300 AAC BLACKOUT making major power factor at the Nationals.
 

Look at the magazine on Daniel Horner's belt:

http://img822.imageshack.us/img822/6...6029924734.jpg

http://www.uspsa.org/uspsa-display-m...ntype=MULTIGUN

I wonder if his free-float tube is long enough?

Any chance the AMU will publish their load data? 155gr bullet must have been going at least 2064 fps. I can't get above 1900 fps without blowing primers.

It would be a stout load, but I don't think it would be difficult to achieve in a 20" barrel. I had 150's going 1800 fps in a 10" barrel, although it was a hot load and the brass didn't last long. I would start with Alliant Power Pro 300 MP. I get pretty good velocity out of it.

I luv shooting 155 vld's in my SB set-up . I get comfortable 1700 fps Vel. from my 8.5" barrel . 155 VLD's in a 16" or up to 20" barrel length, I would imagine the Vel. would be 'very good' with a 20" barrel .
I run the 155's for many years in .308 . & No other 155's runs faster than the Berger 155's . they got the least amount of bearing surface than others .
The 155's feed & chamber-up like they were meant for the .300 blk platform also . Also Hits the short range steel with Hard Authority but not abusive like blazing Vel. of .556 rounds . I would run them exclusively in the 8.5 shorty if Bergers were were not so spendy-$$ .
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I would guess the Huge ( .300 BLK ) lettering on the side of the Mags. could be for safety as much as it is for Sponsor Advertisement .
No one want's to accidentally in a hurry grab a mag. from the gearbag & jack-in a .556 by mistake . It's common practice to keep track of by numbering & marking on your Mags. since they all look alike anyway .
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That lettering is there because I laser engraved it on so that people would know he was shooting 300 BLK.