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Old February 4, 2000, 01:13 PM   #1
Adamantium
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This is soemtihng that has been bugging me. In my reloading book they tested several different kinds of gun powders for a variety of cartriges. And the thing that I can't understand, is if powder X and powder Y shoot the exact same bullet at very close speeds, how come accuracy can vary so much? Does it have anything to do with the charge weight, powder quality, or even the gun itself?

Also, is thier any way to be able to figure out accuracy in your gun without actually testing the given powder?

Sincerely,
Adam

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Old February 4, 2000, 01:28 PM   #2
Mal H
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Yes, yes, yes, and no.

There are so many variables that affect accuracy that a large book could be written on that subject alone, in fact several have. Some of the variables involving powders are:

a) If the powder doesn't completely fill a case, it may be ignited at different times and more/less completely depending on where it is in the case.

b) A slow powder may be more accurate because it doesn't deform the bullet as much as it gets going.

c) A fast powder may be more accurate because it burns completly before the bullet reaches the muzzle and doesn't have as big an effect from supersonic gases racing past the bullet just as it leaves the muzzle.

d) A hot (heat hot) powder may affect a lead bullet and its obduration more than a cooler powder.

e) The barrel length can affect accuracy due to c, above.

We can and will probably come up with many, many more, but you get the picture. As for your last question, "is there any way to be able to figure out accuracy in your gun without actually testing the given powder?", I would have to say no, assuming you have no additional data from previous tests (like a reloading manual that says they got the best accuracy from XX powder).

[This message has been edited by Mal H (edited February 04, 2000).]
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Old February 4, 2000, 01:39 PM   #3
Paul B.
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Another point that Mal did not bring up. Your rifle may not like the particular powder that gave the excellent accuracy in the loading manual. I've run into this more than once.
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Old February 4, 2000, 04:35 PM   #4
Mal H
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So true Paul. I think those "most accurate powder" tips do nothing but sell that particular powder. I'll wager that if the same tester ran the exact same test 6 months later, he would often get a different "most accurate".
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Old February 4, 2000, 05:32 PM   #5
Adamantium
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What about Vertical stringing? Is thier anything that really affects that more than not?

Sincerely,
Adam

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Old February 4, 2000, 06:03 PM   #6
Monkeyleg
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Mal, that has to be the most frustrating part of reloading! I can get a load worked up that shoots as good as anything, then go back in a week and it shoots nowhere as good. Maybe I need to lock the gun in a ransom rest to really tell what's going on.

Dick
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Old February 4, 2000, 11:23 PM   #7
Art Eatman
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With no particular evidence, "accuracy loads" seem to generally--but not always--run 100 to 200 feet per second below the maximum load. Why? Yo no se.

As far as the difference between powders, again with no evidence, it seems to be some problem in barrel vibration. For some unknown reason, the vibrations are not quite as uniform from shot to shot as with some other powder. So far as I know, the "best" powder can easily be different for your gun than for mine.

I guess you could call me a "vibrationist" when it comes to accuracy issues.

Every time I've ever run into vertical stringing, the bedding has been at fault. I would first suspect the forearm of the rifle. What happens is that the steel of the barrel heats up at a different rate than the material of the stock. If the forearm presses on the barrel (particularly out near the tip), the pressure will vary as the steel heats.

Some guns will have a rising string; a mannlicher stock is susceptible to a falling string. Barrel bands are Bad Things.

Also, when shooting from any rest, make sure whatever support you use under the forearm is always in the same location. If you sight in without sling-pressure, and then use a tight sling when shooting, your point of aim can be off--which is one reason for a free-floating barrel.

[This message has been edited by Art Eatman (edited February 04, 2000).]
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Old February 5, 2000, 08:56 AM   #8
MontaniSemperLiberi
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Powder certainly does impact on accuracy from all the reasons given above, plus when you change lot numbers of the same powder, you often find differences in performance as well. As individuals, compared to ammo mfg's, powder is sold to us in small lots or 1-8lb container form, whereas the ammo firm purchases powder in large quantities and and have been told that the powder, even though the same type i.e. 4895,4064,etc. acutally is produced to a desired spec within a given range of performance capabilities of that particular powder. Your 1lb. can of 4895 may exhibit considerable different performance over 4895 as sold to an ammunition mfg. Again, I have been told the above and assume it to be true, but perhaps others would have first hand knowledge of this matter.
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Old February 5, 2000, 03:27 PM   #9
Adamantium
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Art: I'm actually starting with .38spl and the .357. Because thier is no stock touching the barrel, would vertical stringing still be a problem? Also, when I do start reloading for rifle it will be my enfield. How would the fact that the stock completely covers that barrel save the last inch affect the problem you described?

Sincerely,
Adam

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Old February 6, 2000, 07:08 PM   #10
Art Eatman
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I've never had any stringing problem with a revolver. That's a lot of revolver, over a lot of years. If it happens, I'd be guessing as much as would anybody else.

On a military rifle--as near as I can tell from some Springfields and an old Model 1917--the barrel and the wood are not clamped real tightly together. If the wood is not pressing hard against the barrel, if the barrel is a bit of a loose fit out at the band closest to the muzzle, vertical stringing should be much less of a problem.

At each shot the barrel heats up a bit more. So, its outside-diameter and its length both increase slightly. (The exact amounts can be calculated very precisely, from such references as "Marks' Mechanical Engineering Handbook", for instance.) The wood changes very little with a change in temperature. So, if any barrel band clamps the wood tightly against the barrel, the barrel is pulled into a very slight arc--and very little is all that's needed to cause stringing.

Hope this helps, Art
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