Mike-AK
Member
Anybody have any recommendations for a gunsmith to send my 686+ to have the barrel set back? The cylinder gap is 0.009" and I'd like to have it less than half that. Thanks.
Any Recommendations for Having Barrel Set Back?
- Thread starter Mike-AK
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Sorry, I can't help with a suggestion as I've never had that specific work done.
Not sure of your reasons for the alteration, but if you are expecting an increase in velocity, the difference will me minimal. Most of the velocity loss happens in the first .001" - .002".
Not sure of your reasons for the alteration, but if you are expecting an increase in velocity, the difference will me minimal. Most of the velocity loss happens in the first .001" - .002".
0.009" falls within factory specifications and if you think there is something to be gained with a smaller gap, you would be mistaken. A tight gap can actually become a problem when shooting ammo that uses a dirty burning powder or soft lead bullets that like to deposit lead on the forcing cone.
Lot of work and money for not much
Ballistic by the inch took a single action 357 set it tight against the cylinder with various length barrels
then at .001, then at .006. here are their actual results with a 4" barrel
Cor Bon 125 357 No gap-1246fps, .001-1197fps, .006-1184fps
Federal 158 hydo shok No gap-1282fps, .001-1224fps, .006-1211fps
The 125 lost 49 fps in the first .001 and 13fps in the next .005
The 158 lost 58fps in the first .001 and 13 fps with the next .005
I doubt closing your gap from .009 to .004 will gain you 14fps
In order to set back your barrel a smith has to remove it, turn .0277 of the shoulder, then remove .0247 off the face of the barrel extension, recut the forcing cone and reinstall the barrel. He will also have to remove .0277 off the end of ejector rod and center pin as the barrel lug will be that much closer to frame. Depending on method he might mount the barrel before trimming and re cutting forcing cone.
All for 14 fps which is less than the extreme velocity spreed on good ammo
I have done it several times BTW installing and setting up barrels
The last time was on my 22 jet as it had an eroded forcing cone
Ballistic by the inch took a single action 357 set it tight against the cylinder with various length barrels
then at .001, then at .006. here are their actual results with a 4" barrel
Cor Bon 125 357 No gap-1246fps, .001-1197fps, .006-1184fps
Federal 158 hydo shok No gap-1282fps, .001-1224fps, .006-1211fps
The 125 lost 49 fps in the first .001 and 13fps in the next .005
The 158 lost 58fps in the first .001 and 13 fps with the next .005
I doubt closing your gap from .009 to .004 will gain you 14fps
In order to set back your barrel a smith has to remove it, turn .0277 of the shoulder, then remove .0247 off the face of the barrel extension, recut the forcing cone and reinstall the barrel. He will also have to remove .0277 off the end of ejector rod and center pin as the barrel lug will be that much closer to frame. Depending on method he might mount the barrel before trimming and re cutting forcing cone.
All for 14 fps which is less than the extreme velocity spreed on good ammo
I have done it several times BTW installing and setting up barrels
The last time was on my 22 jet as it had an eroded forcing cone
If you want an easy way to do it, you can get a .004 thick endshake shim and put it between the back of the cylinder and extractor. You will probably need to trim the end of the yoke barrel to let the cylinder go forward a bit. This also gives you the opportunity to set the endshake to a close fit. Then you would have around .004 to .005 cylinder gap.
StrawHat
Member
Would that not increase the cartridge to recoil shield distance? Is that the same as headspace?
Kevin
No, that does not increase the cartridge to recoil shield distance (headspace). That is maintained by the extractor. The cylinder moves forward slightly, but the extractor remains stationary. In effect, it is stretching the cylinder.
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I was thinking 
You guys know what can come from that.
If a guy were remove the extractor and drill say 3 small holes evenly spaced between chambers in the cylinder fairly near the center and install pins in them using red lock tight they could be adjusted and used to the extractor up .002 without a shim riding loose.
But, then if you removed the extractor and cleaned up the back of it well and put a bit of red Loctite on the shim and used a tube to press it in place for a few hours it would be stuck to the extractor pretty well.
Head space or rear gauge is held by the round circle of steel that surrounds where the center pin goes out of the extractor. The portion of the case rim setting on it will be plenty to hold the case in spec to the recoil shield.
That is why revolvers bind up from gun under the star, usually form not ejecting muzzle up. But like Protocall said in order to move the cylinder forward you either need more endshake than you want to move it or adjust the length of the yoke tube enough.
But, even having the tools and the ability to set the barrel back and often having time on my hands, I would still just leave it alone. Closing it from .009 to .004 or .005 just isn't worth the trouble and if you had to pay for it the expense. IMHO.
You guys know what can come from that.If a guy were remove the extractor and drill say 3 small holes evenly spaced between chambers in the cylinder fairly near the center and install pins in them using red lock tight they could be adjusted and used to the extractor up .002 without a shim riding loose.
