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kgj1119
08-02-06, 21:27
does anybody have a chart, or can you tell me what grain bullet should be used with a certain barrel length, and twist? ie 14.5" bbl w/1:9 will handle up to? we have both m16a1's with 1:7 and m4's w/ 1:9
Pat_Rogers
08-02-06, 21:53
Partner- the M16A1 is a 1/12 barrel. The M4 is a 1/7.
Are the rifles aftermarket? Re- barreled?
Generally speaking, 55 gr will work in 1/12; 1/9; and 1/7.
Heavier bullets (M855, MK 262 and 75gr TAP) will not work in 1/12, will sometimes be less efficient in 1/9 and work great in 1/7.
svtar15
08-03-06, 12:27
Your 1x9 is meant for 55 gr-62gr bullets. The 1x7 shoots heavier ammo; 62-75 gr.
kgj1119
08-03-06, 21:07
sorry for the confusion. My P.D. has numerous rifles m16a1's, and bushmaster m4's. I know the a1 have 1:12 twist, and the m4 have both 1:9 and 1:7.
Submariner
08-03-06, 21:25
Your 1x9 is meant for 55 gr-62gr bullets. The 1x7 shoots heavier ammo; 62-75 gr.

So 1X7 isn't "meant" for 55 grain projectiles? They seem to work just fine in my 1X7's. In fact, they work so well I sold off all the 1X9's I had and went to 1X7 in every gun. Did I screw up?
Business_Casual
08-03-06, 21:47
Sub,

No, if perhaps you re-read what Mr Rogers posted?

ETA - I just mean that is the most succinct explanation; in my experience 55gr. can be somewhat less accurate in 1x7 vs. slower twists but not always.

M_P
Robb Jensen
08-06-06, 11:26
does anybody have a chart, or can you tell me what grain bullet should be used with a certain barrel length, and twist? ie 14.5" bbl w/1:9 will handle up to? we have both m16a1's with 1:7 and m4's w/ 1:9

1x9 (50-69gr usually works best)
1x7 (55-77gr usually works best)
1x12 (40-60gr usually works best)

That's not a be all do all list, I've seen long 1x9 twist barrels stabilize heavy bullets like 75-77gr just fine. Every barrel is a little different. If you have a 1x9 twist barrel and try shooting 77gr it's not going to hurt it, they may just become unstable at 100yd or more.

Sometimes it's not so much about the bullet weight but more about the bullet length. Longer bullets have to be spun faster to stabilize them.

Twist rate can also vary, one 1x9 twist barrel might be 1x8.5 and one might be 1x9.5 but both might be called 1x9.

From what I recall Maj Jack Muth III USMC Ret., my dad GySgt Robert Jensen USMC Ret. and LtCol Dave Lutz USMC Ret. (all worked at the Firepower Div Quantico, later changed to PM Ground Weapons) telling me about the 1x7 twist adopted on the M16A2 and then XM4 was they went with that because it worked well on the M249 and it was needed to stabized the M856 tracer. The 1x9 was actually was better than the 1x7 for the M855 (62gr) round but the M856 tracer has a very long bullet about the length of a 77gr Sierra MatchKing IIRC and wouldn't stabilze in 1x9 twist barrels.
DocGKR
08-06-06, 12:26
gotM4 is absolutely correct.
Abraham
10-04-13, 15:51
Robb Jensen,

You said: 1x7 (55-77gr usually works best)

Then you said: "The 1x9 was actually was better than the 1x7 for the M855 (62gr) round"

Are you saying on average the 1X7 is better for a 62 gr round, but not always as the difference in 1x7 barrel has so much variance there's way to tell until it's shot with 1x9?

Hey, I'm still learning....and thanks!
ColtSeavers
10-04-13, 16:21
You mean something like this?

http://s19.postimg.org/4sbr48obn/Twist_VS_Grain.jpg


ETA: just saw this thread is over 7 years old.... apologies for adding to the necro.
Abraham
10-05-13, 09:15
ColtSeavers,

Thanks for the bar graph. I now have a confirmed grain/twist rate answer.

Alas, I did a search, but failed to notice the date of the thread...
Failure2Stop
10-05-13, 11:02
ColtSeavers,

Thanks for the bar graph. I now have a confirmed grain/twist rate answer.

Alas, I did a search, but failed to notice the date of the thread...

No worries.

One thing to be aware of:
It isn't just weight, but rather length that makes the projectile require a specific twist rate window. Further, not all marked twist rates are dead on, which leads us down the rabbit hole once again.

Typos brought to you via Tapatalk and autocorrect.
T2C
10-05-13, 11:14
You mean something like this?

http://s19.postimg.org/4sbr48obn/Twist_VS_Grain.jpg


ETA: just saw this thread is over 7 years old.... apologies for adding to the necro.

Thanks. The chart makes it easier for many people to understand.

That being said, a high quality bullet with a long bearing surface of the weight in the red or yellow zone will sometimes surprise you.
markm
04-10-14, 10:06
I got to shoot an old SP1 relic this past Sunday. So I did a stabilization test with paper at about 50 yards.

1/12 Twist 20" barrel of course.....

SS109 bullets punched paper with a slight yaw visible in the holes.

69 gr SMKs shot fine and stacked up pretty nicely.

77 gr SMKs passed through the paper at approximately a 45 degree crab, and scatterd a 4 inch, 3 shot test group.
Pappabear
04-19-14, 21:46
All these numbers are good rules of thumb. As stated by Robb, I have a 1/9 Remmy that shoots 77g SMK's lights out. But it shoots everything well. I can take that same ammo, put it into a 11.5 SBR and shoot great. There was a sticky on twist rates that was very good in one of AR sections.

The only thing you can count on is " the bullet doesn't lie".