"Best" Zero for Mk 262 with BUIS/RDS?

[essjay]

Curious as to what's "best" for this ammo, since it's got a much flatter trajectory than M193 and M855.

Also, how much of a POA shift would there likely be with M193/855/.223 plinking ammo would likely be at 50 to 150 yards when zeroed for Mk 262? I'm guessing it would be fairly negligible and not require sight re-adjustment.

[supertrooper]

It doesn't matter. Zero for what distance you shoot the most.

[Click Boom]

[essjay]

That looks a lot different from the chart I'd been looking at previously.

[Click Boom]

Well it could very well be wrong, in fact it looks like it is, I think they're being too generous with the 55gr BC, but either way I wouldn't zero for a different distance.

[essjay]

Yeah, the other one I was looking at was a straight-up comparison between .308 (not sure what load), Mk262, and M856, all with 100-yard zeroes, using Shooter's Calculator. The Mk262 basically matched the .308 load, with the M855 looking pretty similar out to around 300 and then dropping abruptly. I'll try and post a screengrab later.

[BrianRodela]

What velocity are you using for the 77?

[DRM6000]

What kind of distances will you intend to shoot? I'm guessing that with the RDS the rifle is not intended to be a precision rig. I'd recommend a 50 yd zero.

[essjay]

What velocity are you using for the 77?

I believe it's 2750fps? I'll double-check after I get home from work and post the chart I have.

What kind of distances will you intend to shoot? I'm guessing that with the RDS the rifle is not intended to be a precision rig. I'd recommend a 50 yd zero.

Mostly 100-200 at the local ranges, and less often 300-500 in NF or BLM (assuming I can find a LOS with a backstop that long - couldn't get past 225 on my last NF trip...). And, no, definitely not a precision rig, but I got a good deal on Mk 262 a few months back and would like to use it exclusively for longer range use, since it would presumably be better for that than M193, even with an RDS or backup irons.

[BrianRodela]

Ok, your using the Black Hills OTM match then. With a 100 yard zero, your elevation adjustment for 200 is going to be close to 2 minutes up and 4 1/2-3/4 up for 300 yards. This is a little off from actual MK 262 mod 1 which chronys at 2810-2830 fps. If your looking for a single setting for iron sights, the 200 will probably give you the most bang for the buck if your shooting within 300 yards as it will be a little high at 100 and a few inches low at 300.
Mind you, this data is from a 20" service rifle.

[essjay]

This is the chart I was going off of.

5.56 77 gr MK
Drag Function: G1
Ballistic Coefficient: 0.362
Bullet Weight: 77 gr
Initial Velocity: 2750 fps
Sight Height : 2.5 in
Shooting Angle: 0°	Wind Speed: 0 mph
Wind Angle: 90°
Zero Range: 100 yd

M855 62 gr
Drag Function: G1
Ballistic Coefficient: .151
Bullet Weight: 62 gr
Initial Velocity: 2875 fps
Sight Height : 2.5 in
Shooting Angle: 0°	Wind Speed: 00 mph
Wind Angle: 90°
Zero Range: 100 yd

http://www.shooterscalculator.com/ballistic-trajectory-chart.php?t=ffcf9f57

Ok, your using the Black Hills OTM match then. With a 100 yard zero, your elevation adjustment for 200 is going to be close to 2 minutes up and 4 1/2-3/4 up for 300 yards. This is a little off from actual MK 262 mod 1 which chronys at 2810-2830 fps. If your looking for a single setting for iron sights, the 200 will probably give you the most bang for the buck if your shooting within 300 yards as it will be a little high at 100 and a few inches low at 300.
Mind you, this data is from a 20" service rifle.

Actually, I have the CBC/Magtech load. It's a clone of the Mod 1 loading, from my understanding. I just plugged in 2850 for it into Shooter's Calculator, and it looked like it would drop 2' less at 800 yards, which is way further than I intend to shoot, anyway. It's a 16", regardless, and I doubt I'll be buying or borrowing a chrony for it.

Anyway, I think I'm just going to end up getting a Micro T-2, zero it at 50 and then readjust it for 200 the next time I get out to the 200 yard range, and see how it does.

edit: Now that I've realized how to actual use SC (and am home on my PC, instead of on a cellphone), I came up with this: http://www.shooterscalculator.com/ba...php?t=da318596



Much easier to understand now, and, yeah, 50/200 looks like the way to go - theoretically only a 1.5" difference between the two at 600 yards. And the M855 50/200 lines up decently well at my normal plinking ranges, too.

[BrianRodela]

Great research and data usage. If your calculator has the function, change the drag function to a G7 and input the BC for using a boat tail bullet. The G7 BC for the 77 SMK is around 190. For shorter distances, it may not matter much but over greater distances, it will give a little more reassurance to the shot.

[essjay]

FWIW, the original 100-yard zero data for both the 262 and 855 was taken from a link I found awhile back on M4Carbine.net. I just modified it to fit my "needs" a bit better. I'll definitely try to plug that data in and see how that effects it.

[SuperSet]

It depends on the barrel. My Noveske 18" loved 77gr SMKs but my Voodoo 16.5" shoots 55gr FMJs better.
For my Noveske shooting 77s with a 200yd zero, my 55s diverged about 3" left and 3" down.

[timbo399]

Interesting data being posted on this thread, very helpful.

I was annoyed at myself because I always exclusively used Federal XM193 past 5 years for my ARs but loaded up on some Federal/AE .223 55gr.

I was wondering how much the POI would really change between the 55gr 5.56 and 55gr .223. Yes I understand all the differences between the 2 rounds as far as Federal XM193 having higher pressure/velocity than Federal .223 55gr as well as thicker case, tad longer overall cartridge, etc- But think i'm over worrying- I just need to go out and shoot the new stuff I bought and maybe adjust my zero a tiny bit if needed. Can't imagine too big a difference- I'm more of a plinker out to 300 yrds using irons. Everything will be just fine.