Rebarreling a Remington action I trued many years ago using the sacrificial collar method. I used a mandrel and bushings this time around to check my old work and found that there is only .0005" runout difference on the face between the two different setups. If it were yours, would you touch everything up again or just stick a barrel in it?
Gunsmithing Would you or Wouldn't you?
- Thread starter jrm850
- Start date
For a half thousandth difference I'd probably just put the barrel on there. As you start to dig into the <0.0005" range there are a multitude more things that come into play not the least of which are the headstock bearings and the shop temperature when you dialed it in vs. when you actually cut it or when you dialed it in last time.
0.0005" = <s>50</s> 500 millionths of an inch
Cte|SS ~6.5 millionsth-in/in-F
Meaning that a 1.000000" diameter piece of SS that is at 70F turns into 1.0000013" at 72F
For a receiver that is 1.35000" across at 32F outside and you bring it into a 72F shop that's 1.35*.0000065*(72-32) = 1.350351 which is <s>35/50</s> 351/500 millionths you're already chasing.
That's JUST the temp change for concentricity, what about the headstock bearings that may or may not be capable of holding the other 0.00015"? What about angularity, what about any potential flexure put into the action by your holding method, etc etc.
My advice is that you're going to spend a lot of time chasing this unicorn and the next time you check it, you're going to have to chase it again and again.
ETA: I made a mistake above, 1/2 thou isn't 50 millionths, it's 500 millionths. 1.35*6.5e-6*40 is also 350 millionths, not 35. I was off by 1 decimal place
0.0005" = <s>50</s> 500 millionths of an inch
Cte|SS ~6.5 millionsth-in/in-F
Meaning that a 1.000000" diameter piece of SS that is at 70F turns into 1.0000013" at 72F
For a receiver that is 1.35000" across at 32F outside and you bring it into a 72F shop that's 1.35*.0000065*(72-32) = 1.350351 which is <s>35/50</s> 351/500 millionths you're already chasing.
That's JUST the temp change for concentricity, what about the headstock bearings that may or may not be capable of holding the other 0.00015"? What about angularity, what about any potential flexure put into the action by your holding method, etc etc.
My advice is that you're going to spend a lot of time chasing this unicorn and the next time you check it, you're going to have to chase it again and again.
ETA: I made a mistake above, 1/2 thou isn't 50 millionths, it's 500 millionths. 1.35*6.5e-6*40 is also 350 millionths, not 35. I was off by 1 decimal place
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I had convinced myself that I would just recut everything anyway but I was curious about what others would do in the same situation. I didn't think that little bit of runout would make a measurable physical difference, but I planned to "fix" it so I didn't have five ten thousandths ticks running through my head before each shot. I ended up pulling it out of the fixture without touching anything. Thank you for the feedback.
Very interesting point. Now if someone could prove what those minimal changes produced in error, if anything.
Just rebarrel it!! If it ain't broke, don't fix it!
Off topic a bit, but I'm curious as to what the "sacrificial collar" method is.
I used a ight fitting mandrel through the action set up between centers. Over the outside of the action I made a sacrificial steel sleeve sort of like a short action truing fixture with set screws locking it to the od of the front ring. The set screws are below the surface. Then I took a cut off the sacrifical collar to align it with the mandrel and then did all the threading and facing with a steady rest on the collar. I've seen others indicate the collar in a 4 jaw after cutting, but I couldn't get it to indicate in two spots so I did it between centers. It's definitely not the best method, but I was kind of flying blind back then and had to figure out a lot of things on my own.
A few have tried and many folks then come back and show you an untouched action with a couple thousandths of runout that shoots lights out. The barrel has a huge amount to do with it. You can take the nicest action in the world, screw a premium barrel on it with a crooked ass chamber and the rifle will be lucky to hold 3/4MOA... or you can take a $29 Turk Mauser, recut the face with a mandrel, put on a $90 Adams and Bennett that happened to be made "right" and it will shoot bugholes.
I've seen both first-hand and I own the Turk Mauser version that still shoots 178 Amax's <3/8" @ 100yd. It just flat out likes to shoot. It's a hack job that has turned many heads when it does what it does.
The other one is on another chamber with the same barrel now and when properly installed, it turned that 3/4moa rifle into a tack driver. Go figure. IMO the action has a lot less to do with it than we like to argue about here, however the folks that spend the time continually trying to eliminate (or control) the variables are also the guys that regularly ship rifles to customers which stun witnesses and owners alike.
Sounds like you didn't get it "too wrong" though, nice work thinking on your feet like that.
If you found only 0.0005" TIR difference between Setup 1 and Setup 2, then I don't think I'd be too critical of your first method (considering that your second method likely introduced some amount of runout, however small that may be). In fact, I'd say that you did pretty damn well.
The "sacrificial collar" method is also described in Hinnant's book "Precision Rifle Barrel Fitting", for those that may be interested.
I think I enjoy the chase as much as the result. Having the confidence that everything is absolutely perfect helps me sleep well. If I don't have enough bourbon in me I tend to dwell on things like THE NEW BARREL IS CROOKED IN THE BARREL CHANNEL. ***pulling hair out***. My first thought was that I should have recut those threads. 
After I calmed down I remembered that I had never even heard of indexing the muzzle runout when I installed the old barrel. The new barrel is nice and straight with the minimal runout indexed at 12. Now I'm fretting because the bedding is all wrong. Thank god this will never end.
After I calmed down I remembered that I had never even heard of indexing the muzzle runout when I installed the old barrel. The new barrel is nice and straight with the minimal runout indexed at 12. Now I'm fretting because the bedding is all wrong. Thank god this will never end. Shoot it and see what it does.
The gun can also be crooked in the channel if you didn't index the recoil lug properly too. It will kick the whole action and you end up with an ill fitting setup that needs to be re-aligned and most of the issue will disappear.
