Another question for the group. Aside from capacity, is there a physical difference between 7 and 8 round mags from the same manufacturer that would give one a performance/reliability edge over the other?
It depends, but yes, in general.
A few for instances.
1. In the Wilson line-up, the 7 round 47 (
https://shopwilsoncombat.com/1911-M...ize-7-Round-Standard-Base-Pad/productinfo/47/ ) and the 8 round 47D (
https://shopwilsoncombat.com/1911-M...ze-8-Round-Standard-Base-Pad/productinfo/47D/ ) use the same tube length, but the 47D puts an extra round in that tube. To get that extra round in the tube, they use a lesser follower and lesser spring (my belief) than the spring and follower in the 7 round 47. My view is the 7 round 47 is one of the best mags available, while the 47D is the worst mag in the Wilson line-up, a line-up of very good mags, top to bottom including the 47D, though. Everything has to have a worst even a place like Harvard Medical School, and the 47D is Wilson's bottom of the class.
On the other hand, the 8 round ETM Series (500/800 models) (
https://shopwilsoncombat.com/45-ACP/products/378/ ) uses a longer tube than the 47 Series and is designed from the ground up as 8 rounders rather than converted 7 rounders like the 47D.
2. In the Tripp CobraMag line-up, their 7 rounder (
http://www.trippresearchinc.com/7r-45-wg/ ) and their 8 rounder (
http://www.trippresearchinc.com/8r-45-rg/ ) use mag tube length's designed for their respective capacities. Their 8 rounder has a longer tube.
3. In the CheckMate line-up you need to sort through their feed lip and follower options in addition to tube length differences. In this thread you've seen folks prefer different feed lip designs and what works for one of us, may not work for you. I generally like CheckMate mags, but I won't buy any more non-extended tube 8 rounders, since they are shorter than even the Wilson 47D's and are really tough to seat with 8 rounds in the tube and the slide forward.
There are so many options with CheckMate it's tough to make a choice. I generally stick with 7 rounders, with wadcutter feed lips, and prefer the removable baseplate/bumper pads. However, as you can see in this thread, others will insist my preference won't work for them. I typically buy my CheckMate's from Top Gun Supply.
https://www.topgunsupply.com/magazines/1911/check-mate.html