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Velocity/Energy of bolts v. semis(30'06)

Discussion in 'Rifle Country' started by Col. Plink, Jul 15, 2009.

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  1. Col. Plink

    Col. Plink Member

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    Hey y'all,

    I have a bolt action 30'06 and a Garand, and wondered how much dropoff in velocity and energy there is between the two shooting the same ammo (not that I am, CMP says new ammo up to 180grain is OK but I'm sticking to surplus 150 except a few pops).

    I know that semis use some energy to cycle the round, perhaps more so with a gas-tube action? Just wondering what the commonsense opinion is. Thanks!
     
  2. MTMilitiaman

    MTMilitiaman Member

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    I would and do expect 100 to 200 fps drop off in velocity from my M1A with its 22 inch stainless, medium contour barrel verses a bolt action. For example, I expect around 2700 fps from a standard 147 gr ball round verses about 2900 from a good bolt gun, or 2500 fps for a 175 gr SMK, verses closer to 2700 for a bolt gun.

    When reloading for gas guns, esp the M1/M14/M1A, pressure curve and port pressure are at least as important as peak pressure. Powders must be kept within a certain burn range to insure that both peak pressure and port pressure are within spec. Powders that burn too fast have a tendency to spike and approach allowable peak pressures quickly, while possibly not allowing enough port pressure to reliably cycle the action. Powders that burn too slow, including many that are used in bolt guns, usually approach peak pressure more slowly. This allows for better use of longer barrels, but can result in port pressures that are too high, despite having peak pressures well within allowable levels. This can cause violent cycling problems that at the least tend to damage brass. In more extreme cases, you can bend op rods, crack receivers, ect. I remember an account on another forum of a man shooting Hornady Light Mag out of his Garand. A fine rifle became a grenade. The guy ended up with significant damage to his hands and face, but lived to fight another day. His rifle wasn't so lucky.

    I would expect most surplus ammo in the respective calibers to be acceptable in their applicable gas guns, and I usually trust commercially available FMJ ammunition approximating the weight and velocity of standard ball loads to be acceptable as well. For example, I've shot hundreds of rounds of Win, American Eagle, and S&B 147 to 150 gr FMJs out of my M1A without issue. I would also expect specialized defensive and commercially available match ammunition, such as Hornady TAP or Federal Gold Medal, to be okay, due to the popularity of these systems for those applications. All other commercially available ammunition, including all hunting ammunition, is met with skepticism, regardless of its projectile weight or stated velocity.

    BTW, I don't reload for my M1A, yet. I have picked up 1000 pieces of milsurp brass in preparation for doing so, and have been doing some reading. You might find this article, copy and pasted from Fulton Armory's website (M1 Garand Frequently Asked Questions), helpful:

    http://www.fulton-armory.com/
    Note that I am still going to reload for my M1A at some point. But this article was eye-opening for me, and so acknowledging my limits as an amateur reloader, I am going to wait until I have more experience, and all the necessary tools, dies, and measuring instruments. My dad also has a tendency to load things "hot," as he is a fan of milking every single FPS he can from every single firearm and load he shoots. This isn't a practice I endorse or encourage, so he won't be loading for my M1A, ever.

    Here's a guy with some experience on the issue that isn't so pessemistic about reloading for gas guns as a whole, while still acknowledging the inherent associated risks involved. Note that while the article is about loading for the M14, I would expect much or most of it to be applicable to the M1 Garand as well:

    http://www.zediker.com/downloads/m14.html
     
    Last edited: Jul 15, 2009
  3. USSR

    USSR Member

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    There is simply no way to know, unless you run it thru your chronograph. Example: I have two .30-06 match rifles. Both have 26" barrels. With the same load, one gets 2875fps, while other does 2950fps. However, assuming your bolt action rifle is a factory rifle with the same 24" barrel length that the Garand has, and you are using Garand suitable ammo in both, you are unlikely to see much more than 100fps difference between the two. But this brings on the question, why seriously download your boltgun by shooting the Garand ammo in it? The .30-06 boltgun is capable of much greater performance when freed from the port pressure constrained Garand ammo.

    Don
     
  4. Col. Plink

    Col. Plink Member

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    Right; not gonna bother shooting my surplus ammo in the bolt action, it has its own food supply. It kicks like moonshine, though, even with a Limbsaver. A nice buy at $250, though (WalMart, Mossberg 100ATR synthetic stock). Light, accurate, dangerous on both ends!
     
  5. Jim Watson

    Jim Watson Member

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    The gas port on a Garand is so near the muzzle, I doubt you would be able to detect a difference. As USSR describes, there is enough difference between individual barrels to mask the effect of gas diverted to auto operation.

    If you really wanted to know, I guess you could get one of those adjustable gas plugs or blocks for an auto so you could compare the same ammunition in the same barrel with the port completely cut off versus open for autoloading.
     
  6. Vern Humphrey

    Vern Humphrey Member

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    Absolutely 100% right.

    The muzzle velocity of the Garand is governed by the loads for which it was designed -- which are around 200 fps below what we come to expect in modern ammo, loaded with slower burning powers -- not by loss of gas pressure to cycle the action.
     
  7. rcmodel

    rcmodel Member in memoriam

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    It can be tested in the same exact barrel in any military rifle with a gas shut-off for firing rifle grenades.

    Tests I have seen using the M-14 show no measurable difference in velocity at all with the gas system shut off.

    The bullets are long gone down range before the action even begins to cycle.

    rc
     
  8. Vern Humphrey

    Vern Humphrey Member

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    You can also shoot the M1 wth the gas cylinder removed, if you're curious about possible muzzle velocity loss.

    The M14, with it's internally vented short-stroke gas piston uses very little gas, in any case.
     
  9. Gaiudo

    Gaiudo Member

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    That article from Clint..... another example of him, while still uneducated on the process, making gross claims. This is kinda par for the course with him. Regarding shooting warnings: you will get every malfunction listed above from factory ammo as well. Wear eyepro every time, and be careful.
     
  10. stubbicatt

    stubbicatt Member

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    Vern Humphrey: If you removed the gas cylinder from a Garand, you would have done nothing to prevent gas from diverting through the barrel port, would you?
     
  11. Vern Humphrey

    Vern Humphrey Member

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    Take a look at how close the gas port is to the muzzle. By the time the base of the bullet uncovers the gas port, the nose is nearly at the muzzle.
     
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