Revolver Chamber Throat Size

[Ganderite]

Most revolvers use a throat in front of the chamber holding the cartridge. I don't know the proper name for that short reduced diameter section of the chamber.

I am trying to figure out why my 38S&W revolvers are shooting well with 38 Spl lead bullets (sized .358") I thought .360 bullets would be better, but they were not.

I examined some revolvers, and found that the throat in a Colt is bigger than in a Smith or Ruger.

A tight throat would seem counter productive. It would size the bullet down before it entered the barrel.

My 38 S&W revolvers will pass a .358 bullet, but not a 360 bullet. I am guessing the throat is around 358 to 359.

Is there any know relationship to cylinder throat diameter to accuracy?

 

[B]

In the world of cast bullets you typically fit your bullet to the cylinder throat. Your situation would be surprising to me as well. Not incredible but against the norm. .38 SW is a heeled bullet design I would be very happy if I were getting good accuracy with any reloads.

 

[ryan]

It's been my understanding that the optimal cylinder throat diameter should be about .001 bigger than groove. Lots of other factors too, obviously but at least if the cylinder is a bit tight, it can be reamed out.
I had a Ruger blackhawk years ago, measured .005 larger than groove, accuracy was terrible, and nothing I tried helped at all. That one went down the road to an auction house. Wouldn't have wanted to sell it to anyone I knew.

 

[vagrantviking]

I would expect best results if the throat is slightly bigger than the forcing cone or bore. Bullets might bump up once in the forcing cone but that seems like a dubious thing to reply on in building a gun. There wouldn't be much resistance to an under size bullet and the cylinder gap would vent much of the pressure.

Is it possible that the unsized 360 bullets are inconsistent in diameter whereas the smaller ones are sized to be identical and that's the reason for the lesser accuracy? It's all I can think of.

Also, 38 S&W is not a heeled bullet. If it were there would be no throat and the cylinder chambers would be the same diameter all the way through.

 

[MattE93]

I have the same issue with my .38 S&W revolvers. 200 gr SWC will fit in the first part of the cylinder no problem but they are too large for the throat portion to the point they won’t chamber without significant pressure. This is most pronounced in my Enfield revolver

 

[B]

Also, 38 S&W is not a heeled bullet. If it were there would be no throat and the cylinder chambers would be the same diameter all the way through.

Man I was gonna rip a strip off you but turns out I had .38 Short Colt mixed up. My bad and it really explains a lot about what I was thinking about this cartridge.I even had some .38 SW out to photo before I realized I was wrong... This is the kind of problem you run into when you try and keep every thing in your head.

Some IVI marked goodness I have on hand.. Never even held a .38 SW pistol honestly. The previous prices have tempted me though. 200grns at 700fps would make a nice shooting round for sure.
q

 

[BattleRife]

A tight throat would seem counter productive. It would size the bullet down before it entered the barrel.

Correct. The Cast Boolits forum has seen many observations of tight cylinder throats affecting accuracy. They have a guy on the forum who has built a little home cylinder throat reaming rig and many people on there send their cylinders to him to have them opened to be 1 or 2 thou over groove diameter. Rusty Wood in BC offers the same service up here.