My current optic is zeroed for 55grs at 50 yards on an 11.5inch barrel.
How much will i be off if i switch to the heavy bullets?
I like to train with the 55grs because of cost.
The only way to know is to shoot it and see. Gravity is the not the only force at play.
There’s no way to know without shooting the ammo and finding out for yourself.
With that short of a barrel it is going to be hard to stabilize that heavy of a round. If you want to use that heavy of a round the shortest barrel that you will want to use is a 12.5". If you are just looking at a heavy hitter at 50 meters then go for it. The .77 gr Mk 262 is known to break bolt lugs in 10.3-10.5 barrels.
Doc,
Is there a hypothesis as to what causes the bolt failure with the use of the heavier rounds?
From what I can tell it is because of the higher pressures from that round.
I haven’t seen an issue with stabilization with a 1:7 twist rate in an 11.5" barrel, even down at .223 SAAMI MV.
I have a slightly off topic question. Is there a minimum effective velocity (quoted or just generally understood/accepted) for MK262?
Joe Mamma
Not sure where some of this info is coming from. 
1/7 is way more twist than necessary to stabilize a 77/75. So a 10.5 is just fine with 77s. We shoot this all the time. 1/9 might not work too good at 10.5 however.
Jom Mamma-
I think the minimum effective velocity is around 1500 fps. This is for fragmentation, however. I’ve shot 77s at and just over subsonic, and they’d still likely drop a mofo. They turn sideways and penetrate even deeper than they do when they frag. I tested this twice in plain water jugs and never got my bullets back because the penetration was too good… I only had like 22" if water, and the bullet just left a profile hole in jugs as it passed on through.
How much will i be off if i switch to the heavy bullets?
At what distance? I zero my rifles with 55 gr at MPBR for the round/powder combo.
I have shot both 55gr and 77gr with this zero at 50 yards and the POI was about an inch different.
Just to clearify on the stabilization part. It is to achieve sub MOA groups at 200 plus meters. Most people will not be able to see a differance.
Damn it. Now we have to go test this. A 10.5 with a Nightforce is going to look silly as hell.
Yes it will…
I’d like to see a picture of that rig please!
If we do it, we’ll get pics.
I’m not too worried at 50 yards…but after 100 yards i wonder how much a drop there will be.
POI can shift in any direction when changing ammo.
Yep. We had 77s hitting higher than a lighter bullet just last weekend. This is why I sold off all my M193 stash ammo and went 75/77.
In free-recoil shooting (Benchrest) heavier bullets will hit higher than a lighter bullet when fired at a target at the same distance. This was explained to me as being the result of the heavier projectile taking longer to exit the barrel, resulting in more recoil having occurred by the time the round does exit the muzzle, thus more muzzle rise. I would believe that a shooter who establishes a good/repeatable shooting position would experience similar results.