Do revolvers lose velocity as compared with semiautos?

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Big-Blue

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I haven't been able to find anyplace which dealt with this question, so I hope someone on this forum might be able to answer my question.

Do revolvers lose velocity due to expanding gases escaping from the gap between the cylinder and the barrel?

Or another way of asking the question might be "Does a bullet of the same weight, and with the same powder and weight of powder, shot from a revolver and from a semiautomatic, achieve the same velocity?"

What got me to thinking about this was reading that the same cartridge shot from a 5" barrel would achieve a higher velocity than if it were shot from a 3" barrel. This was due to the increase amount of time the expanding gas had to expand and accelerate the bullet before the bullet left the muzzle and the gas began escaping around the bullet.

Thanks,
 
Do revolvers lose velocity due to expanding gases escaping from the gap between the cylinder and the barrel?
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Yes that's pretty much spot on, the gasses escaping from the cylinder gap is basically energy bleeding out. If you got a 9mm revolver, which they have but aren't all too common, and a 9mm semi auto both with the same barrel length you will see slightly higher velocities from the semi. This is also one of the reasons why revolvers tend to be louder, which is why you see no suppressed revolvers with the exception of (insert model here that I cant think of) that was able to seal off the cylinder gap. They used to use them when clearing tunnels in Vietnam so they wouldn't go deaf from firing a gun in such confined spaces.
 
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There's not a good simple answer for a number of reasons.

First of all, revolver barrels and semi-auto barrels (all non-revolver barrels, actually) are measured differently. Revolver barrels are measured from the forcing cone to the muzzle while semi-automatic barrels are measured from the breechface to the muzzle. So a 4" revolver has a longer effective barrel length than a 4" semi-automatic pistol.

The extra length could mean that a 4" revolver might have higher muzzle velocity than a 4" semi-auto in the same chambering.

Here's an example where a 3.5" Derringer provides significantly slower velocities than a 3.5" revolver.

http://www.ballisticsbytheinch.com/45colt.html

But let's say we eliminate that difference and try to compare apples to apples.

There's still a problem and that is that two different guns, even though apparently identical can provide very different velocities due to relatively miniscule differences in certain aspects of the barrels.

In other words, it's entirely possible that a vented barrel designed to mimic a revolver barrel/cylinder gap loss might actually show a higher velocity than an identical length barrel without the vent.

But lets say we actually get two barrels that are so similar that the only difference is the cylinder gap. Then we would expect to see that the barrel with the gap was noticeably slower than the one without the gap, and that a smaller gap always meant higher velocity than a larger gap, right?

Well, in general that's true, but not ALWAYS, and even when it is true, maybe the difference isn't nearly as much as one might expect.

Here's an interesting graph made by shooting the same revolver with the same ammunition but varying the cylinder gap.

http://www.ballisticsbytheinch.com/magtech1.html

magtech1.png


Note that in some cases the 0.006" gap provided higher velocities than the 0.001" gap and that in several other cases the difference between the velocities provided by the different gaps was negligible.

The same website, if you look at the barrel length section and compare some of the velocities of real-world guns will demonstrate how the velocity can vary in counter-intuitive ways. For example, the 9mm section shows a number of situations where a shorter barreled gun provides more velocity than a longer barreled gun. The Kimber/SIG P210 comparison is an interesting one.

The bottom line is that the loss in velocity due to barrel cylinder gap isn't really a practical issue in most cases. There is an effect, but it's usually smaller than people expect it to be and can be masked, or even cancelled entirely by other relatively minor differences from one gun to another.
 
Conversely, it could be argued that semi-autos lose velocity because a portion of the round's energy is absorbed in pushing the slide back to cycle the action.

Right?
 
Wrong ! If you look at a series of photos of an auto being fired you'll see that the bullet has left the barrel before the slide moves back.
In any case it's a moot point because the ballistic coefficient of the hand gun bullets is low. They all lose velocity quickly.
 
In nearly every test I've seen, the difference in velocity between a revolver and semi-auto is small enough to be negligable even when factors like the difference in barrel measurements are taken into account.
 
As a matter of interest, I have loaded .45 ACP ammo with a 185 gr. JHP bullet that clocked 1290 fps. out of my 5" S&W Model 625, using Accurate powder, the exact powder and weight of charge I don't remember now. Harold Tidwell, then with Accurate Powder, took some of these and tested them in their lab.

The bottom line was these were truly 1290 fps, but I was cautioned never use these in an auto loader.

