I used to carry the FMJ mag in my pocket that way it was distinct in location. To be honest I did/do it because I was sitting in a bar I F'ville one night with a bunch of guys who get it and we agreed it was smart. I have never made the switch in a gunfight. Like I said I mostly do it now out habit. Like I said earlier I, or anybody else, would probably be better off with mags filled with Bonded JHPs. One of the guys at the table that night actually made the switch once and before he could test the thory the car he wanted to shoot up was gone.
Mk262 does poorly through some barriers. Windshield glass in particular. It doesn't do as badly as the mnet would have you believe but it can be unpredictable. Unpreeictable is never good in the shooting people buisness. Mk318 is a better all around performer. It isn't as effective against soft targets but is more reliable when shooting through a barrier.barriers. everything is a compromise. I wish they had made mk318 in 70+ gr. I usually carry a mix of 262 and SOST. I put the 262 in Tan mags so I can tell the diff. The Mag in the gun is 262 because I am more likely to encounter a soft target.
I want to stress that 262 isn't bad. It does go through barriers and kill people. It just can be variable. After you remove luck from the equation the rest of a gunfight is controlling variables.
I found JHP's to work better through car doors than FMJ's. I don't know about glass.
JHP's have "sharper" edges and seem to want to glance less. They can also be found in higher velocity loadings, and velocity helps a lot, all other things being similar, when punching through metal. Hence why an AR out-penetrates an AK on mild steel plates in my experience.
From what I saw, bonded 357SIG was the best against the car doors I shot, followed by .40(any) and 9mm (124gr+P), and finally .45ACP(The 230gr +P+ RA45T did okay). The 147gr 9mm was the worst. Often getting hung up between the outer and inner skin of the door.