Single Six Barrel-Cylinder Gap?

[Montelores]

What is the allowable gap? How does one measure it (cocked/uncocked, cylinder pusher fwd/back, etc.)?

One S/S seems to develop a build-up of carbon and/or lead on the bottom of the top-strap directly above the B/C gap, while another has hardly any (a stainless steel model, btw).

These are both fairly new models. I don't notice any shavings on the side of the barrel end, but could there be a timing issue involved?

Thank you,

Monty

 

[flatgate]

Rimfire B/C gaps are set larger than are centerfires. On a Ruger that translates to something in the 0.006 and larger range.

I've had some fowling issues with my stainless .22. I found that keeping the forcing cone clean helped a lot as did use of Paco's Accurizer.

JMHO,

flatgate

 

[Montelores]

Thank you, Flatgate.

How does that compare to the B/C specifications for a NM Blackhawk .357?

Does one measure while holding the cylinder rearward?

Thanks,

Monty

 

[Driftwood Johnson]

Howdy

Barrel/cylinder gap is measured holding the cylinder all the way to the front, if there is any front to back play in the cylinder. The front to back play is called endshake. In measuring the B/C gap, you want to take endshake out of the equation. According to Kuhnhausen, recommended B/C gap is .004-.006 for jacketed bullets, .008 for lubricated lead bullets.

Practically speaking, somewhere in the vicinity of .005-.008 seems to be about the norm.

22s tend to be pretty dirty. 22s use what is called a heeled bullet. These used to be common, but 22 rimfires are the only ammo commonly using heeled bullets today. The heeled bullet has a shank of slightly smaller diameter that is inserted into the case and crimped. So the bullet is the same diameter as the case. Unlike typical modern bullets, which carry their lube in grooves in the bullet inside the case, heeled bullets are coated on the outside with a waxy lube for their entire length. That large amount of waxy lube is one reason 22s are so dirty, it builds up faster than a little bit of lube in a groove in a conventional bullet. Plus some 22s seem to use some pretty dirty burning powder.

 

[Montelores]

Driftwood -

Thank you for the detailed and clear explanation.

Possibly, my build-up is a combination of lube and carbon. It is easily scraped from the top strap with a sharp knife.

A couple of questions, if you don't mind: how much endshake is permissible, and do I measure with the revolver cocked or uncocked? Is endshake necessary, or just a result of manufacturing tolerances? Also, when the revolver is fired, shouldn't the cylinder move towards the rear, resulting in a different (and greater) B/C gap?

Thank you for the help -

Monty

 

[flatgate]

"As new" revolvers should have minimum endshake. As things wear the cylinder gets looser and looser.

Rugers are definitely looser than, say, a Freedom Arms revolver. My .454 has had thousands upon thousands of rounds down it's barrel and still has very minimal endshake.

You really need to do some research. Try Kuhnhausen's excellent book on 'smithing the Ruger S.A...

www.gunbooks.com

flatgate

 

[Montelores]

Thank you for the recommendation.

Monty

 

[Driftwood Johnson]

Howdy Again

Yeah, I was quoting from the Kuhnhausen Ruger book. I have a bunch of his books, they are the very best that are published on their subjects.

Endshake is easy to measure with shims like you used to use to measure spark plug gaps. Shove the cylinder all the way forward and see what size shim fits into the Barrel/Cylinder gap. Then shove the cylinder all the way back and repeat. Subtract the large shim from the small shim. That is how much endshake you have. I always measure endshake with the hammer down. If the hammer is cocked, the hand (pawl) will be bearing against the rear of the cylinder, possibly limiting how far back the cylinder can go. You want to measure how much it can really travel backwards, you don't want to measure in a limited state.

Very generally speaking, endshake should be zero. In a really well fitted revolver it will be zero. But a few thousandths of endshake is quite common. The less endshake, the better.

