Just decided to see exactly what I can wring out of my 45-70 No3 when I discovered that bullets sized to .452 (which fits snug in the bore) and paper patching the bottom quarter of the bullet (these are the 450 grain Lyman "Volunteer" bullets) to get them to chamber seated out long in the case. I am loading with IMR 3031 and have noticed that the max charges for 45-70 and for 458 win mag (considerably greater case capacity) with comparable bullet weights are compressed loads (making me think that I should not have to worry about pressures during this load development).

My question is which is better: to load up from a safe level seating the bullet on the powder and allowing the OAL to increase as I increase the load or to set my dies to my max OAL and work with loose powder in the case until I reach my max load? I kind of like the lightly compressed loads but I just want to put the question out there in case there is something I haven't thought of that should be considered.

Bullet seating depth is generally a constant while changing powder amounts. Powder amounts are generally constant while varying seating depth. In other words, vary only one thing at a tume.

For the most part, you would ordinarily seat the bullet to what you consider a propitious length and then vary the charge. Whether the case is full or slightly less, or even has a little compression on the powder is not so much of a concern.

One variable at a time, that certainly makes sense. The inspiration of this came when I saw BAW's black powder 45-70 with a tapered 500gr bullet crimped on the rear lube groove of the bullet in an attempt to approximate the 45-90 case capacity. Thanks for the recommendation.

Just start out with the bullet seated out as far as your rifle will allow, and then start working with charge weights - that should do the trick...
That is also the way I do it for my BP 45-70: seat the bullet out to the lands, and then vary the powder charge.

I loaded several tonight and will shoot them tomorrow. I am interested in how these half-jackets perform. I have a 1.10" bullet and a COAL of 2.95", only seating that deep to get a good hold in the case and to seat the patch to the lands. I did not want to make the patch any shorter. Anyway, I have already tested a load of 56 grains of 3031: recoil was mild and it shot to the point of aim. I will be testing and I will stop and back off when the accuracy begins to diminish.