629 tight cylinder gap

[steelslaver]

It will shorten it by 0.002". If a plug gauge shows the minimum dimension already, then the cone would need to be deepened by 0.002" to be correct

The forcing cone is a cut at a steep angle and .002 off the bottom of a steep isosceles triangle with an 11 or 18 degree peak doesn't not cause the base to narrow very much as 11 degrees radian is .192 and 18 is .314 So .002 would narrow a 18 degree cone base about .00063 which is about the thicknesses of a fine human hair.

Here is a handy dandy isosceles triangle calculator BTW
Isosceles Triangle Calculator

S&W factory forcing cones are a compromise anyway. How well they work is a function as much due to bullet's nose shape as it is anything. A wad cutter gun needs more than a round nose bullet gun. Early S&W had very little forcing cone and I suspect the fact that all the bullets all the early were round nosed had something to do with it. Go stick a variety of bullets in a forcing cone. If the driving front driving band is even with the face of extension before the nose in the forcing cone stops it you will have problems. I have over 20 loose factory barrels and the forcing cones are not very uniform one to another.

I have adjusted barrels, set them back a thread or more. One thread is .0277 and then you do need to recut forcing cone. I have a couple cones I use for gauges.

 

[dogdoc]

I have learned some interesting facts concerning concerning the Brownells forcing cone gauges. I own many Smith revolvers in different calibers. I have measured many factory unaltered revolvers from different eras and many forcing cones swallow the gauges. Meaning the cones are much deeper that the gauges say are correct. Some are too shallow. Guess what, the guns shoot fine without excessive leading etc. if I have to recut a forcing cone because it is rough(some are atrocious ), I don't worry about the gauges. I cut to where the rifling begins so the angle is consistent . When I have set a barrel back I may use the gauges to be most correct but I really do not think it makes that much difference . The truth is that these guns we love to tinker with are not as precision as we like to think.

 

[scooter123]

I have a Dan Wesson 15-2, which allows the B/C gap to be adjusted. I keep my gap set at 0.002 inch and have never had a problem with the cylinder "dragging" because it's been shot. I would suggest that next time you think your cylinder is dragging you look to see if there are drag marks in the powder build up on the face of the cylinder. If you don't see drag marks you issue is most likely caused by stray gunpowder particles under the extractor star. In that case keeping a can of Dust Off in your range bag would be very helpful. I would NOT do a thing about your B/C gap because a tight gap will increase the bullet velocity and many feel it's also better for accuracy.

 

[steelslaver]

BTW, I was going through my igmur photos and here is a shot of the cutter that trims the barrel extension. You ca not see the brass guide that just fits in the rifling to keep it centered as it is in the barrel in the photo.

I think I was making a K frame 327 Mag when I took this

 

[wproct]

Just adding my 2 cents, and trust me that's all it's worth. I will take small gap tight fit over the vise versa any day. Metal can always be removed, but can't be added back. If I have to carry a brass brush to scrub it every so often, so be it.

 

[Tom S.]

Moderator Note: Thread moved to Gunsmithing Section.

OP: Unless you have experience working with metal, I would not recommend you do anything to your firearm. As someone pointed out, removing metal is far easier than adding it back. Trying to stone off .002 is certainly doable but is not the proper, nor recommended method of increasing the barrel to cylinder gap. Stoning, even with aggressive diamond stones is a very slow process, but it still leaves the possibility of losing the desired perpendicular surface of the end of the barrel, resulting in an uneven gap. While that wouldn't be the end of the world, it's a sign that an amateur has been at play and would give knowledgeable buyers reason for pause (like buggered up screw slots do) should you ever decide to sell the gun in the future.

If the gun is suffering problems that routine cleaning doesn't relieve, then pleas consider professional / factory help rather than do-it-yourself remedies.

 

[CH4]

Perhaps Smith will fix it for you under warranty

 

[__steve__]

May I ask why would a 0.004" B/C gap be preferred over a 0.002" (so long as cyl never contacts forcing cone during operation)?

 

[armorer951]

May I ask why would a 0.004" B/C gap be preferred over a 0.002" (so long as cyl never contacts forcing cone during operation)?

An added emphasis on maintenance and a slightly larger barrel/cylinder gap is encouraged for those who carry revolvers for personal protection and law enforcement use. B/C gaps under .004" can cause issues with proper cylinder rotation and added difficulty opening and closing the cylinder.

Confirming proper end shake clearance and front gauge were both among the checks our department armorers did each year at our annual tear down and maintenance inspections.

 

[steelslaver]

When I said I would leave it alone there are a couple reasons. While I would not want it that tight on a carry/defense gun, model 29 or 629 don't get that duty much, even hunting your not going to empty a cylinder or 2. If it fouls at the range it is just a small hassle easily taken care of. Especially if you know about it. A couple swipes of a small brass brush on face of barrel extension and cylinder face and good to go.

 

[series guy]

If you don't shoot a lot you may not realize that after each shot powder residue and lead (if you shoot cast bullets) build up on the face of the cylinder. This can cause the fouling to drag on the barrel. If shooting single action the hammer will be a bit more difficult to cock but if shooting double action it can lock the gun up leaving you unable to pull the trigger. Something that some folks may not realize about the action of an S&W revolver is the way the cylinder is actually advanced. The hand begins to rotate the cylinder by pushing upwards on the ratchet but as the cylinder continues to rotate the hand basically slides past the ratchet and the side of the hand actually nudges the ratchet sideways to complete the rotation. This works well when there is little drag on the cylinder and the inertia of the loaded cylinder helps to complete the cycle. I have had guns shooting cast bullets lock up after 10 rounds from fouling. I don't trim the barrel on every gun I own but I have done quite a few of the guns that I use for bowling pin shoots or speed shooting events. Nobody is going to wait on the line while you clean the cylinder face on your gun.