Ok, A week or two ago I put a post up about tight cases when closing the bolt of my 243. I had some great groups but the case was not right so I have turned the sizer very slightly to push the shoulders back a little and this has helped the cases fit and they fit well. The new problem is that the groups are now shocking, can't get any better than 2 inch. Have tried bringing the powder charge up from the low end 37.7 again upto 41.5 The best being 39 grains which was where i was to begin with, which are still the best , but still crap.
I am loading 39 grains of IMR 4320 with 75 grain BT hornady cci primer in a fedral case.
Where do I start from, where do I look first?
Regards
Mark
Mark.
You don't say how much you stepped the powder up by? I generally step up 0.4 grains and then once I have a likely weight try it again and try +-0.2 grains as well.
You don't say what your seating is. The suggestion above of 10 thou off the lands is a good one for a starting seating. However these lighter bullets may not get that near and 50-150 thou range might be where you end up. Once you get a powder weight that's working, tweak the seating by no more than 4 thou at a time.
I am not a fan of Federal brass for reloading and suggest you get a box of Lapua brass and start afresh with that.
Going by the Hornady book, IMR 4320 is listed, but all your loads are over the maximum of 38.8 grains, so I think you need to look at that issue.
I also think you need to look at the resizing that you have been doing. Have you measured how much you have bumped the shoulders back? I suspect you may have bumped them back a bit far?
You've not mentioned trim length, but the trim lengths need to be to spec and the cases deburred.
Given the range of issues here, I think you need to find someone local that you can talk to on reloading on a regular basis and look over your shoulder. Also, you need to update your reloading book on what you are doing, both for brass prep and for actual loading.
One final thought, has something come loose on the rifle? How is it shooting its preferred factory ammo? It can take years to work through issues like these, so take your time and write down what you do.
Good luck. JCS