prefit barrels automatically, but even so, do they not have/know the exact numbers in which the case, Go-gauge sticks out of the breech face,. Point being measuring used perhaps altered parts as a guide, just sounds bad.

 

[xcalibor67]

Jim, your speaking my language, lol

 

[rcmodel]

You could get a brand new bolt head from Brownell's or Midway and start over fresh.

That's what I would strongly suggest you do if someone has been grinding on the one you have!

http://www.brownells.com/rifle-parts/bolt-parts/bolt-hardware/bolt-heads/bolt-head-prod20652.aspx

Rc

 

[Jim K]

Barrel makers typically "short chamber" barrels, leaving final headspace adjustment to be done after installation. Some folks on here claim they ream the barrel before installation, using calipers, yardsticks, bats' wings or whatever, but most of us ignorant folks actually use headspace gauges. Rifle factories now generally do final reaming by pull-through reamers, turned by a rod from the muzzle - just insert the reamer, insert the bolt, and turn the reamer until the bolt closes.

Some folks use factory ammo in lieu of gauges, which misses the point that gauges are used precisely because ammo cannot be trusted to be correct, especially for military ammo in wartime.

Jim

 

[xcalibor67]

Most "Drop-in" savage and now the new Remage barrels with the nuts, come fully chambered, reamed to the correct depth to insure proper case support.
which means, it doesn't matter if the bolt face, bolt tip, or any of the above have shaved etc..You merely screw the barrel in or out to set proper "Head Clearance" and, you know for a fact you have proper case support...This is what im after, Think I call a few barrel makers 2morrow and see if they will share their knowledge,lol. Thanks guys.

 

[Jim Watson]

Old time FLG points out that in his day, any serious gunsmith had a lathe, so replacement barrels were fully or even long chambered. They were adjusted by turning off a bit and checked with a headspace gauge which cost a lot less than a reamer, didn't wear out, and often served more than one caliber.

 

[fguffey]

Headspace and Head Clearance are two different ways of saying the same thing.

According to SAAMI the chamber has head space, SAAMI suggest measuring the head space of the chamber from a datum to the bolt face.

SAAMI has a glossary of terms, in their glossary of terms they identify clearance then go on to say most confuse clearance with head space.

Case head protrusion, I have no fewer than 40 Mauser type barrels, case head protrusion from the Mauser is .110" +/- very few. I have thousands upon thousands of cases for the 30/06. The case head thickness of my 30/06 cases is between .200" to .270" when measured from the top of the cup above the web to the case head. If there is a conclusion to be drawn the case with the .270" thick cases head is safer than the .200" thick case head. The .270" has more case head support.

Old time FLG points out that in his day, any serious gunsmith had a lathe, so replacement barrels were fully or even long chambered. They were adjusted by turning off a bit and checked with a headspace gauge which cost a lot less than a reamer, didn't wear out, and often served more than one caliber.

Old time: Anyone from the old days knew when they purchased a barrel from Douglas the instructions came with the barrel. Douglas offered finished chambers. When installing the barrel they offered options.

F. Guffey

xcalibor has hit on the problem when folks insist that excess headspace can be handled by just neck sizing cases.

I off set the length of the chamber with the length of the case from the shoulder/datum to the case head. unsupported case head/case head protrusion is determined before the barrel and receiver is screwed into the receiver. There are different receiver designs, there are push feed and control feed receivers, there is no blanket statement that is correct.

folks insist that excess headspace can be handled by just neck sizing cases

I insist a reloader should be able to determine the length of a chamber from the shoulder to the bolt face, I have chambers that require formed cases, none of the chambers have excessive case head protrusion and all of the chambers have case head support.

I have heard horror stories about 03s having excessive case head protrusion, all of my 03s and M1917s have more case head support than the Mauser and almost as much as the 303, BUT! there are rumors the 03 has as much as .170" case head protrusion. If one of my 30/06 cases with a case head thickness of .200" was fired in one of the 03s with excessive case head protrusion less than .030" of the case head would be supported.

F. Guffey

 

[krs]

Jim,

I have muzzle driven reamers in both .30-06 and .308 that I bought for finish chambering when installing new barrels onto M1 (Garand) receivers. A special Dewey rod with a hex drive does the turning and I THINK I bought the whole affair from Brownell's some time ago.

Just saying that it's not only a factory method.

It works like a charm and beats the heck out of repeatedly removing the barrel from a Garand (and eventually losing the "squish" and having to reset the whole business) since there's no good way to turn a conventional reamer in that closed back-end receiver.

There's even a springloaded gizmo to apply pressure on the bolt to keep it going toward lockup but I always used my fingers to do it just fine.

If Clymer makes reamers in other calibers with the socket hole in the nose I don't know any reason that hand muzzle drive finish reaming couldn't be done on any rifle. If Clymer doesn't I'd bet Dave at Pacific would find it a fun project to make some up, especially if he could see making a lot of them for home barrel changers to use. With a prechambered barrel only needing to finish out the last .010" or so most anyone with the brains to know the difference between clockwise and counterclockwise could make for a safe shooting job of it.

