Factory Chamber vs. Criterion Chamber

[JoeJoe]

As some of you know, I swapped my factory .308 barrel for a .308 Criterion on Friday. This afternoon, I spent a few hours resizing and prepping brass for load development. I'd saved about 70 pieces fired from my factory barrel, and shot 30 through the new barrel yesterday. While resizing, I noticed the brass from the factory barrel was very hard to full-length size (it was properly lubed), but the brass from the new barrel sized very easily. Is this likely caused by much closer tolerances on the Criterion barrel?

Thanks!

[Robinhood]

I'm thinking about two things that make brass need more effort to size. Chamber dimensions and work hardening.

[Shortbox4x4]

Maybe and maybe not. Manufacturers of firearms can use a SAAMI min spec and or what is called a production chamber. Production chambers tend to be looser/bigger on sizes/tolerances.

That being said headspace dimension from one barrel to the next and or to the same firearm can vary. This can make a difference.

Also the same load run thru one barrel can react different in another barrel. Why? One is the chamber and also another are the actual bore and groove sizes can vary from barrel to barrel. A tighter bore/groove and or a tighter chamber can drive up pressures and or drop pressures. This has an effect on the brass/ammo etc...

Custom barrel makers can and do use SAAMI min spec. Or they’re own spec’d chambers/reamers made to they’re own design.

The best thing to do would be to call Criterion and ask them if they can supply you with a copy of the chamber reamer print that they used. If we get asked I know by looking at the customers order what reamer we used.

Also keep in mind that over time as a reamer is used it can cut differently or should I say very slightly to a different size. A good example....a reamer that cuts even a .0001” (either intentionally or not) under on the throat size and you get a different lot of bullets and or ammo can drive up the pressures easily 4K to 6K psi. That’s data I recently was involved with ammunition test barrels and chamber sizes in the throat and what it can do.

Keep in mind and I’ll say it again....even when the same reamer is used, headspace is theoretically set the same....a tighter or looser bore can effect pressures and have different effects on the brass.

Yes brass work hardens over time not to mention different lots. Same as bullets....different lots of jackets as well as I do believe as the jackets are made they can work harden as well.

We all deal with a lot of variables.

It wouldn’t hurt to call Criterion and ask if you can get a copy of the reamer print that was used in the barrel.

Later, Frank
Bartlein Barrels

[Shortbox4x4]

I/we get asked a question pretty frequently. Do we have a match chamber/reamer? I have to ask the question back right away. Define match chamber? What do you want?

Shorter/tighter throat/freebore?
No turn neck?
Tight neck?
Tight case body?
Or a combination of all of the above or some of the above?

Sometimes before I even get a reply I will say right away....what are you using the gun for? Then go from there.

[Ted_Feasel]

Maybe and maybe not. Manufacturers of firearms can use a SAAMI min spec and or what is called a production chamber. Production chambers tend to be looser/bigger on sizes/tolerances.

That being said headspace dimension from one barrel to the next and or to the same firearm can vary. This can make a difference.

Also the same load run thru one barrel can react different in another barrel. Why? One is the chamber and also another are the actual bore and groove sizes can vary from barrel to barrel. A tighter bore/groove and or a tighter chamber can drive up pressures and or drop pressures. This has an effect on the brass/ammo etc...

Custom barrel makers can and do use SAAMI min spec. Or they’re own spec’d chambers/reamers made to they’re own design.

The best thing to do would be to call Criterion and ask them if they can supply you with a copy of the chamber reamer print that they used. If we get asked I know by looking at the customers order what reamer we used.

Also keep in mind that over time as a reamer is used it can cut differently or should I say very slightly to a different size. A good example....a reamer that cuts even a .0001” (either intentionally or not) under on the throat size and you get a different lot of bullets and or ammo can drive up the pressures easily 4K to 6K psi. That’s data I recently was involved with ammunition test barrels and chamber sizes in the throat and what it can do.

Keep in mind and I’ll say it again....even when the same reamer is used, headspace is theoretically set the same....a tighter or looser bore can effect pressures and have different effects on the brass.

Yes brass work hardens over time not to mention different lots. Same as bullets....different lots of jackets as well as I do believe as the jackets are made they can work harden as well.

We all deal with a lot of variables.

It wouldn’t hurt to call Criterion and ask if you can get a copy of the reamer print that was used in the barrel.

Later, Frank
Bartlein Barrels

I definitely cannot argue against anything you said but criterion and shilen cut their chamber tighter than most production rifles. I've seen it time and time again on just how much tougher it is getting a go gauge into their chambers, I'm sure there is still variances but I can say from 1st hand experienced time and time again I'm always amazed out tight the chambers are on shilens and criterions, shilens even more so.. for example I can take any shilen s/s bare for AR or bolt and it takes a tad bit of force to go into battery, criterion is the same way but not as tight. Most factory rifles I have no resistance getting a go gauge into full battery but definitely your advice is solid

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[JoeJoe]

Thanks all.....one other observation I made, which makes me think the Criterion is a bit tighter, is the fired brass from my factory barrel would not fit into the Criterion.....before installing the new barrel, I dropped a factory shell into the chamber and it dropped right in.....doing the same thing with a once fired brass resulted in the last 1/2" or so of the brass sticking out (I was too chicken to shove it in there and see exactly how tight). Since the pressures are great enough to conform the brass to the chamber, made sense to me the factory chamber was a tad "loose".

