Barrel Reboring

[Protocall_Design]

Your post got me to thinking...so many forum members talk about "IF" S&W would just make an L-Frame 10mm revolver, most of us would beat a path to their door. I wonder if a 686 would be able to handle the pressure of a mid to warm 10mm load, how hard would it be to bore a barrel to .40/10mm and ream 6 chambers to 10mm? And can you go from .357" to .40" on the chambers with just a reamer, or would they have to be bored also? I've only used a finish reamer on semi-auto .40 chambers to deepen them to 10mm and that was pretty easy. Having a 10mm L-Frame snubby would be sweet!

My reamer goes from .357 to .40 in one shot. Very easy. You are taking out a lot of material, so you have to take your time, go easy, and pull the reamer and clean off the chips often. The Manson reamers cut beautifully.

You could ream a 686 cylinder for 10mm. I personally would not do 10mm in an L frame due to the high pressures possible. I'm pretty sure some of the full power 10mm rounds would blow it up. I have magnum guns for any shooting of that nature.

 

[JohnHL]

357 Mag=35,000 psi

10mm=37,500 psi

Will 2,500 psi overload a slightly reamed 357 Mag L-Frame cylinder?

John?

 

[steelslaver]

slightly reamed?
Base dia .357 mag is .379, 10MM is .425 so the area between chambers will get .046 thinner and the outer wal will get .023 thinner.

For an idea using N frames a 44 mag has a .457 base and a 45 colt has a base of .480. That is only an increase of .023 So between chambers you lose that .023 and the outer wall you only loss .0115. I have reamed a few 44 mag cylinders to 45 colt. Now 44 mags run at 36,000psi. (same as 357 mag) I keep my 45 colts under 25,00 psi which is way warmer than factory. No way I would bump them up to 37,500.

But get yourself a L frame 357 cylinder and some good measuring tools and figure out just how much metal you have to work with and what you would have left. If you have more metal left in the critical areas than say a model 19 cylinder has or a N frame 44 mag cylinder has. Thickness between the chambers and outer wall thickness. You might be fine. If your thinner somewhere its not that good and idea.

 

[LoboGunLeather]

Conversions of N-frame (Model 28 and Model 27) to .44 Special were moderately popular in the 1970's and 1980's. Many thousands of M1917 revolvers were made in .45ACP, back in the WW1 era and after. No reason it could not be done by a qualified gunsmith today. Proper tooling would be a consideration; not a job to take on with a bench-top drill press, and the drills and reamers would have to be very precise. A smith specializing in such work will certainly charge an appropriate fee for his time and expertise, but perhaps won't have to factor in the special tooling to get one job done.

I noted in prior comments a suggestion for a .451 bore, which would be an appropriate groove diameter, but the actual bore dimension would be closer to .440 or perhaps .442. Rifling grooves are cut after the boring is done. I may be quibbling on this point, but the issue is valid.

 

[JohnHL]

slightly reamed?
Base dia .357 mag is .379, 10MM is .425 so the area between chambers will get .046 thinner and the outer wal will get .023 thinner.

For an idea using N frames a 44 mag has a .457 base and a 45 colt has a base of .480. That is only an increase of .023 So between chambers you lose that .023 and the outer wall you only loss .0115. I have reamed a few 44 mag cylinders to 45 colt. Now 44 mags run at 36,000psi. (same as 357 mag) I keep my 45 colts under 25,00 psi which is way warmer than factory. No way I would bump them up to 37,500.

But get yourself a L frame 357 cylinder and some good measuring tools and figure out just how much metal you have to work with and what you would have left. If you have more metal left in the critical areas than say a model 19 cylinder has or a N frame 44 mag cylinder has. Thickness between the chambers and outer wall thickness. You might be fine. If your thinner somewhere its not that good and idea.

I read somewhere that the 686 cyl wall thickness is .177" and if you subtract .046" that leaves .131" between cylinders.

The reason that is significant is because the 7 shot 686 has a cyl wall thickness of .055" (much thinner) and still safe to S&W.

All in all, not a big deal to me.

It just didn't strike me as such a radical concept.

John

 

[ddixie884]

How much more pressure for a 10mm over a .40S&W. S&W built a .40 L-frame. My .41spl 686 by CCG is supposed to be good for 215gr at 1200fps...

 

[JohnHL]

How much more pressure for a 10mm over a .40S&W. S&W built a .40 L-frame. My .41spl 686 by CCG is supposed to be good for 215gr at 1200fps...

40s&w=35,000psi

10mm=37,500psi

Is this what you are asking?

John?