Smallbore Ballistics

[John Ceglarek]

I shoot two rifles in smallbore silhouette...Anschutz 64MSR, and a CZ452 Silhouette.  Both guns have the same scope on them, and use the same rings.  I've noticed when I sight these rifles in, I get the same ballistics at 40m (zero), 60m, and 77m.  That is, I can use the same sight settings for both guns.  However, at 100m, the Anschutz requires 1.5 inches more elevation than the CZ to be centered on the target.  I'm shooting standard velocity match ammo, and when I chrono it I get about 8fps more at the muzzle with the CZ than I do with the Anschutz.  But that's nowhere near enough difference to account for 1.5 inches at 100m.  Any ideas?  It doesn't really matter, I just use the settings that work...but I'm curious as to what may account for the difference.

Thanks,

John

[lucky guy]

Do the barrels have the same length and twist rate?

[John Ceglarek]

They are not the same length...the CZ has a longer barrel (22.5 inch, 1/16 twist vs 21.25 inches for the Anschutz).  I don't have the twist rate for the Anschutz.  Why...what are you thinking?  I thought POI is just a function of velocity, and if the starting velocities are similar I don't see why barrel length matters?

John

[303Guy]

Have you checked the ballistic calculations?  You may find that the small difference in muzzle velocity puts the slower bullet into the trans-sonic zone that much sooner, causing an exaggerated velocity difference down-range.  Maybe???

303Guy

[Jerry G]

The distance the center of the scope above the center of the bore is the first thing that comes to mind.  The same rings doesn't mean that the c/c is the same.  It probably is a combination of factors and not just one thing.

I also assume you are talking about shooting off sand bags, not off-hand.