I’m driving to a rifle match right now, and would have some follow up questions, but I’ll be brief here:

First: I’ve been instructing new riflemen for a long time, and 99% of the time when a shooter talks about small groups at 100, and the wheels coming off by 200yrds, it has nothing to do with the rifle or load. The target and aiming reference is half as big, mirage warp is 4 times as bad, and every 1/10th inch of shooter wobble is doubled (recall here - your crosshair width at 200yrds is likely a half inch in itself). Unless you double your target size or double your scope magnification, dollars to doughnuts you’re simply not firing as consistent of POA at 200.

So let’s talk briefly about “what it ain’t,” because lots of folks in your shoes will start looking down rabbit holes and ignoring the real problem in front of them. You’ll do yourself a favor to focus on the most likely issue first.

• It ain’t instability. There’s no feasibility for a 300win mag load in this weight range to be sufficiently stable at 100yrds and shooting 1/2” groups, but destabilize by 200. If it’s over spun, it’d come apart by about 30yrds, if it’s underspun and unstable by 200, it wouldn’t be shooting 1/2” groups at 100.

• It ain’t bad bedding. Bad bedding would present itself at 100, not only present at 200, so you wouldn’t see 1/2” at 100 and 4” at 200.

• It ain’t inconsistent velocity ammo: 200 is not far enough for velocity spread to promote substantial vertical dispersion in the groups.

• Clean bore variability: although it is exceptionally silly to clean between each shot or each group for any other reason than breaking in the barrel (where you’re not really shooting groups anyway), again, if it WERE this you wouldn’t be shooting 1/2” groups at 100yrds. Cleaning does invite variability, but it wouldn’t be range selective. You wouldn’t see 1/2moa at 100 and 2moa at 200. So stop cleaning between groups, or shots, but that’s just to protect barrel life and save time. It won’t fix this 100/200 issue.

Ditch the Lead Sled. It’s about as valuable as a clap factory - nothing but bad happens when you go there.

If you’re really shooting 1/2” groups at 100yrds, then slipping out to 4” at 200yrds with the same load in a 300win mag, 90%, it’s simply inconsistent POA. Pick up a higher magnification optic, or better still, pick up some targets which are more friendly for 200yrd shooting. I strongly prefer shooting diamond shaped targets on square grid backed paper (such as the Shoot-n-c 5 diamond targets). Cutting a circle isn’t nearly as simple as cutting a diamond, the feedback against the reticle with a diamond is extremely fast, whereas you can float around a 2moa circle target a long ways before your eye catches it.

*Note: everything above is predicated on the veracity of the same loads in the same rifle and same optic, shot by the same shooter in the same support and conditions, delivering truthful 1/2” groups at 100yrds and 3-4” groups at 200yrds. If you’ve shot ONE 1/2” three shot group ever with the rifle at 100yrds and the rest are 1.5” at 100, then we’re not talking about anything real here. So everything I posted here is trusting this isn’t another internet sharpshooter with one 3 shot group which went 1/2” and then we hear “it’s 1/2moa all day if I do my part.” If you can set down at the rifle and shoot 5 groups of 5 shots into 1/2” at 100, but then print 5 groups of 5 shots at 200 as big as your palm, then it’s your target and optic.