Burn/tarnish marks on 45 ACP fired brass

I am a newbi to reloading (just 2 years).  Have noticed that my reloaded 45 ACP brass have burn/tarnish marks approx. 1/3 around and down from the case mouth. I use a single stage press, with Lee carbide die set and load 180gr LSWC(flat base) .453 dia (slugged bbl to get proper dia for bullet), CBC and Starline 1-3 time fired cases,  3.5 gr of bullseye, 1.25 AOL, .469 taper crimp.  I use a Lyman "M" die with a very slight bell for flairing. I am very carefull in placing the bullet straight on the case before seating the bullet, then taper crimp (seperate stage). This load functions perfectly in my SA RO Elite w/ 10#recoil spring and 18# hammer spring. Never had a malfunction from day 1 using this process.  Need input from experienced reloaders as to why this is happening?

Lighter charges don’t seal as well as a warmer load. I would tighten the crimp down to 0.465-0.467 because it will help with the burn, but you will still get the burn marks.
Jon

Thanks Jon..I will try that on my next reload session.

I recently went from .469" crimp to .463" crimp and am pleased with the results so far. I feel I get more consistent ignition and am able to slightly lower my charges due to higher pressure per grain of powder.

If you are getting good groups at 50 yards, fogetaboutit!

BE Mike wrote:If you are getting good groups at 50 yards, fogetaboutit!

And good reliability/consistency.

I did the same and went to .463 crimp..better burn and better accuracy.  For me anyway