Hypothetical question.

[tobnpr]

Companies already make shouldered prefits for the Rem 700...McGowen is one...

You don't understand McGowen's shouldered "prefits".
"One variation is the standard Remington Barrel with a shoulder. This should definitely be installed and headspaced by someone qualified."
They are fully chambered- but short-shouldered.
Requires setting up on the lathe and facing the shoulder to set headspace correctly.
Then, the barrel still requires stamping because it can't/doesn't come from McGowen that way.

These are the limitations of "pre-fit" shouldered barrels on factory M700's. They don't work unless you don't care where the ATF required markings end up. Maybe, for some, that doesn't matter.

 

[adam32+P]

You don't understand McGowen's shouldered "prefits".
"One variation is the standard Remington Barrel with a shoulder. This should definitely be installed and headspaced by someone qualified."
They are fully chambered- but short-shouldered.
Requires setting up on the lathe and facing the shoulder to set headspace correctly.
Then, the barrel still requires stamping because it can't/doesn't come from McGowen that way.

These are the limitations of "pre-fit" shouldered barrels on factory M700's. They don't work unless you don't care where the ATF required markings end up. Maybe, for some, that doesn't matter.

I haven't seen one yet. I was just going by a thread here last week where someone said they got a shouldered prefit and they didn't say anything about having a smith install it. Makes sense tho.

 

[shortgrass]

You don't understand McGowen's shouldered "prefits".
"One variation is the standard Remington Barrel with a shoulder. This should definitely be installed and headspaced by someone qualified."
They are fully chambered- but short-shouldered.
Requires setting up on the lathe and facing the shoulder to set headspace correctly.
Then, the barrel still requires stamping because it can't/doesn't come from McGowen that way.

These are the limitations of "pre-fit" shouldered barrels on factory M700's. They don't work unless you don't care where the ATF required markings end up. Maybe, for some, that doesn't matter.

MagnumManiac is "Down Under" (Australia), and I believe his use for these "pre-fits" is for his own personal use. So, what Atfe requires doesn't matter at all, to him!

 

[tobnpr]

^^
Point taken, didn't notice that. I've only been trying to get the point across that it's not just whether it might headspace within tolerance. For some, the timing will be an issue- especially for resale. For a guy that just wants to use for switchbarrel might not matter one bit. Same goes if it has open sights- forget about it.

Theoretically, if you got all receiver ring to boltface dimensions to within a thousandth or two it would work- but there's considerations like primary extraction. If MM has a depth mike, it's easy enough to check that out. Get them all the "same", chamber future barrels accordingly and/or modify existing to match.

 

[ntsqd]

I think it would be more a question of what the cutting tool service interval is. At least with regard to thread size. If they're running the inserts to the ragged edge then they're likely getting a large variance in thread size. If they have found the insert service life that results in a low thread size deviance and stick to that interval, then I think your idea would bear some investigation. Were I running that production line I'd want the lowest deviance (ease/speed of barrel fitment) that I could get from the longest insert life (economics) that will give me that low deviance. It's a question of where they put the balance.

If it is all robotic production then the thread timing could also be pretty close. Not that it's important to this instance, but still.......

 

[tobnpr]

I don't see where thread pitch/consistency comes into the equation, other than the slight variation in thread "crush" that you might see.
I'm referring to where the thread leade originates on the barrel, and on the receiver. This alone determines the orientation of any random location on the barrel after installation in relation to TDC of the receiver. Some even incorporate clocking the muzzle "up" (I'm personally not sold on this, but others are) into this as well.

The companies that make pre-fit shouldered barrels for the precision M700 clones work together with those manufacturers to time their threads, and adhere to other specs for the receiver that guarantee correct fitment of barrels- orientation, and headspace- on any of their actions.

 

[ntsqd]

Obviously thread pitch is important, but for MM's purposes the thread minimum, maximum, and pitch diameters are very important.

Thread timing is what you're talking about. I'm speculating that if the receiver blanks are robotically handled that they might all have the same thread timing or very close to it.

 

[MagnumManiac]

MagnumManiac is "Down Under" (Australia), and I believe his use for these "pre-fits" is for his own personal use. So, what Atfe requires doesn't matter at all, to him!

This is correct.
I only need the caliber marked on the barrel.
The most important factor for me is the shoulder position and thread pitch so I can swap actions AND barrels.
I do my own barrels, I am a machinist and not a gunsmith. I mainly do switch barrels for a few guys and myself, but wanting to be able to do the pre-fit thing myself.

Cheers.

 

[tobnpr]

I'd take the receiver ring to boltface dimension on all the receivers, and use the shortest one as the "reference".
Then, you can set up/dial in the other receivers in the lathe and face their receiver rings so that all measure the same.
Naturally, make sure any other truing work affecting headspace is done prior.
Any barrel chambered to fit one of the receivers, would then headspace correctly on all of them.
You'll want to use consistent torque on the action wrench so that thread crush doesn't vary.
Punch withness marks on the underside of the receivers/barrels.
The caliber marking can end up anywhere, but that's cosmetics.

Should work, "in theory"...

 

[ntsqd]

Regardless of thread timing the barrels will headspace correctly if all of the receivers, all of the barrels, and all of the recoil lugs are made to the same Basic dimensions. Basic dimensions have no tolerance, they're not "1.005 ±.005" If such a dimension is 1.005 then it is not 1.005 ±.005 or even 1.005 ±.0005, it is 1.005 ±.0000000000000

If the thread timing isn't the same, that is both the receiver threading and the barrel threading don't start in the same relative rotational location, then any markings will be in random places when the barrels do snug up.

 

[tobnpr]

and all of the recoil lugs are made to the same Basic dimensions.

Good catch- forgot to mention that.
I'd run all the same precision ground lugs (I've found Holland's to all be spot on in thickness without variation), that way even if you mix up a lug, it won't affect anything.

 

[MagnumManiac]

Yep, I use PT&G 1/4" tapered dual pin lugs on all my builds.
Everyone measures the same.
My rules here are different I think, I only have to mark and register ONE barrel, other barrels don't even require the calibre marked on them or ANY other info.
Even when I re-chamber an existing barrel, it's my choice whether I alter the name stamped on it.

Cheers.