Loss for a revolver's cylinder gap
- Thread starter fatelvis
- Start date
jds holler
Gold $$ Contributor
I'm gonna guess that it probably depends upon -- burn rate of powder, seating depth, caliber, bullet weight, power level, barrel length, chamber pressure, ambient temperature, primer type, -- jd
There really is no ballpark figure.
The old colt revolvers were designed to close the cylinder gap just before firing so there must have been a
decent amount of velocity gain for them to do this. The bad thing is when they get dirty they get sticky.
The old colt revolvers were designed to close the cylinder gap just before firing so there must have been a
decent amount of velocity gain for them to do this. The bad thing is when they get dirty they get sticky.
More like the 44 S&W special in photo? 50 fps loss?
fatelvis
Silver $$ Contributor
I only asked this question out of curiosity. I just read a article about the 357 maximum,And they stated that you lose about 200' per second from a test barrel to a revolver of equivalent length.This table shows even more loss.Quite honestly, I did not think the loss was that Extreme. Wow!
200fps loss sounds like a lot...as in "I doubt it"...I had a Dan Wesson 357 many moons ago and tried it with as little gap as would allow the cylinder to still turn, like a few thousandths. I even let it drag some once. There wasn't a lot of difference over my chrono. Maybe 40-50fps if I remember right. The gun quickly heated up and when things would expand the cylinder wouldn't turn. I think .007" or so was the least I could run and the gun not stop after the first 6 rounds. I think it had to be a little more to work right. Then I went the other way to try it. It didn't really loose a lot until I got up around .020" or so. Most are around .010-012".
I think what happens is with heavy bullets and slower powder if the gap is too much the powder doesn't build pressure to burn more. Probably saying that wrong, but slow powder needs a long barrel to continue the pressure build to burn. Short barrels and wide gaps will leave a lot of unburned powder residue in the barrel. Not sure if it's that or the gap costing velocity. Probably some of both.
I think what happens is with heavy bullets and slower powder if the gap is too much the powder doesn't build pressure to burn more. Probably saying that wrong, but slow powder needs a long barrel to continue the pressure build to burn. Short barrels and wide gaps will leave a lot of unburned powder residue in the barrel. Not sure if it's that or the gap costing velocity. Probably some of both.
fatelvis
Silver $$ Contributor
I agree, I thought 200fps sounded like a lot also, according to the other chart from AccelR8, it looks more like 100fps. Still a lot but tolerable.
I had a S&W 45acp revolver that had a huge gap and it shot awesome. Other than getting dirtier I could see no issues with a large gap and I did target work with it.
I have found the same thing with the ones I have. Interesting fact about the 45acp......barrel length {or shortness} doesn't change velocity. So I guess a large cylinder gap doesn't either.
dellet
Gold $$ Contributor
I have seen studies done by law enforcement, probably FBI, comparing 9mm in both revolvers and semi-autos. The take away was that as long as bullet travel was used vs barrel length there’s was no real difference. So a 4” revolver had the same velocity as a 5” pistol. Keep in mind a 9mm round is basically 1”, making travel almost identical.
As I remember the revolver actually had a slightly higher velocity in what was tested, and that was within what would be expected from barrel/barrel variations. That is what stood out as memorable.
Test groups were small, basically what was being evaluated for duty.
As I remember the revolver actually had a slightly higher velocity in what was tested, and that was within what would be expected from barrel/barrel variations. That is what stood out as memorable.
Test groups were small, basically what was being evaluated for duty.
XTR
F-TR obssessed shooting junkie
Not revolvers, but related to gas venting. I saw some numbers a few weeks ago discussing adjustable gas blocks and comparing those that vented a portion of the gas as opposed to only limiting gas into the gas tube/BCG operation, and I was surprised at the difference in MV between the two. Don't recall the exact numbers now, but it was way more than I would have expected. You lose a lot of gas from the cylinder gap, those numbers might be right.
22 lr standatd velocity. 10" T/C Contender 1083 fps. Ruger MK1 5.5 bbl. 6 vent holes in front of chamber. 777 fps. Same gun, different day 807 fps. (Modified for ISU rapid fire, in the 1970s)
Difference- 276 fps & 306 fps.
My Mossberg 22 lr targer rifle clocked 1093 fps with its 26" barrel.
Difference- 276 fps & 306 fps.
My Mossberg 22 lr targer rifle clocked 1093 fps with its 26" barrel.
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maby someone with a Dan Wesson revolver can help ,,,they had adjustable gap ,,,and they might know more about velocity changes and accuracy variation ,,,,Roger
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