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Old July 4, 2000, 09:13 PM   #1
Doctari
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Join Date: March 27, 1999
Location: Lansing, MI
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Hi,

Is there a standard change in fps velocity based on each 1 inch change in barrel length.
I am reloading for some rifles and the manuals I am using are testing out of a 22 in. barrel where as I have a 24in. barrel. Therefore I am having trouble deciding if my velocities are too high compared to the book values.

As an example I am loading in a 22-250 and have a listed max for my powder of 3500fps out of a 24 in barrel. I am not near my max charge but already have 3740fps out of a 26in. barrel. I don't know if I can push my load or am I out on a limb already?

Thanks for any insight,
Doctari
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Old July 4, 2000, 11:12 PM   #2
alan
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Doctari:

I'm NOT familiar with the 22-250, however generally, with any given load, a longer barrel will develope more velocity than the shorter barrel.

A lot of manuals test fire from 26" barrels. Some used "bond receivers", which are strictly test equipment, every dimension being held to minimum. If howrever, a manual indicated that 22" barrels were used, likely that is what they used. Your barrel, being longer, could also be closer chambered (tighter), which might generate higher pressures and more velocity.

I believe that roughly, 1 inch of barrel length is usually worth 25-50 ft/sec, within the normal range of barrel lengths encountered, but I would NOT swear to that.

The velocity situation you described sounds strange, but then, Iam not familiar with that cartridge. As to whether or not you are at or near "the ragged edge", assuming you are using a bolt action rifle, check the following. Are primers cratered and or flattened. Do you experience "sticky" bolt lift, is the bolt difficult to open. Are primer pockets loosening, compared to factory ammunition. Same consideration re other features. How about case head expansion, compared to factory loads.

The foregoing are all indicators or can be indicators of high pressures. Of course, one rifle will take hotter loads than will another of the same caliber, there are always dimensional differences.

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Old July 5, 2000, 12:40 PM   #3
Art Eatman
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Join Date: November 13, 1998
Location: Terlingua, TX, USA
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Variations in velocity with barrel length are a function of cartridge, bullet weight, and the burn rate of the powder. Various articles over the years have me using an *average* number of 70 ft/sec per inch of barrel. I have seen various testings resulting in everything from 40 or 50 on up to 100 ft/sec.

Mr. Hodgdon's 26th edition used 26" barrel lengths; with H4895 he sez 3,827 ft/sec with a 50-grain bullet. The odds are, then, you're not yet pushing the limit--although you didn't mention your bullet weight.

Alan's comments about primer-flattening, bolt-lift, etc., are right on the mark.

If your load is accurate, the next 100 ft/sec you might get won't be noticed by Mr. Prairie Dog, anyway. And your barrel will last longer.

Regards, Art

[This message has been edited by Art Eatman (edited July 05, 2000).]
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Old July 5, 2000, 03:58 PM   #4
Paul B.
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Join Date: March 28, 1999
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Doctari. Alan left out asking if the ejector on your rifle was leaving a shiny mark on the head of the case? That is also a sign of high pressure.
Ken Waters book, PET LOADS, has an excellent first chapter on determining pressure. His load data is good also. When playing with a new powder, I generally look in his book first, and then compare his loads with the manuals. It is also a good read, especially if you load a lot of different caliber cartridges.
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