Is there a standard gap between the cylinder and forcing cone of a Smith & Wesson revolver? Does is depend on the frame and/or caliber? I have a 25-5 in 45 colt where the cylinder is real close to the forcing cone but not touching. I can barely see light in the gap. I assume there has to be more of a gap. What say the experts? Thanks.
Cylinder/Forcing Cone Gap
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Just about 25 years ago the benchmark B/C Gap was .005" to .006" that is just enough to insure trouble free cylinder rotation and yet kept the lions share of the gas to push out the bullet.
Today, if you get one under .009" consider yourself lucky as S&W now considers anything under .012" acceptable. You also don't wan't less than .003" as that might tend to bind up as the revolver gets dirty.
Today, if you get one under .009" consider yourself lucky as S&W now considers anything under .012" acceptable. You also don't wan't less than .003" as that might tend to bind up as the revolver gets dirty.
dfariswheel
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The first step is to determine if you have cylinder end shake, which is back and forth movement of the closed cylinder.
If you have excess end shake the cylinder moves forward and in extreme cases it can impact the rear of the barrel.
This can also give a false indication of the actual barrel-cylinder gap.
End shake is measured with an automotive feeler gauge set. These are cheap at any auto parts store.
Push the cylinder to the rear and hold it while you gauge the barrel-cylinder gap with the feeler set.
(This is also the actual barrel-cylinder gap).
Then push the cylinder forward and hold it while you gauge the gap again.
Subtract one measurement from the other and that's how much end shake is present.
Colt's were very tight with no more then 0.003" allowed.
S&W was much less tight with up to "about" 0.006 allowed.
The actual barrel-cylinder gap, as above, should be from 0.004" to 0.008" with 0.005" being about perfect.
As above, these days S&W states that anything under 0.012" is "in spec".
Truth be told, unless the gun is spitting bullet metal out the gap, there's not enough velocity loss to make much difference with the wider allowable gap so you're not really losing anything with a wide gap.
It's just the loosening standards at S&W that irks people.
If you have excess end shake the cylinder moves forward and in extreme cases it can impact the rear of the barrel.
This can also give a false indication of the actual barrel-cylinder gap.
End shake is measured with an automotive feeler gauge set. These are cheap at any auto parts store.
Push the cylinder to the rear and hold it while you gauge the barrel-cylinder gap with the feeler set.
(This is also the actual barrel-cylinder gap).
Then push the cylinder forward and hold it while you gauge the gap again.
Subtract one measurement from the other and that's how much end shake is present.
Colt's were very tight with no more then 0.003" allowed.
S&W was much less tight with up to "about" 0.006 allowed.
The actual barrel-cylinder gap, as above, should be from 0.004" to 0.008" with 0.005" being about perfect.
As above, these days S&W states that anything under 0.012" is "in spec".
Truth be told, unless the gun is spitting bullet metal out the gap, there's not enough velocity loss to make much difference with the wider allowable gap so you're not really losing anything with a wide gap.
It's just the loosening standards at S&W that irks people.
Your assumption is based on an eyeball impression. How close is "real close"? Has there been an issue with the function of the revolver that causes you to be concerned with the gap? Generally speaking , if there is no contact , friction or binding you don't need more gap.
Take some good measurements with a feeler gauge and let us know what you have. Without that information we are farting in the wind , and that is damaging to the environment.
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Since you expressed concerned about seeing too little B-C gap, as already mentioned, the only way to know for sure is to measure the clearances like dfariswheel outlined. (I'd argue though that the clearance with the cylinder held forward is the actual B-C gap.)
The cylinder is naturally pushed forward by spring pressure until it hits the end of the yoke's barrel (preferably) or, worse case, it hits the barrel/forcing cone. Rearward movement from either point is play/endshake, ideally ~.001".
When you have excess endshake (.002"+) because the yoke's barrel is too short (farther away from the rear of the revolver) the cylinder gets pushed forward by the cylinder's center pin spring, reducing (closing up) the gap between the face of the cylinder & the barrel/forcing cone. This falsely makes it "look" like you have a tight B-C gap.
Since the center spring is the only force holding the cylinder forward it can be easily pushed rearward until the cylinder's extractor ratchet face contacts the breech/frame. This total rearward distance is the B-C gap plus endshake, combined.
Adding cylinder shim/bearing(s) effectively extends the end of the yoke barrel closer to the breech/frame, & moves the cylinder statically rearward (by a corresponding amount) which widens the B-C gap from what it was previously.
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The cylinder is naturally pushed forward by spring pressure until it hits the end of the yoke's barrel (preferably) or, worse case, it hits the barrel/forcing cone. Rearward movement from either point is play/endshake, ideally ~.001".
When you have excess endshake (.002"+) because the yoke's barrel is too short (farther away from the rear of the revolver) the cylinder gets pushed forward by the cylinder's center pin spring, reducing (closing up) the gap between the face of the cylinder & the barrel/forcing cone. This falsely makes it "look" like you have a tight B-C gap.
Since the center spring is the only force holding the cylinder forward it can be easily pushed rearward until the cylinder's extractor ratchet face contacts the breech/frame. This total rearward distance is the B-C gap plus endshake, combined.
Adding cylinder shim/bearing(s) effectively extends the end of the yoke barrel closer to the breech/frame, & moves the cylinder statically rearward (by a corresponding amount) which widens the B-C gap from what it was previously.
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I have a Ruger Security Six that used to bind up when hot, so I used a feeler gauge to measure the gap and found it was .002. I then measured my S&W 649 and found that it was .006; I machined the Ruger to .006, and it has been fine.
