Considerations In Selecting AR-15 Ammunition
BY Herschel Smith
7 years, 11 months ago
We have previously discussed the Marine Corps battle with the Army and Congress over fielding a different ammunition than the Army, who spent a wad of money on an “environmentally friendly” lead-free cartridge, the M855A1.
Currently, the Marine Corps is trending towards the MK 318, which appears to be a far superior round, and it comes in right at 2900 FPS out of the M4 barrel, higher for longer barrels. The claim is that it behaves better at longer distances and retains its ability to penetrate.
This trend towards heavier rounds has been going on for some time now, and 62 grains isn’t the top weight for the 5.56mm bullet. One reader sends information about Sierra 77 grain, and tells me that the 1:9 twist is just fine with this ammunition. Of course, one gives up something to get something. In the case of heavier bullets, you give up muzzle velocity.
This velocity detriment may seem small. TFB likes the Sierra 77 grain, and informs us that its muzzle velocity comes in somewhere between 2500 FPS and 2600 FPS. But your choice of ammunition will depend upon your target, its distance, any interstitial shielding, potential body armor, etc.
You may do better with M193 than with either the MK 318 or the Sierra 77 grain. Sometimes the smaller rounds with the higher muzzle velocity are what’s needed to penetrate any armor. Do you not believe me? Consider what we learned with the FN 5.7 and its test against bulletproof glass, which only the .454 Casull could penetrate. The open tip 5.7 round at 22 grains penetrated the glass due to high muzzle velocity, whereas the heavier 5.7 round did not.
Do you need more evidence? Very well. Consider that AR500.com sells hard plates it calls Level III, and those plates are rated to stop M855 (steel core) but cannot stop M193. They have to move up to what they call Level III+ to perform effectively against the M193 due to its higher muzzle velocity compared to the M855. There’s nothing wrong with having a safe full of M193.
On December 22, 2016 at 3:30 pm, Ned Weatherby said:
Yep -muzzle velocity is king against steel. Learned that 40 or so years ago with a Mini 14 and 50 gr hollow points against steel and cast iron targets.
On December 23, 2016 at 12:30 am, Herschel Smith said:
Just for clarification, I should have added that (if I’m not mistaken), the NIJ standards on ballistic armor testing require fixed plates or soft armor, not rotating, swinging or swiveling. In other words, I think this tester did it correctly. Somebody could check me out on this.
https://www.nij.gov/topics/technology/body-armor/Pages/testing.aspx
On December 23, 2016 at 6:06 am, DAN III said:
May I suggest the new Barnes Match Burner Precision Match OTM ? The bullet is specifically designed for use in ARmalites.
At 300 yards the 85 grain Barnes’ velocity is greater than the 55 grain, 1,914 fps vs 1,884 for the 55 grainer. The energy of the 85 is 601 ft-lbs vs the 55 grain bullet’s 433 ft-lbs.
At 600 yards the velocity and energy differences between the two bullets is amazing. The 85 grain Barnes is almost 300 fps faster than the 55 grain: 1,413 vs 1,148. The energy of that 85 grain bullet, at 600 yards is more than double that of the 55 grain bullet !
I’m not sold on the 55 grain bullet. At the muzzle it’s great. Beyond that….not so much.
FYI….the above information taken from the current issue of AR-15 Magazine, “Multitask”, page 132.
On December 23, 2016 at 9:32 am, Josh said:
Could you even shoot 85gr ammo out of anything other than a longer barrel with a 1:7 twist?
On December 24, 2016 at 9:00 am, DAN III said:
Josh,
Go spend some Christmas money and buy the referenced magazine. Do some Internet research. Then come back and tell me the answer to your questions.
On December 24, 2016 at 9:58 am, Josh said:
Al my previous research indicates that heavier rounds have stability problems at long distances when fired from short, low twist barrels. 1:9 is good up to 62gr, but anything heavier wants a 1:7. I’ve spent hours and hours researching this.
What’s your opinion?