Is 68g a better choice than 75g for a 1 in 9" barrel?

[Lone_Gunman]

I think I have settled on one or the other of these bullet weights. I am trying to decide which of these is best from a 16" 1 in 9 barrel in .223. I will also shoot it through a scoped 223 rifle with a 20" barrel, also 1 in 9.

I am looking for improved terminal performance when compared to 55 and 62 grain bullets, but still want as good of accuracy possible.

I am assuming the 75g bullets would be loaded to slightly less velocity than the 68 g. Will that affect fragmentation and make the 75g less effective?

 

[Chris Rhines]

The 1:9" twist barrel may not stabilize the 75-grain bullet, especially the 16" one. I'd try both weights in both your barrels, and see for yourself.

The 75-grain bullets will probably have a slightly longer effective range, even at a lower starting velocity.

- Chris

 

[RobZ71LM7]

If you're going to do any really long range shooting a 1/9 twist usually isn't adequate for 75 or 77 gr match bullets.

 

[Lone_Gunman]

Chris, do you think that for a rifle with either iron sights or a zero power red dot, it would make enough of a difference in accuracy to matter?

I can usually shoot around a pie-plate sized group at 100 yds with iron sights, and a little better with a red dot. So if you think we are talking about sub moa differences, I don't think it would make a practical difference to me with that set up. With a scoped rifle it would be different, and smaller accuracy changes would be important.

I think I am thinking about this too much. There are just too many choices it seems like.

 

[jefmad]

Your 1 in 9 twist may not stabilize the bullet which will make a large difference. Stick to the 68 or 69 gr. bullets.

 

[RobZ71LM7]

You can try them and see but with a 1/9 twist barrel the 75gr bullets will most certainly keyhole at longer ranges. In my experience my 16" carbine was fine with 77 gr SMK's at 50 yards, but was terrible with them at 100 yards. It depends on the range you want to shoot at. I wouldn't waste my time with the heavier bullets. I'd use the 68 gr Hornady or 69 gr SMK. When you shoot out your barrel get a 1/8 or 1/7 twist one.

 

[CrackerJim]

Does a 26" barrel provide enough spin in 1 in 9 twist for the 77 gr bullet?

Thanks,

Jim

 

[Bigfoot]

Some rare 1:9 barrels will stabilize the 75/77s. Try a few on paper and see if they keyhole. If they don't, even if they arn't as accurate as a fully stabilized bullet they are good enough for the defensive ranges that you're talking about.

I don't think you're overthinking it considering what's at risk. Here's a good link, it might narrow the choices down for you.

http://www.tacticalforums.com/cgi-bin/tacticalubb/ultimatebb.cgi?ubb=get_topic;f=78;t=001244

 

[DMK]

Some rare 1:9 barrels will stabilize the 75/77s.

I don't think it's that rare. I have two 16" RRA 1/9 barrels and one 20" Bushmaster 1/9. All three will shoot a couple brands of 75gr to within 2" or better at 100 yards, perfect round holes. The Bushmaster spread 77gr out to 3" though, still no keyholes.

Now, it's my understanding that the instability is more apparent at longer ranges, but I haven't had the opportunity to test that.

Now I have not been able to group Black Hills 68gr better than 3"-4" in any of those rifles, one spreads them way out. The 20 rounds of Federal 69gr I shot grouped pretty well though.

Rifles can be picky individuals. You need to test your rifles with your ammo.

 

[M2 Carbine]

I'm getting poor accuracy even with 68gr bullets in my 1 in 9 NM Rock River Arms AR and Kel Tec PLR .223 pistol at 100 yards.
I have a number of bullet weights above 60 grain to try out yet but a few early tests have been very poor.

The RRA will shoot well under an inch at 100 yards and the Kel Tec pistol will shoot under two inches with bullets in the 50-55 grain range. So far the above 60 gr bullets aren't shooting anything that could be called a group. Not key holing, just shooting inconsistently.

 

[Chris Rhines]

Chris, do you think that for a rifle with either iron sights or a zero power red dot, it would make enough of a difference in accuracy to matter?

My experience with running 75-grain bullets through my 1:9" lightweight AR is that the bullets would be fairly well on target out to 75-80 yards, then they start tumbling and the accuracy competely goes to hell. At 50 yards they shoot 1" groups, at 100 yards I can't keep them on a 9" pie plate.

