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Old July 9, 2017, 02:04 AM   #1
HisSoldier
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Maximum and minimum gap in .22 revolver?

I bought a .22 LR revolver recently and the gap seems excessive to my eye. I haven't tried a feeler gage yet but it looks like .010".
Isn't that a lot of wasted energy blowing by?
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Old July 9, 2017, 02:33 AM   #2
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Isn't that a lot of wasted energy blowing by?
Probably not.

http://www.ballisticsbytheinch.com/gaptests.html

For typical revolver barrel lengths, a change of 0.005" of barrel/cylinder gap changes the velocity by 20-25fps in a .38spl.
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Old July 9, 2017, 03:47 AM   #3
Hal
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I bought a .22 LR revolver recently and the gap seems excessive to my eye. I haven't tried a feeler gage yet but it looks like .010".
Isn't that a lot of wasted energy blowing by?
Don't sweat things too much about cylinder gap.

Like John points out - - it just ain't that big of a deal.

Instead, be thankful you won't be tieing up the cylinder with build up.
.22 ammo can be some of the nasty- filthiest stuff you can shoot.

Quote:
For typical revolver barrel lengths, a change of 0.005" of barrel/cylinder gap changes the velocity by 20-25fps in a .38spl.
Although I have no hard data to support my feelings - - only prior ownership of a Dan Wesson .22 - on which I did several experiments with B/C gap...

I'd have to say the change is not even that dramatic & I've seen a lot of data on line from other shooters that show that much & nearly ten times that much change - in shot to shot comparison - from the same revolver using the same loads & having the same B/C gap.


Edit to add - - of course, that's assuming the gun you just bought is used & it's something you really wanted and/or is special.
If the gun is new - or it's still under warranty - that gap is on the wide side, I'd send it back under warranty and have it adjusted.
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Old July 9, 2017, 08:58 AM   #4
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Howdy

The first thing you have to know about barrel/cylinder gap is how to measure it.

Contrary to popular opinion, the proper way to measure b/c gap is with the cylinder shoved as far forward as it will go. If the cylinder has endshake (slides forward and back), endshake can mask the true b/c gap. Yes, a small amount of endshake is common.

Anyhoo, I just grabbed a bunch of 22 revolvers, none of them new, and did some quick measuring.

Ruger Three Screw Single Six --- .003

Colt Officer's Model 22 Target --- .004

S&W K-22 Combat Masterpiece --- .003

S&W K-22 Post War --- .004

S&W Model 17 --- .004

So yes .010, if that's really what it is, is probably excessive.

But in the long run it probably does not matter a whole hill of beans.
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Old July 9, 2017, 10:10 AM   #5
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Isn't that a lot of wasted energy blowing by?
No.

It just SEEMS like it.

How does the gun shoot?? Is it accurate? Does it have a lead spitting problem??

If its accurate (and try several brands of ammo to see) and it doesn't spit, then, you're done. The gun is what it is. If another .22 with a smaller gap shoots a few fps faster, so be it. It might not be the gap, at all, barrels are different.

You CAN spend as much as you want, getting it "fixed". Might spend as much, or more than the gun is worth, getting it worked on, without any practical change. Your gun, your call.

Good Luck.
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Old July 9, 2017, 02:56 PM   #6
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I expect that pressure loss is geometric, that is, .005" gap would lose a lot less velocity than 1/2 the loss of velocity a .010" gap would have. I may not be right on that, but volume and pressure, you know?
I'm a machinist, so it's not money, it's time and the dangers implicit in the learning curve, as I'm obviously not that familiar with revolvers. What I may do is make a steel shim out of .005" shim stock for the cylinder's thrust boss, to see if it functions when that gap is cut in half. If it does I'm thinking I'll bore the back of the cylinder pin hole and press in a hardened bushing that sticks out proud by the old distance plus that of the shim. The thrust boss is tiny, which I guess means that the cylinder doesn't pound back too hard.
The reason I asked is that there may be other mechanical reasons for having it that open, it came with two cylinders (One in magnum) so I'll measure both, and then try the shim. If it functions with the shim I'd like to alter both cylinders to close that gap up some. the mention of .003", that sounds about right, and it's simple to open that up later if need be.
Worst case if I screw it up I just buy another one to replace it. :-)
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Old July 9, 2017, 04:20 PM   #7
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What I may do is make a steel shim out of .005" shim stock for the cylinder's thrust boss, to see if it functions when that gap is cut in half.
If there is 0.005" of play (endshake) in that cylinder then you have other problems with that revolver.
Quote:
...the mention of .003", that sounds about right...
Based on what? Your stated familiarity with revolvers?

