S&W and Ruger chamber variations ?---

[Prince55]

Recently in another posting I was asking about getting the correct fit
for cast bullets in a .41 Magnum Ruger.
Some information received there got me to thinking about my other
revolvers.
I took some factory jacketed bullets and dropped them through each
revolver cylinder's chambers.
Here's what happened with a Hornady JHP and a Remington JHP bullet
and a Speer JSP.
On all the Rugers the bullets dropped through smoothly.
With a S&W model 66 they all went through with little resistance with
one chamber being extremely tight.
With 2 S&W model 65's they went through with slight binding.
On a S&W model 60 .357 they dropped through easily.
About the same on two model 10's
But on a S&W model 37 Airweight the bullets hung about 1/8 inch from
the end of the chamber in all 5 chambers and I couldn't force them
through No Matter What with a wooden rod. They started in very freely
and after they got near the end they got really tight. I never did get any
to go through and had to force them back with the wooden rod.
I can't imagine the pressure that some of these revolvers are mounting
up to get these bullets through.
Any idea why S&W lets these pass inspections like they are. They
surely couldn't be within tolerances.
I figure SL1 probably knows the solution as he's pretty good on these
problems.

Thanks

[WESHOOT2]

And the simple question: How do they shoot?

[Prince55]

The Ruger's shot the best, especially at 25-50 yards.
The S&W 66 .357 with the one really tight chamber usually has a flier
from that chamber.
The others were about normal except the S&W 37 at 25 yards was
from one side of the target to the other, but at about 20ft it was decent,
naturally they're not target guns with a 1 7/8 inch bbl.
The model 66 .357 4 inch was hitting about 5 inches high at 25 yards
with Hot loaded 180gr bullets and the sight is all the way down.
The real surprise of them all was the Ruger Speed Six 2 3/4 inch bbl.
with the identical 180gr load was shooting point of aim and groups were
2-2 1/2 inches.

Thanks

[SL1]

The SAAMI drawings I have for the 357 Magnum show throat diameter as 0.3580" plus up to 0.004" tolerance. They show jacketed bullets as 0.3580" minus a tolerance of as much as 0.0030" and lead bullets as 0.3590" minus a tolerance of as much as 0.0030".

And, the drawings show throat diameter in two places, right at the end of the chamber and half-way between the chamber and the cylinder face. It is the same in both places -- no taper.

So, in theory, all ."357" bullets should be pushable through your chamber throats. But, in practice, pushing a 0.3580" jacketed bullet through a 0.3580" throat may not be something you could do by hand pressure. But, powder pressure would not have a problem.

With regard to your taper, at least is in the right direction. It is best to have throats (and bores) get tighter as the bullet moves along its path, rather than the other way around. It promotes accuracy. The only down-side is that it might also promote a bullet sticking in the bore if you are trying to use really light loads. And, of course, if the throat tapers to less than the barrel's groove diameter, that can reduce accuracy.

I don't see any real problems with the results of the throat push-through tests that you performed. There are many other factors that are more important to both accuracy and pressure. The results from your accuracy tests are what count.

In case you are interested, the latest Speer manual (#14) has a table (page 771) where three identical loads were fired through 30 different .357 Magnum guns and a test barrel. They only recorded velocity, not accuracy nor pressure. The variations in velocity, even for revolvers of the same make and same barrel length, were much larger than most people expect. For example, for 5 S&W revolvers with 6" barrels, velocities ranged from 1307 to 1603 fps with a 125 gr bullet, from 1246 to 1417 fps with a 140 grain bullet, and from 1080 to 1284 fps with a 158 grain bullet. You can tell it was the guns that differed, because the velocity rankings of the 5 guns were the same for all three loads (except for a 1 fps swap between one pair of guns with the 158 grain bullet).

So, guns are not identical nor perfect. It's best to think about how yours actually performs. Taking precise measurements can help you make it perform up to its individual optimum. But it is not worth the worry about whether it is at the best combination of specs, or even if it is slightly out of spec (EXCEPT for head-space specs). Making chamber throats the same MIGHT improve group size for a full-cylinder group if you have optimized your bullet (typically cast lead) for that size, BUT, it won't if you don't do the job right (for instance, make some of them flare at the cylinder face or slant slightly out of alignment) OR if the real problem affecting accuracy is actually different alignment of the various chambers with the bore when the cylinder is locked, or loose lock-up, or ... . So, be careful how yo try to change the gun to make it better, because, unless you have the right tools and knowledge, you are more likely to make it worse, instead.

SL1