BBTI testing the effect of revolver cylinder gap
I was excited to hear from Jim that Ballistics By The Inch will soon be testing how much a revolvers' cylinder gap effects the ballistic performance of a round.
We’ve had a Single Action Army clone in .357 magnum modified to allow for adjusting the barrel position from a standard 0.006″ to 0.001″ to no gap (barrel snug against the cylinder). We have a dozen or so different ammunition loads in .38/.357, and we’ll be essentially repeating the BBTI procedure for each of these, with the normal gap then the minimum gap then without any gap, starting with an 18″ barrel and going down in increments of one inch to just 1″ . Actually, one slight difference – to make sure we get a better statistical sample, we’ll be firing 10 (ten) rounds of each type of ammunition at each point rather than just 3 (three) as we did with the BBTI tests. Because we are limiting this test to just one caliber, we thought this was a reasonable step to take. We hope that this will allow us to conclude with some actual data what the effect of having a cylinder gap in a revolver actually amounts to.
These tests are sure to settle a few arguments.
They’ll need to reduce the “end-shake” of the cylinder as well. End-shake is the distance that the cylinder can move forwards and backwards on the yoke or cylinder pin. I remember one gunsmith writing in an old “Gun Digest” that he had considered setting the cylinder gap to match the end-shake. The idea was that the impact of the hammer/firing pin would force the cartridge and the cylinder against the barrel, effectively eliminating the cylinder gap at the time of ignition.
“These tests are sure to settle a few arguments.”
You must be new here. It’ll shift the arguments from the effects of the cylinder gap to the testing procedures.
Props to Jim and the gang at BBTI. This is neat stuff. Thanks for providing the raw data and letting us draw our own conclusions.
Since it’ll probably come up, the 1895 Nagant pistol closes the cylinder gap, but I don’t think closing the cylinder gap was the primary reason for doing so.
I’m theorizing it’s to guarantee bore alignment, on that particular pistol. The hand and stop could be sloppy as all heck, but with original ammo as long as the “cone” of the case mouth will enter the “cone” of the barrel, it’ll line itself up.
It might have been wiser to use a Dan Wesson revolver for this test, then they could simply tighten the barrel and by use of feeler gauges make the necessary gap. It should be interesting!
Greetings from Texas,
If I recall from my reading the reasoning behind the 1895 Nagant revolvers cylinder “nesting” arrangement had more to do with getting maximum power out of an asthnatic cartridge than reducing muzzle flash. The bullet was recessed inside the case to completed the “gasket seal” effect. In my personal opinion the effect isn’t worth the, I’m guessing, 20 pound trigger pull.
Hi guys,
One advantage of the way we’re doing this (not spelled out in the original post, so there’s no way you’d know) is the way we’re setting up to do the tests. We’ll be using some spacer rings worked up by our gunsmith (who did a right fine job with our custom barrels for the T/C Encore in the original tests) so that we get very consistent and quick spacing on the cylinder gap. Controlling this variable means better data with all the test shots fired.
Freiheit, you’re welcome – while between us we’ve got a lot of skills, none of us pretends to be talented in either statistics or data crunching. Making the raw data available has meant that we don’t need to be – those who are can do the work! Call it “crowdsourcing”, and everyone wins.
Cheers –
Jim D.