The resulting recoil/pressure was too great for the rather thin chamber walls, and the recoil energy was too severe for an auto mechanism.

Bob Wright
 
Wrong ! If you look at a series of photos of an auto being fired you'll see that the bullet has left the barrel before the slide moves back.
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Regardless, the energy to cycle the slide has to come from somewhere. And energy can't be created out of nothing, so unless there's a little gremlin pushing the slide back each time the gun is fired, I can't see how the act of cycling the action would NOT detract from the potential velocity of the round.

Ivan
 
Regardless, the energy to cycle the slide has to come from somewhere. And energy can't be created out of nothing, so unless there's a little gremlin pushing the slide back each time the gun is fired, I can't see how the act of cycling the action would NOT detract from the potential velocity of the round.
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The energy does come from somewhere, the recently fired round. Like others said, the bullet is long gone before the slide is starting to retract. There is no energy loss there.
 
The bottom line was these were truly 1290 fps, but I was cautioned never use these in an auto loader.

The resulting recoil/pressure was too great for the rather thin chamber walls, and the recoil energy was too severe for an auto mechanism.
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I rather doubt the explanation you were given. I would think the real reason for not running these in autoloaders is that the typical 1911 barrel does not fully support the case mouth.
 
I hate to get off topic but didn't David Soul use a suppressed revolver in Magnum Force? Was that just Hollywood overlooking reality for the sake of entertainment. I thought the cylinder gap would allow gases to escape and make alot of noise.
 
The energy to function a recoil-operated pistol comes from (duh!) recoil, and that begins when the bullet begins to move. By the time the bullet exits, the slide has already picked up enough inertia to continue the cycle. So the energy to function the pistol is essentially "free", taking nothing from the gas pressure that moves the bullet. In a blowback pistol, the energy to operate the slide does come directly from the pressure in the barrel, but the inertia of the slide is such that it does not move significantly until the bullet has left the barrel, so there also the operation of the pistol does not subtract from the gas pressure in the barrel.

The revolver does lose a bit of pressure at the barrel-cylinder gap, but the velocity loss is usually less than the difference between the velocity of different cartridge lots, sometimes less than the difference between cartridges in the same box.

A note of caution: some folks believe that they can obtain some significant velocity increase by reducing the barrel-cylinder gap, but if the gap is too small, the cylinder may bind from heat expansion after firing only a few shots. The ideal gap is .006"-.007"; the .001" mentioned above is entirely too small and will give trouble.

Jim
 
I hate to get off topic but didn't David Soul use a suppressed revolver in Magnum Force? Was that just Hollywood overlooking reality for the sake of entertainment. I thought the cylinder gap would allow gases to escape and make alot of noise.
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It was the 70's. Accuracy and realism in the portrayal of firearms' use weren't exactly at the top of most television and film directors' list of priorities.
 
Wrong ! If you look at a series of photos of an auto being fired you'll see that the bullet has left the barrel before the slide moves back.
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Not so fast!!! Why use stills when you can use video? As seen in this video, the movement of the slide relative to the frame occurs BEFORE the bullet leaves the barrel. See 3:36 in the video.

http://www.liveleak.com/view?i=eb1_1233417686

So some energy will be spent there, but it is undoubtedly fairly inconsequential given the tiny amount of movement that occurs before the bullet does leave the barrel.
 
robhof

Dan Wesson revolvers also can use supressors and I believe that is what DS used in the movie. The adjustable barrel can be used to minimize the gap and supressors can be used, but not for very many shots as the face of the cylinder gets gummed up and stops rotation.:D
 
I believe I've always read and heard that revolver barrels typically measured from the face of the cylinder to the muzzle, not from the forcing cone forward. Not enough difference to matter, but I did see a study of variation in the actual length of four-inch revolver barrels, and that's how they measured it.

Makes no difference, I'm back to revolvers in my old age and really don't worry about a tiny loss of energy at the barrel/cylinder gap as long as it isn't spitting lead.
 
csmsss said:
I rather doubt the explanation you were given. I would think the real reason for not running these in autoloaders is that the typical 1911 barrel does not fully support the case mouth.
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I think you mean case head. You may be right, but that was the explanation I was given.

As a matter of interest, I did see a Beretta Model 92 blow out the chamber from about mid-case length to the mouth. The case head was still intact, while a considerable chunk of chamber blew out. this was a police issued Beretta and American made 9mm ammunition, the brand of which escapes me now. Never heard the results of any investigation.

Bob Wright
 
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