I have a 629-3 with a cylinder gap of .0014 and a 629-4 with a gap of .004. The 629-3 just had the cylinder replaced by S&W. Other threads state that .005-.008 is spec. Should I be concerned?
Cylinder gap on two 629s
- Thread starter Shark Bait
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If you really mean 0.0014" that is less than one and a half thousandths which is way way too small! If you really mean .014" (fourteen thousandths) than that is way too large. Either way - send it back because you are way out of spec with either one - assuming that you measured the B/C correctly that is. The other gun that measures .004" should be fine.
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OP
Thanks for the correction. I meant 0.014.
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WAY TOO LARGE A GAP - I would send her back home for a re-do. IMHO even .008" (while within the NEW S&W spec's range) is too large and only a few years ago S&W would have greed! 0.014 is absurd IMHO!
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OP
I am surprised and disappointed that S&W would replace the cylinder and send it back to me like this.
Yea that's a real bummer. On the bright side.004 is where they set PC guns.
OP
Then my 629-4 is good to go. I hope the -3 can be repaired. They replaced the original cylinder because the gas ring was damaged. But they used a new model cylinder. I'll call them tomorrow and see what they can do.
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Just to give you a "head-up" They ABSOLUTELY CAN bring your B/C Gap into spec - (and request one ".004 - .005") but weather they WILL DO IT - OR NOT I can not say. I suspect that many of their old time GS's that really knew their trade are not there any longer. Many who work there now are nothing more than Assemblers and CNC Machine Operators and know little about the products they are building. Maybe a few of the older more experienced guys in the Custom or PC Dept. would be better suited to repair your 629. Hope you make out OK. Good luck.
S&W has long held barrel-cylinder gap to be factory spec between .003" and .010". Per Kuhnhausen, .005" to .006" is an ideal compromise between good velocity and reliable cycling with build-up at the forcing cone.
Kuhnhausen argues that after .008" velocity loss becomes a more significant issue. I've researched the seriously under-investigated or experimented upon question of velocity loss due to B-C gap. Subject to revision, but it seems that the most significant velocity loss due exclusively to gap will happen between .000" and .001" -- in other words, at a point where there's nothing to be done about it. From .002" to .020" velocity loss of about 20fps occurs every .002".
Gap, then, is a less significant issue unless 1) spitting is occurring; 2) accuracy is (theoretically) being affected ; or 3) you're using defensive ammo that due to gap-related velocity loss isn't achieving the velocity required to perform as designed.
So many other factors beyond B-C gap affect velocity -- rifling cut and condition, forcing cone angle, charge hole and throat specs, etc. -- that investigating velocity effects through the lens of B-C gap alone is futile. In the end, each gun has to be media and chronograph tested with specific loads to get meaningful data as to firearm/ammo performance in that particular gun.
That's a lot of work; seeing to it that your B-C gap is within generally recognized preferred specs is simply a smart hedge, but whether or not it will have meaningful positive impact on performance is difficult to determine.
S&W outside specs for B-C gap these days is disputed. Several members report S&W telling them that gaps in excess of .012" are in spec; certainly the number of revolvers leaving the factory with wide gaps these days indicate this, but I was recently on the phone with a very knowledgeable individual in S&W customer service who stated that maximum factory spec for gap is .010".
Shark Bait, since S&W recently replaced the cylinder on your 629, I think it should have returned to you with the B-C gap per their specs. I'd double-check to make certain you've measured correctly, and if confirmed you're at .014", contact customer service to arrange return on their dime, requesting a complete revolver inspection for serviceability and correction to factory minimum specs.
Kuhnhausen argues that after .008" velocity loss becomes a more significant issue. I've researched the seriously under-investigated or experimented upon question of velocity loss due to B-C gap. Subject to revision, but it seems that the most significant velocity loss due exclusively to gap will happen between .000" and .001" -- in other words, at a point where there's nothing to be done about it. From .002" to .020" velocity loss of about 20fps occurs every .002".
Gap, then, is a less significant issue unless 1) spitting is occurring; 2) accuracy is (theoretically) being affected ; or 3) you're using defensive ammo that due to gap-related velocity loss isn't achieving the velocity required to perform as designed.
So many other factors beyond B-C gap affect velocity -- rifling cut and condition, forcing cone angle, charge hole and throat specs, etc. -- that investigating velocity effects through the lens of B-C gap alone is futile. In the end, each gun has to be media and chronograph tested with specific loads to get meaningful data as to firearm/ammo performance in that particular gun.
That's a lot of work; seeing to it that your B-C gap is within generally recognized preferred specs is simply a smart hedge, but whether or not it will have meaningful positive impact on performance is difficult to determine.
S&W outside specs for B-C gap these days is disputed. Several members report S&W telling them that gaps in excess of .012" are in spec; certainly the number of revolvers leaving the factory with wide gaps these days indicate this, but I was recently on the phone with a very knowledgeable individual in S&W customer service who stated that maximum factory spec for gap is .010".
Shark Bait, since S&W recently replaced the cylinder on your 629, I think it should have returned to you with the B-C gap per their specs. I'd double-check to make certain you've measured correctly, and if confirmed you're at .014", contact customer service to arrange return on their dime, requesting a complete revolver inspection for serviceability and correction to factory minimum specs.
