Need help on a 243 ai 1-14"

[stbbo]

I have a 1-14 243 ai with a 20" ss barrel on a rem 7 action. Here is my problem theoretically it should only stabilize up to a 70 gr pill BUT all I can get it to shoot well is 43 gr of 414 with a 80 gr Sierra varminter standard col. I had about 4 boxes of fed premium 70 gr nos ballistic tips that wouldn't group better than 2". I can't figure this dang gun out with that load aforementioned she shot 1 ragged hole at 100 but had pressure problems to the point that I can't reuse brass to fire form because of primer pocket being blown out. Barrel was recently reset for minimum "something" I can't remember. He said it was at max end of tolerance I believe he referenced headspace. Thanks this is for mama so the sooner the better. I built it to shoot 60-70 gr pills at wt's where I'm from. And I'm glad it'll shoot 80's but was built to cover a specific weight pill.