I appreciate all the insight!

Joe

[Stumpkiller]

There's a 50/50 chance anytime you full-length resize with brass fired in a different rifle it will be more difficult to full-length resize in the newer rifle . . . if you are using the same dies. Different rifle makes have different chamber dimensions. Could be tighter chamber, could be shorter shoulder/headspace, etc.

[Shortbox4x4]

I definitely cannot argue against anything you said but criterion and shilen cut their chamber tighter than most production rifles. I've seen it time and time again on just how much tougher it is getting a go gauge into their chambers, I'm sure there is still variances but I can say from 1st hand experienced time and time again I'm always amazed out tight the chambers are on shilens and criterions, shilens even more so.. for example I can take any shilen s/s bare for AR or bolt and it takes a tad bit of force to go into battery, criterion is the same way but not as tight. Most factory rifles I have no resistance getting a go gauge into full battery but definitely your advice is solid

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The go or no go gage only measures from the bolt face to the datum line of the shoulder. It does not measure diameters.

If the go gage is being difficult to install because of diameters possibly being to tight then I would question that.

If the go gage goes in and stops at basically 0 headspace. That’s different from being tight on the diameter. Tight on the diameter can cause problems.

Look at a reamer print per say for 308win. Or 6BR etc...guys try and tighten up the diameter of the chamber at the .200” dimension from the case head. When you do this you can end up getting that tight bolt opening/double click per say. Guys think at times the loads are too hot but they made the chamber to tight on that diameter.

That’s why I say ask for a copy of the reamer print from the gunsmith or barrel maker that did the chamber work/install. That’s the only way your going to know technically what reamer was used and to what spec the reamer was ground/made to. Otherwise it’s a guess.

To an extent we don’t want a loose sloppy chamber but too tight causes problems as well. There has to be a balance.

One ammo maker about a year ago wanted to order special 30cal ammunition test barrels for a special run of ammo for some target shooters. I won’t give out the exact caliber. So when they called to place the order I gave them they’re options as to the reamer spec’s and bore specs of the most popular being used for that type of match shooting. They had no clue what was even being used to begin with. It took data from myself and another party and about 6 months for them to make a decision. I didn’t want to just make what they originally asked for as it could’ve caused some very serious over pressures and after they looked at the data that was given to them they understood why and helped them make a better decision.

[Ted_Feasel]

The go or no go gage only measures from the bolt face to the datum line of the shoulder. It does not measure diameters.

If the go gage is being difficult to install because of diameters possibly being to tight then I would question that.

If the go gage goes in and stops at basically 0 headspace. That’s different from being tight on the diameter. Tight on the diameter can cause problems.

Look at a reamer print per say for 308win. Or 6BR etc...guys try and tighten up the diameter of the chamber at the .200” dimension from the case head. When you do this you can end up getting that tight bolt opening/double click per say. Guys think at times the loads are too hot but they made the chamber to tight on that diameter.

That’s why I say ask for a copy of the reamer print from the gunsmith or barrel maker that did the chamber work/install. That’s the only way your going to know technically what reamer was used and to what spec the reamer was ground/made to. Otherwise it’s a guess.

To an extent we don’t want a loose sloppy chamber but too tight causes problems as well. There has to be a balance.

One ammo maker about a year ago wanted to order special 30cal ammunition test barrels for a special run of ammo for some target shooters. I won’t give out the exact caliber. So when they called to place the order I gave them they’re options as to the reamer spec’s and bore specs of the most popular being used for that type of match shooting. They had no clue what was even being used to begin with. It took data from myself and another party and about 6 months for them to make a decision. I didn’t want to just make what they originally asked for as it could’ve caused some very serious over pressures and after they looked at the data that was given to them they understood why and helped them make a better decision.

The go gauge is tight from chamber diameters, I've measured the many times.. if it was headspace or would not go into battery at at all as clymer gauges as most I reckon dont flex.. I've actually taken ball gauges and compared them to caliper measurements and the chamber is just tighter.. its typical of match grade chambers, the hold it all to exact(or close as possible to coaxial center ) as possible.. believe me I'm by no means new to building championship grade rifles.. I'm just low key about it till now, I'm finally equipped to to do all my own machine work including bore and chamber. I have over 40 years time in learning gunsmithing and precision machining in general thank to my late great master machinist daddy

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[gbflyer]

The go or no go gage only measures from the bolt face to the datum line of the shoulder. It does not measure diameters.

