K-frame forcing cones

[JohnRoc65]

I have a K frame S&W model 65-4 with tight cylinder throats. I wanna blast lead bullets much of the time so I'd like to open them up to .3585". I was considering having the forcing cone reamed to 11 degrees as well.

I haven't found anyone to do this for me yet, so I was wondering if this is a bad idea for the forcing cone of a Smith K-frame revolver, since their forcing cones are thinner and weaker than L frames.

If anyone here could give me some sound advice, I would really appreciate it.

 

[4barrel]

I own 6 and all are .357 throats and shoot .357 or 358 lead boolits well with no leading. The throats are one of the first things I check when buying one.

 

[BLUEDOT37]

Consider using a 5 degree cutter

I was considering having the forcing cone reamed to 11 degrees as well.
...I was wondering if this is a bad idea for the forcing cone of a Smith K-frame

If you don't enlarge the forcing cone's opening diameter you won't have to worry about making it any thinner.

Ideally you don't want to enlarge the opening of the forcing cone, for several reasons. Factory FCs seem to run at the max size commonly suggested, which is .377" diameter for a .38/.357 revolver.

It's been my observation, when I had FCs that needed cleaning up/re-chamfering, that using a 11 degree cutter for the job would enlarge the FC's opening diameter beyond that spec to achieve the desired action.

If a FC hadn't already been cut in it that wouldn't be the case, of course.

The Brownell Chamfering Kit I bought also includes a 5 degree cutter & I found it performed the job needed without enlarging the FC's opening diameter.

Each of my S&W 357s that I used the 5 degree cutter on have grouped superbly afterwards.

However I hasten to add, it never completely stopped any leading I thought might have been associated with the FC, even though the throats were good.

I switched to plated or jacketed, in all my revolvers, & leading is one less thing to worry about.

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[JohnRoc65]

Thank you for the replies.

Smith and Wesson revolvers come out the factory optimized for jacketed bullets I believe. I might just keep this model 65 as is with the FC issue.

The throats seem really tight because a plated .357" diameter bullet cannot be pushed through with even strong pressure. I would literally need to hammer the bullet through the throat with a hammer and dowel to get it through.

Have you guys measured your cylinder throats with pin gages or a micrometer?

 

[stansdds]

Thank you for the replies.

Smith and Wesson revolvers come out the factory optimized for jacketed bullets I believe. I might just keep this model 65 as is with the FC issue.

The throats seem really tight because a plated .357" diameter bullet cannot be pushed through with even strong pressure. I would literally need to hammer the bullet through the throat with a hammer and dowel to get it through.

Have you guys measured your cylinder throats with pin gages or a micrometer?

Measure? No. But in all of my 357 revolvers a 0.357" jacketed bullet will smoothly pass through the cylinder throats, but on some a 0.358" cast lead bullet will drag slightly when pushed through the throats. It sounds like your revolver has undersized throats and that can cause accuracy issues with any bullet and pretty bad leading with lead bullets.

 

[Toolguy]

Thank you for the replies.

Smith and Wesson revolvers come out the factory optimized for jacketed bullets I believe. I might just keep this model 65 as is with the FC issue.

The throats seem really tight because a plated .357" diameter bullet cannot be pushed through with even strong pressure. I would literally need to hammer the bullet through the throat with a hammer and dowel to get it through.

Have you guys measured your cylinder throats with pin gages or a micrometer?

Have you measured the plated bullets with a micrometer? I would not trust that as being exactly on size without measuring. I also would not ream the throats over .357, which they may be already. Your gun, your call.

 

[JohnRoc65]

Have you measured the plated bullets with a micrometer? I would not trust that as being exactly on size without measuring. I also would not ream the throats over .357, which they may be already. Your gun, your call.

I don't have a micrometer but I did measure the bullet with a digital caliper. It was dead nuts on 0.357". The throats are definitely tight. Any reason they shouldn't be reamed larger than 0.357"? I know most people ream their throats to 0.3585" when making em hard cast friendly.

Pretty sure I'm going to have a gunsmith do this. They'll make sure any changes will be done correctly. (If anything needs to be done at all.)

 

[glenwolde]

I'd ream them out. I have a throat reamer but...

.38/.357 Special Throating Cutter - 4D Reamer Rentals

The probably also have a forcing cone reamer but I didn't look for it.

Or send the cylinder to cylinderhone on Facebook.

Reason not to? It shoots great as is and isn't having a problem.

 

[BLUEDOT37]

Have you guys measured your cylinder throats with pin gages or a micrometer?

Pin gages are the best way. They (throats) often can have slight differences & uniformity issues between their openings.

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[cowboy4evr]

About a yr ago I bought another model 19 . It's a dash 5 , nickel plated for a reasonable price . It looked as though it had not been shot much . After checking the cylinder throats I could see why ? A .357 pin gauge would not fit , neither did a .356 . It took a .355 . That would of definitely effected accuracy with such an undersize bullet . I opened up the cylinder throats to .3575 . I also slid a pin gauge down the barrel checking for tight spots , there were none as it slid all the way through easily . It is a very accuracy fire arm and leading of the barrel has not been a problem . Regards, Paul

 

[GBertolet]

I would go to .358, no larger. That is the standard size for 38 caliber lead bullets anyway. It's likely your barrel is the standard .357, which the larger .358 cylinder throat would be the perfect size for. Be sure you have someone experienced do the reaming insuring a true cut. As far as weakening anything, going from .357 to .358 is only removing 1/2 thousandths from each side of the cylinder throat. No weakening at all.

 

[WR Moore]

I've noticed that, at least on J & K frame examples, forcing cones seem to be rather tight on the OD. This may be due to the fairly thin walls of the barrel shank at that point on those frames.

The three I've measured ran about 0.365" maximum diameter. The K frame tended to lead even with plated bullets. A very careful 11 degree forcing cone cleanup with the OD taken out to about 0.368" produced a more even surface finish, better centered cone and touched up the tapered ends of the rifling. No more leading issues. I just can't see where taking 0.001 or so off the thin part is an
issue.

About optimized forcing cones: the industry standard forcing cone angle used to be 18 degrees (from parallel to the bore). At some unknown time around the 1980's S&W seems (but may not have) to have changed to the 11 degree forcing cone. Ruger later took this further with the 5 degree forcing cone. The general effect of the changes was to make the bullet engraving with the rifling and the groove diameter of the barrel both more gentle and to take place further into the barrel where it would have more support from the frame.

Frankly, most S&Ws seem to have tighter than groove diameter cylinder throats. I've never really noticed any accuracy issues that I didn't cause myself by either sight alignment or trigger manipulation.

 

[Dieseltech56]

I think a K frame with the flat spot on the rear of the barrel is best left with minimal material removed from the forcing cone. If you had to recut one without setting the barrel back 5° is about your only option. You’ll get a clean cut without opening the diameter.