So I haven’t run across this issue with my 16” barreled rifles, at least not to this degree.
I train with cheap M193 ball, but our duty ammo is the Win Ranger 64gr softpoint.
I usually use a 50 meter zero, and with M193 ball compared to the Ranger soft points from a 16” barrel at 50m there seems to be little difference… at 200m the 64gr seems to hit an inch or so higher than the 55gr. I attribute this to the 64gr retaining velocity and maybe a bit more oomph from the better ammo.
However, at 50m with the 7.5 barrel the difference is over an inch and a half, the 55gr shooting much lower than the 64gr. I literally can’t get both to shoot to the same POA at 50m. Haven’t had a chance to shoot at 200m but I assume the difference is huge.
I’m unlikely to shoot the 7.5 pistol in the line of duty. So, my plan is to zero it to the M193 ball and figure out what the actual far zero is with this barrel and that ammo and forget about shooting the duty ammo with it.
…unless somebody can think of something I haven’t thought of?
Different guns shoot different ammo differently. I know that sounds weird, but I have had some rifles that have minimal POI changes between different ammo and some rifles that shift noticeably more when I change ammo. I’d say zero with the ammo you would use when it matters, and learn your offset with the cheaper ammo. You may not notice a difference if you are just blasting full size steel targets, etc
It’s not uncommon for heavier bullets to print higher, especially at short ranges. Lower velocity and higher recoil means the barrel is in a different position when the projectile leaves the muzzle.
Like noted above, different barrels shoot differently.
Since heavier bullets are generally moving slower, the barrel has more time to move up during recoil and before unlocking. It’s why .357’s usually strike lower than .38’s
That’s what I was thinking. It’s been my experience that when zeroed with 62gr, 55gr will print a little higher out to 200ish. Always assumed it was due to the higher velocity of the lighter bullet, at that stage.
(And vice versa, if zeroed with 55gr, 62 would be low. All this of course depends on loads, and individual guns, YMMV)
OP, what I do is, zero with the load I intend to use most in that particular gun(s), and learn your offsets for other loads.
I shoot run and guns regularly. The shooters that win are all shooting 16”+ guns. You’re not doing yourself any favors with a 7.5” bbl. I know this is crappy to read, but a 7.5” 5.56 gun is, in my opinion, nearly useless.
Projectiles go in weird directions, and they’re basically unpredictable: thus the reason we have to zero for each different ammo type, and even per lot.
The direction and degree of deviation in comparison is not consistent between factors such as projectile weight or velocity (except at the extremes).
He is 100% spot on. You never know what barrel will shoot bullets crazy. We shoot 77grain SMK’s and 62 grain softpoints and they print very close in almost every gun. But I have one AR that shoots the 62’s 6 inches high and left. Its like WTF. Multiple others spot on.
I think your plan to dial in your 7.5 with your Lake City to play and have fun is fine. Make a note of the offset, just in case. And have your duty weapon dialed in with duty ammo. But for slapping steal in CQB environment both guns will do just fine, an inch here & there don’t mean shit when shooting a bad guy inside your house.
This is the reason, after I zero with my primary HD ammo, I shoot my other ammo types. I then note the deviance from my primary, and put it on a notecard, along with the date. The notecard goes in my grip so if I were to run out of my primary ammo, I know how my back up ammo types shoot.