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Thread: Energy Loss with Semi-Auto?

  1. #1
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    Default Energy Loss with Semi-Auto?

    Hi folks, I have a general question that I've heard a lot of 'urban legends' about over the years, but I'd like to get real answers from you people who actually know something!
    OK, let's look at the simple .22lr as our example. Assuming the only difference is the action, how much are you actually losing (energy, velocity, etc) if you compare a semi-auto to a bolt action or lever gun, something where the bolt is fixed at the time the bullet is fired.
    Same thing with revolver vs. blow-back semi auto, is the energy lost where the cylinder meets the barrel same as energy lost because the bolt is moving rearward? Or are they so close it doesn't matter?
    I've heard lots of opinions, but what are the FACTS?
    Cheers, Dave

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    Funny you should ask about the 22LR.

    I just shot my MK-III hand gun this morning while working on loads with my most accurate rifle. Just for grins I shot 5 shots through the Chrony in normal semi auto mode and 5 shots one at a time while holding the bolt closed.

    The averages where virtually identical. With highs and lows thrown out the averages were the same. I suppose shooting a cartridge with more capability there may be a difference but today's results squash the legend.

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    Yup. The .22 is unique with its blowback action. When it fires, the case swells and 'holds on' to the chamber until the bullet leaves the muzzle. When it does, (talking about milliseconds) the pressure in the barrell starts to lower. At a certain point, the pressure is low enough to let the case 'un-swell' but still high enough to push the action back. That action uniquely keeps all of the pressure that a .22 in a bolt action of the same barrell length would have. Theoretically, a gas-tube operated (ar or ak style) semi auto loses pressure, but not much. I dont own a pair of rifles chambered in the same round and barrell length so I dont know much from personal experience.

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    So for argument's sake, let's say we're shooting a .308 from a Ruger 77 bolt rifle and an AK style Saiga rifle (assuming similar barrel length).
    So the difference will be negligible? I'm not gaining worthy stopping power or range by using a bolt rifle?

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    Member Diesel Nut's Avatar
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    You're not gaining or losing any meaningful performance. Not even close. The difference would be well within standard deviation of the .308 rounds. Gas impingement only takes a very, very small portion of the pressure and redirects it. You'd never know the difference aside from the reduced recoil, which is actually just an increase in time for the same amount of force, thus feeling like less recoil.

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    Revolvers lose a lot of gas between the cylinder and forceing cone

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    Also, the bullet is long gone before the action inertia really begins.

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    Quote Originally Posted by OATS View Post
    Also, the bullet is long gone before the action inertia really begins.
    While this is true w/ certain handguns (1911, CZ75 etc) i am not so sure it is the case w/ some gas operated semi-auto rifles. I do agree with others that the difference in velocity would be negligeble.

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    Quote Originally Posted by Amigo Will View Post
    Revolvers lose a lot of gas between the cylinder and forceing cone
    OK, so let's look at two guns shooting the same round then. If you compare a Desert Eagle 44mag semi-auto and a Ruger Bisley 44mag, is there going to be any noticeable balisitc difference, again assuming same barrel length and so on?
    Amigo, does this loss of gas really make much difference in real-world applications, like handgun hunting? I know most people use long barreled revolvers for hunting, but some serious shooters use Thompson and other one-shot guns.

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    Not enough for me to worry about.

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    I haven't done the chrono work on bolt gun vs. semi auto, but have heard that those who have with an AR-15 vs. a rem 700 say there is no measureable difference in velocity for guns with the same barrel length.

    Concerning revolvers vs. fixed breach, I have tested loads with a 4 5/8" sbh, 7 1/2" sbh, and 10" contender. When you add the cylinder length of a revolver to the barrel, you get effectively a 9 1/4" length for a 7 1/2" barrel, for discussion purposes.

    Anyhow, with the same load which was a 300 gr cast over as I recal 22 gr H-110, the results were 4 5/8" @ 1200 fps, 7 1/2" @ 1300 fps, 10" @ 1400 fps.

    While the contender has more velocity hence more energy, it doesn't turn it into a rifle or double it's range.

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    I have checked 30-06 from M1 and Model 70 and can't tell any measurable difference, barrels are within an inch and the 70 being longer. 45acp from my 1911 auto and 460V revolver also falls within the standard devotion so not measurable. Then there is the recoilless rifles that vent about half the gasses out the back and even that has a minimal effect on velocity. Watch any auto cycle on high speed film and the bullet is long gone before the action moves a lick or you see gas vent from a revolver or recoilless rifle. On the revolver gas loss the Russians had a round that sealed the gap and found the gun preformed the same and was more reliable with trimmed brass that didnít seal the gap.

    Semi auto anything robbing velocity is very much an urban myth in my opinion. However they do require closer load tolerances to cycle properly. Too little or too much gas in the equation and it wonít run right where bolts, levers, pumps, brakes, revolvers, extra will cycle anything because the shooter is doing the work not the ammo.
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    Quote Originally Posted by Paul H View Post
    Anyhow, with the same load which was a 300 gr cast over as I recal 22 gr H-110, the results were 4 5/8" @ 1200 fps, 7 1/2" @ 1300 fps, 10" @ 1400 fps.

    While the contender has more velocity hence more energy, it doesn't turn it into a rifle or double it's range.
    And if you lop the 10" Contender off to 7-1/2" you would likely be close enough that any difference between it and the 7-1/2" SRH would not be measurable and certainly not meaningful.
    Andy
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    If you use breach face to muzzel as a barrel length the revolver will show slower velocities for equal barrel lengths. But in the real world it won't matter much. With autos vs bolt guns there might be a very small difference in a gas operated gun but the difference would be less than the difference between one round and the next in any given box of ammo. On a blowback gun, I don't think you could ever prove any difference. When any two rifles come off the line, one will shoot faster than the other and that difference alone would make any comparison between two different rifles suspect. Some things just can't be answered. How far is up????

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    Quote Originally Posted by rbuck351 View Post
    If you use breach face to muzzel as a barrel length the revolver will show slower velocities for equal barrel lengths. But in the real world it won't matter much. With autos vs bolt guns there might be a very small difference in a gas operated gun but the difference would be less than the difference between one round and the next in any given box of ammo. On a blowback gun, I don't think you could ever prove any difference. When any two rifles come off the line, one will shoot faster than the other and that difference alone would make any comparison between two different rifles suspect. Some things just can't be answered. How far is up????
    good question.... I know that "down" averages 3,959 mi. Beyond that you are once again going "up"...

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    Quote Originally Posted by LuJon View Post
    good question.... I know that "down" averages 3,959 mi. Beyond that you are once again going "up"...
    Or was it going "up" all along...

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