View Full Version : Revolver cylinder gap

December 9, 2010, 02:17 AM
Hi there, I've been searching my physics fueled thoughts for a way to eliminate the pressure escaping from the revolvers' cylinder gap for obvious reasons. Cutting into the top strap of the frame is only one small part of my motivation. Other valid reasons include improved velocity, preventing pressures from blowing back into other rounds, deadly knife cutting pressures that limit how one handles the revolver when firing covers several reasons why this needs addressing as a primary issue. When referring to a high pressure cartridge, it becomes monumental from a safety stand point. I can't understand why this hasen't, at least to my knowledge, been addressed and solved, especially since the revolver and its variations have been around for so long. After nearly 30 years of serious thought and evolving diagrams, I have found a practical solution. Using high tech metal, such as titanium, a quite simple shroud can be easily machined to work on any revolver. To most this wouldn't seem a practical or even necessary modification. But to an individual who has closely observed the effects of escaping pressures, I've realized the magnitude of the design flaw when this type of weapon was created. Although I have found the after market solution to be rather simplistic, a design that includes such a solution during manufacturing is a far more simple process and based on the concept, shouldn't have a major impact on the price.
Thanks for your time to review this thought and I hope to hear some of you to see if I am on to something new and worthy of addressing even. As I stated, a reliable and simple yet precision design will completely eliminate escaping pressures that can actually be applied to the performance of the weapon, eliminate safety issues, and extend the life of parts and main frame integrity.

"When seconds count, the police are only a few minutes away"

December 9, 2010, 02:41 AM
The problem here is that when you "solve" one problem you often create another.

You can tighten up the cylinder gap, but then your revolver will build up carbon & fouling in the cylider gap that much quicker. This can lead to binding.

FWIW when I was doing Cowboy Action Shooting I had a pair of Ruger Vaqueros, beautiful pistols BTW, and after 50 rounds fired they would often bind up to the point where I couldn't even cock the hammer anymore.

Also, investigate the old Dan Wesson revolvers with the interchangeable barrels. You could reduce cylinder gap on those to the point where sound supressers could be attached.

December 9, 2010, 03:52 AM
Its already been done over 100 years ago, probably a much better gas seal then any bolt on shroud I hazard to guess.


Purchase a nagant revolver for 100 bucks or less and find out how it works.

How does this groundbreaking "shroud" seal the gases?

December 9, 2010, 09:42 AM
I doubt that most shooters of revolvers think that the gap is a significant problem and would not want to "ruin" the aesthetics of their revolvers.

December 9, 2010, 11:49 AM
I don't think it's nearly as serious of a problem as it is suggested by the OP. Sure, you lose a little bit of energy in the gap. Sure, it can be a safety issue... if you're an idiot. As others have suggested though, the problem with creating some kind of shroud to contain that energy is that it would have to seal very tightly when the gun is fired, but then it would have to lift up to be able to provide clearance so the cylinder can rotate. Theoretically, you could have a shroud that automatically lifts up during rotation, but that movement would also be susceptible to binding by the carbon residue. I do remember the silhouette shooters playing with their Dan Wessons in the early 80s to find the perfect compromise for the gap. Finding a gap that was small enough to save that energy yet large enough to avoid binding up after 30 rounds of carbon deposits is kind of tricky. One of my Colt 45 revolvers has a very small gap that usually works very well. But one time I made upu some low-pressure loads using AA #9. Too low pressure it turns out. They were very sooty and the cylinder began to bind up after about 35 rounds.

Bottom line for me is if I'm worried about losing some of that precious energy and velocity due to the escaping gas, then I just make a hotter load. On the safety aspect, I simply keep my body parts, or any other valuable items, away from areas where hot gases will be shooting out. The flame cutting is a non-issue if you use common sense about the loads you are shooting.

The cylinder gap issue is no big deal. Consider the fact that on any revolver, you are "wasting" a considerable amount of energy out the end of the barrel. Revolver barrels (at least those less than 14" or so) shoot flame out the end because the gases are still expanding after the bullet has exited. And safety issues? Well, the end of a barrel is kind of a dangerous place to stick your hand also.

