I decided to try a variable optic on one of my AR pistols and ordered the Trijicon Accupower 1-4 with the red segmented circle reticle. The reticle is matched to the 55gr XM193 out of a 16" barrel but the gun it will be used on is a Colt 6933 with 11.5" barrel.

I've never really used or paid much attention to BDC stuff, will having a shorter barrel noticeably affect the holdovers? I'm probably losing 400 FPS or so compared to a 16" barrel (just a guess) so I'm thinking the holdovers will probably be useless on this specific gun.

use standard velocity and trajectory in ballistics program to compare to velocity and trajectory for your length barrel.

Someone made a chart for barrel lengths in gun magazine and I'm sure you can find info with google.

You can download a ballistics program and figure out where the trajectory should be with different rounds in different barrels.

See what MV others get from their barrels.

Find the subtensions of the reticle.

Plug details into a ballistic calculator and compare.

I estimate 3 MOA more drop and MOA more drift at 600yds.

I ran a m193 load for 2750 fps on strelok pro. with a 50 yard zero adding 1 MOA in elevation the holdovers with accupower reticle came out to be 315 yards (@3), 389(4), 467 (@5).Theres no way to know for sure until you shoot it yourself or chronograph your m193

I'll probably just use the holdovers as a reference to get close with whatever I'm shooting. The more I shoot the more muscle memory I'll gain knowing where the hits will be. I typically never shoot M193 simply because M855 and Mk318 Mod 1 are so much cheaper locally, but they're both 62gr obviously.

I may just run a MRO dot on the 6933 and move the Accupower to my 16" 6920 does the road anyway.

I reran it with m855 at 2600 fps. 50 yard zero with 1.25 MOA elevation added. (I believe accupower has 1/4 MOA clicks) Holdovers are at 313, 390, 476 again out to 500 yard holdover.