When you cut the shoulder on the barrel it will not be perpendiculr to the axis of the bore......correct? So this means the muzzle is now 0.050" away from the centerline of the rifle when the barrel is threaded into the action? So it will need to be indexed either up or down perfectly or you'll have all kinds of angular error when shooing from one distance to another?
Am I understanding this correctly? If so, how do you index this barrel perfectly so the bullet leaves the bore in perfect L/R alignment with the scope?
Thanks in advance............
Thanks for asking the question. You machine and thread the tenon, first. Rotate the lathe spindle and place a piece of tape or a mark on top of the chuck when a range rod in the muzzle is at it's highest point. This may be a trifle fussy to do because sometimes the barrel is moving so much that one has to play with the location of the dial indicator, or use a wide flat foot on it, to find the highest point. Screw the action on the tenon (with the recoil lug if one is supposed to be there). Measure the angle in the direction of rotation between the receiver and the part of the barrel that is pointed up. Do the math based on the tenon thread and remove material from the tenon shoulder to allow the receiver to turn just enough to be level when the barrel is pointed up. It almost takes longer to write this than to do it.
Then proceed to face the tenon to length, do the chambering and set headspace with chamber depth as usual.
I was thinking about the post I made early this AM , that would have been this one:
Yes! I had that happen to me with the first barrel I chambered. I'd obtained and watched Richard Franklins video on chambering (he uses the muzzle breech two point sytem) and a friend had loaned me a range rod to use for centering. I'd also watched the Gordy Gritter's video and ordered a Grizzly rod. The barrel was from my Savage .22-250 LRPV. It had the throat shot out of it (looked like a dry lake bed).
I cut the chamber off (removed 2") and rechambered. I set it up in the headstock, centered the muzzle and breech to within .0002, just like Franklin did, which didn't take all that long. Then I put the Grizzly rod in the breech end, ran it in ~2" to the chamber throat and was shocked to see it be out something like .003" (+/- 0.0015), an inch beyond the throat it was off even more. So I aligned it again using the Grizzly rod (a frustrating process the first time - not so much now) and watched in amazement as the bore at the muzzle ran in a circle of about 0.050" (as I recall, it was surprisingly big). At that point the light went on, I knew the muzzle breech 2 point system was flawed, so I've never used it.
Interestingly enough, the indicator rod showed centered within 0.0005" from the breech face to an inch beyond the throat which told me that ~3" of bore was relatively straight, just not aligned with the barrel. I didn't drill and bore, just cut the chamber, and it came out running almost dead true with out being oversize, probably because that bore segment was pretty straight, just not aligned with the the virtual axis from breech to muzzle.
Right after I made it, my bride finished on the elliptical and it was my turn. While I was churning way doing my 50 minutes (625 calories of dripping went exercise a day) on the elliptical I was thinking about this last post and it occurred to me there were a bunch of things related to it that hadn't occurred to me until right then. So I thought I'd share them.
Warning, what you are about to read is not going to be what some folks want to see, continue and you will see why I say that. That said, I'm trying to further my understanding of this chambering process, and how the techniques relate to achieving the best possible conditions for accuracy. My assumptions are:
- The optimum is for the bullet to be perfectly centered in the brass, and perfectly aligned with and concentric to the brass, and, for the bullet to have a perfectly symmetrical entrance to the bore with the bore pointing in the same direction as the bullet is traveling when it leaves the brass.
- The optimum at the muzzle is for the bullet to experience perfect symmetry of escaping gas forces when it leaves the muzzle, which is only achieved with the plane of the crown is perfectly orthogonal to the centerline of the bore segment at and just before the crown.
I won't deal with assumption 2 in this post, but it is one of my assumptions. Given these assumptions, I had the following thoughts related to the earlier post.
For completeness, the situation is that the bore in the first 3", and maybe more, was straight within 0.0005" but skewed .003" to .004" with regard to a line from the muzzle to the breech. There are at least two potential contributors to that skew. One is that the barrel itself isn't straight, the other is that the bore wanders around, or both. In this particular case, the barrel very heavy varmint barrel itself is pretty straight and well centred on the ends with regard to the OD, so it was the bore angling off. In the end, for purposes of this discussion, it doesn't actually matter if the skew is caused by the barrel itself being bent (within reason) or the bore being skewed inside the barrel.
So I got to asking my self what this implied and came up with the following conclusions, some of which surprise me:
- Case 1: Given: Muzzle and breech centered, floating pusher like the one I use, no drill and prebore.
Result: The chamber would be directly in line with the bore segment following because the the reamer pilot would make it follow the bore and the floating pusher would let it do that. This would be about perfect for the bullet leaving the brass and entering the bore.
The barrel tenon, however, would not be concentric with the chamber. The chamber would be skewed with respect to the barrel tenon by the amount the bore was skewed. The tenon itself would be concentric with a virtual center between the muzzle and the breech. With the way bolts flop around I'm not sure this lack of concentricity of the chamber and tenon would matter, but the bullet would have a good a chance for a favorable bore entry as it ever can have.
- Case 2: Given: Muzzle and breech centered, floating pusher used, drill and prebore.
Result: The chamber is concentric with the barrel tenon, and centered on the throat, but not aligned with the bore at and beyond the throat. The bore after the chamber is still skewed with regard to the alignment centerline from muzzle to breech, the chamber and tenon are concentric with it, but the bullet has to make an abrupt change of direction upon entering the bore because the bore isn't pointed in the same direction the bullet is going.
Conclusion, in this case it would have been better to not prebore if one uses the muzle breech alignment approach. I think this may be true more often than not if a floating pusher is used.
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- Case 3: Given: Bore segment in the first 3 inches of the breech is aligned with the lathe centerline, floating pusher is used, no drill and prebore.
Result: The chamber is aligned with the bore segment immediately following the throat. The barrel tenon is concentric with the chamber. The muzzle needs to be indexed to point up in the vertical plane as part of the chambering process.
Conclusion: This results in the chamber and tenon being concentric and aligned with the bore segment immediately following the throat which should give the most favorable conditions for maximizing accuracy.
- Case 4: Given: Bore segment in the first 3 inches of the breech is aligned with the lathe centerline, floating pusher is used, drill and prebore.
Result: Same as case 3.
Conclusion: Same as case 3.
Near as I can tell, drilling and preboring is either of limited value or detrimental if the bore segment in the breech is straight, even though it is skewed,
if a floating pusher is used. As case 2 shows, drilling and preboring make things worse if the muzzle and breech are the alignment points and the bore segment following the throat is skewed with respect to the muzzle breech centerline, which it will almost always be to at least some extent. This is because drilling and preboring established a third point on a line that is not aligned with the bore following the throat, it is only aligned with the (soon to be slightly oval) entrance to the throat.
I haven't attached any indispensible ego to this, but it made sense to me when I thought about it, and it still does now.
Fitch
