This past weekend at Red Glare IV, I flew a F20LMS casing loaded with one grain from a G77R reload. The long term goal is to see whether I can fly a G77LMS without sealing the forward closure with epoxy, and then squeeze another flight out of the single-use casing by reloading with a G77 RMS reload kit. For more rationale why I wanted to do such a thing, you can see this post.
The flight at Red Glare was the third flight on the LMS case. In all cases, I merely added a 1/16" o-ring from a G reload to the top of the grain and heavily greased the plastic threads. For this third flight, I also plugged the delay well. After flight #1, I noted there was no gas leakage through the forward closure. For flight 2, I used the 2nd grain from the F20 2-pack. After two flights, I measured the nozzle erosion to the best of my ability. It appeared the nozzle area increased by about 20% (over 2 flights). For flight three, I used a Redline grain from a G77 reload kit. I expanded the nozzle to about 0.125" dia., which is as close as I could get to the ideal given the available drill bits. This should have been only a few 100ths of an inch off.
The flight went well and again there wasn't any gas leakage. This time, however, the diameter of the throat eroded by 50%. That's big change. I don't know why there was so much more erosion with one Redline flight vs. two White Lightning flights. I checked the before and after for a G77R-SU and in that case the nozzle only eroded by around 1/64". Maybe the convergence cone was eroded by the first two flights. I don't know. Next, I'll fly a Redline grain in a new F20 case and see how the nozzle does.