90gr JLK for 22 BR/Dasher,12 merged posts)

Discussion in 'Small Stuff--22s, 20s, and 17s' started by Forum Boss, Nov 26, 2004.

  1. Forum Boss

    Forum Boss Administrator

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    paul
    . . .You haven’t by chance tested the 90JLK 224 have you?
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    HBC, Ballistics Editor
    No tests on the .224, 90 gn. JLK but Otto Holmberg gave me one to measure. It looks like a mineature Berger, 6mm, 115 grain VLD and weight wise it scales to the same form, i.e.,.224/.243)^3*115 = 90.08, thus the BC should be very close to,.224/.243)*0.60 = 0.55. That BC for the JLK should be pretty close because both bullets appear very similar in form. I have measured the Berger 6mm, 115 VLD at BC = 0.60.

    Looking into my data, I find that all dimensions for the .224, JLK 90 grain bullet are entered and the estimated BC is 0.51. Thus it appears one could expect a minimum BC of 0.51 and possibly as high as 0.55.
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    flatlander
    Henry - I've been using a BC of .580 for JLK 90s in Sierra Infinity with MV of around 2800fps. Infinity's prediction was for 165" of drop at 1000 with a 600yd. zero on the rifle, so in preparation for 3x1000 matches last Thanksgiving at Phoenix, I ran the front sight of my AR service rifle down three revolutions,15 MOA), and came up three 1/2 min. clicks over the 600yd. zero on the rear sight. Sighters were mid X-ring for elevation, so I'm wondering if this is due to Infinity using the G1 drag function, or if the 90's BC is actually closer to the .580 figure I've been using. Your thoughts, please.
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    HBC, Ballistics Editor
    flatlander--I have not used the newer versions of the Sierra program but believe the older versions did use the G1 drag data with multiple BC inputs for various velocity ranges.

    If the Infinity version also uses G1 and you input only one BC value and that was 0.58 then I believe it would give you drop values too low for the .224 JLK 90 grain VLD bullet. I believe the BC of that bullet would be well below 0.58 if determined from the G1 data.

    Another point in trying to determine BC based on sight "come up", it is very important to establish the accuray of your sight adjustments then carefully determine the come up from at least a 10 shot group at say 100 yards then another 10 shot group at say 600 yards and carefully note temperature, site elevation and corrected barometric pressure readings for both groups shot. And of course the velocity of both groups would have to be measured with an accurate chronograph. If possible also note relative humidity but it will have little effect.

    Rev.: I would also measure your sight radius, measure the sight movement for the adjustment you made at Phoenix, then calculate the actual moa' adjustment. Also, a stated M.V. of about 2800 f/s does not sound too close.
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    paul
    Just out of interest here is a quote from another post

    Ok....the Army Marsmanship unit has determined the BC of the 90gr JLK at around .560-.565, not too shabby!....Now if you take a trek over to the Florida Highpower forum there are several threads including a monster of 500+ posts on the 90 in a .223 bolt action with a 30" palma contour barrel, as well as load data and general highpower type experiences with the bullet. I'd give
    it a look just so you can get an idea of what works and what doesn't ...German Salazar describes the 90 in the 30" barrel as a mini magnum or balistically superior to a 300WM with 190gr sierra MK, he is getting about 2900fps from the combo.

    My recommendation would be a .22 Dasher with a 28-30" barrel 1:6.5 twist or 1:7,marginal)using a slowish powder like VV N550 or N560 you should be able to get 3000-3100 fps with no stress on the case, and being a BR case with some "improvement" accuracy should be very good...one thing I do know the jlk's like to be in the lands a fair bit 20 thou in is a good place to start, they
    are a little fussy about loading but once you have them working they hammer. Incidentally the 90 is made with 6mm jackets so they should handle velocity well..

    I have a 1 in 7" twist barrel do you think it will work ok with the 90 in a Dasher?
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    HBC, Ballistics Editor
    Your comment, "marginal" for 7" twist was good.

