Barrel diameter for an old colt revolver

[alor_swe]

I have an old colt officer model match 38 special six inch revolver made around 1956.
This weekend I shot some lyman .358 148grain WC boolits with 2.9grains of vithavouri 310 (old ammo I had laying around) and I ended up with oval holes in the targets. The targets were placed at between 10 to 65 yards and the holes were oval in all of them. First I thought that the boolits was on the slow side but I had no drop at 65y, then I remembered that I've never slugged the barrel thinking that the barrel might be on the large side. Note my surprise when I checked the slug with my micrometer, it came out at .353. After another barrel cleaning the slugs still come out at .353. The strange thing is that I didn't notice any leading after well over 100 rounds.

Does anyone know if this is normal for these revolvers to have tight barrels or if I should send it over to a gunsmith for a barrel check?
BTW. does anyone know what barrel twist colt used on this model?

[MtGun44]

Older Colts are know to have tight barrels, but more like .355 or .356. .353 is very
tight, but again we see it proven that lead boolits are safe in tight bores. I am
surprised at the oval holes, old Colt revolvers are typically very accurate pistols.

Any possibility that the tightness is only at the barrel thread area? This would swage
a boolit down in the threaded area (and a slug used to check the bore diam, too) and
have it rattling down the rest of the barrel if it is in the .356-.357 range. This would
account for poor stabilization.

Try driving a soft slug into the barrel from the front only a few inches. I think you may
be able to get it back out with an appropriate short brass rod, barrel tightly clamped
in a vise (wood blocks, etc to protect it!) and a metal plate resting on the brass
rod - hitting the metal plate outside the frame window with a hammer, the plate
transferring the force sideways to the end of the rod.

[alor_swe]

Thanks for your suggestions MtGun44.

Doesn't seem to be anything wrong with accuracy (either accuracy is fine or my shooting is improving, don't count on the latter), just that the holes are oval sorta like when the bullets starts to tumble in the air.

I will try to slug the muzzle area of the barrel tonight.
When I slugged the entire barrel the slug was a real pain to get into the muzzle, then it felt like a smooth ride through. Only needed soft hammer taps on a piece of wooden dowel to push the slug along.

[alor_swe]

I've slugged the two inches closest to the muzzle now and the slugs still come out at .353.

[KCSO]

My 1956 Colt D Special was 355 on the nose and a Python from the same era was 356.

[alor_swe]

I've slugged two of my other revolvers now just to be sure that my methods doesn't give me any problems.
An colt official police slugs at .355 and an s&w with a match barrel slugs at .357 (the spec says it is a .357 barrel) so this is probably not an measurement error.

So I guess I need to buy a new .354 sizer die...

[Guesser]

I have 3 of the Colt OM revolvers, 1941, 1951, 1961. I shoot HBWC, I've never tried a cast WC but I do shoot my cast SWC and RN 158 gr. sized .358 and have never experienced the tumble with any bullet. I assumed that the bores would be .356+/- like most Colt barrels. Think I'll slug and see!!!

[Wayne Smith]

I'm carrying my Colt Agent from the '20's and have always shot .358" in it without problems. Never slugged anything. It works fine with what I use. Maybe I ought tt for academic reasons.

[Char-Gar]

It was common for these older Colts to run .354 - .355 in the grooves. However I seem them run as tight as .353 and as large as .356. Most often the cylinder throats run large in the .359 range.

In spite of these funky specs the old Officers Model, Officers Model Match, and Official Police usually shot like a house-a-fire. Of course the rifling and cylinder rotation directions were both opposite to the Smith and Wesson.

Bullets in the range of .358 have always done well due to the large cylinder throats and didn't seem to suffer any from the squeeze down the barrels. The lands were more narrow and the grooves larger than the Smiths but they grabbed lead very well. The twist was also somewhat quicker than the smiths. Many of these sixguns had a very short, steep and rough forcing cone. I have seen some early Pythons that look like it was cut with a cast iron burr. Recut the forcing cones to a nice smooth finish with a long shallow angle (11 degrees) and these old Colts will smile and purr. They are fine, fine pistol to be sure.

I don't know what to make of your oval holes, but I suspect that 10 yards was a hair to short for the bullets to settle down and go to sleep. WC bullets most often start to loose some stability past 50 yards and pick up some yaw. But the only thing that counts is how close they land to each other and not the shape of the hole. Anyway... IMHO the tight bore has zero to do with the yaw of the bullets.

[Groo]

Groo here
The python was said to have a tapered bore and started at 365/357 to 355/354 at the muzzle.
maybe your gun was similar