January 5, 2011, 12:58 PM
"I can't understand why this hasen't, at least to my knowledge, been addressed and solved,"

I can; it really isn't a problem. The people who design, make and sell revolvers are not and never have been fools. The Nagant revolver system certainly "sealed" the gap at signficant cost but for no measurable ballistic effect. (Really good drawing hickstick!)

You must presume the gas pressure escapes from the cylinder gap with a force equal to what it applies to the base of the bullet. If so, that isn't so!

Use your physics to consider the density of the gas and it's speed down the bore. The gas is like a high velocity slug of thick syrup and little of it escapes through that gap. A 30kpsi chamber pressure makes the gas some 2,000 times more dense than air and the inertia of that very high density resists a 90 degree change of direction when it leaves the cylinder, so very little of the pressure or gas actually escapes.

Or you could put an "O" ring in the gap. :rolleyes:

January 5, 2011, 03:19 PM
Sorry at 50,000 psi enough gas escapes to cause serious damage.


A member of my range did a stupid trick and was trying to clear a tight sticking case with a cocked .500
The gas cut two of his fingers. The Pointer was just hanging by skin.


James K
January 5, 2011, 11:00 PM
Hi, Phydaux and guys,

Most of the time when a revolver with a tight b/c gap binds up, it is blamed on carbon. That may be the case but more often cylinder binding is caused by heat from firing causing the cylinder to expand lengthwise and close the b/c gap. While some revolver makers consider up to .01" to be within spec, I consider .007" to be close to ideal. Tight enough to prevent gas leakage, but not tight enough to bind even when fired rapidly.

As to some kind of shroud, some ideas along that line have been tried. Iver Johnson had a .22 revolver called the Sealed Eight, which not only had countersunk chambers in case of head failure but had a fairly high ridge around the front of the cylinder to prevent gas escape and lead spitting. (one section was cut away to allow cylinder removal). It didn't actually eliminate the b/c gap like the Nagant does, or increase velocity, but it did prevent sideways spitting and would have prevented gas cutting of the top strap had that been a problem with a .22. (Of course the shield itself would have been eroded with a more powerful round, so it was a case of push in here and it pops out there.) The IJ was a solid frame type; that shield would not be practical on a swing out cylinder revolver since the cylinder could be swung out only at a certain place.


MSD Mike
January 7, 2011, 11:12 AM
Not to big a deal to me. All guns have safety issues if not handled properly. Get your hand in the wrong spot on an auto and see what the slide does to you.


James K
January 7, 2011, 03:12 PM
Hi, wncchester,

Interesting point, except that the gas is not something being compressed by the pressure, it is the cause of the pressure. Hot gas expands (see Mr. Boyle about that) and it is that expansion that pushes the bullet out the barrel. And anytime it finds an opening, it will expand into and through that opening as any fluid will do. While gas escape at the b/c gap is not as great as some believe, it is enough to cut into a revolver top strap and to do damage to anything in its way.

The best way to prevent gas cutting of the top strap is to actually bevel away the outer part of the cylinder and the top of the barrel, so that the gas expands into a larger area where its speed and temperature are reduced.


January 7, 2011, 04:45 PM
Top strap cutting is what killed off the .357 maximum from Dan Wesson.

It was found to be bad enough, and to continue deep enough they worried the action would be weakened long term.

The cylinder gap is normally small enough to have only a minimal impact on bullet velocity, but is DOES cause a loss.

January 7, 2011, 05:17 PM
Trying to address the pressure leak in a revolver, in year 2011? I think you're about 100 years late in worrying about it. Everyone just accepts that it's part of how a revolver works. If enough is leaking that you're not getting the velocities you want in a 4" gun, get a 5" gun. I was suprised that a load fired in a 2.5" .45 ACP revolver attained higher velocities than when fired in 4.25"-barreled auto pistol.