Norc M4 ammo test

[Ganderite]

I use a military ball powder similar to BLC2 to load my 223 ammo because it works well and I have a lot of it on hand. For CQB I have been using a 55 FMJ bulllet over 23gr of powder. This is only about 2450 fps (14.5" barrel) but it has enough power to run all my AR15s and remember power is not required to punch a hole in a CQB target 25 yards away.

A couple weeks ago I did an accuracy test with a Norc M4 and a Dan Defense M5. This included a variety of bullets, mostly loaded with Varget, so others could relate to the powder. I got curious about my surplus powder. How accurate might it be with the two bullets I have the most of, 55FMJ, 62FMJ and 68 HPBT Match?

the Millit 1-4 scope was replaced with a 20X target scope and I shot the FMJ bullets with 22 to 27 gr, in 1 gr increments. The 68 were shot with 23.5, 24.0, 24.5 & 25.0

As usual, some loads look better than others. The most important thing is that this rifle prefers milder rather than hotter loads. This would be a bummer if I was to shoot Service Rifle where I needed enough power to shoot 500 yards. Fortunately, I don't do that any more. If i did, I would use a 20" rifle.

The target was a sheet of paper with 1" black patches for aiming marks. It is easy to aim at one corner of the patch.

The 55s shot best, averaging under 2" (23 gr was 0.725"). The 62s were terrible ( as in past tests with this bullet) averaging about 3". And only the mildest load with the 68 was good (1.3").

These groups show what I meant when I said this rifle prefers milder loads:

 

[Conte]

What's the twist of the barrel ? Isn't like the typical 1-9 for the Norc ? If that's the case that's probably way too slow for a 68 in a 14" using that powder. If you're getting 2400ish out of a 55, probably only getting 2200ish out of the 68's.

The gun liking milder loads is an anomaly to me. I wonder if the access gasses blowing out the muzzle with hotter loads, with the bullet moving that slow to begin with, threw them off as they left the barrel. Just a guess. Not even sure if that concept makes sense.

BLC-2 seems awfully slow for a 14". At least the way I do things with my loading practices. I'm all about matching my burn rate to my barrel length and calculating how much gas I'll need to get the job done, and have gotten great results with that technique. If it was me, I'd be using a much faster powder, like 3031.
That might actually simulate the results of a milder load, while getting that bullet speed up to stabilize better.

I admit, I have yet to load for an AR.

 

[Ganderite]

It is 1:9. I think this is enough for the 68. If it was not, the bullet would tumble. And the hotter loads (more RPM) shot worse, not better. I am not going to argue with the rifle. If it likes the 55 loaded mild, so be it.

I agree the BLC2 is, on paper, the wrong powder for a mild 55 gr load. It is one of the very best for a max velocity load.

For a mild load I would normally run a faster powder. H335 would be better.

But I happen to have a lot of BLC2 type powder, so wanted to develop a good load with it, if possible. I also ran some of this ammo through my 223 CZ58. The 55 FMJ 22 gr load grouped under an inch at 50 yards. Again, the mild load was best, and again, the 62 sucked.

I was just about ready to say the 62 gr bullets were no good, but they shot well in my bolt rifle (also 1:9) and in my Danial Defense M5.

My suggestion to others is to run a spread of powder charges in your rifle and find out if it has any clear preferences.

 

[Conte]

Hmm, I'm under the impression that a tumble is gross under stabilization, but it's still possible to stabilize a bullet just enough for it to not tumble, but not enough to be accurate. I could be wrong about that, but that understanding could explain why the heavier bullets suck. In general, my understanding of ballistics suggests that a heavy bullet in a 1-9 14.5" just don't go together. Maybe you could find a good load, or maybe are jsut herding cats. 55g is a sweet spot for that combo, I personally wouldn't expect better results with a heavier bullet. Just can't shoot as far, but like you said, that's what 20" is for.

Is it possible that the hotter 68g load added just enough extra recoil to throw off your shooting technique ? You might not feel it, but it is there ?
Maybe you hit that cusp where there is just enough muzzle jump before it leaves the barrel ? and the mild loads load bring back down to the physics of the 55g load ?
I have found in practice that shooting a hotter, heavier loads can require me to change my technique to compensate for extra muzzle jump.
Mind you, that practiced difference is more extreme, going from say a 223, to a 308.

H335 is in the same neighborhood as 3031, so I guess we're on the same page there.

 

[Ganderite]

1:9 is not 'slow". It is actually quite fast and will stabilize 69 just fine. I ran a test for Savage on 20 prototype rifles when i was encouraging them to switch from 1:12 to 1:8. They balked at 1:8, but agreed to test and consider 1:9. At that time the "heavy" bullet was the Sierra 80 gr MatchKing. Savage had concluded that a 1:9 was enough for the 80. I had my doubts.

They sent me 20 rifles with the standard 1;12 barrels and 20 spare 1:9 barrels. One by one I swapped the barrels and deepened the throat and then shot the rifles with 80 MatchKings. They all shot very well (sub MOA) if I loaded to max. 1:9 was just barely enough for the 80.

I tried to get them to set 1:8.75 as a twist, but they stuck with 1:9.

I have not tried any, but I would expect the 75 HP to stabilize in this short 1:9 barrel. It would be close, because the short barrel would have less velocity (RPM).

I run a test similar to this broad range of powder charges and several different bullets in each rifle and pistol. It is not unusual for the gun to have a strong preference of bullet, powder or velocity range. I think it is an important test for anyone wanting to get some performance from their gun. Even someone using just factory ammo should try some different brands and bullet weights.

 

[Conte]

How long were those Savage barrels ? 1-9 in a 20-22 and 1-9 in a 14" are 2 diff beasts in my book.

Mind you, testing barrels for a big company ? Man, it does sound like you have way more experience on the subject that I do.
I was just brainstorming some ideas without knowing your level of experience. I've loaded for a 22" 1-8 barrel for years.