TexasCHLforum.com

It looks like my stock of brass for my M&P15 is just about done. I'm starting to see case neck cracks. The brass began life as Remington 223 55gr FMJ and I have been reloading 223 spec loads for my AR.

My question is whether I should restock with 223 ammo or 5.56 ammo? I am aware of the difference between the loadings and my rifle is chambered in 5.56. Can I use the 556 brass and load 223 or is the case wall thickness going to be a factor? If I use 556 brass should I only use the 556 loadings from my Hornady book? Will my 223 dies cause any issues?

It does depend on how you plan to load the rounds. There are several data providers that go up in bullet weight above 65 grs. and call their loads 5.56mm NATO. Very few of them actually load to 5.56mm NATO pressure which is 62,350 PSI/CIP vs 55,000 PSI/SAAMI for the .223 Rem.

You can load down to .223 level in 5.56mm cases, although your loads may differ slightly from the data due to the somewhat smaller case capacity/slightly thicker brass of the 5.56mm NATO. Loading 5.56mm NATO loads in .223 Rem. cases will shorten the life of the cases except maybe in the case of Lapua brass which has a higher test pressure rating. But it is more expensive.

A true source of 5.56mm NATO data is Western Powder Co's. We've been using TAC for some time now and AA 2520 is another good one. We set out to match the spec of the Mk 262 Mod 0 load that uses the Sierra 77 MatchKing OTM (open tip match) w/cannelure that requires 2700 FPS at the muzzle to tumble out to 300 yards. But after testing a few other bullets we found that the Hornady 75 gr. Match OTM w/canelure holds together better at shorter ranges, and the accuracy difference is moot so far as tactical use. The Max charge of TAC is 25.8 grs. for the Hornady 75 gr. bullet, but 25.0 grs. will get 2750 FPS from a 16" barrel and on a number of occasions 10 rounds over the chrono resulted in standard deviations of 10 or less. I would say that that's the slight advantage TAC has over 2520. But for slightly higher velocity at the same pressure level, 2520 does that well. You barrel needs to have a 1 in 8" twist or faster for best accuracy with the heavier bullets.

I hope when you state "tumble out to 300 yards" you mean projectile tumble post target entry and not tumbling in flight. The Hornady 75 and Sierra 77 both shoot well past 600 yards and that would not be possible if they tumbled.

Tumble within a high water content target would just need maintaining a threshold velocity at target impact that provides a center of pressure position forward of the projectile's balance point or center of gravity.

ammoboy2 wrote: ↑Sat Jun 06, 2020 1:11 pm I hope when you state "tumble out to 300 yards" you mean projectile tumble post target entry and not tumbling in flight. The Hornady 75 and Sierra 77 both shoot well past 600 yards and that would not be possible if they tumbled.

Tumble within a high water content target would just need maintaining a threshold velocity at target impact that provides a center of pressure position forward of the projectile's balance point or center of gravity.

A bullet that tumbles in flight wouldn't be worth much, LOL! You might want to read about the Mk 262 Mod 0 development. It's ability to tumble after impact was something of a game changer for the 5.56mm NATO round, and a good bit of its development came from the late, great Chris Kyle. In reviewing the history of the round in combat, tumbling after impact was part of the attraction of going smaller caliber along with lighter recoil and greater mag capacity. Tumbling is not always achieved with the lighter bullets.

Black Hills is now marketing the Mk 262 Mod 1C where they're claiming 2" groups at 300 yards, and therefore sub MOA at 300 yards. With our load using the Hornady 75 gr. OTM w/cannelure 1/2 MOA for 10 rounds at 100 yards has been done a few times with 25.0 grs. of TAC with standard deviations of 10 or less. That load meets all the specs. It's the same bullet that Hornady uses for their NATO Match load as well as the "LEO" TAP 2 and velocity is nearly identical.

K-Texas wrote: ↑Sat Jun 06, 2020 12:28 pm
You can load down to .223 level in 5.56mm cases, although your loads may differ slightly from the data due to the somewhat smaller case capacity/slightly thicker brass of the 5.56mm NATO. Loading 5.56mm NATO loads in .223 Rem. cases will shorten the life of the cases except maybe in the case of Lapua brass which has a higher test pressure rating. But it is more expensive.

Sounds like you are confirming my instincts that if I run a 223 load in 556 cases I will be well below pressure that is safe for the rifle but slightly above the 223 data since the case volume is slightly smaller. Basically I will have ultimately ended up with a dialed back 556 load.

That is correct.

There are some in the ammo industry who believe that the .223 Rem's 55,000 PSI rating is unnecessarily low, but there a number of differences between loads for .223 AR 15s and .223 Bolt rifles. For ARs chambered for 5.56mm NATO and marked as such, you get the full plate of load options.

olafpfj wrote: ↑Sat Jun 06, 2020 1:41 pm

K-Texas wrote: ↑Sat Jun 06, 2020 12:28 pm
You can load down to .223 level in 5.56mm cases, although your loads may differ slightly from the data due to the somewhat smaller case capacity/slightly thicker brass of the 5.56mm NATO. Loading 5.56mm NATO loads in .223 Rem. cases will shorten the life of the cases except maybe in the case of Lapua brass which has a higher test pressure rating. But it is more expensive.

Sounds like you are confirming my instincts that if I run a 223 load in 556 cases I will be well below pressure that is safe for the rifle but slightly above the 223 data since the case volume is slightly smaller. Basically I will have ultimately ended up with a dialed back 556 load.

Now this is easier to say than to practice, and it wasn't until after the development of the Mk 262 Mod 0 that I had any preference for a 5.56mm NATO load over 7.62 X 39mm Russian. But in knowing that Chris Kyle was behind it, I gave up any worry I had for using a .224" bullet for any practical range out to 300 yards. My quest was about the shorter-end implications, while my belief was that any round that can surpass a 75/77 gr. open-tip .224" Match bullet will decrease mag capacity accordingly; simple geometry dictates as much.

Us boys here, bought into that premise, while my shooting partner took it a step farther with a purchase of a "Colt's Competition" CRX-16 (Final assembly and parts coming from good Texans 100 miles north of me in Breckenridge, TX) purchased at less than $900. Google that and see what pops up today in terms of price! It was twisted 1 in 8" and came with a 3-shot guarantee of MOA or less for premium match ammo at 100 yards.

In case I come off as being arrogant, what pushed me into handloading all-those-years-ago was the belief that I could hand-craft better! It will be some time before any rational prices return for firearms or components, But with what I'm interpreting from your comments, I'd suggest investigating the Lapua Match brass, which is exactly what we did before committing to lower price, which meant Lake City.

Look particularly at the pressure that Lapua was willing to test up to. All I can say is that none of our first cases have failed. And as I've mentioned elsewhere, the goal has never been about a MAX Velocity. Something else that I also like to say, whenever the opportunity arises, is that powder selection is PARAMOUNT! And our do-all 5.56mm NATO meets all of the requirements, tactically, with a charge of Ramshot TAC at .8 grs, below the MAX charge. 10 Shot strings with the Hornady 75 I've already mentioned will have an average velocity above 2750 FPS from a 16" barrel, and a standard deviation of 10 FPS or less, and 1/2 MOA, and that includes chronographing from a 16" Ruger AR556.

Some here will get it, some won't. My participation here in terms of posts vs. registration date is kinda a reflection of that. As far as Aesops fables? Never trust the opinion of anyone offerring handloading advice because of their post count or length of tenure after registering. Handloading is a serious matter of pressure concerns where physical science becomes far more relevant science than the science of biology, or PSYCHOLOGY!