    At 3050 f/s muz. vel., 80 ft. AMSL, 50 F, the .224" cal. 90 grain JLK would have an Sg = 1.29 per my calculations. That is too low. I would not want to shoot in a long range match with anything lower than Sg = 1.4 and would prefer 1.6.

    For the same conditions and a 6.5" twist, Sg should be around 1.5, which is much better.

    Here is a test for the 90 grain JLK and someone who has an 8" twist barrel and lives at around 2000 ft. AMSL or a little higher. For a muz. vel. of around 2800 f/s and temp. of 50 F or higher, Sg for the conditions in this paragraph would be about 1.06. At 10 to 20 yards the bullet would likely yaw baddly, making oblong or key holes but at 100 yards or more, Sg should have increased enough that the bullet holes are round, if you can hit the target.
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    flatlander
    Henry - I'm shooting the 90s out of PacNor 6.5 twist bbls. contoured & chambered by John Holliger, a much-repsected highpower AR 'smith. Initially, I loaded N540, and could barely reach 2700fps out of a 20" SR bbl. with good to very good accuracy at 600. Experiments with N550 gave velcities just over 2800 and excellent accuracy, with none of the peaky, quirky pressure peaks I'd seen with N540 - instead, accuracy just got better as I increased the charges with N550. That's not to say that you can't get into trouble with N550 in the little 223 case - loose primer pockets in once-fired cases brought home that point. I'm aware of one Texas shooter who's recently completed a bolt rifle with a 6.5 twist bbl. chambered for the 22BR, specifically built to shoot 90s. He's reporting velocities of 3050fps and very good accuracy. My thought is that the JLK 90s, at this velocity, are going to give the best of the 6mm bullets a run for the money out to 1000yds. I didn't just grab the .580 BC figure out of thin air - instead, both the AMU & a couple of independent shooters who had run tests near Ft. Bliss with Oehler M43 chronos,with the assistance of Dr. Oehler) at the muzzle and 1000 have calculated the BC at that figure. I'm not aware of any data that's been published that would lower the .580 figure, and so have been using it in both Infinity V 1.0 & V 5.5. I was just having a hard time understanding whether my experiences with 90s at 1000yds. were a valid confirmation of the use of that BC value.
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    HBC, Ballistics Editor
    flatlander--One way to look at BC claims is to calculate the form factor, which is sectional density divided by the BC. Many of our long range match bullets have form factors of around 0.55 and down to around 0.48. The Berger 6mm, 115 grain VLD, when one finds a lot with a very small meplat, has a form factor of around 0.46.

    I have placed magnesium and aluminum tips on 6mm 107 grain MatchKings which increased the length to over 1.30" and reduced the meplat to 0.010" to get the form factor down around 0.41. The machined Lost River cupronickel bullets in 6mm have form factors down around 0.40 but they have meplats of around 0.010" also. It takes a streamlined bullet as well as small meplat to get form factors down in the low 0.4's.

    A 90 grain cal. .224" bullet with a BC of 0.58 would have a form factor of 90/7000/,.224)^2/.58 = 0.442. That is a very low form factor for a bullet with a 0.055" diameter meplat. The sample of the 90 JLK had a 0.055" dia. meplat but of course that can vary from lot to lot. About the smallest meplat diameter I have seen on a commercially swaged bullet, without pointing the meplat in a special die, is 0.050.

    Contact the folks who measured the BC of the JLK at 0.58 with Oehler Mod. 43 equipment and ask: What was the sky screen spacing and what was the distance over which the BC was measured? Also, did that 0.58 value represent the high or the average BC of ten rounds or more?

    If the meplat diameters on the .224" cal. JLK 90 grain bullets you are shooting is around 0.030" then I would agree that it would likely have a BC of around 0.58. But with a meplat of 0.055", I don't think so.

