Possible Solution To Carbon Fouled Cases
I finally got around to reloading and firing a small batch of 10 Lapua cases for the 6.5×55 that you may recall were being coated in carbon blowback check out the video “Carbon Fouling & Soot After Firing The 6.5×55 Rifle Calibre”. I cleaned and prepared the brass ‘following the same steps as my non problematic brass’ but I added the extra step of annealing this batch of cases to see if I could solve the problem and prevent them from being coated in carbon when fired. My reasoning as to why I annealed the case neck was to see if I could improve the Neck tension on holding the bullet and if this tension would allow the powder charge to fully burn to create adequate pressure to firslty release the bullet from the case neck and sending it down the bore while simultaneously expanding the case neck to tightly seal of the chamber and prevent carbon and gas blowing back into the chamber and bolt face.
Loss Of Bullet Performance
The carbon blowback would inevitably reduce bullet speed as less forward pressure would be created to push the bullet along the bore and to the target. This could also lead to problems with follow-up shots as carbon build-up would cake onto the bolt face and chamber wall layer by layer with every shot fired, thus reducing the chambers capacity to hold and properly fire-form the next case. Not to mention a lengthy cleaning regime of mopping the chamber with cotton swabs and boretech eliminator after every range or field trip.
If the test group of annealed cases fired represent the larger batch then the process of annealing may be the answer. In my test ALL cases were fired with the same powder charge, bullet weight and bullet seating depth.