Revolver leading

[Brad]

Cylinder throats all measure a pretty consistent .3574-.3575
Bore, near as I can measure, is closer . 354. S&W uses 5 groove rifling and it makes measuring the slug a bit more complicated. By slowly rotating the slug between the anvils on the mic I get .354.
Tight throats and bore, not at all like the rugers I am used to.

 

[Ian]

All my Smiths have been extremely tight on the groove dimension, that doesn't surprise me at all, Brad. It would be perfect for a 9mm cylinder that was counter-bored for moon clips. Ruger 5-groove has been tight, too, come to think of it. My .45 Colt is the exception, it's right on .451.....except for the part through the frame that was something like .445".

 

[freebullet]

That is virgin tight for a 357.

Only had one smith, an older 27. Was a very nice gun, wish I hadn't sold it. Wonderful trigger it had, looked pretty wicked with the hammer cocked.

 

[Eutectic]

Bore, near as I can measure, is closer . 354. S&W uses 5 groove rifling and it makes measuring the slug a bit more complicated. By slowly rotating the slug between the anvils on the mic I get .354.

I'm afraid you may have gotten a bogus undersized reading Brad...........

I've got quite a few barrels with 5 lands and grooves. (one with seven and one three also) Odd numbers don't mic correct. Why? If you were to look at the rifling configuration flat like on a piece of paper one can see that the point to point you feel (land edge to land edge) with the mic occurs on a line that does not go through the centerline of our slug!

How to measure it then?? A piece of shim stock around .006" thick will get you close. Here you wrap a piece of shim stock around you slug sample holding the ends pinched tight between your thumb and 1st finger of your off hand. Get a mic readings in a couple spots and then subtract twice the thickness of the shim stock used. This method will get you close (maybe within a thousandth) The best and most accurate way is to go by the circumference of you slug sample. For this you will need hole gauges and you have the lathe to do it. Start small like .354"? and carefully see if the oiled slug with enter Be careful and gentle..... you don't want to size your sample. Keep opening your hole gauge and test. You can leave your hole gauge chucked up. when you just get a fit that you can feel contact then you have duplicated the circumference of the five land diameter. Micing the hole in your hole gauge then gives your an accurate groove diameter of the 5 land and groove circumference your hole gauge has given you.
Many shooters like myself have push through sizers. I have them from .355 up to .360" in less than .001" increments. I've used these for hole gauges before. When I got my five groove .35 Whelen back from JES I got .3575" with shim stock. The hole gauge said .3585" right where I wanted it. Trying to mic the actual slug would be a few under these readings..

What works most accurate for me......

Pete

 

[KeithB]

Here is a micrometer with a V anvil used to check 5 flute reamers, ought to work fine to check 5 groove slugs.

https://www.ebay.com/itm/Starrett-T...616023?hash=item3afc193e97:g:UygAAOSwH2VaR~Cd

These suckers are REAL pricey. I've needed to measure 5 flute cutters before and didn't want to spend the coin for a dedicated mike. I've been thinking about making a device to fit over the anvil of a regular outside micrometer that would have a 72 degree V notch for an anvil. It would make a 0-1 mike into a 0 -.75 or so and you would have to calibrate it with a set of pin gauges but that should be no problem. If I make one I might just as well make a dozen if I thought anyone else was interested. Price would be under $20.

Sorry, not trying to hijack this thread but this is a perpetual issue that spawns lots of creative workarounds when there is with a fairly simple low cost mechanical solution just begging to be created.

 

[Brad]

Count me in Keith.

 

[Pistolero]

Me, too. Heck of a deal. I'd definitely buy one for that price. Definitely difficult
to measure S&W slugs, but I usually can get the anvil to BARELY overlap two of
the raised portions from the grooves, but it is ticklish and not as accurate as a
V anvil would be.

Bill

 

[freebullet]

I would take one too, Keith. In addition I'd take a mess of star die blanks should you decide to make a run of them.

 

[Ian]

Put me in the "me too" list please.

 

[gman]

I'm in for one.

 

[Pistolero]

Are the std anvils of 0-1" mics a standard diameter? Should we specify an
anvil diam or mic model?

Bill

 

[KeithB]

I'm going to figure out a way to make it fit most standard anvils. I'll post a simple drawing in a new thread a little later.

 

[waco]

My S&W 29-5 44Mag has HORRIBLE thread choke. Run a patch with a brass jag down the bore and it's easy to detect......
Bright shiny bore and you get a pretty bad constriction right where the barrel mates to the frame.

My 1968 K-38 on the other hand has a pinned barrel and no such problems.

 

[pokute]

That's funny! I'm glad you're willing to "concede" about the existence of thread choke.

A .357 is just as bad as any other because the barrel tenon is proportionally as small as any other caliber. I have two .38-cal Smiths with some of the worst barrel choke of any I've seen.

Ruger revolvers made in the past 20-30 years are especially bad due to the timing process of the barrels. Read up on how Ruger sorts and times their barrels (probably have to buy a book, not sure what's published on the net about it), it's enough to make any machinist cringe.

I'm not sure what you mean about the tenon being proportionally as small. What tenon? Each frame size has it's own thread size, and it's all steel from there to the bore: https://www.brownells.com/aspx/search/productdetail.aspx?pid=642&avad=avant

 

[Ian]

Small bore, small frame, small tenon. Large frame, large bore, large tenon. That steel between tenon and bore is "proportionally as small" for any caliber, unless you put a .357 on an L frame or something like that.

Barrel "Tenon" is what I'm calling the thing the red arrows point to in the photo here, I'm sure we're talking about the same thing:



See how small it is on a DW .357 Magnum? They are wonderful because they don't have thread choke...you can't over-tighten them.

 

[pokute]

Ah, okay. Yes, we're talking about the same thing. The OP's gun is, I believe, and L frame in 357. so same tenon as a 44, so quite beefy. I would be very surprised to hear that it had significant bore restriction. Anyway, lead buildup just past the forcing cone is just as much a restriction in the same location as thread crushing, and it would be a shame to go at a little lead buildup thinking it was thread crushing. The OP's gun also exhibits exactly the forcing cone roughness that I found results in lead buildup that gets smoothly joined with the leade and degrades accuracy.

 

[Ian]

You're right, if lead is getting literally shredded off of the bullet by a rough forcing cone....or by forcing a too-large bullet through the cylinder throats....those bits can get deposited in the barrel right past the forcing cone, usually starting right at the end of the forcing cone though, while thread choke causes leading to start right at the front edge of the frame.

 

[Brad]

I have a new sizer made, will see what improvement that makes. I will be turning a brass lap for the forcing cone. That is such a simple fix that I can't see not doing it.
I will load a hundred jacketed up in mag cases and fire them. That will smooth the bore a bit too.

 

[gman]

The worst I’ve run into was a Super Blackhawk 44 mag. 6 rounds and the barrel was coated. Pulled the barrel and it sprang back. Set the shoulder back so it could be hand tightened to 10-12 degrees Btdc. Minimal barrel cylinder gap and trigger job. Shoots fantastic now. Made me rethink fire lapping although that has its place and works.

 

[Pistolero]

Yes, gman, that is exactly how you solve a thread restriction. Have seen it a number
of times. They always spring back just fine.

Bill