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Posted: 2/9/2006 11:42:20 AM EDT
What bullett grain weights do you like for the following barrel twist rates -

1 in 9

1 in 8

1 in 7



???

Does 55 gr work well in 1 in 7??



Link Posted: 2/9/2006 11:44:37 AM EDT
Does 55 gr work well in 1 in 7??


Not the one I just got home from firing.
Link Posted: 2/9/2006 11:58:02 AM EDT
[Last Edit: 2/9/2006 12:11:26 PM EDT by gplg]
Link Posted: 2/9/2006 12:02:43 PM EDT
[Last Edit: 2/9/2006 12:16:04 PM EDT by Yojimbo]
All I own are 1-7 twist barrels and I shoot 45gr-77gr through them with no issues.
Link Posted: 2/9/2006 12:11:19 PM EDT
I shoot 55 gr (M193) in my 1/7 and 1/8, and in my 1/9 when I had that barrel. It all shoots fine, really well actually. There is no definitive answer what twist barrel will shoot what, how well, and so on. All you can do is try it yourself and see what happens. GENERALLY the following bullet grain sizes will work fine for the given twist. However, there are always exceptions.

1/12 - 40 gr. - 62 gr. (not including M855)
1/9 - 40 gr. - 68 or 69 gr. (including M855)
1/8 - 40 gr or 45 gr. - 77 gr.
1/7 - 45 gr. - 77 gr.
Link Posted: 2/9/2006 9:46:01 PM EDT
My RRA Upper is a 1/9, so i try to use M855, though M193 will be accurate, but not as much as the heavier M855.
Link Posted: 2/9/2006 10:00:04 PM EDT
[Last Edit: 2/9/2006 10:24:30 PM EDT by HotIce]
It is common to say that 1/9" stabilize 69gr, but my Bushy 1/9" is not even close to make the 0.984" long Hornady 68gr SST BTHP bullet happy. I get 5-6" groups out of that, whereas it is sub-MOA with 60gr HP for example.
The length of the bullet, more than its weight, is the key.
Anyone has a 77gr SMK handy to measure its length?



- Ice
Link Posted: 2/9/2006 10:02:26 PM EDT

Originally Posted By HotIce:
It is common to say that 1/9" stabilize 69gr, but my Bushy 1/9" is not even close to make the 0.984" long Hornady 68gr SST bullet happy. I get 5-6" groups out of that, whereas it is sub-MOA with 60gr HP for example.
The length of the bullet, more than its weight, is the key.
Anyone has a 77gr SMK handy to measure its length?



- Ice



Exactly. As I should have stated earlier, bullet length and jacket thickness are the biggest factors in whether a bullet will stabilize or rip itself apart.
Link Posted: 2/9/2006 10:22:33 PM EDT

Originally Posted By Black-Tiger:
My RRA Upper is a 1/9, so i try to use M855, though M193 will be accurate, but not as much as the heavier M855.





Link Posted: 2/9/2006 11:04:33 PM EDT
Something confusing you? M855 is designed and intended to be used in 1/9 barrels.
Link Posted: 2/9/2006 11:42:08 PM EDT

Originally Posted By DevL:
Something confusing you? M855 is designed and intended to be used in 1/9 barrels.




exactly the 1 in 9 is the perfect twist for it. They went to a 1in7 so the tracer would stabilize, it's the length of the round not the weight
Link Posted: 2/10/2006 12:24:13 AM EDT
[Last Edit: 2/10/2006 2:05:30 AM EDT by Black-Tiger]

Originally Posted By Dace:

Originally Posted By Black-Tiger:
My RRA Upper is a 1/9, so i try to use M855, though M193 will be accurate, but not as much as the heavier M855.








Are you listening? Pay attention. >



From L to R: M193 Ball, M196 tracer, M855 Green Tip, M856 Tracer, special 100 grain bullet (BT Ammo Labs).

See the differences in bullet lenght? it requires different rifling lenghts to stabilize these bullets. as mentioned before a 1:9 rifle twist is best suited for the M193 & M855 bullets, but for heavier bullets, a 1:7 would work better.

As a matter of fact, here's this link to give you more data on the different types of 5.56mm NATO bullets there are in use with the military.
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