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Thread: Trying to understand rimfire balistics

  1. #1
    Boolit Buddy
    Join Date
    Apr 2010
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    881

    Trying to understand rimfire balistics

    OK so some one started asking me questions about 22lr ballistics...which I'm not really good at except general come ups.
    And what I know from shooting 1040-1070ish ammo through my rifles.

    So he has a nice cz and on no wind days I have seen him post some darn near moa groups routinely so he is a good shot.
    Now he also gets some nice groups with win X rated at 1255fps.
    Now he's only shot some SV at 100 yards and has written down some standard adjustment that hes worked out for his rifle.
    He has a wireless windspeed and direction meter and had a pretty steady 10mph full value wind.
    He called me a bit stumped as his regular load was shooting was on at elevation and even with the wind and cold pulled out a nice group of 1.5" at 100 yard but the wind was pretty consistent and his 3 10shot groups where all close to about 5-5.5" left I don't have pictures but his center of each group is pretty darn perfect.
    Now he wanted to see what the winx 1255fps rn would do he has a 25 yard indoor range so he set his zero for the 1255s by this time the wind died down and he was off to 100 yards. His groups where not as tight as the 1070 target but all under 2" just under. He was dead nuts on elevation with 3 groups settled into the 10 ring on a SR1 target. Then the winds came again with a 8-10mph range. But now his center of his groups are hitting Almost 8" off center. He never adjusted scope for any windage.
    What he thought is the faster load should have had less drift as its traveling faster with less time for wind to push the bullet.

    So I ran some numbers through the calculator.
    I used a .09 as a BC as I have no idea what BC of 22lr is. I used the default weather settings and a 10mph 90' wind
    Sure enough the 1255fps drift at 100 yards is 7.7" while the 1070fps is 5.5"
    The drop from a 25 yard zero
    1070@100yards 9.5" 1255@100yards 7.7"

    What's going on here...opposite of what I thought also.

  2. #2
    Boolit Master

    Join Date
    Mar 2013
    Location
    Northwest Ohio
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    It has to do with the super sonic speeds "slip stream" formed around the bullet causing greater wind drift than the subsonic speeds. You also see this effect with the BPCR rounds that go super sonic.

    Now he needs to move out to 200yds and see what happens there. I have gotten much better accuracy from the standard velocity ammo at 200yds than the Hi Velocity. One of the best 200yd loads I tried was the old federal shilouette loading with the 45 grn bullet.

  3. #3
    Boolit Master


    HangFireW8's Avatar
    Join Date
    Dec 2008
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    Central Maryland
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    Bullets that decelerate quickly are more windage prone. Likewise bullets that transcend the sound barrier. The physics reasons are exceedingly complex.

    As country gent states, better accuracy can be found with barely subsonic standard velocity ammo than high velocity. Yes they may drop less, but your hold-over needs to be known anyway, so might as well use the more accurate ammo.

    High power (308, etc.) rounds don't suffer so much because they are longer, heavier and more streamlined than 22LR. Even if you shot them at 22LR velocities (quite doable for a handloader), they just don't have as much drag, don't decelerate as quickly, and thus don't suffer so much windage.
    I give loading advice based on my actual results in factory rifles with standard chambers, twist rates and basic accurizing.
    My goals for using cast boolits are lots of good, cheap, and reasonably accurate shooting, while avoiding overly tedious loading processes.
    The BHN Deformation Formula, and why I don't use it.
    How to find and fix sizing die eccentricity problems.
    Do you trust your casting thermometer?
    A few musings.

  4. #4
    Boolit Buddy
    Join Date
    Apr 2010
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    881
    his goal is velocity for hunting his range will be aprox 25-40 yards on a small farm. Something i dod not think much of .... he was testing at 100 yards as we tend to have 100-200 yard fun matches and if he keeps shoooting the way he has been we got some work to do on our end!
    Same with barrel length.... the best 22lr shooter i know has always said you want a barrel long enoug to reach peak velocity anf then just long enough so the bullet cant exit faster than the speed of sound....temperture permitting.
    He recently gave me a test take 20 rounds of any ammo and crony it use the rifle with the shortest barrel and then the longest and tell me what you find.....

  5. #5
    Moderator

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    Jul 2013
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    Bullet velocity vs. barrel length also depends on the powder's speed; Load a few rounds of 308 with BLC(2) and another few with say H4831 (put them up to the same pressure.) Now fire a couple of each through a barely-legal rifle barrel, and a couple through a 28" barrel. You'll see that the slower powder will have a slight velocity edge in the longer barrel; And in the shorter barrel, will have one heck of a muzzle flash BLC(2) is great for FAL, CETME, etc. loads if you want no muzzle flash at night, on the other hand. It's harder to handload 22LR, of course, but I imagine different manufacturers use different powder speeds for different cartridges. Pretty sure some of the HP bullets are put atop a little bit slower powders, firing them in a pistol is sorta loud!

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check