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Thread: .223 CZ527 Varmint (1:9) & 75gr A-max, any good?

  1. #1

    .223 CZ527 Varmint (1:9) & 75gr A-max, any good?

    So, I've just moved on my remmy 700 VSSF which was stupidly accurate with 52 gr A-max in favour of a CZ527 laminate varmint primarily because I want to shoot heavier bullets to extend the useful range at the club.

    Having had good success with the 52gr A-max I'm thinking if it will stabilise the 75 grain A-max that will be the bullet for me as it will do the job on fox where necessary and I'll have a URL purpose load.

    Is anyone using this combination, powders I have at the moment are Tac and N140 so if it's with either of these even better?

  2. #2
    Or even a dual purpose load

  3. #3
    I'm glad you started this thread. I too have a cz527 1/9" twist it's the kevlar varmint 23.5" that's been screw cut and target crowned. I started with 55gppu sp factory 1.5" group at 100m The used 69g ppu match 2" group at 100m,then 55g vmax which was 5shot touching groups in a line due to wind,60g hornady tap touching groups ar 100 not as God as the 55g vmax but cheaper.Then started reloading with 52g amax with 24.5g blc2 I get 0.5-0.75" groups with this,but the rifle takes a lot of cleaning. I tried 68g hornady match type heads 2"group at 100. Then some 69 g matchkings I think that didn't perform very well I'm now back using 52g amax and 24.5g of blc2 and seating a max mag length. I have now run out of heads and powder for the 223 and looking at using n140 and a different head or some Ramshot if I can find a local rfd who does it. All the looking on the net I have done regarding th 75g Amax and a 1/9" twist is very random as in yes it grough well and then all the heads whent the the papper sideways. So basically I'm looking for a heavy head that available to use with n140 in the 223 as I us that powder in the 308.

  4. #4
    only one way to tell!
    rifles dont always read the same forums as their owners

    heavy for calibre bullets in .222

    there is likely to be a stabilisation sweet spot when it comes to velocity even on a fast twist barrel and heavies
    this is not the same as the harmonic accuracy node you will normally see but a much more aggressive shift from adequate groups to shotgun pattern

    crack on and let us know how it goes

  5. #5
    What's a URL purpose load

  6. #6
    Every rifle is different, but my varmint Kevlar didn't like 75grain bullets.

    69gr SMK - now that was a different matter

  7. #7
    I don't believe everything I read,but I did see the pictures of the target hit by the 75g Amax all the shot whent side on. I loaded and shot some 40g nozler balistic tips and produced a half inch group with the 1/9 which was surprising. Ok I will bite the bullet and try some and see what happens

  8. #8
    Quote Originally Posted by geordieh View Post
    What's a URL purpose load
    Universal Reliable Live load Norman, thanks for your input

  9. #9
    Quote Originally Posted by Albert 888 View Post
    ... shot some 40g nozler balistic tips and produced a half inch group with the 1/9 which was surprising. Ok I will bite the bullet and try some and see what happens

    Funny you should say that my guns favourite factory ammo was 40 grain Norma as well... go figure.

  10. #10
    It's not the bullet weight that determines the twist rate needed - it's the length, specifically the length as measured in calibres. If you have two bullets of equal length in a calibre but one is long-nose, boattailed and relatively light; the other blunt-nosed, flat base and 25% heavier, the heavy bullet actually needs a lower spin rate to be fully stabilised. Hence the 60gn and 63gn 0.224 Sierra SMP bullets and similar such as the 60gn Hornady that were designed for the .222 Rem and its 1-14" twist rate.

    The 75gn A-Max averages 1.11" OAL. Run it through the Miller twist rule spreadsheet at various twists and here's what you get under 'standard ballistic conditions' (ASL @29.92 inches mercury air pressure; 59-deg F air temperature):

    Let's assume that we get 2,800 fps MV

    1-12" .................. 0.55 Sg

    1-11" .................. 0.65 Sg

    1-10" .................. 0.79 Sg

    1-9" ................... 0.98 Sg

    1-8.5" ................ 1.09 Sg

    1-8" ................... 1.23 Sg

    Because of its plastic tip extending the front end of the bullet out, the formula understates the Sg value for this type, but it won't be that much above 1.0. What's Sg? - It's the Coefficient of Stability. Anything less than 1.0 is unstable; at 1.0 it's theoretically stable, but barely so and a change in conditions (colder air than 59-deg, high pressure etc) will drop it below 1 back into instability. In practice, note the advice to use a combination that produces 1.4 or higher values (the 8 inch twist will definitely be there with this bullet). The latest thinking says 1.5 is needed as experiments have shown that bullets with lower Sg values will appear stable - group well, round holes - but see increased drag in flight, or to turn that around have their BCs degraded.

    For many sporting applications, that's not a great issue but may be with this bullet as it is a long-range design and is favoured by foxers for longish shots in windy environments and is a popular mid range match bullet in 223 Rem for use up to 800 yards.

    The bullet length and barrel twist rate are the key factors, MV has a relatively small effect - although that may swing things either way in a marginal situation. Run the 75gn A-Max again at 3,000 fps in the 9-inch twist and the Sg only climbs from 0.98 to 1.00. On the other hand substitute the 75gn Hornady HPBT (length 0.981") at 2,800 fps and the Sg value rises to 1.40 in the 9-inch twist. The slightly shorter Nosler 77gn HPBT Match (0.973") gets 1.47 largely because of its increased weight.

    The 75gn A-Max and 9-inch twist issue is raised regularly on forums - the answer is 'maybe yes' to basic stabilisation, 'maybe no' because it is a true marginal combination. That also assumes that when the manufacturer quotes 1-9" twist rate that's what you get, which isn't actually so more often than not. Factory rifle barrels may vary by up to a quarter inch either side of the nominal rate. If you specify a bespoke barrel from a custom barrelmaker such as Krieger, Bartlein, Broughton etc, you get exactly what you order on the other hand. In fact, Bartlein takes orders to two decimal places just in case you fancy say 1-7.77".

    This is what the spreadsheet looks like

    Don Miller's Twist Rule
    Caliber 0.224 Inches
    Bullet Weight 75 Grains
    Bullet Length 1.11 Inches
    Barrel Twist 8 Inches/turn
    muzzle velocity 2800 fps
    Temperature 57 degrees Fahrenheit (59 is standard)
    Pressure 29.92 inches of mercury (29.92 is standard)
    Sg = 1.23
    Sg shouldn't be less than 1.4. If Sg is greater than about 2.0, you may
    gain some accuracy by going to a slower twist barrel.

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