Odd 629 bore size: sizing question

[jumping frog]

OK, I've read just enough to be dangerous without really knowing what I am doing.

I slugged the 6 chambers and the barrel for my .44 Mag S&W 629. I cast some pure lead bullets and then smacked the nose with a hammer to make them a slightly oversized diameter. Then I drove them through with a wooden dowel. Each chamber got its own slug and I slugged the barrel twice. I could see where I had shiny lead circumference from being sized as I pushed each slug though.

The chamber sizes came out to:
.4290
.4287
.4288
.4290
.4290
.4291

However, I am concerned about the barrel. It slugs out to .4233!!! I started the slug at the muzzle and pushed it through to where the cylinder would normally (I had removed the cyclinder).

Seems awfully small to me, however, I cannot find anyplace with google that lists what the barrel bore should be, so I don't know.

Now, I bought a .430 sizing die but it seems to me that a .423 barrel is going to be a problem.

Can anyone help enlighten me?

 

[jumping frog]

OK, I've read just enough to be dangerous without really knowing what I am doing.

I slugged the 6 chambers and the barrel for my .44 Mag S&W 629. I cast some pure lead bullets and then smacked the nose with a hammer to make them a slightly oversized diameter. Then I drove them through with a wooden dowel. Each chamber got its own slug and I slugged the barrel twice. I could see where I had shiny lead circumference from being sized as I pushed each slug though.

The chamber sizes came out to:
.4290
.4287
.4288
.4290
.4290
.4291

However, I am concerned about the barrel. It slugs out to .4233!!! I started the slug at the muzzle and pushed it through to where the cylinder would normally (I had removed the cyclinder).

Seems awfully small to me, however, I cannot find anyplace with google that lists what the barrel bore should be, so I don't know.

Now, I bought a .430 sizing die but it seems to me that a .423 barrel is going to be a problem.

Can anyone help enlighten me?

 

[okie john]

In the June 2006 issue of Handloader magazine, Brian Pearce mentioned that S&W holds their 44 Magnum throat diamters to .428" for best accuracy with jacketed bullets. Bore diameter remains larger, however, and that causes problems for the cast bullet shooter.

As for your post, I see a couple of problems. First is how you're measuring the bore slug. S&W has five-groove rifling, which is very difficult to measure accurately without specialized gear. See if your bore slug will slip through the cylinder throats. If it hangs up, your measuring method for the bore slug is the problem. You can read http://www.alphaprecisioninc.com/revolver/default.htm to understand how dimension should line up in an accurate revolver.

The second and more serious problem is the variation in throat diameters. That can be ironed out by an outfit called cylindersmith.com. Once you get a read on the correct bore diameter, they can open the throats up to match. I had them clean up a Model 629 Classic for me and it shot much better after they were done with it.


Okie John

 

[john traveler]

First, your M629 barrel is a five-groove job. It is difficult to get an accurate or even an approprimate measurement of the the groove diameter using a conventional micrometer or caliper. You need one specially designed to measure odd-sized grooves, or a special vee-block and formula to convert your two-point measurement to the actual barrel groove diameter.

Second, the critical barrel measurement is NOT the bore diameter, but the groove diameter that dictates what is the optimum bullet size to use.

I would suggest that 0.423" is way outside the specifications of a .44 Magnum barrel groove diameter. It is even much too small for the old nominal 0.427" of .44-40 barrels, the old .44 caliber size.

That said, your cylinder throats seem to be correct or just a thousandth of an inch smaller than optimum. I would suggest loading and firing the standard 0.430" sized cast bullets and see what results you get. The chances are pretty good that you will be pleased.

 

[jumping frog]

Originally posted by john traveler:
First, your M629 barrel is a five-groove job. It is difficult to get an accurate or even an approprimate measurement of the the groove diameter using a conventional micrometer or caliper. You need one specially designed to measure odd-sized grooves, or a special vee-block and formula to convert your two-point measurement to the actual barrel groove diameter.

I didn't realize the 5 grooves issue beforehand and see how that creates problems. Thank you for the explanation.

If someone has "that special jig" or v-block, I'd be glad to mail them the slug if they would tell me the measurement.

 

[Alk8944]

[/QUOTE]If someone has "that special jig" or v-block, I'd be glad to mail them the slug if they would tell me the measurement.[/QUOTE]

jumping frog,

Give me your e-mail address and I will send you my mailing address and measure a slug for you. Send at least two slugs, muzzle and breech. For the breech just push one all the way through. For the muzzle you can drop a dowel about 1" shorter than muzzle to breech, drive the slug just flush with the muzzle and then push it out using the dowel you put down the barrel. This will give both muzzle and thread choke area dimensions.

Don't think too much of the throat measurements you got, it is difficult to measure something as soft as a lead slug much closer than .0002 or so, and your spread is only .0004 total, from +.0001 to -.0003. You need a very gentle touch to do any better, and very few who don't use precision measureing tools for a living have it.

You really don't need to know groove diameter either. Just try your bore slug in the throats of the cylinder. What you do need to know is that the throats are at least as large as the bore, and the slug will be the same to the throats as a if it were round. If the slug passes the throats with no to moderate resistance things are close enough. Since your throats all measure for all practical purposes, just size or order your cast bullets at .430 and they will do everything needed of them.

Did you take at least 2 measurements on each throat slug for an average? If these are just single measurements for each they don't mean much either.

The other side of this is that if you are shooting cast bullets they rarely are the actual nominal dimension advertised. Many will vary more than .001, so the .0003 maximum variance you list doesn't mean much either from this standpoint.