5.56/.223 bullet weight in a 1:9 barrel

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w squared

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I know that the high-speed low-drag crowd is going to 1:7 twist barrels to stabilize a variety of longer, heavier 5.56mm bullets.

My AR is 1:9, and the XCR that I'm considering is also 1:9. I'm wondering how far I can realistically push the envelope in terms of bullet size before the spin rate is no longer enough to stabilize the longer, heavier bullets.

60 grain?

62 grain?

69 grain?

75 grain?

77 grain?

I'm not looking for anything all that exotic...I just skimmed the Federal and Hornady sites looking for something other than 55gr FMJ and super-light varmint rounds.

I know that some folks here are swearing by 77gr bullets in a 1:7 barrel.

Does the bullet type (FMJ/TAP/HPBT/Nosler/etc) have any effect on the ability of the barrel to stabilize the heavier bullets?
 
w squared said:
I know that the high-speed low-drag crowd is going to 1:7 twist barrels to stabilize a variety of longer, heavier 5.56mm bullets.

My AR is 1:9, and the XCR that I'm considering is also 1:9. I'm wondering how far I can realistically push the envelope in terms of bullet size before the spin rate is no longer enough to stabilize the longer, heavier bullets.

60 grain?

62 grain?

69 grain?

75 grain?

77 grain?

I'm not looking for anything all that exotic...I just skimmed the Federal and Hornady sites looking for something other than 55gr FMJ and super-light varmint rounds.

I know that some folks here are swearing by 77gr bullets in a 1:7 barrel.

Does the bullet type (FMJ/TAP/HPBT/Nosler/etc) have any effect on the ability of the barrel to stabilize the heavier bullets?
Click to expand...
Although not an AR, I have a Savage bolt gun that is 1 in 9 and it stabalizes 75 gr. AMax's with no issue.
 
in the manual for the stevens 200 in 223 it lists 69grain as the preferred round. Although, pretty well anything works. Guy at my club uses 52grain to great effect.
 
ARs need mag length seating (unless of course you're planning on shooting single round slow fire.) This translates to a round that is ~2.250" OAL -you may even push it out to ~2.260" (but not much more or they'll hang in the mag and cause stopages)

It is not so much the length of the bullet as it is bearing area (portion of bullet that is in contact with the lands) that determines whether it will stabalize in a 1:whatever twist. In general you are going to have more bearing area in a longer bullet but not always (the 69gr. SMK has close to/about as much bearing area as a 75 Amax)

Bullet construction and design is a major factor in how it will shoot in an AR(any auto for that matter) - if you are loading to mag length. Mag length bullets need to 'jump' to the lands, and need to be of significant construction to do so. Custom match bullets often don't have the jacket to handle this jump (at least well) -while the SMKs and their ilk have a fairly tough skin. The Ogive design also factors into how they handle chamber loading, and flight. The ogive on the SMKs are more rounded than something like the Amax or other VLD bullets. While this may take from the B.C. of the bullet, it gives them the ability to be less finicky and more consistant coming out of an auto.

The 75 Amax cannot be effectively loaded to mag length, whereas the 77 SMK was designed to do just that.

With a 1:9 you have the effective limit of maybe the Berger 73gr. LTB, but should have no issues with the 69gr. SMK or the Hornady 68gr. HPBT.
 
I found in testing this summer with a Rem 700 Police that the best was the 75gr Hornady HPBT match got to the .375" at 100, and they worked out to 1000 yards using Varget powder. Tryed 77gr smk not bad also. The Berger 75gr VLD would not work for me. I know from a friend at range with same gun he was shooting very nice groups with 53gr SMK match with H4895 consitantly .250" and under.but those bullets won't cut it at long ranges.
hope this helps you
 
This is why I'm a CGN'er

Thanks guys! Excellent feedback, and first-hand information too. Much appreciated!

I don't currently reload (basement space and time limitations), so I'm pretty much restricted to what I can purchase as a factory load...but after reading these replies, I'm leaning towards the Federal 69gr HPBT loading. I guess I'll pick up a few and see how they perform. I may also give something in a 77gr a try.
 
svt-40 said:
My 1:9 does not stabilize 70gr Barnes copper bullets even with maximum load.
55 and 60 gr fly like magic.
Click to expand...

:(

Do they keyhole on you? What are the dimensions of the Barnes 70gr in relation to non-copper bullets? Do they need to be longer than FMJ/BTHP of an equivalent weight due to the difference in density? Will this w squared dude ever stop asking questions???? :runaway:
 
For factory loaded match ammo you could try out Blackhills (I think Milarm carries it or can get it for you) or Federal. I believe TSE has the RUAG stuff as well.
Honestly, the cost of a 1000 rounds of factory made match ammo should push you into loading your own.
 
w squared said:
:(

Do they keyhole on you? What are the dimensions of the Barnes 70gr in relation to non-copper bullets? Do they need to be longer than FMJ/BTHP of an equivalent weight due to the difference in density? Will this w squared dude ever stop asking questions???? :runaway:
Click to expand...

Hi

Stability is related only to bullet length. A given twist will stabilize a bullet that is less than or equal to a certain length. Copper weighs a lot less than lead. That makes a copper bullet a lot longer than a lead bullet. Bullet shape can also impact length. The same is true of things like plastic tips.

You can go through all of the math and figure out how long a specific bullet is, how many RPM it is spinning at a given twist and velocity. From that you can estimate it's stability. Hmmm.....

Yes, it's an estimate, not a calculation. You go through all that and you still really don't know weather it's stable.

The simple answer is to go with a bit faster twist if there is any real question about stability.

Bob
 
To be honest with you, it's the time factor that's discouraging me from loading my own. I can't shoot while on the road, so that means that when I'm home I have to juggle shooting, skiing, riding, and my girlfriend...I place a premium on my time when I'm at home. I absolutely see the attraction of reloading though. I just wish it made sense for me.

Wholesale lists Federal HPBT 69 gr. in their catalog, so that may be a place to start for me...which also happens to be the 69 gr. SMK that you suggested would work well for me, Beltfed. I'm inclined to pick up 100 rounds and see what it does for me.
 
I bought some Blackhills 75gr BTHP from Milarm last time I was in there. Haven't had a chance to try it yet but they did have a good variety of BH .223
 
w squared said:
To be honest with you, it's the time factor that's discouraging me from loading my own. .....
Click to expand...

Hi

Black Hills Ammo is your friend. :D

Try to find somebody who either stocks or can order .223 match ammo from Black Hills. They have a wide range of loads, including some of the heavy long bullets. All of their stuff seems to be quite accurate.

Bob
 
Blackhills loads I've tried included the Hornady 68s and 75 gr. HPBT. I was less than impressed with the accuracy and consistancy.
Federal on the otherhand should do well and is a good place to start.
 
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