Was doing a bit of precision testing yesterday and had some interesting results with Hornady Superformance Match 223.  75gr BTHP.





Rifle used was a RRA 1/8 twist, 18",  Mid-Length Stainless barrel profiled to .750



Range was 100yds... 84 degrees 71% humidity winds SSW @3mph

Velocities obtained from 5 round string using this ammo:

1. 2812
2. 2804
3. 2784
4. 2744
5. 2739

Round One and Two started having pressure signs... primers starting to push out...three and four were pierced primers and the fifth has a "crater" inside the primer strike.



My firing pin now has a "crater" or pit on the tip.  (going to need to borrow a better camera to get a picture of this)

Results on the target....


And results on the same day using FGMM 77gr and Hornady Match 75gr





Black Hills 75gr, FGMM 77gr, Hornday 75gr TAP and 75gr Match all functioned well with out any issues or signs of overpressure.  

Going to contact Hornady on tuesday and will update the post with what they say....

BE CAREFUL using this ammunition.

Those velocities are around 5.56 pressure.



What is the diameter of your firing pin hole?



If the firing pin and firing pin hole are not close in diameter, primer piercing does occur.



 

To be honest I'd have to measure.  The BCG was purchased complete and from a quality manufacturer.  In the past I have had NO issues using 556 velocity ammunition in this rifle.  Using XM193 to "test" the chrono resulted in over 3000fps with no overpressure signs.

I'm pretty sure they said its only for rifle length ar's

No where on the packaging that I saw...

Yes, but this is 'Superformance' ammo.



"Superformance ammunition is tested and is safely within SAAMI pressure guidelines. Gas operated (direct impingement or gas piston) firearms are perfectly safe to use with Superformance ammunition. However, Hornady ballisticians have conducted testing with a variety of guns (including guns equipped with suppressors), and our findings conclude that some systems work far better with Superformance ammunition than others.



It is recommended that to get the best functioning with Superformance ammunition in gas operated/gas piston semi-automatic or select fire guns, rifle length gas systems with 20 inch or longer barrel lengths are best for reliable firing and extraction. Any other configuration, particularly shorter barrels/gas systems are best served with the installation of an adjustable gas system, ESPECIALLY if a suppressor is to be installed."





http://www.hornady.com/ammunition/superformance-in-gas-operated-firearms





 

I was with Tosser while he was shooting these, and a bunch of other loads, and I mentioned that I thought Hornady didn't recommend the superformance in semi autos, but Tosser and I each looked at the packaging carefully and it is not indicated anywhere on there.  There were no restrictions of any kind on the packaging.  My bet is after a bunch of people with ARs complain there will be in the future.

By the way, I have chronographed a LOT of loads, and the measured velocity is above what I have seen with 5.56 pressure 75gr loads.

Thanks for the link.  Now they just need to put a warning on the box, or many other people will see this in the store, buy it for their shorter than 20" semi gun, and possibly damamge it.

I have found the 5.56 pressure heavy bullet loads give 2,750-2,780 with an 18" barrel.



Since this is a .223 load, I can only imagine that Hornady's 5.56mm load is even hotter.