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casingpoint wrote:The author below is cites a revolver flash gap velocity loss of 100-200 fps. Significant by any standard.

I am skeptical of those numbers being typical. They might have meant something a long time ago, but as we can see from Stephen Camp's own test of a S&W 625 against a Sig P220, with one load the revolver was 26 fps faster than the semi-auto, and with the other load, the semi-auto was 14 fps faster; and the difference between the slowest revolver load and the fastest semi-auto load was 60 fps in the semi-auto's favor, and the difference between the slowest semi-auto load and the fastest revolver load was 73 fps in the revolver's favor. So I think that all in all, the differences are fairly insignificant for self defense purposes. And, if it really is a concern for you but you would rather carry a revolver, then just stoke it with +P.

never mind

The Annoyed Man wrote:

casingpoint wrote:The author below is cites a revolver flash gap velocity loss of 100-200 fps. Significant by any standard.

I am skeptical of those numbers being typical. ...... if it really is a concern for you but you would rather carry a revolver, then just stoke it with +P.

I am skeptical of 100to 200 FPS too. That is a lot of velocity. Significant!

I guess what I'd want to see would be a full test, using the same overall legth (breechface to muzzle) of:
1) a revolver with a factory-spec gap
2) a revolver with a gap worn just out of factory spec
3) a delayed-blowback semiauto
4) a straight-blowback semiauto
5) a gas operated semiauto
6) a true sealed-breech gun, such as a breakover

Unfortunately, finding a single caliber available in all those action types - much less meeting the length constraint - is probably impossible.

KFP wrote: I'm still struggling to understand how the recoil of the slide on a semi auto doesn't result in a loss of energy from the round. Any explanations?

For some reason this question has me intrigued, even though I'm not sure there is a definitive answer.

I appreciate the help thus far

Basic physics. Action has to equal reaction. So, if you want a bullet travelling away from you with a given speed, then there must be a rearward force equal to that forward force. You can absorb it all with your wrist, or you can divert some of that force to run the slide and reload the next round. Either way, the forces are in equal measure.

Force = Mass x Acceleration

So you have F1 which is a bullet of relatively low mass with a high acceleration and it must be equal to F2 which is the mass of the arm, hand, frame and slide moving at some lower velocity in the opposite direction.

KFP wrote: I'm still struggling to understand how the recoil of the slide on a semi auto doesn't result in a loss of energy from the round. Any explanations?

In the case of a 1911, the bullet is out of the barrel before the slide moves.

The Annoyed Man wrote:as we can see from Stephen Camp's own test of a S&W 625 against a Sig P220, with one load the revolver was 26 fps faster than the semi-auto, and with the other load, the semi-auto was 14 fps faster; and the difference between the slowest revolver load and the fastest semi-auto load was 60 fps in the semi-auto's favor, and the difference between the slowest semi-auto load and the fastest revolver load was 73 fps in the revolver's favor.

Well, if I understand this correctly, then maybe the issue here is that in the case of a 5" barrel semi-auto, that's 5" from the end of the chamber to the end of the barrel, while with a 5" revolver, the measurement is just the barrel and does not include the length of the "chamber" (cylinder). So it is possible that a 5" revolver might have up to 1" more effective barrel length than a 5" semi-auto.

There are a bunch of other factors that I assume would make a difference as well, such as rifling, useful length of the barrel, etc. It is possible that the rifling has more effect than the length of the barrel within some range of barrel length. And also some research I have read for .45ACP (briefly scanned, I am no expert) suggests that the point at which the barrel length ceases to add to velocity (and may indeed add drag and decrease velocity) is around the 4.5" point, so it is possible that 5" test barrel length may not be the best comparison. A 3" revolver vs. a 4" semi-auto may be a more apples-to-apples comparison, if rifling can be considered the same (such as, use Smith & Wesson revo vs. SA).

Anyway, the physics theory would be that the gap in a revolver is sufficient to make what should be a noticeable, if not significant, reduction in velocity, if all other factors can be held equal (which they probably can't).

The fact remains that for the most part, semi-automatics fire different ammunition than revolvers so it further makes this sort of a moot point. 9mm vs. .38SPL or .357sig vs. .357mag make sensible comparisons but they are really completely apples to oranges.

As promised here are some comparisons between two identical guns. I took both my S&W M&P 40 pistols and an assortment of ammo to the range today. I shot them over an Ohler 33 chronograph at 15 feet. These are averages of three shot strings.

Pistol #1 is the newest it was bought this spring. Pistol #2 is about 18 months old.

Pistol #1
Federal 180 gr Hydrashock 954 fps

Pistol #2
Federal 180 gr Hydrashock 940 fps

Pistol #1
UMC 180 gr jhp 994 fps

Pistol #2
UMC 180 gr jhp 965 fps

Pistol #1
S&B 180 gr fmj 941 fps fps

Pistol #2
S&B 180 gr fmj 906 fps

Pistol #1
Federal Classic 155 gr jhp 1125 fps

Pistol #2
Federal Classic 155 gr jhp 1109 fps


The difference in velocity was ~ 1.5%. Is this enough to cause me concern? In a word NO. There can be as much as 10-15% difference shot to shot from the same box of ammo.

I also found the standard deviation in each string to be less with pistol #1. Maybe a tighter bore or #2 has a slicker bore who knows? Made for an interesting day at the range.