 |  | | | |  | |  |  | Rifling & Penetration |  | |  |  | |
 Posted: Sun Apr 26, 2009 4:03 pm |
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| cissp22 |
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| Joined: 05 May 2008 |
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well i bought my new air gun named : diana rws 350 magnum classic compact , it has a shorter barrell ..so i sold my previouse 350 magnum ..
i wonder to see 1,5 rate rifling in this gun comparing to normal barrell 2,5 rate rifling.
what riflings exactly do for airguns??? better penetarations?flater trajectory??
i realy didnt noticed any diffrence between these 2 airguns ..
thanks .. |
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| Posted: Sun Apr 26, 2009 6:13 pm |
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| fritz |
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| Joined: 25 Nov 2008 |
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Rifling spins the projectile like a good football throw.
Increases accuracy, wind resistance, and distance. Don't ask me how it work or why, it just does. |
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| Posted: Sun Apr 26, 2009 7:52 pm |
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| TONBON |
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different calibers and bullet weights all have a "magic" twist rate that seems to work best. if you have a 308 w/ the twist rate for heavys, light bullets "generally" wont group.
i dont know what an airgun"should" have as far as twist rate, but i'd like to see some numbers if anyone comes across some
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| Posted: Sun Apr 26, 2009 11:29 pm |
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| Slavia |
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Let's say you have a Beeman Silver Jet (the first pellet for which I found numbers): Mass=8.39 grains, head diameter=0.177," length=0.259."
http://www.beemans.net/pellet%20specs.htm
Using the Greenhill formula, an optimal twist rate for that pellet would be one turn in 18 inches (1:18).
http://en.wikipedia.org/wiki/Rifling
I have only measured two guns - my Slavia 631, and an Avanti/Daisy 853. If recollection serves, the Slavia was about 1:18 and the Daisy about 1:21 - both in that same ballpark.
I measured those two out of curiosity, but have not repeated the exercise. I don't believe it possible to match a pellet to a gun by purely mathematical means - there are too many other factors. While it makes a difference in powder burners, in airguns things like head diameter, skirt diameter, lead alloy hardness, etc. become significant. What's more - "diabolo" style pellets are not only spin-stabilized (as in firearms) but also are drag-stabilized in the manner of a badminton shuttlecock.
While it is an interesting intellectual exercise, I think it makes more practical sense to trust that the manufacturer got it close and then try different kinds of pellets to see which works best. |
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| Posted: Sun Apr 26, 2009 11:35 pm |
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| Amigo |
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ciss:
One analogy for an object spinning and being more stable is the classic spinning top. As long as it spins, it remains on its tip. As the spinning of the top slows and comes to a stop it begins to wobble and then falls over.
The same laws of physics apply to the spinning football, bullet or in this case, a pellet.
Some airgun experimenters have found that somewhere between 1 turn in 12" to 1 turn in 18" is a reasonable range. However, some have been so bold as to conclude 1 turn in 14" as near ideal. Personally, I'll leave it to the manufacturer.
Sorry, but I have no idea what is being referred to when a 1,5 or 2,5 rate is given.
Amigo |
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| Posted: Mon Apr 27, 2009 12:09 am |
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| Slavia |
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| I took it to mean turns per meter - 1.5 turns per meter is equal to one twist in 26" and 2.5 turns per meter is equal to one twist in 16". |
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| Posted: Mon Apr 27, 2009 5:00 am |
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| cissp22 |
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No , i just count the rotation of rifling from both extremes of barrell ...i think 350 std has 2,5 rotations ...
so whats the diffrent between shorter and longer barrell ! ..then both have 1 per 16 inch .....???????? |
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| Posted: Mon Apr 27, 2009 5:10 am |
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| cissp22 |
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sorry i think i was wrong !!..i cant measure the rotations just by looking inside the barrell ....350 compact classic has near 16 inches barrell ...
so it would have just 1 rotation of rifling inside . |
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| Posted: Mon Apr 27, 2009 9:12 pm |
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| TONBON |
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1 turn in 16 is the same wether you have a 16, 6 or 20 inch barrel.
some older guns as well as some new big bore hand guns have gain rifling.
it starts as a 1 in 36(or somthing) and progressivly gets tighter. until it reaches the end rate. 1 in 16 or whatever is recommended for caliber.
it's supposed to reduce twist in some handguns, or prevent softer lead bullets from being shaved by the rifling. |
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| Posted: Mon Apr 27, 2009 11:25 pm |
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| Slavia |
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| I have heard of "gain twist" or "progressive rifling" in connection with older black powder rifles. Does anybody know of an AG that uses it? |
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| Posted: Tue Apr 28, 2009 5:22 am |
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| TONBON |
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probaly not worth it in an AG.
i know they currenly use gain twist in the S&W500 revolvers, maybe the 460's as well.
never shot one, but it is supposed to reduce twist when shooting |
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