Any suggestion for how to deal with the extra variable of a "Boss" system? - I have a 300 Win Mag A Bolt with Boss. I don't think the "ladder" method of finding the most accurate powder charge will work, because as charge/velocity is increased, the Boss setting will be affected, & that thing can shoot some VERY wide groups if the Boss isn't pretty close.
I'm trying to find a good powder & weight for 180gr Speer Grand Slams.

Finding the right setting for the BOSS can be very tedious.

Actually, what's worked best for me is trying the settings suggested in the manual for commercial cartridges with the same bullet weight.

Can't begin to estimate how many rounds it took me to get my BOSS dialed in.

Would this work? Take off the BOSS and work up your most accurate load, then install the BOSS to fine tune for even greater accuracy. Starting at the setting recommend by the manufacture for the bullet weight of your load.

Or

Set the BOSS to the recommend setting for your desired bullet weight, lock it in and then develop your load around that setting.

Greenjoy - takinbg the Boss off might be a good option - I'm not sure, but I assume the rifle can be fired without it (its factory - the end of the barrel has a reduced outside diameter, is threaded for the Boss, & has an odd bevel). Setting the Boss to a recommended setting is what I,ve been trying, but as the load parameters change the necessary setting will change also, if you get very far off the right setting, groups are all over the place.
Thanks for the suggestions.

I had a boss on a 270 win and it was useless in a good way. I remember I set it at recomended setting for a 140 grain bullet...it shot 1" and under groups...then I tried some 130's and 150's at the same setting...that darn useless boss sent those bullets right to the same point of impact as the 140's. That damn thing would shoot anything to the same POI and most anything at 1" and under. Only thing is it was more noisy than my 300 wby with a brake...I sold it. (This was before they came out with the non ported boss).

The BOSS can be a handloaders dream or his worst nightmare.

The best way to deal with the BOSS is set it close to what Browning or Win lists for a specific bullet weight. Then leave it alone.

Work up a bunch of loads with different powders, bullets and charges. When you find a load that gives you the velocity you are after with reasonable accuracy, stop. Now, make a bunch of this load, head to the range and start tuning the BOSS.

I have a BOSS on my BAR 300WSM and it will shoot amazingly well when tuned just right.

I would start with a tube cutter and a hacksaw.