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Posted: 10/8/2005 12:23:25 PM EDT
At what range should I zero my Oly Arms upper? It will be for home defense until I can get the mag situation figured out.
Link Posted: 10/10/2005 11:40:12 AM EDT
What is it 'zero-ed' at right now?
Link Posted: 10/10/2005 12:24:21 PM EDT
[Last Edit: 10/10/2005 12:31:46 PM EDT by TANGOCHASER]
It ain't, it's brand new. It shoots about 10 inches high at 50 yards. If I set the sights so the POA and POI are the same at 25 yards, where will the POI be at 5-10 yards and at 50 yards?

Is 15 yards more realistic?

Edited to add; The 5.56, 55gr AR15 round has a POA and POI the is the same at 25 meters and 250 meters. What are the ranges the 230gr, .45 round shares the POA and POI?

(POA- Point of Aim, POI- Point of Impact)
Link Posted: 10/10/2005 8:26:58 PM EDT
Well, I have an Oly upper, and I have yet to figgiet w/ the adjustments. I think you're zero-ed out at 100yds..... if not further. I was hitting steel gongs (200 & 250yds) w/ it using 'cheap' Remington yellow box stuff and I was bearly holding the sights over the target to arc them in....

(Didn't help it was a windy day and I didn't have my usual Winchester ammo....)


What are you using for ammo? I could run some numbers and see it says on the ballistic software, but ti would only be a 'guestimation'.... If ya want me to give it a crack, let me know what ammo it is (manufactuer, bullet weight, velocity.....- or I can look up the info on the manufacture's sight). I'll asume a 20% gain in velocity over the pistol velocity they publish and work from there.....
Link Posted: 10/11/2005 7:33:20 AM EDT
I'm using Winchester white box, 230gr ball mostly. I use Federal, 203gr Hydrashocks for defense. I don't know the velocity of these 2 rounds.

I'd appreciate it if you could run the ballistics for me. Again, I am looking for the 2 ranges where the bullet hits to point of aim. Zeroing at the closest range allows one to aim center mass at all targets out to the farthest range and still get a good hit. Eliminates need for "kentucky" windage between those 2 distances.
Link Posted: 10/11/2005 8:54:29 AM EDT
[Last Edit: 10/11/2005 8:56:46 AM EDT by Mike_L]

... I am looking for the 2 ranges where the bullet hits to point of aim. Zeroing at the closest range allows one to aim center mass at all targets out to the farthest range and still get a good hit. Eliminates need for "kentucky" windage between those 2 distances.

How far from point-of-aim can the trajectory be and still give you a "good hit"? That will drive the "point-blank-zero" that you're looking for.

Federal's site shows the P45HS1 load at 850fps. Using Kaliburz' +20% that would be 1020fps. Using the JBM BC calculator and Federal's numbers I get a BC of .142 for that load.

Putting MV=1020, BC=.142 and a standard sight height of 2.6" for the AR into the JBM trajectory calculator gives:
25yd zero - recrosses at 60yds, +5" (@40-45), -.6" at 65, 6.2" low at 100yds
50yd zero - crosses at 30/50, +2" (@35-40), -1" at 65, 7.0" low at 100yds
75yd zero - crosses at ~20/75, +1.5" (@45-50), -1.3" at 85, 4" low at 100yds.
100yd zero - crosses at ~15/100, +3.6" (@55-60), -3.1" at 115, 5.7" low at 125yds

From those I'd pick the 75yd zero. Keeps it within 1.5" of point-of-aim out to 85yds, and still only 4" low at 100yds. (Out there it's dropping fast though: 6.4" at 110, and 10.7" at 125.)

All of this assumes that the velocity estimate of +20% over Federal's numbers is right. If you use 850fps and the 75yd zero then the mid-range goes up to +2.5" and the 100yd drop goes to 5.9" and 125yds to 15.4".
Link Posted: 10/11/2005 11:32:58 AM EDT
As I read this;


75yd zero - crosses at ~20/75, +1.5" (@45-50), -1.3" at 85, 4" low at 100yds.


If I zero at 20 yards, the round will hit same point of impact at 75 yards. This works. The average center of mass on a human target is 10" wide by 12" high. A 75 yard zero will allow me to shoot center of mass out to 100 yards and still be within a 10"x12" zone.

Thanks for the ballistics check.

Can you do the same chart with a .45 Super round?
Link Posted: 10/11/2005 12:36:04 PM EDT
I told the program "zero at 75yds" and it shows it low before 20yds, .1" high at 20, up to 1.5" high at 45 & 50, then back down to zero at 75yds. Telling it 20yds gave a slightly different trajectory.

According to this thread .45 Super out of a Marlin carbine is 1260fps with a 230gr JHP. Assuming the same BC as the HydraShok this gives:
25yd zero - crosses at 25/80, mid-range +1.1" @50-55, 2.2" low at 100yds
50yd zero - peaks at 50, .5" low at 25, 4.3" low at 100
75yd zero - crosses at ~25/75, mid-range +.8" @50-55, 2.7" low at 100yds
100yd zero - crosses at 20/100, mid-range +2.3" @60-65, 4.1" low at 125yds


If you use the Point Blank Range calculator and a vital radius of 5" (allowing up to 5" high or low) then it says:

.45 Super (MV=1260, BC=.142) -> Max PBR = 151yds, zero at 128yds
.45 ACP (MV=1020, BC=.142) -> Max PBR = 133yds, zero at 112yds
.45 ACP (MV=850, BC=.142) -> Max PBR = 114yds, zero at 95yds

That allows shots to go as much a 5" high at the middle ranges. Shorter zeros drop that mid range down a bit at the expense of being much lower at the longer ranges. If you close up the vital zone to 3" high or low that drops PBR range down to:

1260fps -> 126yds, zero at 108yds
1020fps -> 109yds, zero at 92yds
850fps -> 93yds, zero at 79yds
Link Posted: 10/11/2005 2:20:21 PM EDT
Thanks again for the info. Even though you got a slightly different trajectory if zeroed at 20 yards, it's good enough for the 10"x12" target zone at the same distances. And it's easier to find a 20 yard range around here.

I have access to a range and will verify if i zero at 20, how well it hits at 75.

Thanks again.
Link Posted: 10/11/2005 9:27:59 PM EDT
Well, I guess someone beat me to it......

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