Did you ever run some loads of Lil Gun, in hot weather, where the ends of the spent cases near the mouths changed colors like a half hearted attempt at annealing?
Last Saturday, while testing those 230gr FMJ-FP rounds over Lil Gun, about half of my cases had color transitions down as far as 3/4 inch from the mouths. The color wasn't as evenly distributed around the case as when I've annealed them and more interestingly, the coloration was not reserved to just the upper end of the charge ladder loads, like I would suspect. When I say it got hot, I'm talking in the lower 90's in the shade with a light breeze which made it bearable. I was running my 12VDC vacuum cleaner, barrel cooler at every 5 round break before the next ladder rung for 3-5 minutes, so the barrel was not uncomfortable to touch, but definitely hotter than skin temperature. Over the years, I've run Lil Gun experiments in the summer, but this was the first time I've seen widespread heat coloration. They weren't necessarily top end loads, certainly not in the league as some TSD experiments in terms of velocity. I wish I had photographed some of them. In the case of the ones with the most extreme coloration, some of it still was visible after wet pin tumbling them to a mirror-like finish. I've seen all kinds of variations on sooting and this was not that. As a matter of fact, sooting was very minimal. The 300gr SST bullets over IMR 4227 had a little more sooting but not like some loads I recall from back when I had my "loosey goosey" chambered Bushmaster factory upper. My trusty Bartz chamber is actually on the tight end of the spectrum and well finished. Definitely a two or possibly a three reamer job.
Anyway, it was odd enough to have stuck in my mind, unlike the many other range outings I've done over the past 8 years. I may recall having seen an odd colored case a couple of times but it was more the exception than the rule. As Bob pointed out, Lil Gun does have a reputation of running hot under the best of conditions and I'm a slave to comfortable weather, so perhaps I've just lived a sheltered life with the 450b.
Hoot