AR's, twist rates, and bullet weights

The #1 community for Gun Owners of the Northeast

Member Benefits:

  • No ad networks!
  • Discuss all aspects of firearm ownership
  • Discuss anti-gun legislation
  • Buy, sell, and trade in the classified section
  • Chat with Local gun shops, ranges, trainers & other businesses
  • Discover free outdoor shooting areas
  • View up to date on firearm-related events
  • Share photos & video with other members
  • ...and so much more!
  • OLM-Medic

    Banned
    BANNED!!!
    May 5, 2010
    6,588
    77gr SMK is better anyway, and wouldn't be stabilized except with a 1:7 or 1:8 twist.

    Just pick one, and keep shooting until you're safe.
     

    Scrounger

    Active Member
    Jul 16, 2018
    357
    Southern Maryland
    The AR as already posted had a 1 in 14” twist. The Army didn’t feel that the round was stabilized at Arctic temperatures, as has also already been posted.

    The result was a 1 in 12” twist with ultimately the 55gr FMJ M193. The 55gr FMJ has a couple of shall we say quirks. Most military loads are FMJ or sometimes called Ball rounds. That is per the Geneva Convention requiring non-expanding bullets. Most FMJ bullets when hitting a person will yaw 180 degrees and exit base first. Now it doesn’t always work like that, bone, angles, and all kinds of variables effect what happens. However, the bullet usually stays in one piece.

    The M193 quite often does things a little different. The round frequently breaks at the cannelure. The front triangular part goes one way. The rear breaks into three or four parts and go elsewhere.

    If the round holds together and doesn’t hit bone the wound can be a clean through and though. If it breaks the trauma can be quite impressive. The unpredictability of the round largely accounts for the different stories from its use during Vietnam. Some people praised it, some cursed it.

    If one wants a rifle that will shoot quite accurately for plinking, shooting steel and small game at less than 300 yards it is hard to beat the original setup. I would add use hunting type bullets for shooting game.

    It is when one starts going into longer ranges, trying to shoot one-hole groups and what not one would have a different setup.

    As far as home defense, the M193 has accounted for quite a number of KIA over the years.
     

    OLM-Medic

    Banned
    BANNED!!!
    May 5, 2010
    6,588
    20" barrel is just too darn long.

    I believe the velocity threshold for M193 to fragment is something like 2700fps. So you're pretty much good with any modern setup besides the really short SBRs.
     

    JohnnyE

    Ultimate Member
    MDS Supporter
    Jan 18, 2013
    9,466
    MoCo
    HOW DARE YOU SIR. Our tactical security force wears only the finest 5.11 Tactical apparel! 5.11's concealed-carry-friendly clothes allow us to seamlessly blend into crowds while I carry the "deadly duo" of a Glock 26 and a Glock 34 MOS Gen5 w/ RMR Type-2 carefully hidden in Fobus IWB and AIWB holsters, along with several 33rd Glock magazines for extended firefights. That's in addition to our standard loadout of Kel-Tec SU-16s with twelve 40rd C-Products mags filled with Tula 55gr. I've found them extremely reliable, far more so than the trashy Sig Rattlers with Magpul Gen3s we've eval'd - Mk318 Mod 0 rounds kept going nose-up while feeding in those POS, not that they were all that accurate anyways. In order to keep our low-profile in these urban operations, we've rattle-canned the SU-16s in "stealth grey". We deploy them with shortened stocks, heli-crew-style.

    Let me tell you, you can mock us all you want, but we're keeping you SAFE out there. Just the other day, we had a "situation" in the movie theater. The deputy mayor's stepson had a suspicious man with a boner sit next to him and look at him inappropriately. The mall ownership called in FBI HRT, but the feds were overpowered by the thick doors of screen 7 and overwhelming scent of buttered popcorn. My team did a forced entry with C4, put down the perp, and saved the boy's anal virginity. HRT thanked us later in a secret ceremony where we demonstrated some techniques that they use to this day.

