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Southcountryguy

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First off I want to thank this community. As I move forward on my first build I am learning heaps from you all. Wish I would have found this site decades ago.

I hate to ask questions I don’t know the answer to so I need a little clarification. I am considering buying a custom action that advertises that the customer can swap barrels, prefit. Being a tradesman I know that even metal wears and wondering how many times a person could swap barrels before it impacts headspace. If I go this route I fully intend on using go/no go gauges when swapping barrels but curious to know. I understand how I change, ie torque, will impact this but let’s assume I do it correctly.

Thanks for your time again

SCG
 
I kinda thought that one would use headspace gauges every time a barrel was swapped out? You are right - there can be wear - for some cartridges, there is, what? .004" difference between GO and NOGO - so about thickness of a sheet of printer paper within which to be correct, and everything else is not correct? (not considering the tolerances available for FIELD gauge) But I have never done a repeated barrel "swapping" on a rifle, though I have installed different barrels on several receivers - but always checked with a GO and NOGO gauge...

EDIT: Thinking about this - I lied. For several cartridges, I only have the GO gauge - not the full GO, NOGO and FIELD set - and a set of little discs (.002" to .010") that I punched out of a feeler gauge set - so, I can put, say, a .006" disc between bolt face and GO gauge to know if chamber is more or less than .006" over GO length...
 
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If the barrel is shouldered, ie tightens against the action/recoil lug and is head spaced properly, there should be no need for using go and no-go gauges when switching barrels. As long as the barrel is torqued to the action the same every time. On my rifles I torque the barrels on to 65 ft/lbs I have done a coupe where the action manufacturer recommends 100 ft/lbs. The metal surfaces should not wear as these are not moving parts. If you end up hobbing the barrel into the action or recoil lug when you switch barrels you are using way too much torque.
 
maynard said:
If the barrel is shouldered, ie tightens against the action/recoil lug and is head spaced properly, there should be no need for using go and no-go gauges when switching barrels. As long as the barrel is torqued to the action the same every time. On my rifles I torque the barrels on to 65 ft/lbs I have done a coupe where the action manufacturer recommends 100 ft/lbs. The metal surfaces should not wear as these are not moving parts. If you end up hobbing the barrel into the action or recoil lug when you switch barrels you are using way too much torque.
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That’s interesting as I have talked to several people about this and they are split on opinion if the torque from putting a barrel on compresses it enough to change headspace. I am not a metal guy to know.

Thanks.
 
Potashminer said:
I kinda thought that one would use headspace gauges every time a barrel was swapped out? You are right - there can be wear - for some cartridges, there is, what? .004" difference between GO and NOGO - so about thickness of a sheet of printer paper within which to be correct, and everything else is not correct? (not considering the tolerances available for FIELD gauge) But I have never done a repeated barrel "swapping" on a rifle, though I have installed different barrels on several receivers - but always checked with a GO and NOGO gauge...

EDIT: Thinking about this - I lied. For several cartridges, I only have the GO gauge - not the full GO, NOGO and FIELD set - and a set of little discs (.002" to .010") that I punched out of a feeler gauge set - so, I can put, say, a .006" disc between bolt face and GO gauge to know if chamber is more or less than .006" over GO length...
Click to expand...

Yeah, I figured gauges should be used each time to check, the alternative if something happens isn’t appealing.

Interested in everyone’s opinion.

SCG
 
If you want to set the headspace to the correct absolute minimum, strip your bolt down and set the barrel so you can just feel the bolt close on the go gauge at the bottom of the bolt throw. You need to do this using a stripped bolt for the best 'feel'. If you are reloading this is the best method... and adjust your sizing die to match the fired cases without pushing the shoulder back...

You can also set the bolt so it closes on a go gauge and when using a no go gauge it does not close... but that is not the best way... there is a variance involved with this method.
 
guntech said:
If you want to set the headspace to the correct absolute minimum, strip your bolt down and set the barrel so you can just feel the bolt close on the go gauge at the bottom of the bolt throw. You need to do this using a stripped bolt for the best 'feel'. If you are reloading this is the best method... and adjust your sizing die to match the fired cases without pushing the shoulder back...

You can also set the bolt so it closes on a go gauge and when using a no go gauge it does not close... but that is not the best way... there is a variance involved with this method.
Click to expand...

Thanks! Why I asked, always learn something..

SCG
 
Southcountryguy said:
First off I want to thank this community. As I move forward on my first build I am learning heaps from you all. Wish I would have found this site decades ago.

I hate to ask questions I don’t know the answer to so I need a little clarification. I am considering buying a custom action that advertises that the customer can swap barrels, prefit. Being a tradesman I know that even metal wears and wondering how many times a person could swap barrels before it impacts headspace. If I go this route I fully intend on using go/no go gauges when swapping barrels but curious to know. I understand how I change, ie torque, will impact this but let’s assume I do it correctly.

Thanks for your time again

SCG
Click to expand...

If you are doing it properly, there will be no appreciable wear in your action over your lifetime and many more. You should not apply enough force to distort any of the parts involved... so if nothing is distorted, what would change?

The headspace may vary between barrels due to chambering tolerances but you set the headspace for each barrel (assume you use a barrel nut) specific to your gauges... so the net effect is each set up is the same ... within your install tolerances.

