How is the allignment of a revolvers cylinders and it's barrel (concentricity) measured?

Jon

In the olden days, when there was a hole in the frame for the firing pin, you could look into the muzzle with a strong light shining thru the FP hole and see all but the tiniest of misalignment. Nowadays I suppose the only way is to use a range rod that slides down the bore and into the chamber leade?

Ray

That is how it is done today. With a precision rod down the bore. At least here it is.

Back when I built custom cylinders, after turning the material to exact diameter and length, I would machine the ratchet and cut the notch for the cylinder stop first, then I would make a drill bushing to replace the barrel on the actual firearm I was building the cylinder for, and with the hammer cocked and the cylinder locked in position, I would drill the pilot holes for the chambers. Pretty slick when everything went as planned.

Any particular revolver you're concerned about?

The revolver is a SS Ruger Redhawk 44 mag. (circa 1985) which appears to be in perfect condition. The bore slugs .429 and also looks perfect. But, it shoots 6" to 8" groups with a wide variety of ammo. I've checked everything (muzzle crown, bore for fouling, sights, etc.) I can think of but find nothing wrong. One thing I guess I should have tried is shooting groups individually, one group from each of the six chambers, and comparing them.

I was thinking of turning a close fitting steel "dummy" cartridge with about a .200" hole bored in the front. Then turning a close fitting (.429" dia.) steel rod with a .200" "stud or tip" on the end that would (if everything lines up) fit into the hole in the dummy cartridge when the rod is inserted down the barrel and into the cylinder holding the dummy. It would not provide a measurement but should reveal any gross mis-allignment This is pretty much what Westpac is suggesting but would'nt require removing the barrel and making a bushing. Is there an easier way? What do you think? Thanks...

quote:

Originally posted by Jon:
I was thinking of turning a close fitting steel "dummy" cartridge with about a .200" hole bored in the front. Then turning a close fitting (.429" dia.) steel rod with a .200" "stud or tip" on the end that would (if everything lines up) fit into the hole in the dummy cartridge when the rod is inserted down the barrel and into the cylinder holding the dummy. It would not provide a measurement but should reveal any gross mis-allignment

That should give you an idea, BUT, you might want to make the rod a little smaller than .429. The .429 measurement of the slug is the groove. You want the rod to slide on the lands.

quote:

Is there an easier way?

Yes, have someone stand on each side of you when you fire the gun. They will tell you if your cylinder and bore are misaligned.

A friend of mine had several Ruger SA's redone by a prominant pistol smith in Denver and the problem the smith ran up against was that the cylinder throats were smaller than groove diameter. After the the throats had been reamed to groove diameter or slightly larger, the revolver shot very well. Sometimes they are so inconsistant that the cylinder has to be replaced, some being overly large. I would check the throats in your cylinder for diameter using a small hole gauge and a micrometer. It might reveal a problem right away.

quote:

Is there an easier way?

Yes, have someone stand on each side of you when you fire the gun. They will tell you if your cylinder and bore are misaligned. [/QUOTE]
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Damn Westpac, I almost choked on my sandwich when I read that. Now that's funny. Better make sure they have shooting glasses on too.

Westpac/Masterifleman...
Oops, right, the rod should be bore dia. or about .417".

Mic'ed the cylinder "mouths". All six of them measure within 1/2 thou. of .433". Bore is .417", groove is .429". Still learning about revolvers...is .433 too big for good accuracy?

.433 while a little loose is probably okay. Consitency/uniformity is key to accuracy. Forcing cone and finish plays a key roll in accuracy. Just like the throat of a rifle, a rough, or, abrupt transition from the chamber/cylinder to the bore can creat a false axis for the bullet to spin on and an off axis bullet does not fly well.

Pull the cylinder and measure across the forcing cone.

There is a retired 'smith that hangs out on the Ruger forum that makes brass range rods that allow one to check cylinder to bore alignment. I have them in 44 and 45 cal. They are cheap and work like a charm. He goes by Iowegen there and is a true gentleman that knows his stuff when it comes to revolvers. You can see them in the background in this photo. Also, I agree that your throats are large and, if shooting cast you may want to size them to .431" or .432".

Boxhead...Thanks for the link info and the pictures. I'm beginning to get the feeling that I won't find much of anything wrong with the cylinder timing but will check it anyway. At least I now understand why my .430" dia. cast bullets shoot so poorly. Thanks to everyone for your comments.

Jon