    I don't call myself a hero, but I guess I've heard others say it. Just doing my job in the increasingly violent world of retail security.

    LOL!!! You’re on a roll
    Yup...Gecko...or a relation...or channeling...
     

    rbird7282

    Ultimate Member
    MDS Supporter
    Dec 6, 2012
    18,538
    Columbia
    Let me tell you, son, when I'm patrolling the mall with my tactical team, your old-ass M193 isn't going to get it done. I need the firepower to penetrate STEEL HELMETS at 600yds, because the TANGOS inhabiting the Olive Garden aren't messing around... besides the helmets, they've got daddy's old Rem 700 hunting rifle in 30-06 with API rounds and thermal scopes. You've got to hit them HARD AND FAST from as far away as possible, or your ass is going to be lit up like a pharmacy in a race riot. Don't even get me started on the punks at Lane Bryant... they may like fatties, but they're also packing Barrett .50cals, which is incidentally why I always duct-tape double-layered level IV+ plates to my front and back.






    Sent from my iPhone using Tapatalk
     

    rbird7282

    Ultimate Member
    MDS Supporter
    Dec 6, 2012
    18,538
    Columbia
    HOW DARE YOU SIR. Our tactical security force wears only the finest 5.11 Tactical apparel! 5.11's concealed-carry-friendly clothes allow us to seamlessly blend into crowds while I carry the "deadly duo" of a Glock 26 and a Glock 34 MOS Gen5 w/ RMR Type-2 carefully hidden in Fobus IWB and AIWB holsters, along with several 33rd Glock magazines for extended firefights. That's in addition to our standard loadout of Kel-Tec SU-16s with twelve 40rd C-Products mags filled with Tula 55gr. I've found them extremely reliable, far more so than the trashy Sig Rattlers with Magpul Gen3s we've eval'd - Mk318 Mod 0 rounds kept going nose-up while feeding in those POS, not that they were all that accurate anyways. In order to keep our low-profile in these urban operations, we've rattle-canned the SU-16s in "stealth grey". We deploy them with shortened stocks, heli-crew-style.

    Let me tell you, you can mock us all you want, but we're keeping you SAFE out there. Just the other day, we had a "situation" in the movie theater. The deputy mayor's stepson had a suspicious man with a boner sit next to him and look at him inappropriately. The mall ownership called in FBI HRT, but the feds were overpowered by the thick doors of screen 7 and overwhelming scent of buttered popcorn. My team did a forced entry with C4, put down the perp, and saved the boy's anal virginity. HRT thanked us later in a secret ceremony where we demonstrated some techniques that they use to this day.

    I don't call myself a hero, but I guess I've heard others say it. Just doing my job in the increasingly violent world of retail security.



    Ok that was better than the first one, lol


    Sent from my iPhone using Tapatalk
     

    jrumann59

    DILLIGAF
    MDS Supporter
    Feb 17, 2011
    14,024
    20" barrel is just too darn long.

    I believe the velocity threshold for M193 to fragment is something like 2700fps. So you're pretty much good with any modern setup besides the really short SBRs.


    Thats what she said....NEVER :innocent0
     

    danb

    dont be a dumbass
    Feb 24, 2013
    22,704
    google is your friend, I am not.
    Let me tell you, son, when I'm patrolling the mall with my tactical team, your old-ass M193 isn't going to get it done. I need the firepower to penetrate STEEL HELMETS at 600yds, because the TANGOS inhabiting the Olive Garden aren't messing around... besides the helmets, they've got daddy's old Rem 700 hunting rifle in 30-06 with API rounds and thermal scopes. You've got to hit them HARD AND FAST from as far away as possible, or your ass is going to be lit up like a pharmacy in a race riot. Don't even get me started on the punks at Lane Bryant... they may like fatties, but they're also packing Barrett .50cals, which is incidentally why I always duct-tape double-layered level IV+ plates to my front and back.

