So, OP,
I’m going down the rabbit hole of building a good PRS rifle and REALLY curious what caliber to build. Really this would be to reach out beyond 1000 yards and at the same time, not rip my face off shooting a ton of rounds.
"PRS" and "beyond 1000 yards" don't mix - at least here in the central Atlantic region. Maybe things are different in Texas and other wide-open regions, but the farthest I've ever shot in a PRS-style match is 1100ish yards and the vast majority of targets are inside 700.
I started this class of competition 7+ years ago with a 6.5 Creedmoor. This (2025) is my 2nd year competing with a 6BR. With a 10mph full-value crosswind, 1000-yard elevation/wind holds for 6.5mm 140gr and 6mm 105gr bullets at 2775fps vary by around 1.0/.5 mils respectively. At 500 yards, there is less than .2 mils difference between the two.
In return for dialing in that extra bit of "up" and holding a tenth or two or three more wind, I cut my powder consumption by a third, barrels last longer*, and it's easier to control recoil and see splash off props. Worst downside less splash to aid in determining correction. I'll take the tradeoff for sure.
Of course, if I shoot a match at one of the venues where longer ranges and higher wind are the norm, I'll screw the Creedmoor barrel back on. I've shot the mile my Creedmoor. It is in no way shape or form meant to shoot that far with consistent accuracy. Expecting a 6GT-class round to shoot accurately at that range is just silly.
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* Anecdotal. I sold two 6.5CM rifles before their barrels wore out (with full disclosure of round count to the buyers), and my current 6.5CM barrel still shoots well at 2500 rounds. My buddies all report 2500ish round barrel life for that caliber with "sane" handloads. No one I know has worn out a 6BR barrel yet; one guy has 3500+ rounds on his and it's still good.
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once I reach out to 1250 and beyond, it is much tougher to hit. Mile is almost impossible.
So now you're in "ELR" territory, not PRS. In this space, a .300 NM makes sense. If you want to stay with factory ammo, .300 PRC may make more sense from an ammo availability perspective.
I've only shot a .300 PRC once; it was a buddy's 12ish-pound hunting rig. It had a big 5-port brake on it. Recoil wasn't terrible, but I wouldn't want to shoot a match's worth of rounds (75-100) through it. And muzzle blast was ferocious.
If you want to shoot 3/4-plus mile targets and find it difficult with a 6.5PRC, you'll kick yourself hard for wasting money on any 6mm caliber. Get your .30-cal or larger boomer and enjoy.
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EDIT: Rob and sheepdog beat me to the "post" button....