How hard would it be to set up a Model 70 CRF action as a switch-barrel rifle?
Rifle is currently a 7mm Rem mag, and I think it would be kind of fun and interesting to have several pre-threaded/pre-chambered barrels set up for it that I could swap here at home with little more than a barrel vise and an action wrench. Say a .257 Wby, 7mm mag and .338 Win mag... Or something like that.
Would this be a horribly expensive project, or relatively inexpensive, sort of like just having the barrel replaced a couple of times?
I got the idea because a few years back I bought a used Model 70 match rifle from another shooter, along with several spare barrels he'd already had threaded and chambered (all were .308 Win) for the same rifle. When I wore out the first one, it was a very quick and easy procedure for me and the local gunsmith to unscrew the worn out barrel, and screw on one of the other barrels. The rifle shoots great after the swap too...
So, got to thinking that it might make an interesting setup for a hunting rifle as well.
BUT each time you make the barrel up you will lose some head space and eventually have
I've got a couple of commercial Mausers and push feed Winchesters that I've had for years.
I've rebarreled them time and again for whatever cartridge struck my fancy at the time.
I've kept the rest of the barrels around, with the brass, dies, etc. In a way, I guess they are "switch barrelled".
Although, every one of those barrels has been on and off the receiver no less than three times. First, checking headspace and test firing after fitting and chambering. Second, removal of the barrel for caliber engraving. Third, removal for replacement of something else.
The receivers haven't changed a bit. I kept measurements from the first time I squared them up, nothing has changed.
I've experienced no galling of the receiver shoulder or barrel shoulder on the Winchesters, or the inner torque shoulder or face of the barrel on the Mausers. Always assembled with moly grease.
Loss of head space is very gradual and if you are only going to change
2 or 3 times it probably would not matter ,But I assumed you were going
to change once or twice a year for different types of game.
All of the rifles I build have less than .002 and depending on what type
of action I use I calculate .001 to .002 crush or strech on the first make
up of the barrel to action.At 90 to 100 ft/lbs.
No mater how well the thread fit there will be some ware/upsetting
of the thread's it may be only .0002 each time but this will add up
over time and with only .001 head space that would be 4 or 5 times.
Of course if your rifle has .004 to.006 head space it may never give
A case in point , Some rifles have a extractor cut in the barrel .To make
this setup you have to make the barrel and recever up several times to
take the initial stretch/crush out and then lay out the extractor groove
and index the barrel then remove and mill the extractor groove ,then
make up the barrel and the action per the index mark .
If the action has no threads and is pinned the head space remains the
same same . But most high power rifles are threaded.
Long winded and I hope this explained it.
J E CUSTOM
I used to barrel up M1 Garands, M-1A's, and FAL clones. Setback becomes very apparent because all of them have to be clocked to the receiver. If one of them made up properly the first time I torqued it in, I left it alone. If it under-rotated a few degrees, I broke it loose and repeated the makeup. Sometimes only once was enough to bring it into time. They definitely wear, stretch, crush (or something) with repeated making and breaking. If a barrel ever over-rotated, it didn't matter which time, it was unusable. (The Brits did have a "breeching washer" arrangement on L1A1's that accomodated rotation and headspace, mostly rotation). The M1 and M1A could adjust headspace a little by changing bolts, and FALS and L1A1's a lot by changing locking shoulders.
I'm not sure how many times it would take to materially shorten headspace by breaking out and remaking a sporter barrel, but I agree with JECustom that the first few times it should be measurable. The thinnest shimstock that I have is 1 mil and I have seen that much difference on a go gage with repeated makeup and breakout of the same barrel in the same receiver. I do not like hand finishing a chamber, so sometimes I have to go back to the lathe (sometimes more than once) to get it exactly where I want it. And always break it out at least once for a breech that requires an extractor cut.
I have been tempted to use a good E/P grease on barrel threads, both square and V threads, but don't because of the potential for over-torqueing. Instead, I just use a light gun oil. Torque comes up smoothly, quickly, and holds where I stop without creeping. No galling so far.
I sure get long winded. Some of this is experience, some opinion. I do not believe that it is the only way, just my way.
Texas State Rifle Association Life Member
NRA Endowment Life Member
A big fast bullet will beat a little fast bullet every time