Slugging bore on S&W revolvers

[mustanggt]

They have 5 lands and grooves right? I slugged a k-38 and M27 as well as a Colt Officers Model and I can't get a good reading with my micrometer. How do I measure it when the lands and grooves are not 180 from each other? I used a plug gauge set to measure the chambers. So am I missing anything that is so obvious I just am not seeing it?

[MtGun44]

If you are careful, you can kind of straddle, measuring on edges. Tricky to do.
Some wrap .002 shim stock and measure carefully, subtract .004.

Bill

[Char-Gar]

If you are careful, you can kind of straddle, measuring on edges. Tricky to do.
Some wrap .002 shim stock and measure carefully, subtract .004.

Bill

Yep, I was measuring slugged Smith and Wesson barrels for years with a micrometer before somebody told me it couldn't be done. Rotate the slug as you open the jaws of the mike until you can just feel the contact as it passed the edges at the widest point. That will be the groove diameter. Don't horse the slug through as that will damage the slug and give you a false reading.

[littlejack]

mustanggt:
I used the method that Bill mentioned, just last week. I slugged and measured my Model 57. I used .002 feeler gauge wrapped around the slug, and pulled tight.
As Char-Gar mentioned, one has to be carful. With the feeler gauge, not that you will damage the slug, but to get the proper reading by NOT forcing the wrapped slug through a tight micrometer.
As Bill stated, after getting your measurement, subtract .004.
Regards
Jack

[mustanggt]

Thanks for the help fellas I'll give it whirl.

[Outpost75]

To accurately measure 5-groove barrels you need a V-anvil micrometer, but the important dimension for sizing bullets to properly fit revolvers is NOT the barrel groove diameter, but the "ball end gage" or "ball seat" diameter of the cylinder throats ahead of the case mouth in the transition portion before the bullets exits the cylinder and enters the barrel forcing cone.

The easiest way to do this is with a set of plug gages, but you can disassemble the cylinder from the gun and take pure lead, soft round balls, and drop them into the chambers from the rear, and then tap them through and out the front and measure these with a micrometer, and THAT is what you want to size bullets to, or 0.0005 under, but not larger if you can help it.

[mustanggt]

Sorry I should have included what I did before slugging the bores. I have a plug gauge set and it is a minus set. M27 measured .3576 for four throats, .3566 and .3560 which explains why 4 of 6 shots were touching and the other two were outside that group by an inch consistently. The K38 was all .3566. Colt was .3576 for five throats and the 6th was .3556. The bores all slugged just under .357 after trying the .002 feeler gauge method. So what the hell now??? I have worked up some NOE 155gr WC with 3gr of Bullseye loads to try which I sized to .358 so I'll see this weekend what they do.

[practical_man]

Ream the cylinders to .358 and enjoy. That should make things better all around.

[9.3X62AL]

Many thanks for those 2 methods of obtaining groove diameter from 5-land barrels. I had a V-block for my mic before moving in 2008, and haven't seen it since (serial expletives deleted).

I don't have a good enough mic to measure in "tenths". I can guesstimate roughly (quarters? thirds? halves?) via the indicator's position within a .001" delineation, but that isn't precise. And I'm not sure that such precision is needed for this purpose of getting accurate results from our castings through a wheelgun. There is a lot of trauma inflicted on a cast boolit as it gets launched from the case--into the throat--then to and through the forcing cone--engraved into the rifling--and down the barrel, then out the muzzle. I strive to have throats at or just above groove diameter in my revolvers, and this condition has been consistently maintained by most makers throughout my shooting activity with rollers since 1976. The sole and glaring exception was the Ruger Bishawk in 45 Colt, and it got the reamer home remedy.

I kind of "idealized" the Bishawks internal measurements while I had the chance. Grooves are .452". I polished the honed-out throats (.4525") to .453", which took a few seconds' time each. I size boolits to 454", and this revolver went from a One-Bullet Wonder to being tractable and decent with everything tried, from 200 to 310 grains.

While I don't think tri-metal alloy boolits "bump up" a whole lot under the influence of the progressive burn of smokeless powder, I think it possible that a few tenths of this flexibility might be at play. You won't get the .002"-.003" of expansion caused by the low-order detonation of black powder and lead/lead-tin alloys, but there is a slight bit of "fudge" going on, I'm pretty sure. It kinda stands to reason. So, I don't sweat the tenths, but do my best to make sure that boolits fit, and that throats and grooves either do not vary OR form a very subtle "funneling" effect.

[mustanggt]

Where do I get the reamer from? It doesn't sound that difficult. Is it something I can do myself. Is there a must read book or procedure I should really get to know?

[John 242]

A few links for you, I hope they help:

http://www.cylindersmith.com/
Click on the 'What we do' button to the left.

http://www.lasc.us/Fryxell_Book_Chapter_6_ThroatGroove.htm

http://castboolits.gunloads.com/showthread.php?54691-Want-to-ream-cylinder-throats

http://castboolits.gunloads.com/showthread.php?12464-Revolver-throat-reaming-with-drill-press-mill&highlight=cylinder%20reaming


Brownells and MidwayUSA usually stock reamers, if they're out of stock you can call Manson or maybe Clymer. If you don't want to buy, the reamer rental place of your choice should be able to get you what you need.

http://www.mansonreamers.com/
See page 10 of their online catalog.

4D reamer rentals:
http://4-dproducts.com/displayitem.php?rowid=408&tname=rental

Youtube videos on throat reaming.
This one's by 4D reamer rentals:
http://www.youtube.com/watch?v=YZK1GRUR3xE

This one's by Super Sneaky Steve:
http://www.youtube.com/watch?v=FTb9cNKNavQ