    One word of warning on the very small meplat bullets,meplats less than 10% of bullet diameter): The BC can be increased by placing an aluminum tip on the bullet, increasing the bullet length and reducing the meplat to below 10% of bullet diameter but high BC variation will result. I have seen BC variations in a 10 shot group, with the very sharp pointed bullets, vary as much as 13%. A BC variation of 13% will kill a group at 1000 yards with lots of vertical stringing. I know from experience.

    Here is a quote from R.L. McCoy's book MODERN EXTERIOR BALLISTICS, p 71, just below Fig. 4.24: "sharp pointed ogives are utterly impractical for either ordnance or sporting use." McCoy recommends a minimum meplate diameter of at least 10% to 15% of bullet diameter.
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    flatlander
    Henry - Thanks for taking the time to explain that to me. I measured a couple of meplats on the current lot of 90s I'm loading, and they are indeed between .050"-.055". I've been hoping for a follow-up article in Precision Shooting on the experiments done near Ft. Bliss, but I think the guys who set the original up had their fill of gophers chewing through the cables stretched between the firing line & the skyscreens 1000yds. away. Maybe Doppler radar at Aberdeen would give us better answers.
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    HBC, Ballistics Editor
    flatlander--It finally dawned on me the M43 BC test you were refereing to. Larry sent me a copy several years ago. It is a bit difficult to navigate since the tests are identified with only a sequential number. I found the test for the JLK 0.224" cal., 90 grain bullet over 1000 yards. The sky screen spacing was 8 foot, which is not bad but not good either but 10 rounds were fired for an average BCg1 = 0.502, with a high of 0.507 and a low of 0.492.

    Here is the data,average for the 10 rounds) if you want to calculate BC w/your program:

    Altitude---3935 ft. AMSL
    Temp.------53 F
    R.H.-------55 %
    Baro.------30.24" corrected,26.16" Hg uncorrected, or local absolute pressure)
    Instr. vel. @ screen #2-----3138 f/s,avg. of two M43s)
    Distance from sky screen #2 to acoustic target---999.23 yd.
    Time of flight from screen #2 to acoustic tgt.---1.321605sec

    Henry

    Rev.: Sorry, had temp. wrong, 53 F is correct. Also did not include instrumental velocity,kinda hard to calc. BC w/o that.)
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    paul
    Henry--Does velocity make a lot of difference to usable twist? I see the 22Br produces about 3050 with the 90 JLK, I guess a Dasher should be capable of another 100 or 150fps would this help with a 7” twist?
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    HBC, Ballistics Editor
    Not much of an effect on the gyroscopic stability factor, Sg, at least per my estimate below:

    .224" caliber, 90 grain JLK VLD out of a 7" twist, 800 ft. AMSL, 80 F, 78% R.H.:

    3050 f/s-----Sg = 1.41
    3200 f/s-----Sg = 1.42

    To really answer your question would take equipment and tests that are not available to me.

    Read McCoy's article in the 1996 P.S. Annual about the 30 cal. 168 grain smk. I know that is a different bullet but he has plotted a curve in that article showing the overturning moment Coefficient, Cma, versus Mach number, p.183. The rate of change of Cma relative to Mach number would be roughly similar to other hpbt match bullets. That curve relates inversely to Sg. In other words Sg is proportional to 1/Cma, thus at Mach 3, Sg would achieve its highest value when launched from the same twist barrel since at Mach 3, Cma reaches its lowest value.

    In the region of Mach 2.5 to 3 you can see that Cma does not change much, percentage wise. The percentage change for Sg would be exactly the same as Cma but with reverse sign.
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    paul
    Thanks Henry--Given those conditions the Sg looks a little better? Have you had much to do with the various 80grn .224 bullets? I’m looking for something with a little better BC than Sierras.
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    HBC, Ballistics Editor
    No, for shorter ranges I would probably shoot the Clinch River 6mm, 100 grain VLD but I have also used it for 1000 yard BR with good results.

    Henry
     

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