I finally had the chance to work up a good Subsonic 7mm-08 load with a Speer 160 grain SP bullet
. Barrel was 20" long with a Shark Tiger Shark suppressor. Rifle was a semi custom Tikka build with a 9" twist (Thank you FiremanJG!). They were running right at 1040 fps, right where I want them.
Also why use a 160 grain Speer SP (soft point) flat base, instead of a BTHP, VLD or match bullet? When shooting at subsonic speeds, bullet stability becomes a huge factor for the bullet to properly stabilize and for it to shoot well. Bullet length is a major factor in how stable it is out of the muzzle. In a given twist rate (like a 1:10" or 1:9" barrel twist) and slow subsonic speeds, a shorter, flat base bullet is more stable than a longer BTHP or VLD match bullet of the same weight. The 160 grain Speer SP flat base is a much shorter bullet than a similar weight BTHP bullet, like a 162 A-max or 168 Berger VLD. This allows the 160 grain SP flat base to be more stable and have the potential to be more accurate at subsonic speeds than a BTHP design. Also, BC (ballistic coefficient) is for supersonic flight, and does not matter at subsonic speeds. Having a high BC bullet at subsonic does not benefit the shooter at all. This is why the 160 SP flat base bullets work well as subsonic round!http://dallasreloads.com/product/160-sp-subsonic/
4 shot group and a 3 shot group during testing at 100 yards.