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Posted: 3/31/2006 10:02:12 AM EDT
Am building a 16” upper that will be a keeper for a long time so am thinking of building it “right”, for me.

Am going mid length and will be shooting 62 grain bullets. Rather than “this twist covers all these bullet weights” or "all these twists cover that bullet" I would like to have the barrel twist designed for the 62 grainer. What would that exact twist be?

Next, by going to an exact twist, is the cost to have that done prohibitive?

FYI, I am planning to match that with the ACOG NSN sight (designed for 16” barrel and 62 grain bullet”

Thanks for your input… Borg
Link Posted: 3/31/2006 10:13:52 AM EDT
Uh..

M855..

Or just plain 62gr lead?

Reason I ask is, the M855 bullet wieghs 62gr but uses a steel penetrator.. and steel is not as dense as lead, so its a long bullet...

If your shooting M855..

1/7 is the way to go.. military found that to be the optimal twist rate for it.
Link Posted: 3/31/2006 10:15:21 AM EDT
[Last Edit: 3/31/2006 10:15:53 AM EDT by Frens]
take a look at the Ammo Oracle
Link Posted: 3/31/2006 10:16:25 AM EDT
[Last Edit: 3/31/2006 10:20:12 AM EDT by Hokie]
I'll make it easy for you...

1:9

Don't have a wet dream and beg someone to create an oddball 1:9.5 twist or whatever, that's flat out stupid.

Look at it like this:

1:9 will do 55-69 grains.

1:7 will do 62-80 grains.

There's some overlapping but that's the general idea. As you can see both twist rates will handle some stuff the other can.

You could also custom build a 1:8 I suppose....
Link Posted: 3/31/2006 10:19:13 AM EDT

Originally Posted By jonathon:
Uh..

M855..

Or just plain 62gr lead?

Reason I ask is, the M855 bullet wieghs 62gr but uses a steel penetrator.. and steel is not as dense as lead, so its a long bullet...

If your shooting M855..

1/7 is the way to go.. military found that to be the optimal twist rate for it.



Not quite.

M855 -> 1/9

M856 -> 1/7
Link Posted: 3/31/2006 10:21:04 AM EDT
Thank you Jonathan… I am thinking of not going with the M855 as other bullets are more accurate, as I understand.

So the 1 in 7 twist was designed for the M855 that makes a lot of sense. And I imagine for non-M855’s that is still probably a very close ideal twist.
Link Posted: 3/31/2006 10:21:41 AM EDT
[Last Edit: 3/31/2006 10:27:35 AM EDT by Hokie]

Originally Posted By Jonathon:

If your shooting M855..

1/7 is the way to go.. military found that to be the optimal twist rate for it.




uh.....no.

Check the link above....here's a quote:

"Rounds in flight spin for stability because of the rifling on the inside of the barrel. Depending on how much they spin, they are more or less stable in their flight and therefore more or less accurate. The earliest AR15s from the early 1960s had a twist rate of 1 complete twist every 14", or 1:14. This was increased to a twist rate of 1 turn in 12" for the M16, XM16E1, M16A1, and later rifles and carbines. The current M16A2s and up and the M4 carbines have a much faster twist rate, 1 turn in 7". The reason for the 1:7 twist is mainly to stabilize the M856 tracer bullet, which is much longer than other bullets. You will recall from above that the M856 was designed to provide 800 meters of trace out of the SAW."
Link Posted: 3/31/2006 10:28:13 AM EDT
[Last Edit: 3/31/2006 10:31:02 AM EDT by jonathon]
Okay I was wrong, but instead of insulting me, perhaps it is better to be nice about it? And some folks really wonder why ARFCOM has a huge rep on the net for being a place being very unfriendly.

Nice edit there Hokie
Link Posted: 3/31/2006 10:34:21 AM EDT
Another quote:


Q. What twist rate do I want for my rifle?

Probably 1:9, but it depends on what kind of bullets you intend to shoot.

Special purpose rifles often have uncommon twist rates. For example, if you are building a varmint rifle and want to shoot the short 35 grain, 40 grain, and 50 grain bullets, a 1:12, or even 1:14 twist would be best. On the other hand, long range High Power shooters often select 1:8, 1:7.7, 1:7, or 1:6.5-twist barrels to stabilize the long 77, 80 and even 90 grain bullets used for 1,000 yard competition. Additionally, new testing of heavier rounds (68-77 grains) seems to show that they perform very well in simulated tissue and may be a better defensive choice than 55 grain or 62 grain rounds. The majority of shooters, though, typically shoot bullets of 50 to 69 grains in weight (note that the 62gr SS-109/M855 bullet is as long as a 71 grain lead core bullet) and should select 1:9 twist barrels. At typical .223 velocities, a 1:9 twist will stabilize bullet lengths equivalent to lead-core bullets of 40 to 73 grains in weight.

