I just checked the barrel/cylinder gap on my 442 UC and found that a .012” feeler will go through from one side and a .013” will go half-way from the other side. Seems excessive to me. The gun shoots fine and doesn’t seem to be spitting lead. What do you guys think: leave it be or pursue it as a warranty issue? They may just tell me it’s within factory specs, anyway.
B/C gap question
- Thread starter JackM
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Alk8944
US Veteran
Based on numerous posts over the past several years, the permissible barrel-cylinder gap is now .012", and has been for several years. The smaller measurement is what prevails if the gap varies slightly side-to-side. You will be wasting your time to send the gun to S&W because it is within current tolerances for new revolvers. All you will accomplish is being without the gun for several weeks to several months just have S&W tell you the same thing! Barrel-cylinder gap is an issue greatly over-rated as it has little to no effect on either velocities or accuracy! As long as the gun isn't shaving/spitting just live with it!
Just for the record, I have reduced the B-C Gap on several revolvers of my own that had B-C gaps between .006" and some more to as little as .002", just because I was curious! Velocities as chronographed before and after the change resulted in exactly zero change in velocities because of the change/reduction of the gap!
Just for the record, I have reduced the B-C Gap on several revolvers of my own that had B-C gaps between .006" and some more to as little as .002", just because I was curious! Velocities as chronographed before and after the change resulted in exactly zero change in velocities because of the change/reduction of the gap!
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Since you said the revolver shoots fine and there is no spitting, I'd leave it alone. The fix is not exactly cheap as the barrel must be removed, the crush shoulder turned back, barrel reinstalled and properly torqued, then recut the barrel extension for proper gap.
Green Frog
Member
I’m a little surprised at the experimental results obtained by ALK8944. I have seen other reports where there was significant variation in velocity with large vs small BC gap. Articles where similar S&W revolvers, differing primarily in BC gap! Showed a decrease in velocity as gap increased to a degree greater than the difference between 4” and 6” barrels.
Of course it was held by target shooters as an article of faith that a tighter gap was better. It is also true that fouling will begin to cause drag when the BC gap is tight, so it’s a trade off.
Recent reports of inquiries of S&W concerning their current spec for acceptable BC gap seem to be running at .012”, so the OP’s revolver is within current spec, but this has definitely changed in recent years. At one time, factory spec was reported to be .004-.006”. Less fouls to quickly and more brings loss of velocity.
If the OP’s revolver is functioning well otherwise and not spitting lead, I’d say he has all he can expect from a new S&W. If he’s losing a little velocity, it is probably not significant in the big scheme of things.
Froggie
Of course it was held by target shooters as an article of faith that a tighter gap was better. It is also true that fouling will begin to cause drag when the BC gap is tight, so it’s a trade off.
Recent reports of inquiries of S&W concerning their current spec for acceptable BC gap seem to be running at .012”, so the OP’s revolver is within current spec, but this has definitely changed in recent years. At one time, factory spec was reported to be .004-.006”. Less fouls to quickly and more brings loss of velocity.
If the OP’s revolver is functioning well otherwise and not spitting lead, I’d say he has all he can expect from a new S&W. If he’s losing a little velocity, it is probably not significant in the big scheme of things.
Froggie
Lou_NC
Member
This would be an easy experiment for me to run since I have a Dan Wesson model 15. Unfortunately it will have to wait till next March when I retire........
You are trying to fix a problem you do not have. With the reputation the factory has earned, a trip to the maker will only relieve you of your handgun for a couple months before it is returned with the “meets factory specs” note enclosed.
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My previous trr8 had a .008 cylinder gap and was spitting terribly. My 386 is .006 and appears to be working fine. If it’s not spitting it should be ok
8shot
Member
Did you ever check the timing with a range rod? Lead spitting is associated with lack of cylinder/barrel alignment. (ie worn cylinder lock)
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Ballistics by the inch took a Uberti 1873 Cattleman Single Action Revolver in 357 and set it with no gap, .001 gap and .006 gap and fired a variety of ammo through it first with 18" of barrel, then 16" then 14" and so on all the way down to 2"
BBTI - Ballistics by the Inch :: Cylinder Gap
In almost every case the loss from zero to .001 was greater than the difference from .001 to .006 especially when the barrel was 6" or less
For instance the Cor-Bon 125gr 357 lost 49fps from zero to .001 and just 13fps from .001 to .006 with a 4" barrel.
There are some interesting variations, but most of the time the change from .001 to .006 was similar to most ammo's standard variation.
While i like .004 to -006 I don't believe a gap of .012 really losses that much velocity over .006.
They have a lot of information pertaining to barrel length, gab and different revolvers using .identical ammo, especially if you click on the raw data link and explore it
p.
