Results 1 to 10 of 10

Thread: How is MV affected by barrel length and twist rate?

  1. #1

    How is MV affected by barrel length and twist rate?

    I chrono'd some homeloads today and found them about 300ft/sec off the quoted values in the manual. I'm not hung up on velocity and know I wouldn't get book values. My loads are accurate and that will do for me, I'm not chasing speed, just curious to understand the science behind it.

    My load is 25grn of Benchmark under a .224 55grn Nosler BT.

    I know my rifle is nowhere near the same as the one used in the Nosler manual, there's is 24" 1in12 twist mine is a 20" 1in9. I'm wondering which bit is effecting my speed, barrel length or twist, or probably a combination of both.
    Last edited by timbeech; 16-12-2014 at 21:55.

  2. #2
    SD Regular Greener Jim's Avatar
    Join Date
    Jul 2014
    Location
    Yorkshireman in Darkest Cornwall
    Posts
    2,572
    Both mate. Barrel length affects it to an extent due to less time in which the bullet is under pressure. A faster twist slows bullets down as it creates friction.
    I'm guessing you have a .223. For 55gr bullets a 1-12 is more usual than 1-9. The advantage of the 1-9" I s that you can run heavier bullets which wouldn't stabilise in a 1-12.

    As as you said velocity isn't everything. If you are going after deer it matters as you need to meet a specific mizzle energy, as I'm sure you're aware. But for fox, 300fps won't make a difference so long as the bullet performs at the impact velocity.

  3. #3
    Quote Originally Posted by Greener Jim View Post
    For 55gr bullets a 1-12 is more usual than 1-9. The advantage of the 1-9" I s that you can run heavier bullets which wouldn't stabilise in a 1-12.
    Yeah .223 (can't believe I missed that in the post) I got the 1-9 with a heavy barrel so that I can use 50/55grns for Fox/Vermin and the ability to use the big heavy stuff to muck about with 500yd stuff on range days. Not bothered using it for deer got .308 for that.

    My homeloads are more than sufficient for foxes, just the engineer in me likes knowing how **** works.
    Last edited by timbeech; 16-12-2014 at 21:54.

  4. #4
    If you look closely at the reloading data in the manufacturers reloading manuals, they more often than not use rifles with long barrels.. Ie 24 inches and sometimes even longer! So we are never going to match the quoted figures with for example a rifle with 20 inch barrel.

  5. #5

  6. #6
    SD Regular Greener Jim's Avatar
    Join Date
    Jul 2014
    Location
    Yorkshireman in Darkest Cornwall
    Posts
    2,572
    Quote Originally Posted by timbeech View Post
    My homeloads are more than sufficient for foxes, just the engineer in me likes knowing how **** works.
    I'm an engineer too so I fully sympathise with that! I do love fixing and tuning firearms like, may need to invest in an RFD lol

  7. #7
    Lab data by propellant/bullet/ammunition manufacturers is all produced under controlled conditions to SAAMI spec. The barrels used are not really like your average sporting barrel. Most certainly homeloads with varying brass quality either new or previously fired, then field tested on average commercial chronographs using different length barrels, are never going to produce matching MV data.

    However, you will get an idea of what your ammunition is doing and can use the info for various downrange exterior ballistic use.

    Incidentally, I understand that the Birmingham and London proof houses will for a charge test your home loaded ammunition in their barrels.
    Of course, it will be their barrels the results of which will be different from your own barrel.
    ATB
    Blaser K95 Luxus Kipplaufbüchse .25-06Rem. Zeiss 8x56, 110gn Nosler Accubond = Game Over!

  8. #8
    1:9 will stabilize most 55 grain bullets. 1:9 is what FN came up with for some new bullet designs after Vietnam. They had the M-16 contract for quite a while after that. Then Bushmaster also got a contract for the Marine Corps, all with 1:9 twist, to shoot the 55-gr ball and the 62-gr SS-109 penetrator. It will also shoot the 64-gr Winchester SPBT hunting bullets, and up to the 69-gr match bullets. 1:12 shoots the 55, 53, 52, 50, 45 grain FMJ, target and varmint bullets well.

    If you want to see the MV losses, just compare various loads between the AR-15 with a 20-inch barrel with the other carbines with 16.5, and some of the USGI M-4s with even shorter barrels. Then look at something like a Steyr SL Varmint rifle with a 26-inch barrel. You can find real world shooters with all these online with every load imaginable.

  9. #9

  10. #10
    Quote Originally Posted by jcampbellsmith View Post
    Very interesting article. .

Similar Threads

  1. .223 barrel twist rate
    By timbeech in forum Rifles & Calibres
    Replies: 8
    Last Post: 09-11-2013, 14:32
  2. Replies: 1
    Last Post: 26-12-2011, 10:37
  3. Twist Rates - how to find what your twist rate is:
    By deeangeo in forum Ammunition, Reloading & Ballistics
    Replies: 0
    Last Post: 20-08-2011, 06:29
  4. Twist rate?
    By W16OEN in forum Rifles & Calibres
    Replies: 10
    Last Post: 10-06-2011, 10:06
  5. .204 barrel length and twist recommendations
    By force64 in forum Rifles & Calibres
    Replies: 8
    Last Post: 18-09-2010, 20:22

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •