Some of his observations sound good but not all. Lots of playing around with twist in muzzle loaders. (I asked about his on the Yellow Forum but didn't seem to get a reply.) Basically, the Greenhill Formula says that the closer the bullet length to bore size, the slow the twist required to stabliize it. Those long .30-06 spitzers he shows require about a 1:10 (one full revolution in ten inches) rate of twist to stabilize them because they have a lot of intertia to overcome. More speed, alone, will not improve bullet performance. If you have a slow rate of twist and go for greater speed, it is possible to have the projectile "strip out" or "trip" over the lands, resulting in a lack of rotation and, hence, destabilization.
As I mentioned, rate of twist is something I have been wondering about lately, especially in Benjamin Sheridan Blue Streaks. Long ago, the only .20 pellet for these was the old "ash can" profile. (Very much like a Minie ball of Civil War fame.) Now, everyone says these are inaccurate, can keyhole, et cetera, and that the diablo pellet style is superior. I asked if the older Sheridans had a different rate of twist. Heck, since diablos are relatively new, what is the rate of twist in a pre-war or early post-war Diana? Guess they had to shoot cylindrical pellets, too.
As to marks or scorings on the surface of the pellet, it has been demostrated that you can hammer the nose of a bullet out of shape and still have reasonable accuracy. However, mess with the bae of an, otherwise, perfect bullet and you have groups opening up all over the place. So, the pellet's frontal area is not so critical. Perhaps that is why a dented base which does not fully open into the rifling causes shots to go off the mark.
If anyone has rates of twist for the different Diana's it may be fun to play with the Greenhill Formula to see if you can establish which pellets might prove best in a certain gun. Also may explain a bit towards why heavy pellets do so well in high powered guns.
[FWIW, the Greenhill Formula is not cast in stone. The constant value as published is good for a certain range of high powered rifles. If you push the speeds up as in wildcat cartridges, or slow them down as in black powder guns, you have to fiddle with the constant to make it work.]
All I said was I thought some might enjoy this I did not say I agreed with all of it any more than I agree with all of every thing posted on this form .Digest what you want and through the rest out .Marvin
Just a couple of observations on his observations. Did get a very good response to my post about the Sheridan rates of twist. Go dig it up on the Yellow. Fellow posted a very nice 1.10" hundred yard group - with his late 60's Blue Streak!
When you boil it all down and have done the hour's of computer simulations, calculations, equations and frustrations, it ends up that the most accurate pellet for your gun is the most accurate pellet for your gun. (That make any sense, LOL?) What I mean is, hands on experience trumps theory every time.
the author talks about many issues comparing .22 rimfire to .22 air rifles, talking about twists turns in barrels' and pellets
my turn here guy's;
the only things' imo is the breech size, choke barrel and pellet. these 3 things are what accuracy is all about in air guns. nice observation from him about different DIE's from Crosman which to him and I agree is like getting different pellets from the same company. I stll stand by die # 7 from crosman
breech and choke will when not done with proper tolerances be either small or to big. EX. my 460 swallows the CP, still a snug fit but seats itself very well, then my 48 is the opposite, tight fit and needs help to push it in all the way. the 48 blows some of the skirt lead when shoot. i find deposits outside the breech area, tiny slivers of lead
in conclusion, the three factors I wrote about are very important to keep the wobble flight of the pellet at 85% which to me is fantastic and the author does a fine job at this
he did not go into details of the wobble of the pellet but there are 2 factors that create this effect. Precission which is the "cork screw" travel of the pellet and Nutation which creates the "wobble". anything less than .85% of these two effects in the pellet flight will hurt accuracy
warren
and remember "it's 30% the gun and 70% the shooter"
Used to have to set torpedo gyros by hand when changing lattitudes to offset the precession effect. Had a chart that showed by how much an uncorrected torpedo would go off course. I believe it is to the right in the northern hemisphere. You have to go the other way below the equator. Whichever way your toilet flushes.
Now, do we have to hold slightly to one side to correct for this? Are scopes zerod at the equator going to be off in New York? (Bet they will be, if only fractionally.)
Please, we have enough to consider without adding this! Once we have set up and corrected for every eventuality, it will be too dark to shoot.
