Odd S&W 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). I am measuring with a micrometer that reads to the nearest ten thousandth.

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?

[redneckdan]

Is it 5 groove rifling? If so you need a circular gauge to meaure the slug accurately. The throats on my 629 vary between .4281 and .4288 I contact the cylindersmith and he said to send her out anytime....gotta get off my butt and get it done.

[JIMinPHX]

Take one of your barrel slugs & drop it into a chamber. If it doesn't just fall right through, then you didn't measure it right. If it does just drop right through, then either you didn't expand the slug enough or you have a barrel problem.

[Jumping Frog]

Take one of your barrel slugs & drop it into a chamber. If it doesn't just fall right through, then you didn't measure it right. If it does just drop right through, then either you didn't expand the slug enough or you have a barrel problem.

Oh, the barrel slug drops right through the cylinder all right. The slug started at .435 being being driven through the barrel and came out at .423.

I should mention this a "new to me" revolver.

[Dale53]

S&W barrels are VERY difficult to measure without a proper jig. As suggested, see if your barrel slugs will slip through your cylinder throats. If it will, then you are good to go. The throats need to be a bit bigger than the barrel to work properly.

From the sound of your cylinder measurements, you should be good to go.

Dale53

[Char-Gar]

If the barrel slug you measured at .432 will drop through a cylinder throat you measured at .429 you has mismeasured something for sure and for certain.

Barrel slugs from Smith and Wesson five groove barrels are tricky to measure, but not impossible with an ordinary micrometer. It just takes rotating the slug until you find the high spot on the edge of opposing lands, which is pretty small spot and easy to miss.

Even so, no matter where you measured the slug, if it read .432, it would not drop through a .429 hole without a shove.

I would size your bullets .430 and go shooting. Not to worry, the bullets will size down in the throats with no increase in pressure to be concerned with.

I have three 44 magnum pistols with cylinder throats, .430, 431 and .432. I size all of my bullets .432 and shoot them in any of the sixguns. Yep, it takes a custom die to get .432.

[Firebird]

S&W uses a 5 groove rifling where the lands and the grooves are the same width. This makes them very difficult to measure without having the correct angle v-block micrometer, there was a post here that spec'ed the correct micrometer to use. You can get pretty close (but don't count on accurate to the .0001") by measuring at the edges of the rifling which are across from each other.

[Crass Whackwords]

S&W barrels are spot on, I wouldn't even bother measuring the barrel.

[Larry Gibson]

Jumping frog

Take an empty beer can and cut a strip 1/2" wide by 4" long (doesn't have to be exact, just close). Mic the thickness (Bud Lights are usually .004"). Wrap the strip around the barrel slug and pinch tight on one side with fore finger and thumb. With the other hand mic the diameter being careful not to push the metal into a groove. Subtract twice the thickness of the strip from that diameter which will give you the actual goove depth diameter of your 5 groove S&W barrel.

With those measurements of the cylinders throats I'd go with a .430" sizer but a .429 would probably do as well.

Larry Gibson

[JIMinPHX]

S&W barrels are spot on, I wouldn't even bother measuring the barrel.

I don't know how many smiths you've measured, but your statement does not concur with what I've seen. I bought a brand new K-frame, back when they still made them. The groove diameter was .362 right out of the box. I sent it back to S&W to have it looked at. They sent it back to me with 3 dirty chambers & a letter saying that it was just fine the way it was.

20 years ago, when I had an FFL, they were a first class company to deal with. These days...I'm not so sure. I've seen a lot of really nice S&Ws over the years. I've also seen some lemons.

[McKee Boykin]

His chamber pressures should be very high with a barrel groove diameter of .423!

[mtgrs737]

I have used a pin gage to find the land to land size of S&W barresl then I measure the groove to outside dia. and the land to outside dia. to get the groove depth. I add two groove depth measurements to the pin gage size and come up with a ballpark groove diameter. 5 groove barrels are tough to measure without the proper equipment.

On one of my 629's there was a burr on tje front of several cylinder throats that would not let a pin gage pass. I used a brass rod and some fine sand paper to lap it out of those throats and now they pass the pin gage like the rest of the throats. I just got a 41 mag smith and three of the throats have the same thing, just a burr on the very front of the chamber but enough that the pin gage will not push on through. Without a set of pin gages you won't be able to tell it you cylinder has these burrs.

[Jumping Frog]

If the barrel slug you measured at .432 will drop through a cylinder throat you measured at .429 you has mismeasured something for sure and for certain.

No, you were misreading. I stated .423 and you changed it to .432.

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

Thanks for the beer can idea.

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

[Throwback]

The barrel diameter is unimportant unless it is greater than the chamber throats. As Larry suggests though, size .429 or .430 and load away. I would be astonished if either one was not the bee's knees. (excellent)

[leftiye]

S&W 5 groove rifling DOES have a point at which you can measure directly with a micrometer. Ie. there is a point on the slug that is full diameter of the grooves. It is the 'leading edge of one groove and the trailing edge of the opposite groove on the slug. The grooves and lands are of equal width and therefore the assessment that the front of one groove and the rear of the other are opposite (ie the lands and grooves are tenths of the circumference). The largest measurement that you can get is probly correct, and do pay attention to the opposite thang (ie - measure across the widest point). BTW, this is also, though not perfectly accurate, possible to measure directly from the barrel with a digital caliper.

[JIMinPHX]

If your slug is long enough, you can measure the groove diameter by putting a pair of calipers over the slug longways. I know that a pair of calipers is not as accurate as a mic, but it's a quick little trick & it will get you close.

[Gunslinger]

Ahhhh so that's why I just can't seem to figure out how to measure my 2 slugs from my 686

I knew the answer would be here somewhere

I've always just sized to .357 and it works fine. But over the summer I'll be experimenting with 50/50 ww/range lead (softer than I've ever gone before), and then thought chances of leading would be decreased if I tailor the boolit. I'll just size these to .358 and see how they turn out...