My point is 300BO is unlike the other mentioned cartridges because when loading supersonic ammo most bullets will still have a significant jump before engaging the bore. Not all bullets like that much jump… it’s worth testing your rifle’s accuracy with these before getting really pregnant with a large order. Probably will be fine in 300BO, but never hurts to confirm.
This is a big problem with both 300 BLK and H’amr for opposite reasons.
Many bullets still can not be loaded to magazine length in the 300 BLK. Some
Classics are the various 150 FMJ cheap plinking bullets. Better check max loaded length and not trust some of the manuals out there that give COL of 2.260”. Another is the 110 VMax. In a Blackout it hits the lands before it leaves the case, in a bolt action you can load it to jam and have about .065” left in the case.
How many people realize that there is not a single Berger bullet that you can use in the H’amr?
The trim length for H’amr brass is 1.600”. Magazine length is 2.260”. That means max nose length is .660” before the bearing surface of the bullet is below the neck opening. Shortest nose on any Berger bullet is on the 115 fb. It’s .699” I don’t think Berger makes a bullet that can’t be loaded into a standard magazine and used in the BLK.
That leaves a lot of 308 bullets off the table for the H’amr, and a long jump in the Blackout. At least you can load them in the Blackout.
In the BLK the 125 SMK which was designed for the cartridge, has a jump in excess of .200” at 2.260”, while a 175 SMK has about .010”.
So it’s back to careful bullet selection, and why muzzle velocity can be a pointless rabbit hole. The H’amr is destined to shoot short nosed relatively low BC bullets. The Blackout will accommodate most VLD profiles. Many times by 300 yards the velocity difference is minimal or reversed.
Take away the magazine length restriction and the H’amr with more than .100” inch of freebore and close to 5 grains of powder, that’s a 25% increase, and there is no question which should have the better performance.
So when
@Oso, who shoots both says choose your bullets carefully before buying in bulk, pay attention.