RogueNathan
Member
Yep. Called a trace machine. Works wonderfully. Its like a CMM for chambers.
Checking headspace LR308 build
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Yep. Called a trace machine. Works wonderfully. Its like a CMM for chambers.
... which, to me, means a 308 Win chamber has headspace at 1.630". Other dimensions can be at SAAMI spec. Best thing about that is new case bodies stretch minimally; head clearance is a couple thousandths but let's hope case shoulder setback from firing pin impact is minimal. Case life will be longest. And if the bolt face is properly squared up, once fired new case heads will be minimally out of square for cases not too uniform in wall thickness.
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1stmarine
Member
the chambers headspaced with gold match and black hills ammo and reloads will end up in the 1.631 gauge. On the sticky side at 1.630.
They also "stretch" a bit after torqueing and with the natural use of the rifle.
Any SAAMI chamber in the 1.631-1.632 range is considered an accurate trouble free chamber for that type of match ammo and many other brands.
They also "stretch" a bit after torqueing and with the natural use of the rifle.
Any SAAMI chamber in the 1.631-1.632 range is considered an accurate trouble free chamber for that type of match ammo and many other brands.
I'm a bit surprised any commercial 308 match ammo's headspaced longer than 1.630".
However any ammo needs enough head clearance to let the bolt go into battery exactly the same for every shot. If the bolt binds even the slightest, it's lugs and head will be at different places for each shot. The barrel won't whip and wiggle the same for each shot because reward forces from bolt lugs to their receiver abutments aren't the same for each shot. Accuracy degrades 1 to 2 tenths MOA. May never be noticed on a 1 MOA rifle, but it's a 25 to 50 percent change for the worse in an otherwise .4 MOA rifle.
That said, lots of folks like their bolts to have a "snug, slightly tight" fit on chambered rounds. They don't realize the firing pin drives .308 Win cartridges full forward in the chamber before the primer fires. That centers the cartridge front in the barrel; centering the bullet there, too. The case body is clear of the chamber wall around it except at one point on the pressure ring area that's typically touching the chamber by the extractor opposite that place pushing it there. The case doesn't lay in the bottom of the chamber when fired as so many think it does.
However any ammo needs enough head clearance to let the bolt go into battery exactly the same for every shot. If the bolt binds even the slightest, it's lugs and head will be at different places for each shot. The barrel won't whip and wiggle the same for each shot because reward forces from bolt lugs to their receiver abutments aren't the same for each shot. Accuracy degrades 1 to 2 tenths MOA. May never be noticed on a 1 MOA rifle, but it's a 25 to 50 percent change for the worse in an otherwise .4 MOA rifle.
That said, lots of folks like their bolts to have a "snug, slightly tight" fit on chambered rounds. They don't realize the firing pin drives .308 Win cartridges full forward in the chamber before the primer fires. That centers the cartridge front in the barrel; centering the bullet there, too. The case body is clear of the chamber wall around it except at one point on the pressure ring area that's typically touching the chamber by the extractor opposite that place pushing it there. The case doesn't lay in the bottom of the chamber when fired as so many think it does.
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I will assume you are using Gold Medal Match and Black Hills ammo to head space the chamber when reaming? I was trying to sort out the 1.631" measurement and the 1.630" and I wondered why would the 1.631 be 'sticky measurment'. And then I wondered of you were referring to the length of the case from the datum to the case head and still you do not know how much clearance there is between the ammo and chamber.
F. Guffey
I think he knows how much head or shoulder clearance there is with both. And he uses grade school math and reasoning with case head space numbers to determine chamber head space to the nearest .0005" which is close enough for all purposes.
1stmarine
Member
Hi,
I am not inventing anything new here.
I don't do anything different than many other people do chambering a match rifle.
There is no need for short cambering a rifle once you have a barrel dialed on the lathe.
I guess one could go back to the chamber reamer but I see no point once you are done
reaming and have a very clean chamber to check headspace. you work with the shoulder or the barrel
nut if that is your system.
In a R700 for example the tenon is cut a tad sort and then adjusted. Once you get closer all you do is
shaving whatever you need from the shoulder so slightly until you get the headspace you want.
Again, this unless you have a barrel nut system obviously.
The brass is used to headpsace by making sure the brass is snug but w/o resistance on the bolt
when closing. With a stripped bolt and everything squeaky clean the bolt should almost drop
by itself. This is when you know you have zero tolerances between your loads and resized
brass. then when using the 1.631 gauge many times feels the same as the brass but this might
change with your choice of ammo or your own sized brass. It should be minimal.
You use your sensory input from your hands and the tips of your fingers when the bolt is dropping
and how it feels to you to make sure you are not crushing the brass when closing the bolt.
And of course later the go and no go mandatory check.
This process might not work for someone who wants the gun to run any sort of ammunition
including surplus or whatever they can find. So there are trade offs depending on ones goals.
