Pin Gauges and throat size

[MikeS]

Hi All.

I just got a pin gauge set I bought a couple of days ago, so I thought I would use it to check all the throats on my revolvers. Well, I got some surprise sizes, and wanted to ask for advice. I have 3 revolvers that shoot 45LC, so I started with them. The first one is a Cimmaron Thunderer I had rebarreled to 45LC from 44Spec. The gunsmith I had do the job told me the throats were 'fine for using .452 sized boolits', and the 45LC cylinder throats measured at .454, and the 45ACP cylinder measured at .452 The bore diameter is .439 Next up is a RBH and it's cylinders measured at .450!! with a .443 bore with .001 of thread choke at the threads. The last one is a ROA with a Taylor's 45LC cylinder. The throats measured .452 and the bore is .442

I know I need to get the RBH's cylinder reamed out, just not sure what size I should ream it to. The first option is to ream it to .454, and then also ream the ROA to .454 as well, and then get a new sizing die for my lubesizer. Or I could ream it to .452 and see if the gunsmith has a cylinder for my Thunderer that has .452 throats, and then be standardized on .452 for all my 45 boolits, so I can load the same boolits in either my 1911, or any of the revolvers. I would rather stay with .452 and was wondering, if the gunsmith doesn't have a different cylinder that has .452 throats, how bad would it be to shoot boolits sized to .452 with .454 throats? I've only shot this gun once so far, and I put slightly more than 50 rounds thru it, with no leading using boolits cast from Lyman #2 sized to .452 I also shot about the same number of boolits from the Rugers too, and neither of them seems to be leaded, any dirt in the barrels came out with a couple of passes with a boresnake after shooting. As all 3 guns had different bore sizes, what size is a 45 bore supposed be?

I did the same measurements on 2 Model 60 Smith & Wesson revolvers, both bores were .345, but one of them had .002 thread choke, while the other didn't have any choke at all. One had cylinders of .356, and the other is .355, again what is the proper bore size for a 38Spec? Neither Smith is probably going to be shooting lead boolits, so I don't think I need to worry about them (they're my mother's guns, thats why no lead). Thanks!

PS I didn't slug any of the bores yet, just used the pin gauges, so don't know the exact groove diameter of any of them.

[Bambeno]

The most important thing is, How do they shoot?

[noylj]

Where did you get the pin gages and what are the Barrel groove diameters (not the bores) of the revolvers?
Are you having problems with the guns? The pin gages can help to find a problem, but, if there isn't a problem, you don't need to worry.

[Iron Mike Golf]

You want to set up the throat diameters relative to the groove diameter. That means you need to slug the barrels and measure with a micrometer (not calipers). Shoot for cylinder throats .0010-.0015 larger than groove dia. For your BH, you will *probably* want to ream to .452. Most common reamers made for cylinder throat reaming are .4525.

A .001 rame constriction *might* give you accuracy or leading problems. Be sure to experiment with powder, charge weight, and alloys before worrying about the constriction.

[Char-Gar]

You are sticking pin gauges into the barrel and that will give you no useful information. It will tell you the land diameter, but not the groove which is the critical number.

So your starting point is way off base.

You want the cylinder throats to be the same size or a little larger than the barrel GROOVE diameter.

1. You are good to go with .454 throats in your converted pistol. The alloy and load pressure will be the major factors in what size bullets will work in your pistol.

2, Most likely your Ruger has a barrel groove diameter of .451-452. You will need to open up those .450 cylinder throats. .4525 is the usual number, but it will do no harm if you open them up to .454. However, the alloy and pressure will be the major factors is what size bullet will do best.

On those Smith snubbies, just forget about throat, barrel and all of that, just shoot the little boogers. However those numbers for the throats seem on the tight side to me. They should run .357-.357, which leads me to ask;

You did clean all of those cylinder throats down to bare steel didn't you. If you did not, those pin gauge numbers will be off.

Pin gauges are neat little gizmos, but they have only limited use for what you are trying to do and like most things mechanical are "operator dependent".

[MtGun44]

barrel groove diam is important, bore diam is almost totally irrelvant.

My Ruger BH convertible had .449 and .450 throats. I reamed to .452.

I agree with Chargar, too.

Bill

[MikeS]

I know the bore diameters don't mean much, I just measured them because I had the gauges there. The only dimension I'm concerned about is the .450 throats in the RBH, and the .454 of the other SA. I didn't know if throats .002 over the boolit's diameter would make a big difference or not, but I do know that .002 too small is a problem. And while the actual bore diameter isn't important in and of itself, it is a good indicator of thread choke which both the RBH, and one of the Smith's show they have. Next I will slug the barrels to see where they're at.

As for the 2 .38's, neither has been shot in a long time, and they were cleaned before being put away, but I didn't actually clean them before measuring them. Thanks for all the answers.

[geargnasher]

Pin gauges are for measuring round holes. Revolver cylinder throats are seldom round. There's just no substitute for soft lead slugs, a brass rod, and a good micrometer.

Gear

[Nrut]

Pin gauges would be great for measuring "bore dia." for PP esp. on barrels with odd number grooves which I have..
I was just looking on the net yesterday as to were a set might be purchased and came up with Enco for $46.00 that should cover all rifles bores..

[noylj]

Nrut:
I looked on Enco and couldn't find any pin gages for less then $134.
Do you have a URL for what your found?
Thanks.

[Nrut]

I saw the high price also but ended up clicking the catalog page and came up with this:

http://www.use-enco.com/CGI/INPDFF?PMPAGE=386&PARTPG=INLMK32

Enco is the only place I looked..
There may be better prices else where..

[alamogunr]

I got mine on Ebay. It is a Meyer M2 Minus set. There were several gages missing and I took a chance that they wouldn't be ones that I needed. Luckily they weren't. I'm not sure what is available on Ebay now, but it wouldn't hurt to look.

[mdi]

"I didn't know if throats .002 over the boolit's diameter would make a big difference or not, but I do know that .002 too small is a problem"

I would think a bullet .002" smaller than throat diameter would cause leading. My method is to size bullets to cylinder throat diiameter. Two of my .44 Magnums have .431" throats, so the bullets for these two guns are sized .431". One has a groove diameter of .429" (Ruger SBH), and the other .430" S&W 629) and I get very little to no leading in these two guns shooting straight wheel weight alloy Lyman 429421 boolits...

[MtGun44]

Ideally you want the boolit to be throat diameter or .001 larger. Try both and see what
shoots the best. The more gap the more the boolit can tilt when launched and get
distorted when it slams into the forcing cone of the barrel.

Bill

[PacMan]

Pin gauges are for measuring round holes. Revolver cylinder throats are seldom round. There's just no substitute for soft lead slugs, a brass rod, and a good micrometer.

Gear


I agree that the throats may be out of round but doubt if it would be enough to make a diffrence is most cases.
Just curious what you do if you find one slightly out of round.

[MtGun44]

This is why shooting .001 oversized is sometimes helpful. You can ream them but if the
nominal diam is OK, probably won't cause much of an issue.

Bill

[cbrick]

I saw the high price also but ended up clicking the catalog page and came up with this:

http://www.use-enco.com/CGI/INPDFF?PMPAGE=386&PARTPG=INLMK32

Enco is the only place I looked..
There may be better prices else where..

From the picture the one shown on the bottom of the page appears to be the set I got from Enco several years ago when they had them on sale.

I agree that it's possible to have throat(s) out of round but it's something I've seen very little of. If you use a minus set and place the largest pin that will go in a throat and hold it up to a strong light you'll see light around the pin if it's at all egg shaped. My experience has been that very few are.

Rick