Several related questions here:
1) Glocks and a few other firearms use "polygonal rifling" instead of the standard land-and-groove rifling most guns use. Glock suggests that you shouldn't use unjacketed bullets in their guns. (They also say don't use reloads -- like most other manufacturers also say, and which all of us ignore completely.) Glocks developed a reputation for experiencing a certain kind of explosive malfunction (everyone calls it the "Kaboom") which MAY have been related to lead build-up in polygonal rifling in some cases. The problem there is that blowing out the case and damaging the gun has been attributed to four or five possible root causes, or interactions of several root causes, and the problems have been blown way out of proportion in any event. In other words, everyone's got a pet theory and "most" folks have decided that lead bullets and Glocks don't mix. If that makes folks happy, they should keep on doing what they do.
2) You have traditionally-rifled 1911 pistols so Glocks and polygonal rifling have nothing at all to do with you. You may rest assured you can fire hundreds of thousands of cast bullets through your 1911s without fear of damage.
3) Cast bullets come in different hardness levels. Harder lead alloys work better with higher pressure loads, but there's a wide range of hardness and pressure that work well together and the odds that you'll get outside that window with common cast bullets and common target loads are pretty minimal. In other words, you probably won't get heavy lead fouling, but run a few hundred through and make sure your combination is working well for you.
4) As I said before, some folks feel that heavily leaded barrels make Glocks "Kaboom." No one ever claims that lead fouling made their 1911 "Kaboom." Bad leading will eventually mess up your accuracy, but it isn't something you're going to have to FEAR. If it happens at all.
5) Cleaning -- You probably really won't hurt your guns by "religiously" cleaning them every time you shoot, but you aren't doing them any favors either. A scrub down every 500-1,000 rounds or so is my preferred regimen, and I find that keeps things working reliably. I rarely do more than swab out my barrels and they all see many hundreds, or over a thousand cast bullets between cleanings.
