View Full Version : O.D. at chamber section of barrel??? minimum?

12-29-2007, 09:11 AM
I don't think I've seen barrel dimension question like mine before so I hope it's interesting as well as informative.
I have a Shilen barrel, chrome moly sporter 24" as I left it after contouring on my own equipment.
A bit of info: I chambered it to .250 Ack Improved. I know better now, but then I used a solid pilot reamer of a friends, an older Clymer. The flutes measure .470", I cut a .472" dia head [some slope in my setup]. The pilot was not the best fit but that's not the reason for the .472" head area. Ok,,,present day Winchester .250 Savage brass is about 0.464". Loading hot in a 0.472" chamber is not a good idea.

I'm thinking of chambering to .25-284 to get a correct chamber and clean up the old .250 chamber. HOWEVER, in polishing the OD {EXTERIOR} of the chamber section of this barrel, I turned it down a bit past 'standard' for a Ruger 77 Mark II action. I'll go check the measurement, but my QUESTION IS:

What is the minimum safe OD of a CM barrel chambered in .284 Winchester? I'm talking the OUTSIDE of the barrel at the chamber end. How much steel is necessary for any particular cartridge?
I guess I could call/e mail Shilen, too.
Thanks, and ask anything you need to know if I've left it out.

12-29-2007, 10:30 AM
When you're talking about safety, I doubt anyone will give an absolute minimum. The best info on barrel diameter I've seen is in an old book, Hatcher's Notebook. Julian Hatcher was an Ordinance officer during the glory years of the springfield armory. He writes about several experiments in his book.

One experiment was turning down the outside of a 1903 barrel a bit at a time & firing GI ammo at each diameter. At the smallest diameter (surprisingly small) that he tried, GI fired fine, but a proof load caused the barrel to fail.

If you're worried about the slightly undersized brass in your chamber, a cheaper solution is to form some brass from some 308 brass (etc) that might have a slightly larger case head. It may be that you're just stacking tolerances all one way.
Regards, Ron

12-29-2007, 11:08 AM
making 250AI brass from .243/.308 is probably the best solution. I could make a 20 round batch with little time involved.
I think I'm totally safe with the barrel I have. I have considered a .25-284 in the past and it seemed like a possible 'easy' solution what with all the 6.5x284 Lapua brass around. I have a friend that builds 6.5x284 match prone rifles so brass is easily obtainable. I don't really feel a "need" for a 25X284,,,just an idea. I have 3 Ruger .250 Savage rifles,,,found two factory rifles - Ruger 77Rs, and then the one I built for me in .250 Savage Ackley Improved [whew,,lots o typing,,heretofor known as the "250SAI"].
By the way, this Shilen barrel is a 10" twist that had an interesting 'first groups' session at the range. I had loaded up 2 batches of 100 grain loads over a starting load of H414. The first groups were with Speer 100 gr HP jacketed bullets. Group was about 2 1/4" at 100 yards [:mad:]. Figured I had put hours of contouring, threading, chambering and polishing into a tomatoe stake. Then I tried the other load,,same everything except capped with Nosler 100 gr Ballistic Tips. First three into 3/8",,and this was repeatable with more groups!:)
I left this deer rifle with 24" of barrel to help hold muzzle blast down and save the old ears. My wife thinks her name has been changed to "WHAT":D

I"ve killed many deer with many rounds [I have a list] and none have died much better than with these little 25 cal rounds.
I've posted many times how I think the factorys have come short because they have not offered us a factory 25-08.
Thanks guys.