I'll throw a couple things in here. An early reply in this thread said he starts with the max charge and works down. I would advise against that for safety reasons, because even though the "book maximum" has always ended up being safe for me so far, there is no guarantee that this will always be the case, and it is simply safer and more logical to start somewhere below max and gently work up. If you start getting pressure signs, you simply stop. But if you've already blown up the case/rifle/yourface..... Anyway, I have just finished (for the most part) load development of my 280AI, and here is how I did it this time (not the only method, and feel free to chose for yourself): Having measured the throat dimension to find the maximum COAL (using an ogive bearing comparator insert) I loaded a test batch using 5 rounds of each charge starting with 59.5gr of Retumbo behind Berger 168VLD hunting bullets, and increasing by 0.5gr for each group, all the way up to 63.5gr. Note: the maximum listed charge in the manual is 63.0gr, but with a longer COAL, it can take a little more charge weight to reach normal pressure/velocity in the same case. YOU DO THIS AT YOUR OWN RISK. I shot these rounds while doing the shoot/clean barrel break-in process, with each charge weight on a separate target. In virgin brass, the max book (63.0gr) shot the smallest group, with the "over-max" a close second. All other groups were noticeably larger. Next day, I loaded another test batch, all using 63.0gr, but with COAL as the variable, using Berger's suggested method of starting at longest possible, and moving back 0.040" at a time until SAAMI. This test was done with 6 rounds of each COAL, two three shot groups of each fired at separate targets. The longest COAL was the clear winner @ 0.338", with the next shorter being slightly larger @ 0.366", and progressively larger until SAAMI grouped 0.911". The average of all the test groups, best to worst, was 0.6278", so clearly I have a good barrel, and the load is working well. So far, 70 rounds expended to learn this much. Next, I took the once fired brass, measured headspace to set the reloading die to match with minimal bump to the shoulder (I use Redding competition shellholder, in this case the +.008") and loaded the 63.0gr charge as before, as well as the remaining virgin brass. Chrono testing showed 2960fps avg in virgin cases initially, but after passing 200 rounds fired through the barrel (I call that fully broken in) I re-tested velocity, using 3 samples: the remaining virgin loads, the once-fired @63.0gr, and the once-fired @63.5gr again. The virgins are now averaging 2973fps, the once-fireds @63.0 2992fps, and..... Final load spec is now 63.5gr @ the max COAL in partial re-sized brass, and running 3024fps avg according to the chrony and the tightest groups came from the highest charge. When I get back out to the 1000 yard range for Trajectory validation, that figure will probably go down just a bit, as I have found my chrony to be slightly optimistic in the past, but I am expecting it will still be right at 3000fps. My old 7RemMag was only slightly faster with the same bullet, so I am a happy camper. This is the simplest load development I have had with a new barrel so far, and maybe it can work for you too.