    :lol2::lol2::lol2::lol2:
     

    Rockzilla

    Ultimate Member
    Feb 6, 2010
    4,516
    55.751244 / 37.618423
    to throw some math in it... from some place else..


    The required twist is given by:

    twist rate.png
    The factors are:

    twist
    air density
    gyroscopic stability factor
    lateral and longitudinal moments of inertia
    cross-sectional area
    diameter
    overturning moment coefficient


    Greenhill Formula for Optimal Rifling Twist Rate
    https://www.vcalc.com/wiki/AndrewBudd/Greenhill+Formula+for+Optimal+Rifling+Twist+Rate


    -Rock
     

    Jerry M

    Ultimate Member
    Jun 13, 2007
    1,688
    Glen Burnie MD
    77gr SMK is better anyway, and wouldn't be stabilized except with a 1:7 or 1:8 twist.

    Just pick one, and keep shooting until you're safe.

    Based on what? Clandestine did a video that did not support your 77 SMK HD position.

    Also, 77 SMK may shoot very well out of a 1-9 twist barrel. I have shot mine several times out to 600 yards, F-class and field matches.

    I have shot out to 550 yards +- with both 52 gr SMK and 55 gr Hornady Soft point flat based bullets at prairie dogs. A few trips and 7,000 rounds later I can tell you for certain that the SMK doesn't kill a 2 pound rat as well as the soft point bullet will. My buddy also had better luck with factory loaded Fiocchi 55 gr soft points. The SPs would blow the PD in half, the SMK would do so sometimes under 300 yards, but at 400, 500 yards and beyond, it would hit like a FMJ.

    Original 1-14 twists with 55 grain FMJ bullets were devastating on flesh according to early use in Viet Nam.

    I agree with you to keep shooting till you are safe.

    Good Luck

    Jerry
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818

    OLM-Medic

    Banned
    BANNED!!!
    May 5, 2010
    6,588
    Based on what? Clandestine did a video that did not support your 77 SMK HD position.

    Also, 77 SMK may shoot very well out of a 1-9 twist barrel. I have shot mine several times out to 600 yards, F-class and field matches.

    I have shot out to 550 yards +- with both 52 gr SMK and 55 gr Hornady Soft point flat based bullets at prairie dogs. A few trips and 7,000 rounds later I can tell you for certain that the SMK doesn't kill a 2 pound rat as well as the soft point bullet will. My buddy also had better luck with factory loaded Fiocchi 55 gr soft points. The SPs would blow the PD in half, the SMK would do so sometimes under 300 yards, but at 400, 500 yards and beyond, it would hit like a FMJ.

    Original 1-14 twists with 55 grain FMJ bullets were devastating on flesh according to early use in Viet Nam.

    I agree with you to keep shooting till you are safe.

    Good Luck

    Jerry

    I think the thing is that 77gr SMK is a good performer at close ranges. The tests of fragmentation seem pretty reliable.

    At longer ranges it does not fragment and performs as a FMJ, as you mentioned.

    I still prefer it for shooting far.
     

    Rockzilla

    Ultimate Member
    Feb 6, 2010
    4,516
    55.751244 / 37.618423
    Well that clears that all up. Thanks!

    figured to change it up a little...:D
    just to see what happens....some want the answers so
    others provide the equations to figure it out, but have
    to admit, when some one provided me with the links and
    equations, basically said "you figure it out"...;)
    another site gets into the ballistics of it, thrust, COAL,
    twist, trajectory, with equations..and is interesting to
    say the least. Bryan Litz has some great reading material,
    If all you want to do is pull the trigger hear a bang then
    a clang so be it... not trying to be smart.... then it boils
    down to the person / operator.....

    anyway over the years have barrels with 1-14,1-12,1-10,
    1-8,1-7 twists and lengths from 7.5"-24", have an old 788
    in .223 that i used for a lot of testing with 45gr-62gr bullets
    including ones made from .22LR cases. but same thing what
    works for me and my firearm may not work in yours, chamber
    throat, etc.. what reamer was used and how many barrels has
    it been used for... a little off topic but...

