of the people I know with them, roughly half are 1/2MOA and half are 1.25MOA rifles with factory ammo. Mine happens to be one of the 1/2 MOA (and I'm talking 5 round groups at 600 yrds) but it's apparently pot luck.
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Out of the few people I know that shoot the 1,000 yard line, none of them use factory ammo. They reload thier own brass, not to save money, but to use cartridge data made especially for long distance shooting. They spent a lot of time developing these long range loads, and are tried and true with those guys. I personally have only shot my rifle at 600 yards, half that distance, and still had to load my own ammo to get the most potential out of my rifle. We stop using factory ammo at 300 yards. After that, sometimes a better bullet, more powder, the right primer, and the correct combination of these components give you the edge your looking for, especially in an AR. But be warned, that long range ammo don't fit in you magazine. The C.O.A.L. is too long and it must be fed one round at a time into the rifle. Hence the term "slow fire Prone" I personally don't know how "semi-auto" is going to pay off for him otherwise, with factory ammo and a full magazine? Unless he just want to see how fast he can send em' down range. Oh, and I hope you got a really big target to shoot at, the ones we use at 1,000 are humungus. And these guys got $1K to $2k invested in high power scopes to say something about the glass they use to see that far. If I was him, I'd stick with the M1A varients, they been shooting them at 1,000 yards for years. I know they work that far out. Just havent seen anybody try to use factory ammo from the service rifles at that distance. I am sure some one does somewhere I guess, but the folks I know don't.