Rechambering 7x57 to 280 AI

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Potashminer

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Looking for some advice from folks that have chambered or re-chambered on a lathe. I am fairly new to the lathe business, but catching up quickly. I have in mind to re-chamber a Ruger #1A from 7x57 to 280 AI. Alternatively, I have a couple real good shape military 7x57 barrels with long throats that could be "transformed".
My plan so far - remove rear sight/rib, remove front sight, unscrew barrel (Barrel Vice and Action Wrench on hand). Run some amount of barrel through headstock and grab with three jaw chuck); set up close to chamber end on centre rest - dial in centre rest to align to existing chamber.
Install live centre in tail stock - T handle on 280 AI finish reamer, drive reamer forward with tail stock travel, holding reamer handle in my hand.
Is this going to work, or am I way out in left field? I am especially concerned about the AI reamer pilot will not likely to get into the rifling until after the AI reamer shoulder has bit into the chamber wall.
 
Potashminer said:
Looking for some advice from folks that have chambered or re-chambered on a lathe. I am fairly new to the lathe business, but catching up quickly. I have in mind to re-chamber a Ruger #1A from 7x57 to 280 AI. Alternatively, I have a couple real good shape military 7x57 barrels with long throats that could be "transformed".
My plan so far - remove rear sight/rib, remove front sight, unscrew barrel (Barrel Vice and Action Wrench on hand). Run some amount of barrel through headstock and grab with three jaw chuck); set up close to chamber end on centre rest - dial in centre rest to align to existing chamber.
Install live centre in tail stock - T handle on 280 AI finish reamer, drive reamer forward with tail stock travel, holding reamer handle in my hand.
Is this going to work, or am I way out in left field? I am especially concerned about the AI reamer pilot will not likely to get into the rifling until after the AI reamer shoulder has bit into the chamber wall.
Click to expand...

Potash You may want to check the outside neck diameter of the 7x57 chamber. Most 7x57 necks are .320" while the 280 neck diam is only about .315" . The length of the 7x57 case goes up on about 1/3 of the 280 neck. When you re-chamber the 7x57 you end up with a .005" step in the neck of your 280 chamber. Same thing if you re-chamber to 7mm Rem. One of the few calibres that clean up the 7x57 is the 7x61 S&H.
 
Often 7 x 57 neck diameters are larger than the 280 necks. This results in a two step neck in a fired case... looks weird but does not affect anything.

#3 beat me by seconds
 
Blastattack - FWIW, the lathe is an Atlas TH54 - 25/32" listed as spindle internal diameter; let's say 36"+ between centres (max). The lathe is actually in pieces being rebuilt / realigned / "gussied up". (Was working very well, for home hobby type work - setting up a new workshop, so I thought I would clean it up, before building new stand for it).

Rokoro and Guntech - Thanks! I will have to try to find out how John Barsness had it done to one of his 1A's - will have to dig out his article in Rifle or Handloader a few years back and see if that detail about neck sizes is mentioned. I guess I was all taken by the 3,000 fps with 150 Partitions from a 22" #1.

All that said, I've read the pros and cons about chuck and spider, chuck and centre rest, centre rest and spindle bushing, but was really wondering about the handling of the reamer. So far as I can tell, the pilot will not be in the bore when the AI shoulder starts to cut the chamber wall?? And is handheld reamer a viable practice - if not, how else to hold it, to allow it to "float" a bit?
 
Potashminer said:
Blastattack - FWIW, the lathe is an Atlas TH54 - 25/32" listed as spindle internal diameter; let's say 36"+ between centres (max). The lathe is actually in pieces being rebuilt / realigned / "gussied up". (Was working very well, for home hobby type work - setting up a new workshop, so I thought I would clean it up, before building new stand for it).

...