A set of headspace guages, the reamer, the original bolt, and the driver handle - why not? Might probably need to temporarily remove the extractor if it keeps the guage off the boltface.

 

[Jim K]

Hi, krs,

I didn't say that pull through reamers were used only by factories, though until fairly recently there were none available to gunsmiths/hobbyists. Before that, there were reamer wrenches that could be used on rifles like the M1; tedious to use, but better than removing the barrel.

Jim

 

[Zeke/PA]

O.K., Here's my take.
Let's start with a fairly simple Mauser 98 action.
First, with a Depth Micrometer, measure from the FRONT of the receiver ring to the INTERNAL locking surface of the action.
THEN measure to the bolt face of a fully locked (disassembeled) bolt.
Subtract the first measurement from the second and that's what you strive for when chambering using ,once again a depth mike and headspace gauge.
Usually, a set of headspace gauges will function as proper clearance as MINIMUM headspace is not desireable.
A set of headspace gauges should include a "Go", No Go", and a "Field" gauge.
If you are skilled enough, your desired headspace will be attained while the barrel is still in the steady rest of your lathe.

 

[fguffey]

Some folks on here claim they ream the barrel before installation, using calipers, yardsticks, bats' wings or whatever, but most of us ignorant folks actually use headspace gauges.

Jim K, I did not say ignorant, you did. I do not believe the OP wants to know 'what you ACTUALLY use', I believe the OP wants to know "How you ACTUALLY use the head space gage.

Zeke/PA, I agree,

Subtract the first measurement from the second and that's what you strive for when chambering using etc.

I use case head protrusion from the chamber. If I am going to use the receiver I check the length of the chamber first from the shoulder/datum to the bolt face. After removing the barrel I check case head protrusion. Remembering to add case head clearance or make a bat wing head space gage that includes case head clearance.

Then there are instructions from barrel manufacturers. Douglass included instructions for chambers that were finished,

F. Guffey

 

[fguffey]

Lets say I take a thread barrel and only ream the chamber 3/4 of the way. I can then screw the barrel in the action, use the Go-Gauge, and still set the

That would be impossible, if you placed the go-gage into the chamber before screwing the barrel into the action you would know how much case head protrusion you have. I have no fewer than 40 Mauser barrels, I know the case head protrusion before I measure. Case head protrusion on my Mauser barrels is .110" +/- very few. Same for my 03, 03A3 and M1917 barrels, case head protrusion on the 03 and M1917 barrels. I have .090" case head protrusion from the bottom of the extractor cut, except for the extractor cut my 03 and M1917 barrels have almost as much case head support as the 303.

O.K., Here's my take.

F. Guffey

 

[Zeke/PA]

Finished Chambers?
I haven't done any chambering in awhile BUT, I would certainly steer away from this process.

 

[xcalibor67]

@ fguffey.. " Here is an exaggerated example of why I say this..' Was exactly that, an exaggeration to give a reference as "what" I was pointing out...
Not sure how many 100k's you could realistically be off, but im sure a few.
But I sorta found an answer I can live with. Found a factory 222mag barrel and measured the protrusion with a go gauge and my calipers. Spot on .160 of the gauge sticking out of the chamber. .The main reason I wanted to know was so I could finish ream the chamber, then merely screw it in the action and adjust head clearance with gauges. Yes I could screw the barrel in, adjust the chamber face clearance by measuring the bolt face depth etc.. ream it in the action, or take the barrel in an out a few times, but im getting old and lazier, or smarter dunno which...Hey if the factory feels that .160 is right, i'll go with it...

 

[fguffey]

ream it in the action, or take the barrel in an out a few times, but im getting old and lazier, or smarter dunno which...Hey if the factory feels that .160 is right, i'll go with it...

Found a factory 222mag barrel and measured the protrusion with a go gauge and my calipers

The part that is scary, everything that comes after "HEY!".

Head space (length of the chamber) is measured from the datum/shoulder to the bolt face. The protrusion from the barrel you measured is the distance from the datum/shoulder to beyond the end of the barrel. You have omitted the bolt face.

I purchased 4 Mausers that were sold as suspect. The barrels were modified M1917s and wasted. I tested all 4 receivers with one barrel and one bolt. The total difference in the length of the chamber of all 4 receivers was .001".

I cut the barrels off and made chamber gages with what was left over.

F. Guffey

 

[xcalibor67]

"You have omitted the bolt face." I assumed this is acceptable to merely get the case/chamber relationship correct? Once this has been established, I merely screw in the new barrel, adjust with go gauge, and lock down the barrel shank nut. If im not mistaken the mauser used a Flat chamber face and screwed into the action until the breach and inner shoulder made contact with a couple k crush fit, and then ream to set head space...Im thinking were on the same page, we just got there in different routes, im old and my thought process leans to the left..