That sounds very small for a .22LR revolver to me. As soon as you get some fouling on the cylinder face/forcing cone it will bind. It might be workable (but still tight) for your .22WMR though since that ammo is jacketed and probably won't foul as much.

If you really feel like you have to do something, something in the 0.004" to 0.006" range is probably more reasonable. And that's based on a conventional measurement of BC with the hammer cocked and the cylinder held as far to the rear as possible.

Also, barrel/cylinder gap should be adjusted by moving the barrel relative to the frame, not by shimming the cylinder. As noted, the cylinder should have very little endshake.
Quote:
I expect that pressure loss is geometric, that is, .005" gap would lose a lot less velocity than 1/2 the loss of velocity a .010" gap would have. I may not be right on that, but volume and pressure, you know?
Off the top of my head, I would expect the velocity loss to be related to the "surface area" of the missing barrel/bore due to the gap. Since that surface area increases linearly as the gap increases, I would expect velocity differences to change linearly with the gap increase.

There's a post in the linked thread below with data that seems to bear that out, at least for the .38spl. It shows a linear drop in velocity as the gap increases.

https://www.thehighroad.org/index.ph...er-gap.504608/
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The first thing you have to know about barrel/cylinder gap is how to measure it.
Exactly correct.
Quote:
Contrary to popular opinion, the proper way to measure b/c gap is with the cylinder shoved as far forward as it will go.
And this is why it's important to measure it correctly. Because if you don't, the resulting measurements can't be compared with the numbers other people have measured for reference.

Given that everyone else measures b/c gap with the cylinder held to the rear, the numbers you provide that you have measured using your personal method are going to confuse the issue.

http://www.friedmanhandguntraining.c...inspection.pdf
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Old July 9, 2017, 07:53 PM   #8
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Also, barrel/cylinder gap should be adjusted by moving the barrel relative to the frame, not by shimming the cylinder. As noted, the cylinder should have very little endshake.
I failed to mention that the shim was just to determine functional minimums, once that's determined there are two ways to make it permanent I think.
The barrel threads look to be 20 TPI, or .050" per revolution. One revolution being needed at the least to line up the sights again that means machining the rear end of the barrel to the established gap requirement (After the .050" move back I mean). Then that produces other possible problems with other things attached to the barrel. Still it may be the option, and baring extreme difficulties it's the correct option.
However, since the cylinder (Again, I still haven't measured the gap) may only need to move forward .005" that may not impair functions of the hand and lock bar. To do that permanently I may be able to drill/bore the center hole out to the diameter of the thrust shoulder and maybe .300" deep and make a hardened steel bushing and press that in place, essentially making a new thrust shoulder that sticks out .005" farther out.
That eliminates the problems with the barrel accessories if I can see that there will be any.
Moving the cylinder forward .005", just thicker than a piece of paper, should not effect the function of the hand or lock.
So, the answer to maximum barrel gap depends. I only have one other revolver to check it against, a model 1858 Army reproduction.
Thanks for the responses, it made me think more about this, and I may decide it's not worth the effort.
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Old July 9, 2017, 07:56 PM   #9
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I was wrong, that "thrust shoulder" is at the front, so that won't work. Have to turn the barrel in a turn.
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Old July 9, 2017, 08:04 PM   #10
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Gonna leave it as is. The sides of the receiver and barrel would need to be ground after turning the barrel in a turn, too much work for any benefit.
Thanks though guys.
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Old July 10, 2017, 01:46 AM   #11
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Contrary to popular opinion, the proper way to measure b/c gap is with the cylinder shoved as far forward as it will go. If the cylinder has endshake (slides forward and back), endshake can mask the true b/c gap. Yes, a small amount of endshake is common.
One more question per that. If the cylinder is as far back as it can go, let's assume with empty cartridges in it if that matters, are you implying that the hammer strike sets the cylinder as far forward as it can move, and that it doesn't move back against the impulse of the bullet moving into the forcing cone?
As I said, revolvers are not my area, so it wouldn't surprise me that there is something counter intuitive involved, but why would not the laws of motion slam the cylinder back?

Before sending this I decided to look into it, I found a lot. Here is a retired gunsmith talking about it (Post #2 http://rugerforum.net/gunsmithing/68...measuring.html) and it is much clearer now. What a lot of forward and backward slamming is going on in a revolver! I had no idea.

