If you have a scope with a BDC calibrated for a 62 gr projectile out of a 20" barrel, how close would the calibrations be for a 55 gr projectile out of a 16" barrel?  I'm thinking that the lighter bullet will negate the velocity loss due to the shorter barrel.  How do the ballistics of a 62 gr NATO projectile out of a 20" tube compare to a 55 gr NATO projectile out of a 16" tube?

Thanks,
Bradd

Go to [url]http://www.realguns.com/[/url], and look for "ext trajectory calc." You'll need to input the Ballistic coeffecient for each bullet (.243 for M193, .304 for M855), the muzzle velocity for each bullet from each barrel (from the tech section at [url]http://groups.msn.com/TheMarylandAR15ShootersSite[/url]), and the height over bore of the sights you plan on using.


I do the same thing all the time lately, trying to decide which ACOG I need to get. (leaning toward the TA01NSN)

I used to do the same thing, too, until a friend (w/ a great deal more practical experience than myself) pointed out the frivolity in such thinking.  Per the Trijicon FAQ, they estimate that the difference will be within the thickness of the stadia lines anyways.  The true factor to consider is your own ability to judge distance/range.  Really, how good are you at judging whether your target is at 400m or say 425m?  The width of the stadia lines are a good built-in WAG, but a rather crude one at best as the premise is based solely upon the talents of the individual utilizing it.

First off...thanks, Zardoz, for the great links!  After crunching some numbers, it appears that my suppostion is true to about 300 yds or so.  Actually, the 62 gr out of the 16" tube is almost identical to the 55 gr out of the 16" tube to about 400 yds.  Then the 55 gr starts to drop dramatically while the 62 gr maintains about half the drop of the 55 gr.  It appears that I'd be better off using 62 gr.  Even at 800 yds I could put the crosshair on the top of a man's head and hit him in the chest.

Thanks,
Bradd