Scooter1911
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Thanks for the info
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Smith and Wesson barrel torque
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We have some certified armorer types here to get you a specific answer on that. My personal experience is that there isn't a specific torque value achieved on a torque wrench. Rather, there's an angular specification between hand tight/solid frame contact and aligned in proper position. This is a widely used method of establishing a proper tension on the threads.
BTW, you can watch videos of factory guys in the Performance Center installing barrels. Not a torque wrench in sight.
Now about the "crush fit" thing. S&W barrels have always been tightened to a certain tension on the threads. Pin or no pin. In fact, on a pinned barrel, the barrel can rotate a surprising amount before the pin interferes. (Pretty much the same thing is true in cases where nuts/bolts are safety wired in certain applications. Doing safety wiring to appropriate specifications is a massive pain.) It was there mainly for insurance purposes. Back in the day, loose barrels weren't all that rare in products from certain manufacturers. The pin was kind of window dressing to assure the purchaser that a S&W barrel wasn't going to fall off.
BTW, you didn't mention the model. It doesn't take 60 ft/lbs to crack the barrel socket on a J frame. That won't show up immediately, but will shortly.
BTW, you can watch videos of factory guys in the Performance Center installing barrels. Not a torque wrench in sight.
Now about the "crush fit" thing. S&W barrels have always been tightened to a certain tension on the threads. Pin or no pin. In fact, on a pinned barrel, the barrel can rotate a surprising amount before the pin interferes. (Pretty much the same thing is true in cases where nuts/bolts are safety wired in certain applications. Doing safety wiring to appropriate specifications is a massive pain.) It was there mainly for insurance purposes. Back in the day, loose barrels weren't all that rare in products from certain manufacturers. The pin was kind of window dressing to assure the purchaser that a S&W barrel wasn't going to fall off.
BTW, you didn't mention the model. It doesn't take 60 ft/lbs to crack the barrel socket on a J frame. That won't show up immediately, but will shortly.
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I've never heard of an arbitrary torque specification on proper barrel to frame fit, at least from the factory reps or any of my instructors at the armorer's school or recert classes. The topic never came up, because barrel replacement was not something that normally fell within the scope of an armorer's duties or training......at least for me personally. We would just send the revolver back to the factory for any barrel work that was required.
I've installed and changed several barrels on my own S&W K and N frames over the years, and installed many aftermarket bull barrels on PPC revolvers I constructed. I always used an MGW brand frame wrench, and installed the barrels by "feel", and never thought about checking them for proper tightness with a torque wrench. To my knowledge, I've never had one shoot loose.
I'm not a machinist, but considering the thread size on the K-frame, for instance, at .540" X 36, 60 Ft. Lbs. seems like a lot of torque to place on the frame/barrel during installation. I know there are many talented machinists here on the forum who can comment on the 60 ft. lb. figure your gunsmith gave you, and give an opinion as to the proper specification.
I'm with WR, as I have no idea where the term "crush fit" originated, and how it applies to this type of installation. The barrel should stay put with or without a barrel pin if it is properly installed.
I've installed and changed several barrels on my own S&W K and N frames over the years, and installed many aftermarket bull barrels on PPC revolvers I constructed. I always used an MGW brand frame wrench, and installed the barrels by "feel", and never thought about checking them for proper tightness with a torque wrench. To my knowledge, I've never had one shoot loose.
I'm not a machinist, but considering the thread size on the K-frame, for instance, at .540" X 36, 60 Ft. Lbs. seems like a lot of torque to place on the frame/barrel during installation. I know there are many talented machinists here on the forum who can comment on the 60 ft. lb. figure your gunsmith gave you, and give an opinion as to the proper specification.
I'm with WR, as I have no idea where the term "crush fit" originated, and how it applies to this type of installation. The barrel should stay put with or without a barrel pin if it is properly installed.
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Scooter1911
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It is an L frame and 60 lbs was a guess as he did use a torque wrench. I was just wondering before I shoot it
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i have built a lot of custom revolvers over the years and measured a lot of factory barrels. On the factory guns, the amount of "crush fit" varies a good bit, but too much causes a lot of problems. I've seen ones that had the threaded part of the barrel squeezed down as much as .001 to .002 right ahead of the forcing cone.
