9 twist 223
- Thread starter gman47564
- Start date
My son(Dylan) & I both shoot 1/8 twist Barrels(Dylan's is 16" & mine is 18"). We have shot up to 77 grain SMK in those.
My cousin was wanting to come in from out of town to shoot a 600 yard NRA Mid-Range Prone Tactical Rifle(AR) with us. We borrowed a 20" 1/9 twist rifle from my dad & I took it to a 600 yard club match the week before my cousin came down. He is just getting started in Mid-Range shooting and I wanted to make sure the rifle would do OK at 600 yards. The barrel is a 1/9 twist Anderson 20" Bull Barrel(SKU# B2-K004-A011).
I figured from what I have heard/read on the interwebs that the 69 grain SMK's would be the hot ticket in the 1/9 twist barrel. Conditions remained fairly consistent throughout the day and I decided to test this for myself. I shot Match #1 with the 69 SMK's(196-8x), Match #2 with 77 SMK's(199-9x) and then I went back to the 69's for the final Match(195-3x). The 77's shot significantly better than the 69's!
The 77 SMK's run about 2730 fps at 60F(BP=29.87"Hg @ just above sea level) out of the 20" Tube. Miller Stability Index=1.4 to 1.5 depending on the temperature/velocity.
Note: The 77's were a Minute and a Half High as compared to the 69's(had to come down 6 clicks in match #2 & come back up 6 clicks in match #3).
I would guess they would go subsonic somewhere between 700-800 yards at sea level.
We're using LC Brass with 23.4 Grains of 8208XBR with Federal GM205M Primers at 2.260" COAL with both the 69 SMK's and the 77 SMK's.
Hope this helps(YMMV).....Andy
My cousin was wanting to come in from out of town to shoot a 600 yard NRA Mid-Range Prone Tactical Rifle(AR) with us. We borrowed a 20" 1/9 twist rifle from my dad & I took it to a 600 yard club match the week before my cousin came down. He is just getting started in Mid-Range shooting and I wanted to make sure the rifle would do OK at 600 yards. The barrel is a 1/9 twist Anderson 20" Bull Barrel(SKU# B2-K004-A011).
I figured from what I have heard/read on the interwebs that the 69 grain SMK's would be the hot ticket in the 1/9 twist barrel. Conditions remained fairly consistent throughout the day and I decided to test this for myself. I shot Match #1 with the 69 SMK's(196-8x), Match #2 with 77 SMK's(199-9x) and then I went back to the 69's for the final Match(195-3x). The 77's shot significantly better than the 69's!
The 77 SMK's run about 2730 fps at 60F(BP=29.87"Hg @ just above sea level) out of the 20" Tube. Miller Stability Index=1.4 to 1.5 depending on the temperature/velocity.
Note: The 77's were a Minute and a Half High as compared to the 69's(had to come down 6 clicks in match #2 & come back up 6 clicks in match #3).
I would guess they would go subsonic somewhere between 700-800 yards at sea level.
We're using LC Brass with 23.4 Grains of 8208XBR with Federal GM205M Primers at 2.260" COAL with both the 69 SMK's and the 77 SMK's.
Hope this helps(YMMV).....Andy
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Some of the stuff I read on the internet had me questioning using the 75-77's in the 1/9 twist tube....not anymore.
Is yours an AR or a Bolt Gun? Who made the barrel?
I think your good to go. Out to 300 I can't tell the difference in the 69's and the 77's(group size). Past 300 I'd certainly give the 75 grain Hornady's or the 77 SMK's a shot.
Is yours an AR or a Bolt Gun? Who made the barrel?
I think your good to go. Out to 300 I can't tell the difference in the 69's and the 77's(group size). Past 300 I'd certainly give the 75 grain Hornady's or the 77 SMK's a shot.
it becomes an issue when the bbls get short like the very common 16's.
in a 22 just keep trying till you find what will not work'
from a 75 horn match, I would try the 75atip..a bit longer.
in a 22 just keep trying till you find what will not work'
from a 75 horn match, I would try the 75atip..a bit longer.
Ned Ludd
Silver $$ Contributor
Stability of a given caliber bullet is generally determined by its length, not its weight, although bullet linear velocity also has an impact on its spin rate from a given twist barrel (i.e. faster velocity = faster spin rate in RPM = greater gyroscopic stability). The effect of velocity is typically small; a significant increase in velocity is necessary to overcome an insufficient twist rate.
For a given bullet weight, the shorter it is, the slower the twist rate you can get away with. I have shot 77 SMKs in factory ammunition out of a 10-twist .224" barrel and they worked just fine. I have also heard of instances where a 9-twist [factory rifle] barrel was apparently insufficient for the 77 SMK. Likewise, Hornady's 75 gr BTHP will sometimes work in a 9-twist barrel, sometimes that combination appears to be on the edge of gyroscopic stability.
When running close to the margin of whether a given twist rate may effectively stabilize a certain weight (length) bullet, sometimes the only way to know for sure is to shoot a few and determine empirically whether they exhibit stability issues. If a bullet exhibits slightly oval or oblong holes in the target, or even key-holing, the twist rate is clearly not sufficient.
For a given bullet weight, the shorter it is, the slower the twist rate you can get away with. I have shot 77 SMKs in factory ammunition out of a 10-twist .224" barrel and they worked just fine. I have also heard of instances where a 9-twist [factory rifle] barrel was apparently insufficient for the 77 SMK. Likewise, Hornady's 75 gr BTHP will sometimes work in a 9-twist barrel, sometimes that combination appears to be on the edge of gyroscopic stability.
When running close to the margin of whether a given twist rate may effectively stabilize a certain weight (length) bullet, sometimes the only way to know for sure is to shoot a few and determine empirically whether they exhibit stability issues. If a bullet exhibits slightly oval or oblong holes in the target, or even key-holing, the twist rate is clearly not sufficient.
I bet it shoots fine, run it!
Surely it shoots better than me!
Surely it shoots better than me!
Rick300
Gold $$ Contributor
My exact experience also
USMCDOC
Silver $$ Contributor
73 gr LTB's from Berger..
USMCDOC
Silver $$ Contributor
might have worked in yours, don't mean it will work in all.. just sayin'
Shot 70 Berger VLD, Hornady 75 BTHP and Hornady 73 & 75 ELD's from a 9 twist in matches. It did not like anything under 70gr and wanted everything I fed it pushed hard. You lose a little BC on the 75gr class bullets but it's not enough to really matter.
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