But, my conclusion is there are several factors that will effect velocity as much or more than B/C gap
BBTI - Ballistics by the Inch :: Cylinder Gap
In almost every case the loss from zero to .001 was greater than the difference from .001 to .006 especially when the barrel was 6" or less
For instance the Cor-Bon 125gr 357 lost 49fps from zero to .001 and just 13fps from .001 to .006 with a 4" barrel.
There are some interesting variations, but most of the time the change from .001 to .006 was similar to most ammo's standard variation.
While i like .004 to -006 I don't believe a gap of .012 really losses that much velocity over .006.
They have a lot of information pertaining to barrel length, gab and different revolvers using .identical ammo, especially if you click on the raw data link and explore it
p.
But, my conclusion is there are several factors that will effect velocity as much or more than B/C gap
.455_Hunter
Member
It's pretty pathetic that my 1916 wartime emergency production Webley MKVI has a tighter cylinder gap than many new S&W products. I understand that in the BP days, .012" would have been necessary due to expected fouling, but now anything more than .006" is lazy and sloppy.
I had one corrected that was spitting very badly. I bought it used cheap, probably because it spit so badly. The forcing cone was cut at a noticeable angle. I had the barrel set back one turn and everything trued up. It now shoots very, very well indeed. I also had a Colt b/c cleaned up as part of some other work being done. Generally if it isn't spitting and doesn't otherwise bother you it is an unnecessary "fix."
Green Frog
Member
What this testing regimen omits is the B/C gap range from .006” to .012”, which is apparently the change in allowable specs from S&W over the last few decades. There have been several less scientific comparisons that suggest velocity change through this range may have been shown to be significant.
The NRA did the barrel length shortening test as early as the 1930s if somebody wants to look it up. Theirs was done with a 357 Mag, IIRC.
Froggie
While it doesn't include.006-.012 testing the fact that the first .001 causes more V loss than thee next .005 does indicates increasing the gap has a diminishing effect on V
As
Maybe next time I go to replace a barrel I will check it then trim it and check again. But I do always set mine fairly tight when I work on them
As
Maybe next time I go to replace a barrel I will check it then trim it and check again. But I do always set mine fairly tight when I work on them
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As a matter of interest, S&W Customer Service told me today that their B/C gap parameters are .004”-.010”. Mine is at .012”, as stated in my original post. They’ve sent me a shipping label. Yes, I’ll be without it for a month or two, but I’ve got others. For that kind of money, I want it right.
As a general answer, I normally say if t works good leave it alone!
Only the owner/shooter can make that determination.
Only the owner/shooter can make that determination.
Yendor357
Member
Jack, just because they sent a shipping label doesn’t mean they’re going to do anything meaningful to it.
If you’re a machinist, .012” is a country mile. There’s no excuse for that. The last 4 Colts that I bought, they’re 4-6 thousandths b/c gap. They all shoot fast.
If you’re a machinist, .012” is a country mile. There’s no excuse for that. The last 4 Colts that I bought, they’re 4-6 thousandths b/c gap. They all shoot fast.
While I wouldn't get to concerned about it myself on a carry gun like the 442, I have to admit that it would seam pretty easy to tighten the gap on 2 piece barrels. A hand operated reamer with the correct shape could remove .006 from the shoulder in an alloy shroud pretty fast and allow the barrel to turn back a bit.
I have a 431 32 mag I pocket carry in a pocket holster a lot. I have fired quit a few rounds through it with no problems, but have never bothered to check the gap. I fail to believe 20 fps is going be what makes the difference if I ever need to use it. I also have a 642 I converted to 32 mag with a 2" barrel, its gap is .005.
But, it is pitiful that the factory doesn't make a bit more effort and put out a superior product.
I have a 431 32 mag I pocket carry in a pocket holster a lot. I have fired quit a few rounds through it with no problems, but have never bothered to check the gap. I fail to believe 20 fps is going be what makes the difference if I ever need to use it. I also have a 642 I converted to 32 mag with a 2" barrel, its gap is .005.
But, it is pitiful that the factory doesn't make a bit more effort and put out a superior product.
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A gap of .012 seems wide. I have one revolver that is that "loose" - a RIA M200 Colt clone. Measures .012 or better. It spits powder on me, but shoots wadcutters where I aim, so I'm ok with it. My Smiths vary from my 637 at .008, 617 at the same. Measured .006 - .008 for my 60's, 70's, 80's J's. Very old Smiths (older than me) are tight - .005 seems to be average. My .44 HE (1923) is so tight I declined to stick a .002 gauge in it.
I find it ironic that folks are more worried about barrel/cylinder gap than group size.
