30-30 - I've read a lot about it:
Sam Fadala wrote with much praise about the 30-30 AI, specifically in lever-guns and, if I'm remembering this correctly, experimented with shooting the 30-30 AI in a Winchester 94 with the bolt lugs removed to prove the point regarding reduced back-thrust. Aside from worthwhile velocity gains, he also noted a big increase in brass life. I've never had a 30-30 AI myself, but I don't shoot any 30 caliber jacketed, so I don't think I'd benefit from the alteration. Increased brass life and less back-thrust would be appealing to me but I don't even use all the case capacity as it is unless I use one of the 4350s.
257 Roberts - First-hand experience with a couple:
My dad and I have shot the 'Roberts and it's more modern twin, the 25 Souper side by side for years. He was getting worthwhile increases in velocity from some projectiles when he improved one of his chambers, but I don't remember which weight. He also shot the unmodified Roberts at very pedestrian velocities to begin with and his powder choices were based on a few he started shooting before I was born and hasn't ventured into "modern" powder formulations. I'm sure there could have been some optimization by considering other powders along with the volumetric increase. He still shoots one as his main rifle.
7x57 - First-hand experience with ONE:
I had a 7x57 Improved done up on a tang-safety Ruger 77 with a 24" Douglas barrel. Velocities I was getting were about equal to the highest velocities I've seen in some older reloading manuals for the 7x57 from 154 grain to 175 grain bullets. I clocked a whopping 2700 fps with some 120 grain HPs, but was using 3100 powder. Probably could have dine much better with another powder. The Hornady 162 grain Spire Point was the bullet I worked with the most and just barely made 2700 fps with those. We worked out of an old wildcat reloading manual (Lyman, I believe?) and some of the data shown for the 35 Whelan (before it was "legitimized" by Remington), the 257 AI and 7x57 AI, and especially the 25 Souper were very hot in my opinion. Many of the attractive increases in velocity seemed more by virtue of exceeding established pressure limits (very low in the case of the 257 and 7x57).
than from the extra powder capacity.
One especially annoying point on the 7x57 AI in the Ruger was that the plunger ejector would force the body of the case into the right lug race as the bolt was pulled back and it would hang up the bolt. Took some fiddling and cussing to dislodge and remove the fired case. Fixed ejectors in the Mausers never did that.