Coffield article about reaming throats

[MtGun44]

Well, looks like this has hit the big time. I don't know if it is the 450 threads here about
how to fix a revolver with undersized throats, but Reid Coffield (and I like his articles in
Shooting Times and Shotgun News) wrote a nice article about reaming up the
throats of an old .455 Webley to make it more accurate. Went from 10" groups
to 5" groups. Still no target pistol, but a huge improvement.

I think we are getting the word out. . . . . Not that this is new stuff. . . a post I made in
2007 and it wasn't new then!

http://castboolits.gunloads.com/showthread.php?12464-Revolver-throat-reaming-with-drill-press-mill

Bill

[bhn22]

Some day they'll listen.

Thanks!

[Petrol & Powder]

So, along that line; I have a new to me S&W K-38 that has tight throats. It is in beautiful condition and I don't want to open the throats up if I don't need to but it does lead the barrel a little at the forcing cone. I haven't had the chance to shoot it from a rest but it's fairly accurate from an unsupported hold.
Because it's a lot harder to put metal back on :wink:, I intend to do a lot more experimenting before I start reaming. That being said, it seems that it would benefit from cylinder throats that didn't swage the bullet down .002" or more smaller than the bore diameter.
Here's the weird part, it leads more with solid wadcutters than with SWC's ? Same alloy, same sizing die and same lube.

[Old School Big Bore]

Same powder & load? Same protrusion from the case into the throat? Same etc etc?

[Petrol & Powder]

Same powder, ww231,
not he same load, 4.3 grs for the SWC 4.0 grs for the full WC,
both seated to the crimp groove but obviously the SWC protrudes from the case more.

[35remington]

Just a gentle reminder we use the term "bore diameter" when we really mean "groove diameter".all too often here.

I have an older K frame that has tight cylinder throats, but given it shoots well in this case I'll leave it alone. Hard to measure the 5 groove barrel and I've never bothered on this one.

[Petrol & Powder]

true dat. I misspoke - groove diameter.

[dubber123]

So, along that line; I have a new to me S&W K-38 that has tight throats. It is in beautiful condition and I don't want to open the throats up if I don't need to but it does lead the barrel a little at the forcing cone. I haven't had the chance to shoot it from a rest but it's fairly accurate from an unsupported hold.
Because it's a lot harder to put metal back on :wink:, I intend to do a lot more experimenting before I start reaming. That being said, it seems that it would benefit from cylinder throats that didn't swage the bullet down .002" or more smaller than the bore diameter.
Here's the weird part, it leads more with solid wadcutters than with SWC's ? Same alloy, same sizing die and same lube.

I am curious as to how you measured the throats? I ask as I have probably 30 S&W's here in .38 or .357, and all of them have measured .3580" to .3585". Very consistent dating from the pre-1920's to the 1990's. Maybe I got lucky.

[MtGun44]

I have never previously heard of an older .38 Spl S&W with tight throats. I am curious about
your measurement. If other than gage pins, I tend to doubt the accuracy of measurement
and I would never consider reaming one of these without measuring with gage pins.

Not saying it is impossible, because clearly it is not impossible. But it IS improbable.
I have gage pinned a significant number and never found a tight cylinder in this particular
caliber in a S&W revolver.

If it turns out to be actually tight, then normal dimensions should shoot better.

Bill

[Petrol & Powder]

A bullet sized .358 cannot be pushed into the throat and a jacketed 9mm bullet that measures .355 by my calipers just fits through with some pressure. The throats are clean and lead free.
So, no pin gages or micrometers but it seems to be tighter than my other S&W .357 cylinders.

I'm not about to start reaming anything based on those anecdotal measurements but it would seem to explain the leading at the forcing cone.

[leftiye]

If you're getting resistance with the .355 bullet, then the chamber mouths are about .355 + about .0001" or.0002" (or .3552"). Now you need to know what size your grooves are. You're right about can't cut metal back on, but .001" over is a good spec for accuracy (so is .002 over), and .002 to .004" over isn't horrible (works well) too. In other words, you still need to know the groove diameter, but it isn't fatal if you were to come out with .003 over. But if you KNOW THE GROOVE DIAMETER that won't happen. Thread hijacked sucessfully?

[Petrol & Powder]

Roger that. And of course my calibers could be off as well.

[btroj]

Never have reamed one. I fixed my 45 Colt BH with a split rod and emery cloth. Worked well, took little time, and was pretty cheap. I tested for for with a .452 jacketed bullet and got a snug slip fit.

Sometimes a gun just needs some tinkering to work for your needs.

[Airman Basic]

Never have reamed one. I fixed my 45 Colt BH with a split rod and emery cloth. Worked well, took little time, and was pretty cheap. I tested for for with a .452 jacketed bullet and got a snug slip fit.

Sometimes a gun just needs some tinkering to work for your needs.
How'd you power your split rod? Have a BH that would benefit from that treatment.

[btroj]

Cordless drill, go slow. Very slow. Don't let emery go too far out of cylinder or it makes front end bigger. Remove a bit, measure, repeat. Be sure to clean up before checking fit.