But, then if you removed the extractor and cleaned up the back of it well and put a bit of red Loctite on the shim and used a tube to press it in place for a few hours it would be stuck to the extractor pretty well.
Head space or rear gauge is held by the round circle of steel that surrounds where the center pin goes out of the extractor. The portion of the case rim setting on it will be plenty to hold the case in spec to the recoil shield.
That is why revolvers bind up from gun under the star, usually form not ejecting muzzle up. But like Protocall said in order to move the cylinder forward you either need more endshake than you want to move it or adjust the length of the yoke tube enough.
But, even having the tools and the ability to set the barrel back and often having time on my hands, I would still just leave it alone. Closing it from .009 to .004 or .005 just isn't worth the trouble and if you had to pay for it the expense. IMHO.
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You know Protocalls idea of a shim under the extractor and mine of the pins. I was looking at an N frame cylinder and do believe you could actually thread and tap the cylinder for a couple small allen heads under the star and have an adjustment. Once you had the adjustment figured out, turn the allen out 3 full turns using the L of the wrench as a locator put a touch of Loctite on its side and then turn it back in the same amount.
You can get 6-40 allen head screws. On turn is .025, but with the short L of an allen it would be pretty easy to do 1/12 of a turn 1/2 a flat. That is .00208 It is workable.
An adjustable cylinder to barrel gap cylinder. LOL
You can get 6-40 allen head screws. On turn is .025, but with the short L of an allen it would be pretty easy to do 1/12 of a turn 1/2 a flat. That is .00208 It is workable.
An adjustable cylinder to barrel gap cylinder. LOL
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I'm going to echo the advice from replies 2-4. It's a lot of work for an insignificant, really non-issue, issue. Yeah, your b/c gap is larger than ideal, but it works in it's present state. Leave it alone.
In my admittedly conservative opinion, trying to shim the cylinder forward has you messing with two items (yoke and cylinder) that are only factory available if there's a problem. Yes, there's GB and flea bay, but you still have extra work ahead if there's an issue. Finally, should you decide to sell it, if the prospective buyer notices the work, the reaction may well be negative.
In my admittedly conservative opinion, trying to shim the cylinder forward has you messing with two items (yoke and cylinder) that are only factory available if there's a problem. Yes, there's GB and flea bay, but you still have extra work ahead if there's an issue. Finally, should you decide to sell it, if the prospective buyer notices the work, the reaction may well be negative.
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hobby-gunsmith
US Veteran
I would remove the end shake to zero. Now, keep in mind, removing the end shake will not remove the barrel cylinder gap. They are two separate fixes. If you are not shooting a great deal, I would leave the BCG alone. A barrel set back is more Indepth and purchasing the tools for the setback can be costly and the return of the expense for one gun is not practical.
Nick
Nick
An actual zero end shake is not ideal either. You need a bit of endshake for the cylinder to turn freely. It is like to tight of B?C gap. Any fouling works its way in there and you will get drag. I prefer about .001 end shake and I would not mess with .002. An .003 I would install a .002 shim. I also prefer the hardened steel shims over stretching the yoke. Thee shims are as smooth as it gets, one side turns on yoke tube and the cylinder turns on other.
While my pins and allen set screw ideas are workable I would never do them for such a small problem.
Like I said earlier, I can spend 3-4 hours setting the barrel back a thread adjusting the extension, timing the ejector rod etc etc and all it cost me is time and a little electricity. But, I would not do it to one of my guns because it had a .009 gap.
The set screw thing would be an interesting experiment. You could set up a gun at say .015 gap, fire it over a chrono then go to .012 fire over chrono, repeat at .009. .006 and .003. But, then I have a small stack of cylinders, and barrels.
While my pins and allen set screw ideas are workable I would never do them for such a small problem.
Like I said earlier, I can spend 3-4 hours setting the barrel back a thread adjusting the extension, timing the ejector rod etc etc and all it cost me is time and a little electricity. But, I would not do it to one of my guns because it had a .009 gap.
The set screw thing would be an interesting experiment. You could set up a gun at say .015 gap, fire it over a chrono then go to .012 fire over chrono, repeat at .009. .006 and .003. But, then I have a small stack of cylinders, and barrels.
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The dreaded and much maligned "end-shake" is necessary for the revolver to function. "Zero endshake" is not only impossible, but a misnomer, as some gauge (.001" - .002") is required for the cylinder assembly to open and close, accommodate lubricant and debris, and rotate freely inside the confines of the frame. This necessary "gauge" is built into the frame and cylinder components at the factory during assembly.
The OP hasn't been involved in this discussion he started, and he/she didn't mention the existence of excessive end shake, but removal of the excess gauge, if there is any, by shimming or stretching the yoke would only move the cylinder assembly back, and make the barrel/cylinder gap larger.
The OP hasn't been involved in this discussion he started, and he/she didn't mention the existence of excessive end shake, but removal of the excess gauge, if there is any, by shimming or stretching the yoke would only move the cylinder assembly back, and make the barrel/cylinder gap larger.
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