What I've come away from all this with is what you gents said, the gap doesn't matter that much (Which I measured just now), cylinder held back against fired .22 LR empties in all chambers, a .014" gage pin will slip through, only just barely, and will stay there as the revolver is turned all directions. A .011" pin was loosey goosey. I detected very little end shake.

For what it all means I don't know, but it's not an expensive revolver and I've wasted too much time on it, except for learning about end shake and barrel/cylinder gap.'
Thanks guys.
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Last edited by HisSoldier; July 10, 2017 at 02:11 AM.
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Old July 10, 2017, 02:56 AM   #12
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What I've come away from all this with is what you gents said, the gap doesn't matter that much (Which I measured just now), cylinder held back against fired .22 LR empties in all chambers, a .014" gage pin will slip through, only just barely, and will stay there as the revolver is turned all directions. A .011" pin was loosey goosey. I detected very little end shake.

For what it all means I don't know, but it's not an expensive revolver and I've wasted too much time on it, except for learning about end shake and barrel/cylinder gap.'
Believe me.....if you "get it" about B/C gap being not a big deal, then you've learned one heck of a lot more than thousands of others here will never understand! .
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Old July 10, 2017, 03:47 AM   #13
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Ok, just to muddy the water a little, I know where the "perfect world" revolver is (mentioned in the link). I have 2 of them and they aren't necessarily "high end" or overly expensive either! They are my 2 converted Dragoons. Going by the procedure for measuring normal B/C gap and end shake, I have as close to the "perfect world" setup as you can get (according to the link).

Caliber - 45C
B/C gap - 0
End Shake - .0015"

The result is 2 of the most accurate revolvers I've ever owned for roughly $740.00 ea. (New Dragoons and new Kirst Gated Conversions). Any "build up" on the cylinder face is automatically "cleared" by the 0 B/C each time the action is cycled. The maximum resulting B/C clearance is minimal which allows for more efficiency and a much cleaner revolver at the end of a shooting session. So, if "bragging rights" are in order or sought after, that's where they can be found. I found them purely by accident while looking for the best setup to keep my revolvers from beating themselves up from shooting smokless powder. These are permanent conversions, not "convertibles".

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Old July 10, 2017, 10:34 PM   #14
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Here is a retired gunsmith talking about it (Post #2 http://rugerforum.net/gunsmithing/68...measuring.html) and it is much clearer now. What a lot of forward and backward slamming is going on in a revolver! I had no idea.
Iowegan definitely knows what he's talking about when it comes to revolvers.
Quote:
What I've come away from all this with is what you gents said, the gap doesn't matter that much (Which I measured just now), cylinder held back against fired .22 LR empties in all chambers, a .014" gage pin will slip through, only just barely, and will stay there as the revolver is turned all directions. A .011" pin was loosey goosey. I detected very little end shake.
Very little endshake is very good.

0.014" is a pretty big B/C gap. If this is a new gun from a respected company, I would contact them and tell them about it. If it's a bargain-basement-brand, used gun, I would shoot it and enjoy it like it is unless you notice any problems when you fire it.
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Old July 11, 2017, 03:11 AM   #15
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Another way of looking @ gap is this:
In over 180 years of revolver history, there has only been one revolver that used a gas seal design.
If there was any significant gain to be had, doesn't it make sense that more would have been brought to market?

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Old July 11, 2017, 04:47 PM   #16
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From Ruger:

BC gap of .003-.011 is 'normal'.

Ideal is BC gap of .003-.005.

End play/shake of .001-.005 is acceptable, but ideal is .001-.003.

If it isn't spitting lead and is relatively accurate, with no more than .003 of end shake, I wouldn't sweat it.

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Old July 11, 2017, 10:18 PM   #17
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Many people think that the tighter the b/c gap the better, and it is if you think ONLY of gas escape. But if you have a too small gap, (.002-003") you can have the cylinder expand enough from heat in firing to cause it to bind in only a few cylinders full of rapid fire, (depending on several other factors).

If one is setting up a revolver after re-barreling, I consider a gap of .006-.007" to be about ideal.