Jerry
 
Can see what you are in to - one system is relying on a solid shoulder on barrel that tightens to front of receiver ring, another system is using a locking nut to "jam" barrel tenon threads against the receiver threads. A third system tightens rear of barrel against an internal collar within the receiver ring. All systems can work very well for headspace. Got to be sure which system that you are using and which system that you are talking about. I am still not convinced that a person who wants to hit minimum or near minimum headspace, repeatedly, can do that without using gauges to check - at least a GO gauge as Guntech describes.
 
No mechanical engineering or metallurgy back-ground to explain, but go by some engine re-build manuals - some head bolts - very specific to not re-use them - undo previously torqued ones - look fine, but on re-assembly you are supposed to use new ones, and torque them to spec in approved manner. I suspect when a thread is "torqued" that the male and female threads have to get slightly deformed, in order to hold tension. When you "un-torque" - do those threads return perfectly to their previous shape, or do they retain some deformity? Perhaps about 5th or 6th time that the fastener is being re-torqued - is now being turned to a new location? - not in the same place it was previously? - you got to the correct "torque", but new location. Might be very flawed thinking on my part, but why I would want a gauge to be confirming all is well.

As was mentioned above - might be very much different if a two part - barrel with shoulder - torqued onto a receiver shoulder or internal collar - versus a three part system where barrel turned into receiver, held there, and then threads are "jammed" by a lock nut. In latter instance, I assume "torque" is measured as applied to the jam nut, not by the barrel threads in the receiver - I have never worked with that system, so do not know.
 
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You are no where near twisting hard enough to distort metal... With barrel nut prefits, you will pull the threads into the V so any slop is taken up.

With a shouldered headspaced barrel, I set so when it goes hand tight, I am there.

Some Benchrest shooters change barrel by 'torquing' to hand tight... leave the action in the stock and just spin on and off barrels.

We do not want nor need to be gorilla'ed up as you can find in some factory rifles and definitely many surplus rifles. Now if you are building a working rifle, then do what you need to survive the workplace. For accuracy, this rarely ever helps.

We have swapped barrels at a match where one person holds the action and other twists off the barrel. As long as the barrel is tight enough to not loosen, that is all that you need.

Having swapped many many barrels in various formats for close to 20yrs, there is no need nor benefit to torque on the barrel hard enough to distort steel (even though some will install a barrel that way).

Same with action bolts... but that is another story.

YMMV

Jerry
 
That was my thinking as well. If not that deformation maybe the action of rubbing up against each other is enough. As I said before, while not here, at least on smith I talked to figured there would be “wear” each time.

I am basically asking because I am currently sourcing parts for a build and spending upwards of $2k on an action doesn’t hurt as much if I can swap barrels out myself. I can then have my bench rest off season paper puncher, my lightweight 25 cal hunter and maybe a boring 308 for moose. Lol. I would probably get gauges for each swap and have a smith initially check each barrel setup anyways.

Just curious.

SCG
 
Jerry - thank you for explanation in Post #12. Has so many implications about what some of us do, based on our limited experience with store bought "hunting rifles" and milsurps. Like thinking to be competitive in a Formula One race, with a 3/4 ton 4x4. (unless the course has multiple 12" deep snow drifts, and a couple of mud holes...)
 
Take two pieces of steel (how about 2 wrenches) and rub them as hard as you dare together... for as long as your arms will handle.

Was there any wear?

Now imagine just doing that ONCE..... But with a little twisting motion.

Unfortunately, the internet is more likely to supply poor information as it is to provide good/useful info nowadays
 
A competitive bench rest shooter/machinist (quite successful) I know in the US will snap a barrel as tight as he can by hand, then make a pencil mark on the action and one on the barrel an eighth of an inch apart... and then with a wrench turn until the pencil marks line up...
 
There is a lot of confusion with regards to torque. The head bolts of your engine have a torque or an angular tightening spec so that the bolt is stretched to an engineered dimension. Often times it is to the yield point of the bolt and is known as "torque-to-yield". This is why they are not re-used. This of course has absolutely nothing to do with holding the receiver onto your barrel. You are just bringing two machined surfaces together with enough force to hold them from loosening. As you tighten further you are just stretching the threads on the barrel shank. Even then, the relationship of the bolt face and chamber's shoulder don't really change which is why the headspace will not significantly change no matter how much torque is applied.
 
Mystic Precision said:
Take two pieces of steel (how about 2 wrenches) and rub them as hard as you dare together... for as long as your arms will handle.

Was there any wear?

Now imagine just doing that ONCE..... But with a little twisting motion.
Click to expand...

It really was my thought but I am not a machinist nor a gunsmith and know enough about guns to be extremely dangerous. I would rather ask than have a life changing accident.

Unfortunately, the internet is more likely to supply poor information as it is to provide good/useful info nowadays
Click to expand...

Yes, one really has to know how to wade through all the opinions and extract the good stuff. All to often things are accepted as gospel because “everybody” is regurgitating the same BS when nothing is farther from the fact.

I do appreciate all the insight.

SCG
 
With a typical shouldered barrel, removing and replacing will change the timing and the headspace after several changes.
 
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