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Old June 28, 2019, 08:46   #1
raubvogel
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Learn me some twisty ratios

So I was reading the original twist was 1:14 but artic tests moved it to 1:12.

How accurate was the 55gr in that ratio (since 4moa I thought was the required but 1 moa ARs nowadays is commonplace)? Also, I remember reading that the original round really started to cause large damage after 300yd; before that it would just go through. Is my recollection remotely accurate?

Was the 62gr round designed to be more effective at shorter distances or what?
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Old June 28, 2019, 09:06   #2
Southern 7.62
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Quote:
Originally Posted by raubvogel View Post
So I was reading the original twist was 1:14 but artic tests moved it to 1:12.

How accurate was the 55gr in that ratio (since 4moa I thought was the required but 1 moa ARs nowadays is commonplace)? Also, I remember reading that the original round really started to cause large damage after 300yd; before that it would just go through. Is my recollection remotely accurate?

Was the 62gr round designed to be more effective at shorter distances or what?
I've not shot in the Arctic, but I never had any issue shooting in minus 20 degree weather in Montana unless I used CLP Breakfree, it seemed to get tacky and gum up the action (also experienced this when it gets rained on), but others might have different experiences. This was using 1/12, 1/9, and 1/7 twist barrels on AR's. Plenty of data on the web of bullet weight vs barrel twists. I've always had good accuracy with 1/12 (55gr), 1/9 (55/62gr) and 1/7 (62gr). My 1980 SP1 will shoot 1-1.25 inch groups bench at 100 yards using 55gr Vmax handloads from BVAC. Also, I have ran 62gr SS109 in my 1/12 twist barrels, just seems to drop a bit lower than the 55gr I sighted in with. Just get an SKS and never worry. Ha, joke
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Old June 28, 2019, 09:56   #3
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62gr SS109 was designed to punch holes in Soviet Helmets at 500yd using the best technology 1980 had to offer. The USSR invading western Europe was the thing then.

The angle was - this new modern 5.56 bullet with a steel core gives better penetration at long range than the standard M80 ball projectile.

It was a way to get the 5.56 cartridge accepted by our allies as the NATO standard infantry rifle cartridge. You know, after we forced the 7.62 X 51 on them and then unilaterally abandoned it.
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Old June 30, 2019, 10:43   #4
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Iím not sure if his really is what you are after or not, but I believe the military testing found that the 1:12 barrel didnít provide the accuracy that they were wanting at the time, minute of bad guy at X yards. This is due to the M855/ss109 round being longer than a 62 gr FMJ because of the steel core and itís placement in the bullet. The steel core is in the front 1/3 of the bullet only. They switched from the 1:12 to the 1:9 twist rate in the M16 then when the M4 showed up the 1:7 twist showed up too.

My personal preference is a 1:8 twist rate as it seems to bridge the bullet gap for what I like to shoot. I donít shoot anything lighter than a 50 gr and nothing over 80 gr.
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Old June 30, 2019, 12:03   #5
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1-14 worked fine in .222 , .222 Magnum and .22-250 with 45-55 grain flat base bullets for decades.

55 grain military boat-tails are a different animal, comparatively.



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Old July 02, 2019, 11:04   #6
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Have twist rates from 1:6.5 to 1:14 and barrel length vs intended bullet weight range plays hard into the equation as well. I really like 18" to 20" 1:8 twist barrels. Seldom shoot anything heavier than 69 grain SMK's in my SDM role rifles. The 1:8 in 18" and longer will stabilize 77's quite well and if need the accuracy of 90 grain VLD's then it's time to reach for a bolt action IMHO. For general purpose 16" and shorter generally go with a 1:7 knowing most any bullet will stabilize at that rate of twist.

Sometimes a fellow just has to build a rifle to fire a single load and then is when choosing the twist and length right on the money imperitive. Lots of shooters are using 1:7.5 and 1:6.5 for specialty rifles but if put a light fast bullet in them it will tear itself apart or have issues with spin drift. If you want to spit 50 grain bullets at warp speed a 22" or longer 1:12 is a good choice thus the reason I have a myriad of different lengths and twists based on task rifle is going to be used for. A person can over think this issue. Unless your killing Prarie Dogs at long distance or shooting world class Service Rifle most will not see the difference in a small variation in rate of twist.
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Old July 03, 2019, 20:39   #7
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Just for information: the length of bullet is what affects what twist rate you may need, not necessarily weight. Longer bullets tend to be heavier. A tracer bullet is very long, and needs a relatively faster rate to stabilize. A 55 gr or smaller varmint round doesn't need as fast... But, say a 62 gr copper plated lead and solid 62gr, the solid copper may favor a faster rate as well. Copper is not as heavy as lead, and tends to be a longer bullet. Just food for thought.
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