The 180gr Speer needs 2400+ fps. It's a tough bullet too.
In my tests I have found the countersink is unneeded with enough velocity. It works well to ensure expansion in my subsonic tests.
Thanks, Dinny
I've been using180 grain Speer bullets in a Marlin 336 35 Rem for a long time. No published 35 Rem loads reach 2400+ fps and it's killed lots of deer and a bear over the years from almost point blank range to over 100 yds. The bullets expands at 35 Rem velocities and just plain works.