    Everyday day is a learning experience...
    and we try different things..and learn different things..

    -Rock
     

    outrider58

    Eats Bacon Raw
    MDS Supporter
    Jul 29, 2014
    49,818
    figured to change it up a little...:D
    just to see what happens....some want the answers so
    others provide the equations to figure it out, but have
    to admit, when some one provided me with the links and
    equations, basically said "you figure it out"...;)
    another site gets into the ballistics of it, thrust, COAL,
    twist, trajectory, with equations..and is interesting to
    say the least. Bryan Litz has some great reading material,
    If all you want to do is pull the trigger hear a bang then
    a clang so be it... not trying to be smart.... then it boils
    down to the person / operator.....

    anyway over the years have barrels with 1-14,1-12,1-10,
    1-8,1-7 twists and lengths from 7.5"-24", have an old 788
    in .223 that i used for a lot of testing with 45gr-62gr bullets
    including ones made from .22LR cases. but same thing what
    works for me and my firearm may not work in yours, chamber
    throat, etc.. what reamer was used and how many barrels has
    it been used for... a little off topic but...

    Everyday day is a learning experience...
    and we try different things..and learn different things..

    -Rock

    :D :lol2:
     

    Attachments

    • weeds.jpg
      weeds.jpg
      19.4 KB · Views: 1,109

    Blacksmith101

    Grumpy Old Man
    Jun 22, 2012
    22,163

    Biggfoot44

    Ultimate Member
    Aug 2, 2009
    32,884
    The Spirit of Greko Lives ! Long Live Greko !

    ***********

    The version of the Legends that sticks in my mind for 1:12 twists , was Arctic temperature instability with Tracers

    But to reproduce the desired effects of 1:14 with a 1:12 bbl , try shooting lead core 62gr . ( NOT M855/ SS109 , but old school lead core ).
     

    Huckleberry

    No One of Consequence
    MDS Supporter
    Oct 19, 2007
    23,313
    Severn & Lewes
    Let me tell you, son, when I'm patrolling the mall with my tactical team, your old-ass M193 isn't going to get it done. I need the firepower to penetrate STEEL HELMETS at 600yds, because the TANGOS inhabiting the Olive Garden aren't messing around... besides the helmets, they've got daddy's old Rem 700 hunting rifle in 30-06 with API rounds and thermal scopes. You've got to hit them HARD AND FAST from as far away as possible, or your ass is going to be lit up like a pharmacy in a race riot. Don't even get me started on the punks at Lane Bryant... they may like fatties, but they're also packing Barrett .50cals, which is incidentally why I always duct-tape double-layered level IV+ plates to my front and back.

    Is that You, Gecko45? Is this Me?
     

    Huckleberry

    No One of Consequence
    MDS Supporter
    Oct 19, 2007
    23,313
    Severn & Lewes
    Let me tell you, son, when I'm patrolling the mall with my tactical team, your old-ass M193 isn't going to get it done. I need the firepower to penetrate STEEL HELMETS at 600yds, because the TANGOS inhabiting the Olive Garden aren't messing around... besides the helmets, they've got daddy's old Rem 700 hunting rifle in 30-06 with API rounds and thermal scopes. You've got to hit them HARD AND FAST from as far away as possible, or your ass is going to be lit up like a pharmacy in a race riot. Don't even get me started on the punks at Lane Bryant... they may like fatties, but they're also packing Barrett .50cals, which is incidentally why I always duct-tape double-layered level IV+ plates to my front and back.

    Is That You, Gecko45? Is This Me?
     

    Users who are viewing this thread

    Forum statistics

    Threads
    274,930
    Messages
    7,259,487
    Members
    33,350
    Latest member
    Rotorboater

    Latest threads

    Top Bottom