I guess one could take the largest NATO and surplus one could find and use those to headspace
but then will end up with a commercial type of chamber that might not be the best for
top accuracy with match loads. For an AR a chamber around 1.634 might be a better choice.
I am not inventing anything new here.
I don't do anything different than many other people do chambering a match rifle.
There is no need for short cambering a rifle once you have a barrel dialed on the lathe.
I guess one could go back to the chamber reamer but I see no point once you are done
reaming and have a very clean chamber to check headspace. you work with the shoulder or the barrel
nut if that is your system.
In a R700 for example the tenon is cut a tad sort and then adjusted. Once you get closer all you do is
shaving whatever you need from the shoulder so slightly until you get the headspace you want.
Again, this unless you have a barrel nut system obviously.
The brass is used to headpsace by making sure the brass is snug but w/o resistance on the bolt
when closing. With a stripped bolt and everything squeaky clean the bolt should almost drop
by itself. This is when you know you have zero tolerances between your loads and resized
brass. then when using the 1.631 gauge many times feels the same as the brass but this might
change with your choice of ammo or your own sized brass. It should be minimal.
You use your sensory input from your hands and the tips of your fingers when the bolt is dropping
and how it feels to you to make sure you are not crushing the brass when closing the bolt.
And of course later the go and no go mandatory check.
This process might not work for someone who wants the gun to run any sort of ammunition
including surplus or whatever they can find. So there are trade offs depending on ones goals.
I guess one could take the largest NATO and surplus one could find and use those to headspace
but then will end up with a commercial type of chamber that might not be the best for
top accuracy with match loads. For an AR a chamber around 1.634 might be a better choice.
I could ask: "How do you do that?" That does not work so I will tell you what I can not do: I have 68 reamers, I have access to 250 more, I do not have a reamer that will allow me to work on the shoulder, all of my reamers are 100% contact reamers, if my reamer touches the shoulder of the chamber the reamer is also contacting the neck and body. When my reamer advances the chamber advances.
Short chamber? I purchased a new barrel that was advertises as a short chamber barrel. How Short? I was told it was a sort chambered barrel and it was cut with a finishing reamer to within .010" of being completed. To determine the length of the unfinished chamber I formed 270 Winchester case with .010 added to the length of the case between the shoulder and case head. When checking the chamber the case protruded .250" from the barrel. The case should have protruded .110" from the barrel had there been any truth to their claim the chamber was .010" short. I know, most are confused, I could have started with a minimum length full length sized case; that would have caused a case head protrusion of ..260". I would have been happy with moving the chamber forward .010" but I can not expect a reamer to cut more than 25 chambers. Moving the chamber forward .250" could be the equivalent of cutting 25 chambers at .010" each.
F. Guffey
I agree, I just can not find a reloader. smith or manufacturer that list the length of the chamber in thousandths. Reloaders are basically 'fire formers', I form first then fire.
F. Guffey
1stmarine
Member
Reloaders do not sell chambers so you will not find anything there.
A Smith will build you a chamber with zero tolerances for your ammo and/or brass if that is what you want.
Commercial chambers are on the loose side to work with most commercial ammo including surplus like 308 & 7.62x51.
Short Chambers are the ones you can finish yourself w/o a lathe.
Midway sells them...
A Smith will build you a chamber with zero tolerances for your ammo and/or brass if that is what you want.
Commercial chambers are on the loose side to work with most commercial ammo including surplus like 308 & 7.62x51.
Short Chambers are the ones you can finish yourself w/o a lathe.
Midway sells them...
If the reamer has a floating pilot .0003" smaller than the barrel's bore diameter, that'll well center the finished chamber on the bore.
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1stmarine
Member
Correct, they will.
the key is to go very slowly because if you go too far then you will need the lathe and adjust by cutting from the shoulder.
Also given there is still plenty of clearance between the bolt and the tenon.
It is possible for a reloader to measure the length of a chamber in thousandths. The length of the chamber from the shoulder/datum to the bolt face could become part of the history of the rifle. Again, reloaders have mastered the .002" bump (?).
F. Guffey
Reloadron
Contributing Member
Has anyone ever used the Clyner Pull Through reamers to finish a short chambered barrel?
Ron
Ron
I am convinced nothing new is going to be introduced into this thread but I have experience with the pull through reamer. I never found it necessary when cutting a chamber in a barrel meaning the pull through reamer works on rifles with a closed in heel like the M1 Garand. And then there is that part about stopping when the bolt closes.
Back to the gun show: I have taken parts to gun shows in an effort to sell, problem I have never found a smith, gun enthuses or resource person that knew what the parts/tools were. I went to a member of the OLD CSP that I respected as a resource person; he did the research and found a picture but did not know how the tool was used. The nicest and most kind response I received was: "That looks like something you would make" and still they could not figure how the tool could be used and they were not interested in how the tool could be used. I posted pictures and ask questions on the OLD CSP forum, problem, the OLD CSP archives were dumped and I thought that was a good thing.
F. Guffey
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