Interesting findings.

[mao0720]

Found out today that in my 16" 1-9twist AR15 that 69gr SMKs shoot very well over 24.5gr varget, but 68gr Hornady BTHP don't stabilize and key-hole at 100yds. I couldn't keep 5 shots on an 18x24" paper at 100yds. Its a good thing my Mossberg MVP will shoot the hornadys or Id have 500rnds loaded that I couldn't do anything with.

 

[jonbearman]

What powder charge do you use with the hornadys? I have shot them out of 2 of mine with a 1in9 and they fly great.Something sounds odd with your problem with that bullet.

 

[mao0720]

Same charge as with the SMKs, 24.5gr of varget. The Mossberg MVP has a 9 twist at it shot them just fine. Might be that Im not getting enough velocity for them with the 16in barrel or could just be that specific barrel doesnt want to stabilize them.

 

[markm87]

Interesting. My buddy's Rem 700 5R with nominal 1/9 will shoot 80 gr SMKs and keep them stabile to 1000.

I dare you to try some H322 in place of Varget.

It shoots heavy Matchkings and Nosler CCs amazing. (and meters way better)

 

[jonbearman]

I agree with Mark,try a different powder.H322,benchmark,blc-2 etc.You may get better results.

 

[mao0720]

So here is the big question. What kind of velocity is your buddy getting out of his rem 700 223? Because it is RPMs not just twist rate that stabilize a bullet, and with increased velocity you get increase RPMs. My thought in my situation is that my 16" barrel is too short to create enough velocity to give the RPMs needed to stabilize the Hornady 68gr HPBT (which is longer than the 69gr SMK), but the added velocity I get from my MVPs 20" barrel is enough boost in RPMs to stabilize the hornady.

Im considering trying to load up the Hornady hotter, and see if I can get enough velocity to stabilize them. Part of me just doesnt care. the 69gr SMK shoots very well for me and they are available again, so why bother.

 

[markm87]

Because it is RPMs not just twist rate that stabilize a bullet, and with increased velocity you get increase RPMs.

These are just .223 max, Hodgdon published loads... in other words, not hot loads at all.

There's a trade off with that notion... as I understand it.

The slower a bullet travels, the less wind resistance, and thus the lower the RPM necessary to stabilize. I read this comment in an article published in Handloader Magazine (the Author seemed to have a grasp and was citing Litz, etc. so... ??)

Essentially the assertion was that there was only a very slight gain in stability with increased velocity, all else equal. :-\