Hi, new here but had a question and in searching for an answer I keep getting a lot of info telling me that bullets lead the barrel because they are either too soft, sized too small or are being pushed too fast.
Here is my problem. I am new to the 9mm and also new to casting for the 9mm. My 9 is a RP9 with a tight chamber and barrel. The barrel slugs at .355 and my bullets are being sized to .357. .356 sized bullet showed more signs of leading than the .357 and .358 sized bullets seemed to do just fine also however I had to seat them so deep to get them to chamber that I went back to the .357 size. I am using Hitec coating on my bullets. I am using w231 powder and my average velocity is 925 fps. slowing it down much farther and it will not chamber the next round with the stock spring. I have captured quite a few fired bullets to see what was happening and to see if I could find a solution. My lead mixture started off at 50/50 COWW / Pure lead. These bullets tested at a BNH =9 (lots of leading and bullet skidding). I am now using 100% COWW tested at BNH = 18 and am still getting just a little bit of leading.
The skidding can be seen in the pictures and what is happening is the groove left in the bullet is so wide with the skidding that it leaves a nice gap for the gasses to bypass the bullet and melt the lead. When using only COWW the skidding was almost nonexistent but the bullet was still pressing hard against the rifling on one side and rubbing off the Hitec coating and a little lead was left in the barrel.
So the question is do I go a little harder on the alloy (maybe BNH =22) to see if it will stop leading altogether or is there something else I might be overlooking.
Pease note that the lands and the grooves in this barrel are almost equal in width so the pictures show how much wider the indentation is in the bullet than the land actually is.