Temperature, muzzle velocity, and barrel length can affect the range at which the bullet starts tumbling, and I've personally seen a few 1:9" barrels that seemed to stabilize heavy bullets out to 300 yards. They're the exception rather than the rule.

In general, I'd stick with 70-grain bullets and under in a 1:9" barrel. Try some heavier stuff, though. You may get lucky.

I think I am thinking about this too much. There are just too many choices it seems like.

This is true. I'd just try a couple brands of ammo, 68-77 grain, and buy more of whatever works best.

- Chris

 

[Bartholomew Roberts]

75gr will be superior to 68gr in terms of effectiveness.

Some 1/9 barrel handle 75gr just fine. Some don't. Even in the worst case scenarios that I've seen, a 1/9 will still do 4-5MOA groups at 100yds with 75gr, which should be adequate for most defensive needs.

 

[RockyMtnTactical]

They are both excellent in terms of terminal performance. Shoot whichever is most accurate and/or affordable.

 

[Quintin Likely]

It depends. Shoot 'em both and see. I had a 1:9 bolt gun with a 24" barrel on it and it wouldn't shoot 75gr Hornady HPBTs or 77 SMKs too well. A 1:9 Bushmaster HBAR I had shot the 75s very well, never tried 77s out of it.

 

[MikeH]

I loaded and shot some 75gr Hornady HPBTs a couple of months ago on a 1:9 24" barrel. Five-shot groups at 100 yards were around 0.5 - 1.0 MOA. Not as good as what that rifle could do with 68 or 69gr.

Maybe the 75gr will show its advantage at a longer range, say, 300 yds or more.

 

[DogBonz]

I'm no expert

But I don't think that barrel length has anything to do with it, within reason, or course. By going to a longer barrel, you will not solve the "spin" problem. Think of it in terms of RPM. Heavier bullets need higher RMP's to stabilize. Also heavier bullets usually (all else being equal) need more distance to "sort themselves out".

The 1:9 twist is really not good for many bullets. It was the best compromise that could be found. 40-50 gr 223's will do best in a 1:14-1:12. 55-69gr do best in a 1:10-1:8, 72-and up do best in 1:7.5 or less.

 

[DogBonz]

Mike

Maybe the 75gr will show its advantage at a longer range, say, 300 yds or more.

Yes... and no. As I said in my post, the 75's are probably a little heavy for the 1:9. But in the appropriate barrel, yes they will "hold" more of their accuracy than a lighter bullet.

In my Grendel, the light 90gr Speer TNT's are very accurate at 100 yards .3 moa. But at 200 they open up to almost .6moa, and more than 1 moa at 300. The Lapua 123's however, are an unimpressive .6-.7 moa at 100, but don't open up at 200 at all, and shrink to about .4-.5moa form 300 - 400. After that they open back up, but that is probably more my lack of skill and practice at longer ranges.

 

[rangerruck]

dogbonz is right, bbl length has nothing to do with bullet stabilization. a 1/9 twist should do the 60 plus grainers, but will have a hard time up in the 70 grainers. Especially if you do not have a bll made with the upmost precision. Absolutely no loose, then tight spots, especially if you have a loose spot right at the muzzle. That is why the military uses a 1/7 twist, especially to use the longer , sniper type long range bullets , and the tracer stuff.

 

[Don't Tread On Me]

Like others have said, the 75 will be supeior to the 68. However, that doesn't make the 68 a sloutch. It is superior to 62 or 55 gr ammo.

The main problem with 75gr ammo in a 1/9 is that even if you can stablize it, that will not hold up in cold weather. One day might be 85 and you're hitting bullseyes, another day it is 40 outside and you're keyholing 12" left.

This is especially true of carbine length barrels as they impart less spin on the bullet.

Just barely stabilized is not good enough. Hitting is more important than 7gr more weight.

If you have a 1/9, use the 68 hornady or the 69 SMK ...you will not be undergunned with either of those. You will know with total certainty that in any scenario, your rounds will be on target.


If you are buying a new rifle, then go ahead and make the effort to find a 1/8 or even better yet, a 1/7 and then you can shoot anything in any weather.