Acceptable Cylinder Gap ?

[hylander]

Just bought a new GP100
How much cylinder gap is acceptable ?

Also anyone have a pet load you would like to share.

[rintinglen]

IIRC, S&W used to say .008 was acceptable. I prefer .004 to .006. Some top drawer revolvers go even tighter. An FA of a friend of mind went .002! I would think that would lead to binding as the gun crudded up but at least for 20 rounds it didn't seem to matter.

[OuchHot!]

I used to set dan wessons to .004. If they were past .006-.007, I tended to get particles abrading my face and arms. I don't know what a minimum would be.

[osteodoc08]

I personally prefer .004"-.006". .008" is generally the accepted upper limits. Remember to check at every cylinder stop as measurements can vary.

[Outpost75]

In calibers where lead bullets will be used, a new revolver should pass 0.004" through DA on all Chambers and hold 0.006", in which the cylinder will not pass a full revolution with the rear gage in place.

Max. allowed for a duty gun back in the day was 0.008", with endshake taken out and rear gage in place. Above 0.012" THE REVOLVER SHOULD NOT BE FIRED because you risk lodging a bullet in the bore, especially with jacketed ammo.

[gray wolf]

My GP 100 is .002 at rest and almost .003 when the cylinder is held back.
It's the tightest Ruger I have seen. it shoots lead bullets and does not get any lead spatter at all. Accuracy is very good with a 158 grain bullet
and 6.9 Unique 4.2 tight group 12.5 2400 9.8 blue dot
These are the loads I shoot and your loads should be worked up for safety sake.

[shooting on a shoestring]

I've noticed on the few new guns I've bought, the cylinder gap quickly opened up about 0.002" to 0.004" larger than where it started. The tightest one I've started with was 0.004" and I've had a couple near 0.006". Once they open up a couple of thousandths, they seem to hold there for a long time. I suspect its a matter of peening off the microscopic top peaks of fractured metal on the machined surfaces of the rear of the cylinder, and possilby the frame as well, or maybe both.

Several of my well used revolvers are in the 0.008" to 0.010" range and seem to be settled in, shooting well without problems.

[seaboltm]

.012" is generally the extreme upper limit. S&W currently considers .012" to be in spec, according to the S&W forum. I have a BH convertible. The 357 cylinder is .007". The 9mm cylinder is a whopping .017", but it shoots fine. Of course on target pistols .002" to maybe .005" would be desirable.

[seaboltm]

Pet load: 38 special, 148 WC Lee TL, 3 grains of Bullseye for maybe 750 fps.

[williamwaco]

I like .002 to .004.

[Newboy]

I adjust to minimize the end shake more than the gap.

[hylander]

I have .006 cylinder gap
Is that GTG or is there a way to close that up a tad.
How do you adjust end shake ?
I will be shooting mostly 158gr. SWC, would like to shoot both GC and plain base.
I have Unique, 231, HP38, Power Pistol and 2400

[Multigunner]

The 9mm cylinder is a whopping .017", but it shoots fine.
When the cylinder, and the chamber throat is long compared to case length very little velocity is lost from a wide cylinder gap. At least that appears to be the case with my .22 Sentinel with .008 gap.

Testing of the Nagant 7.62 suggested that very little velocity was gained by the zero gap gas seal mechanism.

[lar45]

I have a 4 5/8" Stainless Blackhawk in 45Colt that I put a Bisley cylinder on. I made it as tight as I could and ended up with .0015". I've been told that this is too close and that it will lead to the gun locking up, but I've never had a problem with it.

[MtGun44]

I have had good results with .004 to .006.

Here are a couple of favorite loads.

http://castboolits.gunloads.com/attachment.php?attachmentid=50446&d=1244513448

http://castboolits.gunloads.com/attachment.php?attachmentid=50443&d=1244513091

Using the RCBS 38 - 150 -SWC (used to be maked 38 - 150 - K or KT) in the first load gives about the
same results.


Bill

[PAT303]

Bill,does the 14.5grn of 4227 give any pressure signs or ignition problems?. Pat

[seaboltm]

I have a 4 5/8" Stainless Blackhawk in 45Colt that I put a Bisley cylinder on. I made it as tight as I could and ended up with .0015". I've been told that this is too close and that it will lead to the gun locking up, but I've never had a problem with it.

I doubt you would have problems unless you use large charges of H110 and boolits over 300 grains. With that little amount of cylinder gap a heavy recoiling round could cause boolits in other cylinders to creep forward just a tad. Just a tad is all it would take to lock up your revolver with .0015" gap.

[Outpost75]

When I inspected revolvers which were being purchased with your tax dollars for federal law enforcement, 0.005" was Mean Assembly Tolerance, measured on the shop floor prior to proofing. After firing six proof loads, a blade feeler gage was inserted between the barrel extension and cylinder, with GO headspace gages in every other chamber, the gun being pulled through six times had to rotate freely and "pass" .004" and feel noticeable resistance or "hold" .006". A .007" would be counted as a Minor Category defect and passed, whereas .008" would be sent back to asembly for refit of a new cylinder and reproofing.

[9.3X62AL]

Good thread, especially Outpost's hands-on real-world experiences. I try hard to NOT miss any post made by the man.

Some more real-world results, just for drill--I own a S&W pre-27 x 6.5" and a S&W 686 x 4". The longer-barreled N-frame has a cylinder gap of from .010"-.011", while the shorter-tubed L-frame has uniform .004" clearances around the clock. Throat specs, groove, bore diameters, and twist rates are practically identical. The longer-barreled pre-27 will uniformly produce from 90-125 FPS LESS velocity than will the shorter-tubed 686. This ranges the wide span of 357 Magnum loads from 125 to 200 grains--factory and handload--cast and jacketed--current SAAMI spec and former SAAMI spec (36K PSI vs. 41K PSI). Gap can matter significantly from a performance standpoint.

[Outpost75]

In .38 Special shooting +P lead bullet service ammunition, such as the Winchester X38SPD, Remington R38S12 or Federal 38G, the expectation over the long run is a 10 fps Delta-V for each 0.001" change in cylinder gap from Mean Assembly Tolerance. It is entirely possible for a new 2-1/2" revolver with minimum cylinder gap of 0.004" to produce higher velocities than a 4" model of the same gun, having maximum cylinder gap of 0.008" permitted for guns out in the field.

You also get higher velocities with .38 Special ammunition firing it in a .38 Special chamber than in a .357 chambered gun of the same barrel length and cylinder gap. Accuracy of .38 Special ammo is also a bit better in the .38 Special chamber than when jumped in the .357 chamber, but the difference is not significant for service use. If the .357 cylinders have good chambers and throats of proper size with correct alignment, they will shoot very well. The key is the axial length of the bullet, in that bullets having a greater ratio of length to diameter will shoot better in the long chamber, because their forepart will enter the throats and maintain alignment before the bullet base exits the case. The fly in the ointment is hollowbased bullets, such as wadcutters, in which the skirt may inflate, locking against the mouth shoulder of the .357 chamber, elongating the bullet as the forepart acquires translational velocity more quickly than the skirt. This raises hob with accuracy. The 110-grain JHP bullet in the Olin Q4070 +P+ service load in .38 Special has a deep hollow base to lengthen its bearing surface to improve accuracy when fired in .357 chambers. Winchester used to sell this bullet as a component, and it would rival the very best match ammunition in test groups at 50 yards from well set up revolvers.

[9.3X62AL]

More good stuff. Thank you, sir.

[MtGun44]

No probs with either load. Now, I have not shot thousands of them,
but hundreds have worked well.

Bill