If the go gage is being difficult to install because of diameters possibly being to tight then I would question that.

If the go gage goes in and stops at basically 0 headspace. That’s different from being tight on the diameter. Tight on the diameter can cause problems.

Look at a reamer print per say for 308win. Or 6BR etc...guys try and tighten up the diameter of the chamber at the .200” dimension from the case head. When you do this you can end up getting that tight bolt opening/double click per say. Guys think at times the loads are too hot but they made the chamber to tight on that diameter.

That’s why I say ask for a copy of the reamer print from the gunsmith or barrel maker that did the chamber work/install. That’s the only way your going to know technically what reamer was used and to what spec the reamer was ground/made to. Otherwise it’s a guess.

To an extent we don’t want a loose sloppy chamber but too tight causes problems as well. There has to be a balance.

One ammo maker about a year ago wanted to order special 30cal ammunition test barrels for a special run of ammo for some target shooters. I won’t give out the exact caliber. So when they called to place the order I gave them they’re options as to the reamer spec’s and bore specs of the most popular being used for that type of match shooting. They had no clue what was even being used to begin with. It took data from myself and another party and about 6 months for them to make a decision. I didn’t want to just make what they originally asked for as it could’ve caused some very serious over pressures and after they looked at the data that was given to them they understood why and helped them make a better decision.

^This.

Example:
I’ve got an Obermeyer spec 7-08 reamer built by the NW tool maker that starts with a P. It’s too tight. The first chamber I reamed with it I thought I had a primary extraction issue. My chambers usually get bigger not smaller....lol. So I reamed another one. Same. So I tried another action. Same again. After a conversation with a custom action maker in PA that I’m a loyal customer to, I sent the reamer to Dave Manson to have him check out with his optical comparator. Long story short he was unable to fix it due to dimensional issues. I was able to polish one of them out just enough that I don’t have to use a small base die every time as I did before. The other I haven’t messed with as I still get grumpy about it. The reamer is a nice sharp little paper weight now.

Anyway, through all, the go gauge was never tight. If a go gauge is tight in diameter, I’d say there is something wrong with the gauge or the hole it’s going into. I doubt Shilen or Criterion sends out undersized chambers as a standard practice. Minimum spec....sure.

[tobnpr]

I definitely cannot argue against anything you said but criterion and shilen cut their chamber tighter than most production rifles. I've seen it time and time again on just how much tougher it is getting a go gauge into their chambers,
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Apples and Oranges.
A chamber is cut to the dimensions of the reamer. Assuming the manufacturer cuts the entire chamber with a single reamer, it's a form tool and will be ground to SAAMI (or CIP ) specs for a factory barrel. This is because it's critical that factory barrels, be able to shoot all factory ammo, within the specified tolerances.

Headspace on a Savage is controlled by how far you screw the barrel into the receiver, the chambers are cut so that there's specified case/go-gauge protrusion of around .125.
Nothing to do with the reamer. Want light resistance with bolt close on a factory barrel? Re-set to zero headspace.

Like Frank said, custom reamers may have tighter necks, longer freebore, and other slight modifications. Criterion does offer non-SAAMI chambers (such as "Match" which usually means more freebore), but again- different than a "tight" chamber.

[Shortbox4x4]

Thanks tobnpr for the nice comment!

Also guys just because a reamer is ground to a given spec doesn’t mean it will cut to spec!!!!!

Like gbflyer had the problem with the 7-08Obermeyer reamer. We had to grab a new reamer for 50bmg for doing a batch of ammunition pressure test barrels. We have to measure the chambers in 10 different areas with ball gages and have to depth mic to the ball gage. We are given tolerances we have to hold for each individual gage.

The reamer was cutting big on five of the different gages. I sent the reamer back to the manufacturer for them to inspect it. They told me it was in spec. I said it might be in spec but it’s not cutting to spec. So I sent one of the barrels with the inspection report along with the gages. I told them to measure the chamber and tell me what they get. All I got back was the reamer was in spec! I said I was done. Send my tooling back. We scrapped almost $5k worth of barrels. I refuse to buy anything from that maker anymore. Any of they’re tools come into our shop for like a customer fitting etc....we take the tool and will run it into a piece of scrap barrel etc...and we will see how it cuts for finish and size as well as how it cuts before we run it into a good/finished barrel.

Later, Frank
Bartlein Barrels

[Ted_Feasel]

As some of you know, I swapped my factory .308 barrel for a .308 Criterion on Friday. This afternoon, I spent a few hours resizing and prepping brass for load development. I'd saved about 70 pieces fired from my factory barrel, and shot 30 through the new barrel yesterday. While resizing, I noticed the brass from the factory barrel was very hard to full-length size (it was properly lubed), but the brass from the new barrel sized very easily. Is this likely caused by much closer tolerances on the Criterion barrel?

Thanks!

I would agree with robinhood... either tighter chamber on criterion ( all my criterion and shilen barrel brass resized easier) and just maybe needs annealed

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