50yd IBSZ: 62gr --> 77gr

[MikeDawg46L]

I've tested my 69gr loads against M855, which is what my scope is zeroed to (Mk6 CMR-W). Shooting 6" swingers at 300m, both were on using the reticle BDC. Not a precision check by any means, but more than useable. Maybe I got lucky?


Tapatalk'd

[T2C]

I am going to wade in on this. Zero your weapon with your primary ammunition, then note the change in clicks of elevation and windage for other ammunition and write it in your rifle log. If you are zeroed for 77g and want to shoot 62g, dial in the correction noted in the log.

You may not notice much difference at 50 yards, so in my opinion you should check the difference between zeros at a minimum of 200 yards before making log entries.

[Onyx Z]

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.

The barrel harmonics react differently to different bullets and bullet weights. Gravity is not the only factor in play.

[user]

Ballistic AE will easily allow you to see the differences in zero'd load and the 262. Check it out. I use it on iPad & iPhone.

[ABNAK]

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.

I'm certainly not doubting you, but if a bullet had a left or right shift from the muzzle you could theoretically never zero it except at a specific range, right? Because any shorter or longer than that specific range the bullet would be left and then right (or vice versa) of the target. Not trying to split hairs but I can't wrap my head around that concept! In the vertical plane you can use hold-overs/unders.....what the hell do you use for a continually left or right shifting bullet?

I hope I'm explaining my conundrum on this issue adequately.



ETA: a bullet will fire in an arc up and down as it goes forward, given that the sights are angling the weapon to hit at a desired distance. Since a bullet shifting left or right would also be expected to move in an arc as it spins (?) and not in a straight line, you would have a continually widening variance from POA as distance increased, i.e. it wouldn't be linear and therefore not able to adjust for indefinitely with your sights/optic.

[sinister]

M118LR from a 22-inch AR-10T will group center on an E-type at 300 Meters.

Change mags to 180-grain Nosler Ballistic Tips and the entire magazine will print 3 to 4 inches right of your zero.

Load a 20-inch M16A4 with 62-grain M855 or 69-grain Sierra Match Kings at 300 on the same E-type. Change magazines to 77s and you'll see a group printing right as well.

It's only a zero if the center of the group is in the center of the target for that range and ammo.

[ABNAK]

M118LR from a 22-inch AR-10T will group center on an E-type at 300 Meters.

Change mags to 180-grain Nosler Ballistic Tips and the entire magazine will print 3 to 4 inches right of your zero.

Load a 20-inch M16A4 with 62-grain M855 or 69-grain Sierra Match Kings at 300 on the same E-type. Change magazines to 77s and you'll see a group printing right as well.

It's only a zero if the center of the group is in the center of the target for that range that ammo.

Gotcha. Just kinda rocks my ballistic world thinking about it. So to extrapolate, *in theory* when you adjust a scope (even with the same round) say from 300 to 500 meters you would also have to make a windage adjustment as the round would continually drift farther to the right of LOS the farther out you go (I assume to the right given the RH twist on U.S. barrel rifling)? Assuming no wind of course.

Just boggles my mind as I've always thought of range adjustments as simply in the vertical plane! Pathetic it's taken me all these years to find this out.

[sinister]

Esoterica like drift is really a minor consideration (unless you're changing types of ammo -- tracers are longer than ball).

Artillerymen and mortarmen correct for drift. For a sniper shooting 7.62, 30-06, 300, or 338 Lapua you're only talking 1 MOA at 1,000 yards. Drift will bite you in the ass once you're past 1,000 if you're trying for a first-shot hit.

[ABNAK]

Esoterica like drift is really a minor consideration (unless you're changing types of ammo -- tracers are longer than ball).

Artillerymen and mortarmen correct for drift. For a sniper shooting 7.62, 30-06, 300, or 338 Lapua you're only talking 1 MOA at 1,000 yards. Drift will bite you in the ass once you're past 1,000 if you're trying for a first-shot hit.

That one I should know! (see sigline) Actually not for the smooth-bore 81mm's but the Four-Deuce was rifled (yeah, dating myself) and it was accounted for.

The way you explained it was quite helpful, thanks. So drift does occur but it is a minor issue unless changing ammo types, which is primarily a factor of bullet length and not *necessarily* weight. Also, extreme distances will need for it to be accounted for.

[sinister]

Check. For normal ranges you'll hardly notice. Going from a light to heavy (say 55s to 75s/77s) you might be a half to a minute right at 300 meters -- 3 inches (big deal).

In mortar talk, switching from an HE to a WP in a (rifled) 4.2 or 120 you may need to compensate left for a little right drift once you get WAY out there.

At iron sight or direct-lay range you may never notice a difference.