I'm just getting into bullet casting and took some good advice to measure the cylinder throats on a given gun before buying a size die. The throats on my -2 measure .433"-.434". I haven't slugged the barrel yet, but I suspect it will be .430". I don't think I'll get top accuracy with this combination of dimensions.... If I size bullets to fit the throats, they'll be sized down a minimum of .003" when they hit the forcing cone and that's going to increase pressure. If I size them to fit the barrel, they'll rattle through the throats and probably enter the bore slightly crooked.

If you've slugged your barrel or throats, what dimensions did you come up with?

machinisttx,

By your "handle", I take it that you are a machinist? If so, then you probably know that slugging the cylinder chambers and then miking the slugs should produce a good measurement. The other method is to use accurately ground pin gages, and to measure the one that gives the closest slip fit. Using most other measurement methods, one is lucky to come within 0.001" of the actual measurement.

Measuring the five-groove barrel slug is an "iffy" thing unless you have access to the uncommon three-point micrometer and the conversion charts. I've found that pressing the slug through precisely drilled and reamed holes gives a good approximation.

I've learned to stop worrying about the exact size of bore and groove diameters on the .44 Magnum. In this caliber, S&W revolvers tend to be pretty uniform. With heavy .44 Spl and .44 Magnum loads, the bullets will upset in the chamber throats to give good accuracy.

Cast and sized bullets in this caliber tend to adhere to 0.430". Copper jacketed slugs tend to measure 0.429"-0.430". Using these size slugs, it is indeed a rare S&W that shoots poorly.

Why don't you buy or borrow some batches of commercially cast .44 slugs and load them up for firing tests? You may be pleasantly surprised.

Yes, I am a machinist. Due to a change of employers, I no longer have free access to equipment for personal projects, so I'm having a run of special V blocks made to allow accurate measurement of slugs from five groove barrels.

V anvil micrometers aren't uncommon, but they are expensive($400 or so) and there are two different ones available, one for three flute/groove and one for five flute/groove. They are direct reading and no math is required to obtain a correct measurement.

This gun has had one box of jacketed loads through it since I obtained it, with all the rest being commercial cast. It hasn't shot as well as I think it ought to. I have no use for loads above a 240 to 250 at 1200 fps. If the gun requires loads heavier than that to shoot well, then it's of no use to me either.

.430 cast bullets have always worked well in all my guns with minimal leading depending on the hardness of the bullet and the velocity I am pushing. I limit non gas check cast bullets to about 900-1000fps

Throats up until 1990 will usually maesure .432" - .433". In 1990 they were tightened up to the correct measurement of .430". Some of the classics, and classic DX's have throats that mesure .428".
There is an excellent article on shooting the .44 magnum at long range in the October-November issue of Handloader magazine, by Brian Pearce. In it, he gives a lot of good info on the early guns, their throats, and the actual bullet dimensions of early ammo which was .432", and is why throats of guns made before 1990 have throats of .432".

Issue #262. The article starts on page 74.

I bought that issue specifically because of that article. :-) Mine is an N prefix with a high serial number and 6" barrel. I should have looked up the mfg date by now in my standard catalog, but haven't gotten around to it until right now. Looks like it was made mid to late 1983. I'd much rather have the .428" throats since I could at least fix that.

The throats on my 29-2 made between 1972-1974 also measure .434

Does this mean I am screwed for accuracy? The gun is not grouping very well at 25 yards with 24.0 grains of H110 and 240 grain Hornady XTP's.

If you have not already tried it, try adjusting your load a little before anything else. I have found very small changes can really help with accuracy in some guns. I have a couple that are picky.

The amount of pressure increase from a 432 bullet entering a 430 forcing cone and bore would be practically zilch. Read up on some of P O Ackelys experiments with firing oversized bullets down undersized bores.

Ackley took a standard .30-06 chamber, enlarged the throat to .35, seated .35-caliber bullets into that .30-06, and fired them through the .30-caliber bore. With standard .30-06 loads, the .35-caliber bullets resized and passed with no signs of excess pressure. However, wrong-dimension brass can let gas escape with dramatic results.

That is what I am doing today. Rather than 24.0 grains of H110 I will be trying 23.0 grains, 22.5 grains and 22 grains with the Hornady 240 grain XTP’s.

Hmmmm... I have a 29-3, considered by many to be the worst of the model 29 series. At the time, I did not know that the 29-3 was supposedly such a dog and I got it on the cheap, so it came home with me.

I have not slugged nor measured anything, just loaded up some commercially cast 0.430" SWC bullets... maybe they are .430"... maybe they are .429"... maybe not... might vary a little or a lot, I never checked, over charges of Unique that gave me mid-range velocity. Accuracy was... let's just say I'm positive that this revolver is much better than me and I was quite happy with my efforts at 25 yards. Personally, I think cylinder throats that are just a couple thousands of an inch larger than the groove diameter of the barrel will provide you with good accuracy. If anything, it will be the forcing cone and the potential for the internal dimensions of the barrel being slightly undersized in the area where the barrel is attached to the frame that will adversely affect accuracy.

The 24.0 grains of H110 was too hot as you basically suggested and the 22.5 grains of H110 looks much better even if it was at 20 yards and shot from a sandbag.

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Exactly. In my various 29-2s I’ve found I can’t put a loaded round (Remington and Winchester brass) in the chambers if the bullet is larger than 0.433”. I use bullets sized to 0.4325” and have no issues with accuracy, leading, or pressure. Worrying about pressure with cast lead bullets that are a couple thousandths over bore size is not worthwhile, IMO. I’ve never seen any indication it is a problem. Just be sure the loaded cartridges are not overly snug in the chambers.

You are onto something there. That's a respectable group.