Black Hills 5.56mm 77 gr TMK and 69 gr TMK Review

[_Stormin_]

My model of Magnetospeed won't work with suppressors.

That's an interesting one. Do you know why? I would think that all it's looking for is an object breaking two radar planes, but I'll admit, my chrono-knowledge is limited to reading online and a base knowledge of physics.

[markm]

Here's some of the chrono data for those interested:

16" barrel:

77 gr 2713 fps, SD 13 -------> with no suppressor 2703, sd 15
69 gr 2833 fps, SD 10


14.5" barrel:

77 gr 2648 fps, sd 21
69 gr 2776 fps, sd 31


11.5" barrel:

77 gr 2520 fps, sd 12 -----> with no suppressor 2498 fps, sd 20
69 gr 2520 fps, sd 20

[markm]

We seemed to see a little free bore boost above.

10.5 and 10.3 Colt were a little interesting:

10.5"

77 gr 2436, sd 8
69 gr 2540, sd 19

10.3"

77 gr 2406 fps, sd 13 (30 fps slower than the 10.5)
69 gr 2499 fps, sd 14 (41 fps slower than the 10.5)

[markm]

We had one bad mag that "bolt overed" in a few of our guns, ruining 3 live rounds. So we threw the mag down range and shot it. The TMKs in this load have a cannalure. You can't see it peeking out of the neck, but it's there. I found the cannalure when I pulled apart a few of the 77gr rounds that the bad mag destroyed.

The SDs are all really good for our 5 round strings. The ammo is hot, for sure. I can feel it on my 14.5 bcm middy, and most of the shorties. But there aren't any pressure signs on the brass at all. No case head swipes or anything.

[opngrnd]

...So we threw the mag down range and shot it.

This is about the best part of any thread. I hate bad mags.

[Ryno12]

That's an interesting one. Do you know why? I would think that all it's looking for is an object breaking two radar planes, but I'll admit, my chrono-knowledge is limited to reading online and a base knowledge of physics.

It's not the why, it's the how. They attach to the muzzle end of the firearm. Some models aren't compatible with suppressors.

Magnetospeeds don't measure velocity by "breaking two radar planes". (Not sure any chronos do). They're electromagnetic, not radar or optical.

[Pappabear]

We seemed to see a little free bore boost above.

10.5 and 10.3 Colt were a little interesting:

10.5"

77 gr 2436, sd 8
69 gr 2540, sd 19

10.3"

77 gr 2406 fps, sd 13 (30 fps slower than the 10.5)
69 gr 2499 fps, sd 14 (41 fps slower than the 10.5)

This one surprised me the most. Lost that much speed going from 10.5 to 10.3, wow. Im sure other factors are at play. Any of the great minds know if the shorter the barrel, the more speed you lose per inch of barrel. And would you have expected that drop?

FYI, the 10.3 was a Colt 6945 monolithic upper with a Sig can on it.
The 10.5 was a CL Noveske with AAC can on it.

Mark has some can , no can data as well. But everything pretty much played out like it should with the test as a whole which proves out once again the ammo is very consistent and reliable.

PB

[gaijin]

My guess would be the slower Colt barrel being the culprit- or the Noveske is "fast".
.2" shouldn't account for the velocity loss you experienced.
Tighter/looser chambers would be where I'd start looking.
Of course you could cut .2" off the Noveske and see what velocity you lose.

I'm really enjoying your experiences here, so much so that I've ordered some 69 gr. TMK to try myself.

[Pappabear]

I have a DD 10.3 that Im going to have to chrono just for shits and giggles. I didn't want to take 9 million guns out, but It would have been more data. We'll find out who was fast or slow and post.

PB

[gaijin]

Good plan.
Let us know the score.