Home Forums Reloading Varmint Rifles Tale of two twists 1/9 and 1/7 in 5.56

I ordered a big box of the 75 grain Hornady BTHP match bullet with a cannelure and shot them in two different uppers twisted 1/9(16 inch) and 1/7(20 inch). The 20 inch 1/7 twisted barrel was slightly more accurate with the bullet but neither barrel is a match barrel and both barrels shot this bullet under 1 1/2 inches at 100 yards. Water jug testing revealed a difference though. The 1/7 barrel kept the bullets point on with half the core and the expanded jacket ending up in the third water filled milk jug with small bits of lead and pieces of jacket in the second jug. The bullets from the 1/9 twist barrel tumbled, bent and the lead core ended up in the third jug leaving the broken up jacket and very little lead in the second jug. The lead core being bent but nearly complete. I ran this test twice with the same results, the jugs were shot at 100 yards. Load was 24.5 grains of BLC-2 with a Wolf mag primer. Both tore up the first two jugs pretty good but the third jug just had a small hole in it where the last of the bullet penetrated it,knocked over but still intact with the lid on the milk jug. Hard to choose but I like the performance a bit better from the 1/7 twisted barrel.

Thanks for that informative post. Gives something to think about.

Twist rates for different weight bullets are different. The heavier the bullet the faster the twist rate should be..ie........

55 grain is better with 1:9 twist

75 grain is better with 1:7 twist

Generally true, however, bullet shank length also has a lot to do with the best twist rate for accuracy.

BTW, Welcome To The 'Fire!

Ed

It does show that the 62 gr. FMJBT's the military switched to when used in 1-7 inch twist barrels probably didn't tumble and do as much damage to a target as the 55 gr FMJBT did coming from a 1-12 twist barrel. This could be why the 62gr. bullets seem to have a dismal reputation for stopping power.

More testing. I shot a big doe a couple of weeks ago with the 75 gr, BTHP Hornady cannelured. Damage was a rather thin wound channel of around an inch through the meat under the shoulder blade and exiting over the shoulder blade where it attaches to the upper leg bone. Hole in upper part of lungs was a square almost 2 inches across, exit hole was a cross section of the bullet going through sideways. I found the bottom of the jacket sticking out of the shoulder under the hide, all of it up to the cannelure with no lead inside. The doe ran maybe 35 yards and was down. This from my 1-7 inch twist 20 inch barrel and powered by the above load. I saw the bullet hit, she jumped a bit, took off and went down. I like the 60 grain Hornady HP better, for more damage but the 75 grain bullet did quickly kill the deer and it did exit.

Interesting.

No new news here. Being saying it for years, most don't want to listen.

If seen a few cases of Barnes bullets not behaving right on the 'Fire (dipshiet Brad comes to mind) that I know were minimally stabilized, at best.

But there are a LOT of thick skulls on the 'Fire.

Isn't this the bullet Stick likes for AR's?

I guess I will have to shoot a deer in the same spot with a 1-9 twist barrel for a comparison!

Yes

The 1-9" twist for the .223 is marginal. Slowing speeds down with the 16" tube isn't going to help anything.

That being said I was shooting offhand with this bullet yesterday in 7 and 9 twist AR's and hit percentage was the same out to 250yds. Damage to jugs at 50-100yds was the same. That's @ 2,500' for elevation and a temperature of 7*.




Dave

Got a 9 twist in a deuce and its very versatile, but Im only shooting bullets up to 63 grains. For heavier stuff in the .223 or even the longer lighter bullets like Barnes TTSXs the tighter twist is mo' beta.
Ive got an 8 twist .223AI that will shoot anything I stuff into it...a 7 should too.

The 75 grain HPBT doesn't shoot as well out of my 1-9 twist barrel but it hugs MOA. Not that far off sea level here in Fort Worth and the humidity if thats a factor is often over 60%.

I found out that lower elevation stuff REALLY IS a factor! Especially with longer bullets! The 1 in 8 twist cleared it right up!

I'm only about 1200 ft elevation at our range....

I have found if a match longer bullet is shot with the one in 9 fast enough, there are no stabilization issues..

however with a one in 9, if one can live with a 68 grain BTHP over the 75 grain version... that bullets is almost the same in length and actually seems to be as flat shooting as the 75s out to about 600 yds is the most I've tried it....

but being a little lighter, ( and I use faster powders than most).. you can give it some extra velocity over the 75s...

H 322 is the powder I usually reach for, when loading either bullet... and so far my shooting of them has been strictly in bolt actions...throated to magazine length.

The 68 or is it 69 grain Hornady bullet is actually a couple thousandths longer than the 75 grain Hornady bullet. I may do some trading to get some of the lighter bullets.

H
What makes you run the faster powders 'fire?

I have a hobby lathe and I may set it up to take .020 off the pointy end of the 75 grain bullet. This would also make the HP opening a bit bigger. Something to play with anyway.