One of the quailties us wheel gun guys look at when choosing one, is cylinder gap. It's certainly not much of a primary factor to the average shopper, but for some it bares importantance. Having said that, has anyone with more regard for this element ever considered having it done, or has had it done? I've researched this a bit, and have found it can be accomplished with very little work by adding a very small shroud of titanium. The bennefits to having it improved is, pressure cutting to the top strap goes away, and velocity goes up quite a bit, and no more pressures blowing back into other chambers.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an alternative browser.
You should upgrade or use an alternative browser.
Closing the gap
- Thread starter 700cdl
- Start date
Bob Knizner
New member
I have read that as long as the B/C gap does not get really excessive, it has little effect on velocity.
Here is a semi-scientific article:
http://findarticles.com/p/articles/mi_m0BQY/is_1_51/ai_n7581216/
Too small of a B/C gap obviously causes reliability problems as the front of the cylinder collects fouling.
Guys with the Dan Wesson revolvers with the user-adjustable B/C gap did quite a bit of experimentation over the years, because it was easy to do. There was always an optimum gap that seemed to hover around 0.003" to 0.005".
My suggestion would be to get a Dan Wesson revolver and run a bunch of tightly controlled chrono tests.
Good luck with your research!
Bob
Here is a semi-scientific article:
http://findarticles.com/p/articles/mi_m0BQY/is_1_51/ai_n7581216/
Too small of a B/C gap obviously causes reliability problems as the front of the cylinder collects fouling.
Guys with the Dan Wesson revolvers with the user-adjustable B/C gap did quite a bit of experimentation over the years, because it was easy to do. There was always an optimum gap that seemed to hover around 0.003" to 0.005".
My suggestion would be to get a Dan Wesson revolver and run a bunch of tightly controlled chrono tests.
Good luck with your research!
Bob
Dfariswheel
New member
"Ideal" barrel/cylinder gap is about 0.005".
Apparently S&W has determined that a wider gap has no adverse effects because they now say that a gap as wide as 0.012" is in spec.
A tighter gap may lead to cylinder drag due to heat expansion or fouling build up.
In a revolver that's in proper condition the only way of changing the barrel/cylinder gap if it's wide, is the fairly expensive method of having the barrel set back one thread, and the barrel/cylinder gap re-set and the forcing cone re-cut and lapped.
Potential gain versus the cost is not a good trade off.
Experiments with the Dan Wesson indicate that velocities do not "go way up".
Velocity gains are not very significant.
Apparently S&W has determined that a wider gap has no adverse effects because they now say that a gap as wide as 0.012" is in spec.
A tighter gap may lead to cylinder drag due to heat expansion or fouling build up.
In a revolver that's in proper condition the only way of changing the barrel/cylinder gap if it's wide, is the fairly expensive method of having the barrel set back one thread, and the barrel/cylinder gap re-set and the forcing cone re-cut and lapped.
Potential gain versus the cost is not a good trade off.
Experiments with the Dan Wesson indicate that velocities do not "go way up".
Velocity gains are not very significant.
Hey there Drail,
It's been a couple of years ago since I discussed this topic, but it was with a ballistic or physics expert type of guy. I actually never thought of this before, any of it, the effect of no gap. But what I do remember is he said that the reason revolvers haven been modified, or why manufacturer's haven't changed the design, other than the Dan Wesson that offered a way to adjust the gap, is it would open up a can of worms from a legal perspective. Apparently there have been a good number of incidents in which the pressure escaping through the gap has seriously injured shooters who have inadventantly put there hand or finders to close to the gap. And an example of what he gave as to how much velocity is decreased by the gap is, testing for data is done in a closed chamber, I guess something that doesn't allow pressures to escape anywhere except through the muzzle. Because of the test chamber not losing pressures, the velocities stated in hand loading manuals is always much higher than what we can achieve from our revolvers. I'm going to try and find his web site again, depending on if I can remember how I stumbled onto in the first place. I thought it was rather interesting. According to this guy, he knows a couple of smiths that will modify certain revolvers with this shroud design. But some he said can't be completely sealed, like some of the S&W models because the barrel is cut flat on the bottom to accomodate the cylinder. Anyway, if I do find it he has a couple of revolvers shown that have been modified, pretty cool and as I stated, apparently not an extremely difficult modification if a guy knows how to some machine work.
It's been a couple of years ago since I discussed this topic, but it was with a ballistic or physics expert type of guy. I actually never thought of this before, any of it, the effect of no gap. But what I do remember is he said that the reason revolvers haven been modified, or why manufacturer's haven't changed the design, other than the Dan Wesson that offered a way to adjust the gap, is it would open up a can of worms from a legal perspective. Apparently there have been a good number of incidents in which the pressure escaping through the gap has seriously injured shooters who have inadventantly put there hand or finders to close to the gap. And an example of what he gave as to how much velocity is decreased by the gap is, testing for data is done in a closed chamber, I guess something that doesn't allow pressures to escape anywhere except through the muzzle. Because of the test chamber not losing pressures, the velocities stated in hand loading manuals is always much higher than what we can achieve from our revolvers. I'm going to try and find his web site again, depending on if I can remember how I stumbled onto in the first place. I thought it was rather interesting. According to this guy, he knows a couple of smiths that will modify certain revolvers with this shroud design. But some he said can't be completely sealed, like some of the S&W models because the barrel is cut flat on the bottom to accomodate the cylinder. Anyway, if I do find it he has a couple of revolvers shown that have been modified, pretty cool and as I stated, apparently not an extremely difficult modification if a guy knows how to some machine work.
hickstick_10
New member
I thought you had a design in mind?
The problem with trying to reduce the bbl/cyl. gap to nearly zero is you'll end up with a revolver that will cease to revolve after a couple of cylinders worth of fouling builds up. Historically there have been several attempts to decrease the bbl./cyl. gap to stop gas loss and the expected velocity increase was minimal. If it were very much of a real advantage I'm quite sure that all the engineers after all these years would have gone in that direction. I just don't think there is all that much to be gained. I have not seen a dramatic difference in muzzle velocities between vented and non vented bbls. when chronographing my handloads. No more than 20 - 30 FPS. On the subject of gas cutting - that is really only been a problem where ammunition with slow burning powders driving a very lightweight bullet creates a situation where the pressure and temp. of the expanding gas is very high as the bullet crosses the gap. My experience has also shown me that even when gas cutting is seen it is self limiting. As soon as a shallow groove is formed in the top strap it seems to redirect the flame front out the sides of the gap and no more cutting takes place. Actually more damage is caused by using those loads due to the effects it has on the forcing cone. Fire enough 110 or 125 gr. .357 loads running at max. pressure and you will see the forcing cone become brittle and cracks will start. I have personally seen this effect on a GP 100 that was fed a heavy diet of very hot 125 gr. handloads. I no longer load ammo using light bullets and max. charges of slow burning powders. It just isn't necessary and the gun will last longer with standard loads.
Last edited:
jglsprings
New member
The bennefits to having it improved is, pressure cutting to the top strap goes away, and velocity goes up quite a bit, and no more pressures blowing back into other chambers.
I can honestly say - NONE of my revolvers have a problem with flame cutting on the frame. And I'm not sure that "pressures blowing back into other chambers" is a valid consideration.
I think you are looking for a solution that will be cost prohibitive, impractical and unnecessary. Your are initially interfering with the reliability of the weapon. And you are trying to fix problems that don't exist.
If maximum accuracy and maximum efficiency are desired get a single shot, i.e. a Contender or the like.
If you are being injured by your revolver (other post) put it down until you learn how to shoot it.