J_Jacobson
Lil-Rokslider
- Joined
- Jan 10, 2020
- Messages
- 122
Last year I had a 6mm CM built using an IBI barrel and a Pacific Tool reamer. The freebore diameter for this reamer is as per the SAAMI specs, which is 0.2435".
I purchased 500 112gr Match Burners (7276476-8 153U LB-M) to load in this rifle recently. I already had a load for this rifle with a previous lot of Match Burners, which shot well. I had set the COAL to jump to the lands based on this previous batch. When I loaded the new lot number, they would not chamber. I used a permanent marker to show witness marks on the projectile when chambering it, and discovered that the shank of the bullet was making significant contact with the freebore and not the lands. I even seated the bullet back so it was jumping 100thou further, which made no difference.
I have since investigated further, using a micrometer the projectiles in this lot number are 0.2437" in diameter at the top of the shank and taper up to 0.2445" at the junction where the shank meets the boat tail. This means the projectiles appear to be outside of the maximum allowable tolerance in a 6mm CM freebore diameter. Ive contacted Barnes to let them know, but interested to know if anyone else has seen similar problems with the match Burners.
It really seems outside of the ordinary, especially when comparing to my 108eldms and 107smks, which are consistently 0.2430".
I purchased 500 112gr Match Burners (7276476-8 153U LB-M) to load in this rifle recently. I already had a load for this rifle with a previous lot of Match Burners, which shot well. I had set the COAL to jump to the lands based on this previous batch. When I loaded the new lot number, they would not chamber. I used a permanent marker to show witness marks on the projectile when chambering it, and discovered that the shank of the bullet was making significant contact with the freebore and not the lands. I even seated the bullet back so it was jumping 100thou further, which made no difference.
I have since investigated further, using a micrometer the projectiles in this lot number are 0.2437" in diameter at the top of the shank and taper up to 0.2445" at the junction where the shank meets the boat tail. This means the projectiles appear to be outside of the maximum allowable tolerance in a 6mm CM freebore diameter. Ive contacted Barnes to let them know, but interested to know if anyone else has seen similar problems with the match Burners.
It really seems outside of the ordinary, especially when comparing to my 108eldms and 107smks, which are consistently 0.2430".
