Re: 178 amax / 175 SMK
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 96C</div><div class="ubbcode-body">Tag - looking to switch to 178.
How do you think they will fly from a 20" Rem factory 1:12" barrel?
I'm running 168 AMAX currently and they're doing well... Do you think 1:12" 20" will run into stability issues?
Most shooting is about 200-600 meters ASL. </div></div>
Hi 96C,
If most of your shooting happens inside 600m stick with your 168 AMAX rounds. I had no problem getting 168 AMAXs to go faster than 2700FPS with no pressure signs with a well under max powder charge too.
For 168 AMAX rounds I use commercial RP brass with uniformed primer holes and pockets, cases trimed to 0.005" under max SAAMI .308Win case specs and set the case shoulders to headspace at 0.002" and 0.001" neck tension. The 168 grain AMAX bullets were seated with a base to bullet ogive height of 2.190" yielding a COAL of 2.810" and charged with 43.1 grains of H4895. These rounds shoot very well at about 2,730FPS all the way out to 1,000 yards.
The same cannot be said for the 178 AMAX bullets using the same components. With the highest powder charge I could use was 2,550FPS with mild pressure signs. Initially I used the same case set up and the same base to ogive height which gave me the same COAL of 2.810" so then I tried setting the bullets farther out to get back some of the case volume I lost due to the slightly longer ogive to base dimension of the 178 AMAX bullets. This slightly improved this round but I cannot seat the bullets far enough out to reproduce the 168 AMAX load's case volume because I cannot fit a 2.860" COAL in my Rem700 BDL internal magazine. So I got to 2,570FPS by moving the bullet out to a COAL of 2.830" but this round does not shoot well in my rifle and is an over-max load at least in the Hornady reloading manual anyway.
The most interesting thing about the 168 and 178 grain AMAX bullets is that there is not a lot of difference between them in the field. The 168 AMAX performs as well as the 175 grain SMKs which the 178 AMAX preproduces perfectly. Dimensionally the 168 AMAX is nearly identical to the 175 SMK. But I could not push the 175 SMK as fast (best I could get and still shoot well was 2,600FPS vs. 2,730FPS) as a 168 grain AMAX and they end up being about the same basically all of the way out to 1,000 yards with the 168 AMAX shooting a bit flatter with less flight time to target.
So unless I can find a way to make the 178 grain Hornady Match bullets to shoot well and move at least 2,600FPS the 168 grain AMAX will still be the winner. Even if I can get the 178 grain Hornady Match to move and shoot well at 2,600FPS the 168 AMAXs will still be the equal of the 178 Hornady Match out to 700 yards.
Makes me wonder why I bother and don't just be happy plugging along with the 168 AMAX loads I have. But it does give one something to do doesn't it? 8^)