Paul Harrell: AR Platforms In 10.5″ vs 20″ Barrel
BY Herschel Smith
4 years, 5 months ago
My takeaways: (1) The heavier bullets (77 grains) are more effective than the 55 grain bullets, and (2) The muzzle velocity even at close range for the 10.5″ barrel hovers around 2200 FPS, right at the threshold for hydrostatic shock.
On July 25, 2020 at 9:47 am, Houston said:
I use IMI 77gr Razorcore in my AR 10.5 pistol. Chose this after a lot of research and the price is right. Or at least it was.
On July 25, 2020 at 1:43 pm, Silence DoGood said:
With 5.56, hydrostatic shock isn’t where the rubber meets the road, it’s fragmentation. By (Stoner’s) design, the majority of the 5.56’s lethality is tied up in fragmentation. As evidenced at the 1993 Battle of Mogadishu, when 5.56 doesn’t tumble on impact, neither does it fragment. And if it doesn’t fragment all you get is an “ice pick wound.” With the exception of 77-gr Mk262, all 5.56 NATO rounds fail to fragment reliably at impact velocities of less than 2700 fps (~832 m/s). The Mk262 is good down to nearer 2200 fps.
This is exactly why the SpecWar community felt the need for the 6.8 SPC. Because they are fond of their ten-inch SBRs but weren’t so keen on the 5.56’s lack of terminal performance from such a short tube. So if you’re going shorter than 16″, and definitely if you’re going shorter than 14.5, it’s in your best interest either to be very picky about which ammunition you choose to use (BH Mk262 & Hornady TAP 5.56 should be near the top of the list) or to look at an alternative to 5.56, like the (aforementioned) 6.8 SPC or .300 Blk.
From a study done by Dr Martin Fackler on fragmentation of M193 ammo:
On July 25, 2020 at 1:43 pm, Silence DoGood said:
Sorry, the photo failed to come out. The image is here:
https://farm5.static.flickr.com/4026/4212874291_6774d9c7cc.jpg
On July 25, 2020 at 2:43 pm, Herschel Smith said:
@Silence,
I disagree based on what I’ve studied. It’s both, with perhaps shattering of the bullet being the more significant of the effects. The 10.5″ barrel is all around a bad idea in my opinion.
But it does behoove shooters to have some of the 75 – 77 grain in their safe. It’s not cheap.
On July 27, 2020 at 12:01 pm, brunop said:
If you reload, you can buy Hornady 75gr. BTHP + Varget and match ballistics (2789FPS @ 0) to the Hornady .223/5.56 “Match” – which is much more accurate out of multiple barrels than their “Superformance” (2915FPS @ 0) line.
And you can load it for half the Big Box price ($19.99/20 = $1/round…).
Both the “Match” ammo and my reloads shoot 2″ at 200 yards out of ARs with good barrels – ranging from heavy Noveske SS “target” barrels to DD CHF “pencil” barrels. They’d shoot better, no doubt, if I’d bag the rear of the gun – but then I wouldn’t be shooting – I’d be playing at benchrest.