Manson Revolver Cylinder Throat Reamer

[ThomasT]

Thanks Pintler.

 

[Mixed Nuts]

Well, I haven't slugged the bore yet. Will do this weekend. But I got the remaining pin gauges. 5 of the cylinder throats are .357. One is smaller than .357. So weird. Before this thread I never would have thought the throats wouldn't match.

I'm hoping for a .357 bore slug. An excuse to ream to .358 and make the cylinders consistent.

 

[Mixed Nuts]

Update on original post - Originally: I have a .357 revolver that shoots jacketed, magnum ammo very well. It shoots 18BNH hardcast 158 LSWCs okay at full and near full magnum power (but not as well as jacketed ammo) but, when those same 18BNH boolits start to slow down they lead the gun and barrel. This inspired me to slug the bore, hoping to find a cylinder throat that was too small relative to the bore....

Well, I finally slugged the bore. I did it twice and then used my dial caliper to try and take a measurement of the slug's diameter across two high points.

I'm not confident in the measurement at all. The lands ridges aren't quite oriented opposite of each other and the calipers may cut into the slug as I close the tool. My best guess is .3562 - .3563, and though I got that measurement a few times on both slugs but it feels like a half-guess.

As for the cylinders. All will take a .356 pin gauge. Five cylinders will take a .357 gauge (but one will not) and none will take a .358 pin. So I know one of the cylinder throats is smaller than .357 and all are smaller than .358.

I have two basic questions and am open to any advice or opinion.

Question one - Why not just ream each cylinder out to 357.5 or .358? Is there some reason this might be a bad Idea?

Question two - Is there a way to measure the slug that would work better?
View attachment 793849

 

[Varminterror]

Whether pintler believes in measuring between parallels or not, the shimstock method I described months ago will give you a repeatable measurement, accurate for you to order the proper reaming diameter.

I like all of my throats to be the same, then cut my forcing cone to suit. .358” is the standard for the Manson .357 mag throat reamer, so you should be in fine style for a very, very standard throat reaming job.

 

[Mixed Nuts]

Redneck method:

Slug the bore. See if the slug drops through the chamber throat. If it does, the chamber throat is larger than the bore and the throat will not need reaming.

If the barrel slug is larger than the chamber throat then of course you will need to measure the slug to determine which reamer to use. But you can answer the big question without using caliper or micrometer at all.

I just tried this... slug is still a very tight fit in the barrel, if I want to put it through I have to drive it with the rod. However, I can put it through three of the cylinder throats effortlessly and the other three with maybe a hair less force than it take to push the slug down the barrel.

Three of the throats are bigger than the bore. That's sure. The other three are very close in size - maybe even the same size because in the cylinder I only need to force the slug through the throat and there is less contact there than in the bore. My measurement of the bore was wrong, the bore is at least .357.

Varminterror referenced his previous shim method for measuring and I went back through the thread. This was an awesome thread.

 

[Mixed Nuts]

I would say you will not have solved the problem without softer bullets. I did all that and only changing to 38 Special bullets cured my 357 Magnum leading. On the throats issue, I would not be aiming for .358 but the more common .3575. To follow the rule of thumb, bullet is larger than the throat, is larger than the bore would yield the sequence .358-.3575-.357, assuming the bore slugs at spec. All I did to know which cylinders to ream throats on was to see if I could lightly tap a nominal diameter, lead bullet through, e.g. a .358 through a .357 Mag or 38 Special. I learned to pretty much know that Smiths were not setup to shoot lead until modified and that newer ones generally had the wrong type of rifling. On the Rugers I had my heartaches with the older SIX series with mildly cut rifling but not much on newer guns, zero problems on 327 Fed Mag.

Hello RealGun, what did you mean by "I had my heartaches with the older SIX series with mildly cut rifling." ? I ask because the revolver in question is a security six. And the mildly cut rifling does make measuring the slug hard. How was it a problem for you?

 

[RealGun]

Hello RealGun, what did you mean by "I had my heartaches with the older SIX series with mildly cut rifling." ? I ask because the revolver in question is a security six. And the mildly cut rifling does make measuring the slug hard. How was it a problem for you?

I have experienced that leading is less likely to occur with good definition between lands and grooves. The mild definition of the older Ruger Sixes and the ECM rifled Smith's are about the same in pretty much demanding jacketed or gas check bullets when fired with any real pressure. My best example is replacing a Smith 625JM with a 625PC, ECM versus cut rifling. I sold the Sixes for multiple reasons and most of the ECMs.

 

[Mixed Nuts]

I have experienced that leading is less likely to occur with good definition between lands and grooves. The mild definition of the older Ruger Sixes and the ECM rifled Smith's are about the same in pretty much demanding jacketed or gas check bullets when fired with any real pressure. My best example is replacing a Smith 625JM with a 625PC, ECM versus cut rifling. I sold the Sixes for multiple reasons and most of the ECMs.

So, do I understand you like the new Rugers and the Old Smiths for cast lead at higher speed?

 

[RealGun]

So, do I understand you like the new Rugers and the Old Smiths for cast lead at higher speed?

Yes, I currently shoot lead in a Match Champion with adj sights, a Smith 625PC, and a couple older prelock Smith's. All of my single actions use lead bullets, although I may have to give up on leading issues and use semi-jacketed in the 44 Mag. Of the remaining newer Smith's, the 60 Pro Performance Center is very accurate with jacketed bullets (Speer Short Barrel) and wouldn't be used much as a range gun wanting lead anyway. Same for the 637 Wyatt as a tuckaway in my go bag.

 

[Mixed Nuts]

Okay, went ahead and did the job. Reamed the throats to .358. As per Varminterror and Ratshooter's advice I made the brass collar for the reamer so that the reamer had guidance from both the pilot and the collar. And although making the collar was a bit of pill (first time for me), it sure felt right when I was doing the cutting. I kept the collar in with the pilots. It's like gold.

View attachment 795608

 

[Walkalong]

Nice!

Now we look forward to the range report.