M67 was right the link was not complete.
Yeah Pat, bastard
I have a 1-4 Vortex PST with capped turrets (MOA only), like it, the glass is clear, but personally I find the reticle a little hard to pic up, wish it was FFP but that would increase the cost of the scope a good $150. Nice scope, but that being said, it's going on a S&W M&P 15-22 when it gets here (it's a spare scope at the moment).
I also have a 1.25-4 Trijicon TR21, glass is amazing (like every Trijicon I've handled), but it has a triangle post reticle which is great for target acquisition and rapid shots, but nothing precision since there's no marks to go compensate for drop or windage.
For a 12.5" barrel, I think a 1-4 would be just fine, a 1-6 may be overkill in terms of weight increase (just shy of a half pound increase in weight, Razor vs Viper) and I think the reticle in the 1-4 PST would be better suited for your needs because of the reticle having more compensation for drop. I however have never shot a 300 Blackout at 300-400 yards so I have no clue how far it drops. I've only shot it a couple times suppressed with subs at 50 yards on in
Leupold also makes some nice 1-4s and 1-6s, and every now and then you can find a Nightforce 1-4 used (AFAIK they discontinued it a couple years ago).
One thing with 1 power optics, and it's an anal, depend on the shooter thing, is if you want a true 1 power on the low end, a 1.1 power, a 1.25, 1.3, or 1.5.
Some companies advertise 1 power on the low end and it's actually 1.1 or 1.2 (in Leupold closer to 1.3)
True 1 power makes everything look a little smaller than normal. 1.1 is scaled properly, other powers you notice some scaling differences more. Depends if you can shoot with both eyes open, how you brain reads the reticle and the magnification differences, and if you actually care.
that being said, on the low end for my TR21, I usually just leave it at 1.5 power to match my ACOG.