The problem with this is that the bullet gets squeezed down, then rattles down the bore the rest of the way. Also, lead bullets get rubbed off and lead up the forcing cone. If you take the barrel off, the constriction disappears. Turning a little off the back face of the barrel makes for less crush and doesn't choke down the barrel. You can check this with gage pins. The biggest pin that will fit in the muzzle should slide all the way through. Oftentimes, the gage pin will get stuck at the front of the frame area. Then you try smaller pins in .001 increments until one goes through. The difference between the biggest one and the one that goes through is the amount of constriction.
The problem with this is that the bullet gets squeezed down, then rattles down the bore the rest of the way. Also, lead bullets get rubbed off and lead up the forcing cone. If you take the barrel off, the constriction disappears. Turning a little off the back face of the barrel makes for less crush and doesn't choke down the barrel. You can check this with gage pins. The biggest pin that will fit in the muzzle should slide all the way through. Oftentimes, the gage pin will get stuck at the front of the frame area. Then you try smaller pins in .001 increments until one goes through. The difference between the biggest one and the one that goes through is the amount of constriction.
I too have noticed that the amount of torque necessary to loosen a factory barrel varies quite a bit. Usually not all that tight though. I have never done the pin gage trick, but, I would think it would take a bit and a thinner barrel. It would be harder to squeeze an N frame 357 barrel than a K frame. An N frame 45 barrel easier than a N frame 357. I wonder how much it does take to do this. I am sure it has a bad effect.
If you do end up with a constriction at the forcing cone, there are "lapping" bullets made to shoot that will lap the barrel and remove the constriction.
Yes - the 2 ways to fix this are - Lap the barrel or Turn back the shoulder.
The barrel threads are not that hard to squeeze down, even on .357 N frame.
The barrel threads are not that hard to squeeze down, even on .357 N frame.
cmj8591
Member
How does the bore become restricted? Isn't the inside diameter of the frame and the outside diameter of the threaded part of the barrel the same?
It can get constricted if the barrel is tightened too hard or it's too tight of a fit. When you crush the outside it can also deform the inside, constricting the bore by a .001" or two, at the frame/barrel union.
I've found a constriction on two different new S&W revolvers that I hand lapped out. Both were Performance Center models.
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rkrcpa
Member
To follow up on this...isn't constriction caused by the o.d. of the barrel threads being greater than the i.d. of the frame threads? If the i.d. and o.d. are correct how would over tightening cause the barrel to get squeezed?
Check out the point at 2:30+ in this video at the S&W Performance center where the barrel is installed in the revolver. Very scientific. Padded vise, aluminum wrench, eyeball.
[ame]https://www.youtube.com/watch?v=WRbUn214yUs[/ame]
[ame]https://www.youtube.com/watch?v=WRbUn214yUs[/ame]
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Exactly, the barrel shoulder is turned back so there is about 1/8 turn crush fit to center the barrel regardless of pin barrel or no pin barrel. Almost no one understands this. The pin does not hold the barrel in place. It amazes me how many think the pin holds the barrel in place. It really is redundant which is likely why they did away with it.
Actually the human eye can detect very small deference. I have installed a few barrels and have always used my eyeball and they come out perfect. The eye baller has to care and take the time to do it right.
From Wiki
Under normal lighting conditions (light source ~ 1000 lumens at height 600–700 mm, (23-27 inches) viewing angle ~ 35 degrees) the angular size recognized by naked eye will be round 1 arc minute = 1/60 degrees = 0.0003 radians.
From Wiki
Under normal lighting conditions (light source ~ 1000 lumens at height 600–700 mm, (23-27 inches) viewing angle ~ 35 degrees) the angular size recognized by naked eye will be round 1 arc minute = 1/60 degrees = 0.0003 radians.
In this day and age of computer driven machines and lasers, I can't believe there is still a problem with canted barrels. Almost all of the hand fitting has been eliminated and this seems like a perfect job for a machine that can measure to tolerances far smaller than .001".
I've noticed that the barrels don't have assembly numbers.....does anyone have first hand, current knowledge concerning how the production barrels are mounted to the frames? Surely they don't install all of them by hand with a frame wrench and an eyeball.
I've noticed that the barrels don't have assembly numbers.....does anyone have first hand, current knowledge concerning how the production barrels are mounted to the frames? Surely they don't install all of them by hand with a frame wrench and an eyeball.
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