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Old July 12, 2017, 02:50 AM   #18
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I've never had a problem with the clearance I have on the Dragoons ( .0015"). I set all my customers open tops B/C clearances at .0025" as well and many are CASS/ SASS shooters. Never have had a report of "heat" lock up. Maybe the cylinders in the Dragoons are big enough to absorb the heat? Likewise, the bp cylinders of the open tops? I got my numbers from Freedom Arms and Mag.Research years ago when I was researching my tolerances for my service. I have set up some as fanners (and are used that way) with no ill effects as well. A tight clearance increases efficiency (measurable or not) and much less wear (open tops) and since most everything is going out the barrel, a much cleaner, longer running revolver is the result. Typical is 160/180 rounds from an open top with no binding (bp). Of course the cartridge set ups are as reliable as any fine modern S.A.

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Old July 12, 2017, 03:50 AM   #19
Hal
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I've never had a problem with the clearance I have on the Dragoons ( .0015").
Then the gap gods must have smiled favorably on you.......or BP leaves some softer residue.

My Dan Wesson .22 would bind up solidly on me after very few shots if I set the B/C gap too small.

Anyhow - it's rather a moot point since the burning characteristics of black and smokeless are far, far, far different.

Not saying your practice is wrong or you are fibbing - - just saying the OP asked about .22, not black powder .45LC......
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Old July 12, 2017, 08:44 AM   #20
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Hal, I haven't shot black powder in almost 15 yrs. All my shooting is smokless. Smokless is much cleaner than bp. My results are pretty much a testament to Kirsts quality products as well as today's machining we get from Italy. The run-out on some 2nd Gen Colt open top revolver cylinders won't allow anything tighter than .003" because of interference . . . . . and they're Colts!

So, though my favorite platform may be of a different time period, smokless is smokless and as I pointed out, they are as reliable as a FINE modern revolver. Even the rifling has the correct twist for .45C. So not so much a "moot" point.

I didn't realize the link that was brought into the thread describing B/C gap and end shake was about .22s as well (I don't believe it was). I was just pointing out that a tight gap/clearance can be had and I also pointed out where I got my specs. from. I would have to check again but I think FA gap is .002" or less, MR is .003". Personally, I think close tollerances are from hand fitting and time consumption. Production line revolvers can't be held to that tollerance without being cost prohibitive which gives you .006" - .009". That's why FAs cost what they cost.

BTW, 22s are a heel based bullet and I think that's why they are probably not as clean in use as the inside lubed "modern" cartridges are (thus needing "fouling" room). I could be wrong.

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Old July 13, 2017, 02:54 AM   #21
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I didn't realize the link that was brought into the thread describing B/C gap and end shake was about .22s as well
The title of the thread is gap in a .22 revolver....

Anyhow - yes - .22 rim fire is a heeled bullet. & I agree there also, that very well could be why they are so filthy.
Although - - some of the Red Dot .357 mag loads I worked up once could give them a real run for the title of "Dirty bird" .

Quote:
Personally, I think close tollerances are from hand fitting and time consumption. Production line revolvers can't be held to that tollerance without being cost prohibitive which gives you .006" - .009". That's why FAs cost what they cost.
I absolutely agree with that....but....I also concluded long ago that B/C gap was/is much ado over nothing.
Chamber to chamber velocity variations can be a whole lot more than a "wide open" B/C gap(not really wide open per say, but something someone would consider as "excessive".)

However - w/FA, I believe a buyer has the right to be on the picky side.
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Old July 13, 2017, 09:14 AM   #22
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Well, I'm pretty sure the bigger the gap, the more loss of energy/velocity (I'm sure Mr.Newton would agree) and that's what I was trying to express. So, with variables already present from chamber to chamber, it seems the condition of the gap would be the multiplier (since it would be the same for each chamber). Even though it may not be monumental, it is still a factor and as you mention, it seems the "Finer" revolvers have the tighter gaps. Likewise, I like to give my customers the best revolver that their particular revolver can be. There is a sense of "refinement" in a close tolerance, mechanically accurate revolver that not only gives the owner a little more pride in their "as new" baby, not to mention the much more durability of the revolver. Sloppy revolvers beat themselves up, close tolerance revolvers are inherited.

Please understand, I'm not trying to be a smart a$$, I'm just trying trying to point out what I think should be obvious. When stats are laid down (0 this and .00 that) that would be considered the "perfect" situation and a revolver from the mid 19th century can in fact have those conditions (with todays ammo), then, it is what it is. That is at the point that I jumped into this thread . . . . (I pay attention when folks talk B/C gaps/clearances.)

Ok, now . . . . back to .22s ! Lol!! (No hard feelings meant or taken)

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