1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bullet out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use.

There is, of course, an exception: if you want to use loads utilizing the heavier, 75-77 grain match bullets currently used by Spec-Ops troops and other selected shooters, you'll want a 1:7 twist barrel. Although military loadings using these bullets are expensive and hard to get, some persistent folks have managed to obtain a supply, and will need the proper barrel twist to use them. Anyone who foresees a need to shoot this ammo should consider a 1:7 twist barrel.


Link Posted: 3/31/2006 10:37:01 AM EDT
[Last Edit: 3/31/2006 10:40:33 AM EDT by Hokie]

Originally Posted By jonathon:
Nice edit there Hokie



I made the edit so you don't run away all butt hurt. Still.......you should homework before you post in a technical thread and you can avoid big mean bullies like me correcting you.

sorry to ruffle your feathers up there

Don't make me fly to WA and give you a warm & gay ARFCOM hug & kiss.
Link Posted: 3/31/2006 10:49:16 AM EDT

Originally Posted By Hokie:

Originally Posted By jonathon:
Nice edit there Hokie



I made the edit so you don't run away all butt hurt. Still.......you should homework before you post in a technical thread and you can avoid big mean bullies like me correcting you.

sorry to ruffle your feathers up there

Don't make me fly to WA and give you a warm & gay ARFCOM hug & kiss.



Hey now, I am not TRG!



Sorry if I took it the wrong way..

I honestly LIKE being told when I am wrong about a fact, means I can correct my own personal error..

I still prefer 1/7 twist though, but I actually do shoot 75gr and 77gr bullets often enough(and I use them for defense loads as well). Personal preference.. but yeah
Link Posted: 3/31/2006 10:53:03 AM EDT
i would think 1x8 would be the happy medium is 62gr. is all you are planning to shoot.


but in my exp. the 1x9 would fair much better if you plan on shooting 62 or less
Link Posted: 3/31/2006 10:57:33 AM EDT

Originally Posted By jonathon:

Originally Posted By Hokie:

Originally Posted By jonathon:
Nice edit there Hokie



I made the edit so you don't run away all butt hurt. Still.......you should homework before you post in a technical thread and you can avoid big mean bullies like me correcting you.

sorry to ruffle your feathers up there

Don't make me fly to WA and give you a warm & gay ARFCOM hug & kiss.



Hey now, I am not TRG!



Sorry if I took it the wrong way..

I honestly LIKE being told when I am wrong about a fact, means I can correct my own personal error..

I still prefer 1/7 twist though, but I actually do shoot 75gr and 77gr bullets often enough(and I use them for defense loads as well). Personal preference.. but yeah





For what it's worth I also choose 1:7 but also have a 1:9...either will run 62 grain just fine. If 62 was all our hero is gonna shoot, then I think a 1:9 would be best for his application.
Link Posted: 3/31/2006 8:12:23 PM EDT
I have a 1 in 8 on my Oly PCR-1, that way I have a wider range. I mostly shoot Sierra 89grs BTHP but sometimes will shoot 55grs FMJs and Sierra 80grs HPBT and all shoot sub 1" at 100 yards. It works well for me but the 1 in 9 should also work quite well.

Jim
Link Posted: 4/1/2006 2:38:51 AM EDT
62 gr works well in my 1:9
Link Posted: 4/5/2006 9:57:03 AM EDT
I have shoot 55's from my 1/7 it works fine I have shoot 45 gr -77 in my 1-9 never had a problem. I shot 62's out of 1/12 it was fine to .
Link Posted: 4/5/2006 12:43:15 PM EDT
Link Posted: 4/5/2006 1:04:53 PM EDT

Originally Posted By Teknic:.

...Or do as most do, buy both.




it's the only real solution here
Link Posted: 4/11/2006 10:34:29 PM EDT
I believe the military's decision for 1/7 was a compromise between the optimun 1/6 twist for tracers and optimum 1/8 twist for M855. I myself prefer 1/9 and use it exclusively for all my builds.
Link Posted: 4/12/2006 10:15:19 AM EDT
Wow, found this web site and you can compute the exact twist....

stevespages.com/page8e.htm

Now thats the ticket
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