I don't see any reasons not to do it if you want the performance from the longer, higher BC projectiles. Throat/barrel life will suffer if you push it harder than the SAAMI MAP of 55ksi, but at or under 55ksi, it shouldn't be too hard on throats.
A lot of 5.56 NATO loads run 58-62ksi, for example.
I took the specs of the .224 Valkyrie and input them into an internal ballistics model that has proven to be dead-on with 6.5 Grendel. Narrowed the neck, case capacity, and baseline figures appropriately based on SAAMI and Sierra published data for a 24", then started modeling shorter barrels.
For a 77gr TMK load going 2900fps from a 24", I wanted to see what the numbers should look like for 18" and 12".
18": 2750fps (should be between 2700-2800fps with a wide range of barrels and rifling profiles)
12": 2514fps
11.5": 2487fps
Those aren't much different from 5.56, so shooting the 77gr TMK doesn't seem to make sense.
With the 69gr TMK 24" reference at 3100fps
18": 2940fps
14.5": 2809fps
12": 2687fps
11.5" 2658fps
10.3": 2582fps
Same thing
With 55gr going 3350fps from 24" Valkyrie reference
10.3" 2791fps
Sanity check 5.56 55gr:
11.5": 2910fps with PMC, 2958fps with XM193
The speeds aren't that different with bullets that fit inside 5.56 mag-fed. The real advantage is being able to shoot the longer-ogive projectiles from the mag in the AR15 in the .224 bore. For those that want to chase that for the real long-range benefits, I think the 88 ELD-M is going to be one of the main bullets to beat.
I've been extremely impressed with 88 ELD-M from .221 Fireball Improved, even at 1000yds. You can actually hear it impact.
The Valkyrie will give target shooters several great options for long range, low recoil, and hunters a few options for heavier pills that will penetrate more deeply into vitals of medium game.
Going SBR with lighter weight projectiles doesn't seem to offer much over existing 5.56 NATO, but Valkyrie SBR with the 80-100gr class of .224 bullets will provide real performance advantages for hunting and distance.
The cartridge makes sense for those that have switched from mv focus, to BC focus, because of the real downrange benefits of higher BC. If you're looking for impressive numbers at the muzzle just for the sake of a mv race, Valkyrie probably isn't the cartridge for you.
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