All that said, I've read the pros and cons about chuck and spider, chuck and centre rest, centre rest and spindle bushing, but was really wondering about the handling of the reamer. So far as I can tell, the pilot will not be in the bore when the AI shoulder starts to cut the chamber wall?? And is handheld reamer a viable practice - if not, how else to hold it, to allow it to "float" a bit?
Click to expand...

Hmm... 25/32" likely won't let you pass the barrel through the bore... The way you described is your best bet, really. Holding the reamer with a T or Tap handle and being pushed by the center will work fine. It is not the absolutely most precise way of doing things, but it will be more than adequate for a hunting rig.
 
I recently attempted just such a project. In the end I bought a new barrel from Bits of Pieces.

I had a chopped 7x57 barrel that came off a Brazilian M1935. The barrel came out of a garbage can of take off barrels for $5 and was very decent but only 22in long. The threads are different of course but they can be turned down. I was lucky because the threads on the large ring mauser barrel could be turned off completely to give me the max diameter necessary for the Ruger No 1 receiver. You will have your take off barrel to compare it to.


1"-16. 60 degree threads. Turn the shank to about 0.995" before threading.

There is an extractor slot that needs to be milled in the end of the barrel. Of course, this slot for the extractor must be made in such a manner to allow the extractor to fully engage the extraction ring on the case and it must be milled in the proper time to allow the barrel shoulder to butt up tight to the receiver and still maintain proper head space.

Personally, I cut the threads and finish off the length of shank and turn in the barrel until I have it very close to where I want it. Within a sixteenth of a turn. This way I can set up the proper indexing for the extractor and make the necessary mill cuts so I can install the extractor with ease once it is all together. Of course, you will want to screw the barrel in before cutting your chamber. You will want to partially assemble the rifle so the breach block can be checked for clearance and make sure it isn't hanging up. About .010 between the barrel and the breech block is about right. A few thou one way or the other won't make any difference.

Take off the barrel and ream out the chamber. If you have gages to measure with that is nice but not really necessary. The Number1 breach block and barrel are so close that the cartridge head is completely enclosed. Very easy to set headspace.

In the case of my mauser barrel, I was able to push back the shoulder enough to clean up the original chamber completely. I would advise against using a M93-95 barrel, there isn't enough to work with.

In all honesty, the mauser barrel performed well. In the end it was a short length and handy, accurate rifle but in truth, it just didn't look right. I took the barrel off and am in the process of contouring and installing a new Green Mountain barrel that looks just fine. Hopefully it will shoot as well as the others I have used.

I took the mauser barrel off this spring and turned it into bedding pillars. Not much else to be done with it anymore so make something useful.

Ruger makes a 280 barrel for the No1 and there is a very good chance their repair facility in Montreal has one in stock or can get one for you. I have ordered parts from them and I can tell you, if you go onto the Ruger website and look at the part numbers, they will quickly let you know if they have the parts or will order them for you. Very nice and polite people indeed.
 
357Maximum said:
Why not sell the 7x57 and purchase a #1A in 280 from Prophet River, then run a AI reamear in the .280 chamber ?

357
Click to expand...

In order to chamber an existing chamber to the correct headspace for the AI version requires setting the barrel back... it isn't as simple as running a reamer in...
 
Might be able to finish ream a 20 thou short chamber to length through the action (by hand), (since the finishing reamer pilot will be well up the rifling) but if you look at the drawings for a 280AI and a 7x57 you will see that the shoulder of the 280AI will be cutting long before its pilot gets anywhere near the lands, so I just can not imagine "free handing" for, what, an inch?, before the pilot gets to the throat and then up into the lands. I am no "old time pro" with a lathe, but I just can't see anything good happening trying to ream a chamber with the action spinning around, at least on my little 10x54 machine. As well, the point made above by Rokoro and Guntech above got my attention - I had missed the difference in chamber neck sizes, so, unless live with the extra should on the neck, would have to turn in a Ruger barrel a full turn to line up the sights, then face of the barrel and ream to proper depth, then figure out how to shorten up the barrel rib....
 
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