200 Gr. Reed's Ammo going supersonic

[Garrett]

I bought some loaded .300 Whisper from Reed's Ammo a while back and just got the chance to try it out. This was the 200 gr. SMK loading that is advertised as being subsonic.

When I shot it over my chrono, I got an average velocity of 1166 fps. Definitely not subsonic. I was shooting through my 10" Contender. It was around 36 degrees f. outside.

I may have to try some of their 220 gr. loads to see if they do any better.

On the up-side, I'm very happy with the accuracy of this load. All hits were touching at 50 yds. That's much better than the 220 gr. RN handloads I was shooting.

[justshoot]

only my 2-cents.and I am pretty new to the 30-221 chambering but I have many years of Handloading for builds.Plus a lot of bricks of match .22 rim. and different suppressors also. (in my honest opinion). I would not buy/Trust any factory loaded ammo and expect it to shoot exactly like they got it to Chrony. Unless I new the exact barrel, make, twist and length and if was a semi. or bolt action it was test fired out of. For factory bought ammo to meet my expectations.
Also the weather was cold and crisp and sometimes that will make a load bust over 1100 and snap but you were using 'only a 10" barrel' and it still broke the speed limit. If you were running a common length of 16" it really would have been a little FPS faster yet...
I think you might be wasting your time/money with there ammo running threw your specific build.
.

[Artful]

Your barrel may have a tighter chamber, shorter throat, tighter bore, bore may be causing less friction than theirs, your can may have tighter bore exhibiting freebore boost.

Lots of stuff can cause this - if it's warm you can cool your ammo (thou that didn't sound to be the problem)