XM256, XM256E1 question

Weights are for the full cartridge.

I have one FA65 that weighs 310.2 grains. Believe this to be XM256
I have 3 FA66 that weigh 316.4, 316.5 and 319.2 Believe these to be XM256E1 but what’s with the heavier round?

Jestertoo, and for the rest of us: what caliber is being talked about???

Sorry ! 7.62x51

According to HWS III:

The initial reduced recoil XM256 cartridges used the forward 82-grain projectile (FAT 92) from 7.62mm NATO duplex rounds. These were loaded into ⊕ FA 66 cases.

Accuracy issues arose due to the cavity in the back of the FAT 92 projectile, so they made a projectile without the cavity which weighed 90 grains. Cartridges with this projectile were designateed XM256E1. HWS indicates that these were loaded into F A 6 6 cases and at least one pilot lot was loaded into ⊕ FA 67 cases.

Both projectiles were also tested with aluminum cases.

My bad. The lighter weight is FA 66, the heavier ones are FA 6 6. Thanks for the correction.

Any idea as to the almost 3grain difference in the later version between the two at 316 and the heavier one at 319? No outward differences.

I’ll have to dig my examples out and see how they compare. Off the top of my head I don’t have an explanation for the difference. I have no idea what the manufacturing tolerances were for the various components, although 3 grains would be about 1% which seems a little high.

For what it’s worth, my ⊕ FA 66 round weighs 310.6 grains and my F A 6 6 round weighs 315.6 grains.