The 10 barrel in 7mm BR requires a fast to medium burning powder, otherwise, there will be substantial muzzle blast and fire breathing dragon effect.. I have a 15 and 1 18.5 barrel. I shoot 162 Grain Hornady Amax bullets with 28.8 grove BLC-2 for a velocity of 2050 fps (chronographed velocity.)
The suggested loads below are moderate loads. I would recommend that you start lower by a couple of grains and watch for pressure signs. I also, suggested Hodgdons H322 powder, It is more efficient and faster in the short 10 barrel than H335.
120 gr. Sierra SST Pistol bullet 36.1 gr. of H335 OAL = 2.11 Bullet down in the neck 0.4
Velocity 2204 fps and 89% of the powder will burn in the barrel: There will be lots of muzzle blast and fire.
++++++++++++++++++++++++++++++++
120 gr. Sierra SST Pistol bullet 30.3 grains of H322 OAL = 2.11 same as above
Velocity will be about 2222 fps and 92% powder burn in the 10 barrel. Less flash and blast, but still some.
+++++++++++++++++++++++++++++++++++++++++++++++++++++
130 grain Sierra SST Pistol bullet: 31.6 gr. Of H335 OAL = 2.15 Bullet down in the neck 0.4
Velocity about 2123 fps and 90% of powder burn in the 10 barrel.
+++++++++++++++++++++++++++++++++++++++++++++++++++++
130 grain Sierra SST Pistol bullet: 29.4 gr. Of H322 OAL = 2.15 Bullet down in the neck 0.4
Velocity about 2125 fps and 93% of powder burn in the 10 barrel.