I think Waco said it best, It only matters when it does. My default OAL is a light kiss on the nose or front driving band, nose preferred but not always an option. I have two 03-a3's. #1 was shot a lot by my Dad with max loads, hence a lot of throat erosion. It has to have a 200 or heavier tight into the lands and will shot MOA at 100, 60% of the time. Any bullet not touching produces patterns not groups.
#2 rifle is a two groove Remington that I don't think was ever issued. Lyman 170 round nose(311291 I think) will shoot MOA 90% of the time again with a light kiss on the driving band. If you back off on #2, say 1/1000, the group opens slightly all the way to 3/1000 off, no difference. ???
Change guns to a savage 340, in 30-30, It hates to be touching, will not shoot any cast bullet I have tried if it touches. It has to be about 3/1000 off before it calms down.???? Same savage with jacketed 125 hp will only group with that bullet crimped in the cannelure near the bottom of the groove. Again???
My default position with cast and bolt guns is a light kiss first with all the powders and charges I want to try. 90% of the time I find what I want. When I don't find happiness then I start playing with the OAL. If that dosen't work then I'm not sure because it hasn't happened yet. BUT I have a Star rolling block in 30-30 from the 70's that might be the first one that none of the above has worked. Not sure what I'm gonna do about it.
I tried once and only once to have one single load that would work in three different lever guns, I never found it.
Tony