50yd IBSZ: 62gr --> 77gr

[ABNAK]

I always zero using the 50yd POA/POI zero (IBSZ), and I always use M855 62gr "green tip" when doing so. Without zeroing specifically for Mk262 77gr (5.56 NATO full power load, not .223), what would be the difference trajectory-wise if I slapped in a mag of the heavier stuff? Is there much variance within the 50yd-to-220meter window that the IBSZ is good for?

[MikeDawg46L]

Not much and you can use any of the online ballistic calculators to see the difference in trajectories through a wide range of distances.

The difference in trajectory is going to be dependent on velocity, not necessarily weight of the projectile. You will need some info to plug in to the calculator, such as muzzle velocity, ballistic coefficient, sight height over bore, etc.

I'd say off the top of my head they would be within an inch of each other out to 200m.


Tapatalk'd

[vicious_cb]

I always zero using the 50yd POA/POI zero (IBSZ), and I always use M855 62gr "green tip" when doing so. Without zeroing specifically for Mk262 77gr (5.56 NATO full power load, not .223), what would be the difference trajectory-wise if I slapped in a mag of the heavier stuff? Is there much variance within the 50yd-to-220meter window that the IBSZ is good for?

You POI would be completely different to the point where you should worry more about whether you POI shifted left or right rather than the difference in trajectory. Why not just zero for the ammo you are going to shoot?

[ABNAK]

You POI would be completely different to the point where you should worry more about whether you POI shifted left or right rather than the difference in trajectory. Why not just zero for the ammo you are going to shoot?

Left or right deviation, huh? Why would that be? I can see up or down but the windage too?

Reason is that in my "rainy day" ammo can I have 1K rounds consisting of Mk262, TAP T2, Mk318, and SSA 70gr TSX (the "brown tip" stuff in the military). Instead of zeroing one weapon for X, another for Y, and yet another for Z, I was thinking that if I zeroed all with M855 I could "wing it" with reasonable accuracy if I needed to reach into the stash. I'm not talking a gnat's nuts at 500 meters but COM shots out to 300 or so.

[MikeDawg46L]

Left or right deviation, huh? Why would that be? I can see up or down but the windage too?

Reason is that in my "rainy day" ammo can I have 1K rounds consisting of Mk262, TAP T2, Mk318, and SSA 70gr TSX (the "brown tip" stuff in the military). Instead of zeroing one weapon for X, another for Y, and yet another for Z, I was thinking that if I zeroed all with M855 I could "wing it" with reasonable accuracy if I needed to reach into the stash. I'm not talking a gnat's nuts at 500 meters but COM shots out to 300 or so.

Those were my findings as well according to the ballistics calculators. 2900 fps for M855 vs 2700 fps with my 69gr loads were only off by 3-4" at 500 yards IIRC.


Tapatalk'd

[Failure2Stop]

I have seen significant discrepancy between different types of ammo. The ballistic differences are minor compared to the actual zero shift.
Changing ammunition will generally still keep you within a head at 50, but that's not what I would want to rely on if I needed to take a low-percentage shot. Generally, I zero with my "real" ammo (be it precision or duty type), and then check my offset with my close-range training ammo.

[HKGuns]

It really depends on your objective. You will be minute of bad guy out to 200 yards. You won't want to shoot a match without adjusting your sights a bit.

I always verify at the range using 50 - 100 - 200 yards for verification.

[sinister]

It's not a zero until you've shot and confirmed it at the range you intend to shoot it.

I've seen MOA shift on the same target, same range, same weapon at 300 Meters just by changing bullets weighing 5 grains more (following one magazine with a mag filled with another projo). Ogives and bullet length can do that.

[MikeDawg46L]

Elevation shift I understand completely as it's the velocity of projectile that changes trajectory. However I do not understand how you would get a change in windage between two different cartridges that would render one cartridge unusable with another cartridge's zero.


Tapatalk'd

[sinister]

Try it. Different ogives can cause a left or right shift.

You may not see or note it if you're only shooting at 25-50 yards.