As far as where the cylinder goes when the revolver is fired, there are several opinions on that. My favorite gunsmith says that when the firing pin or hammer first strikes the cartridge, if there is any endshake, or if the cartridge is not fully seated, the round and the cylinder will be shoved all the way forward. Makes sense to me, but I dunno if it is true in reality. When the cartridge fires, stuff happens pretty quick. I would have to see high speed photography of such an event to be sure. It's possible that there could be enough inertia in the system that the cartridge fires before the cylinder is shoved all the way forward. And the act of cocking the hammer probably caused the hand to shove the cylinder forward in the first place.

Then when the cartridge fires, the first thing that happens is the cartridge jumps backwards. That does not necessarily mean the cylinder jumps backwards. There is always a little bit of play between a cartridge and a chamber, and the shell will jump backwards and may or may not take the cylinder backwards with it. Depends on how much of a grip the expanded brass gets on the chamber wall. Wherever the cylinder goes when the round fires, chances are the bullet has already exited the cylinder and is at least partway down the barrel before the cylinder gap is affected.

 

[Montelores]

Thank you, Driftwood. Great explanation.

Monty

 

[Fox Mike]

The explanations were informative but the initial question has not yet been answered. What is the 'allowable gap'?

 

[flatgate]

Kuhnhausen, page 139.



OK, he states 0.004" to 0.006" for jacketed bullets and 0.008" for lead, however a good quality "hard cast" bullet won't give any trouble with a "snug" jacketed bullet sized B/C gap.

Case in Point: F.A. revolvers with their 0.001"-0.003" gaps shoot hard cast lead bullets very well with no unusual leading troubles. At least my pair are that way.

flatgate

 

[Ale-8(1)]

"The explanations were informative but the initial question has not yet been answered. What is the 'allowable gap'?"

The gap that does not produce either cylinder/barrel interference or side spitting with the loads you wish to shoot. This will vary from gun to gun and load to load. There is no fixed answer. The 0.004" to 0.006" range is what is agreed upon by most 'smiths.

That's probably the best answer you're going to get.

:mrgreen:

 

[Fox Mike]

The gap that does not produce either cylinder/barrel interference or side spitting with the loads you wish to shoot. This will vary from gun to gun and load to load. There is no fixed answer. The 0.004" to 0.006" range is what is agreed upon by most 'smiths.

That's probably the best answer you're going to get.

:mrgreen:

Kuhnhausen, page 139.



OK, he states 0.004" to 0.006" for jacketed bullets and 0.008" for lead, however a good quality "hard cast" bullet won't give any trouble with a "snug" jacketed bullet sized B/C gap.

Case in Point: F.A. revolvers with their 0.001"-0.003" gaps shoot hard cast lead bullets very well with no unusual leading troubles. At least my pair are that way.

flatgate

I have a Kuhahausen on order but not here yet. Thanks to both of you for the answer.

 

[Montelores]

Ale-8(1) -

Why would one have loads "side spitting" and not at the top or bottom?

Thank you -

Monty

 

[flatgate]

I'll address that.......

because the cylinder frame will stop the particles. You are correct, the spitting will be 360°.

flatgate

 

[Montelores]

Thank you, Flatgate.

I understand that the answer will most likely be "No", but do you have any problems with your Freedom Arms revolvers?

Monty

 

[Ale-8(1)]

As a matter of normal operation, the spitting should be present all around the barrel/cylinder gap, but you probably wouldn't notice it at the top and bottom from the standpoint of seeing or feeling it. But if you do have spitting, a close examination of the frame above and below the "window" opening will reveal residue deposits in the form of soot, lead, and occasionally powder particles.

As a matter of fact, you will very likely see such evidence on all guns. The "spitting" is pretty much a byproduct of firing the gun, to one degree or another. The term "side spitting" is used because it's the stuff you usually notice immediately if you see or feel it taking place.

 

[Montelores]

Thank you, Ale-8(1).

I have fired an older (most likely 1960s era) S&W model 17 which does spit markedly when using high-velocity .22 ammo (in addition to having extremely erratic groups).

When we switched to standard-velocity ammo (almost double the price), there was almost no side-spitting (or top- or bottom-), and the gun regained its accuracy, as well.

Monty