New #2231 200gr SMK for F/TR

Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by Quickoz, Jan 18, 2018.

  1. XTR

    XTR Gold $$ Contributor

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    Greg, I think that it may just be that we are reaching a limit on the bullet length:bearing surface ratio to achieve consistent precision. Then again, I'm just guessing.

    One thing that coaching teams brings home hard is that you lose way more points in the corners on good wind calls than you do to squeakers at the water line. As long as the difference in BC isn't dramatic (like the 155vs200s) then you will agg much better with a load that shoots ½ MOA at the targets than one that shoots 3/4 MOA.
     
  2. mysticplayer

    mysticplayer

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    If you are finding the new 200gr MK fussy, consider a slower twist.

    Been really enjoying these bullets and just sent some out to 1652yds with excellent accuracy. I am using my FTR rifle.

    YMMV,

    Jerry
     
  3. Jdne5b

    Jdne5b Gold $$ Contributor

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    What is your velocity and what is your twist?
     
  4. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    Running a twist much slower than 10 will likely defeat the whole reason for using the 200 SMKs. They may be less finicky with regard to loading, but if you're giving up more than a few percent of the intrinsic BC, any advantage the 200 SMKs enjoyed over other similar offerings by different manufacturers is gone.
     
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  5. D.Stone

    D.Stone

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    Has anyone had any major issues of using these in a 1:10 twist? The Berger calculator seems to say that they'll be marginally stable with an SG of 1.37.

    I am planning on shooting these out to 2000 yards in an ELR match...for giggles mainly.
     
  6. D.Stone

    D.Stone

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    I think I might have came up with a load that might work.

    My barrel is a Bartlein 1:10 twist at 28 inches with a fairly short throat. I am seating these bullets to 3.135 OAL to get them just off the lands.

    41.7gr H4895
    3.135 OAL
    V= 2615fps

    That was on a 50 degree day. I was able to test up to 43.5 grains of H4895 with no issues, but I would expect anything more than 42 grains to give problems in really hot weather, or in the rain. I shot a 10 round group at 300 yards that is maybe a touch over 2 inches by 2 inches; nothing spectacular, but about average for what I shoot off a harris bipod. If you saw how much the reticle was moving, you would see that I definitely added to the group size.
     
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  7. damoncali

    damoncali Bullet Maker Site $$ Sponsor

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    The trouble with these bullets is that they’re too long and spinning too fast. I think Sierra was just responding to the market’s perception that BC is the primary way to measure a bullet’s performance. But that’s not true. Long bullets, as we’re seeing, are not as accurate and can complicate stability issues. We’re trading too much precision for BC. I think we’re gradually discovering though trial and error that there is an optimum balance - a bullet with a BC that’s relatively high, but still well behaved. I think these Sierras overshot the mark and have too much BC to be controllable.
     
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  8. Crosshair1

    Crosshair1

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    Ive tested 250 of the 230smks recently in a 9twist 308.
    I was hoping that they may have provided a suitable/better alternative for 215 hybrids at 600yd Ftr.
    I know that the 9 twist is not maximising the bc and stability is in region of 1.4 for this setup.

    I found the 230s to group excellently at 200yd testing , possibly having the edge over the 215s, but once i went back to 600yds the groups opened significantly every time- in all directions.

    I had a gut feeling that at 600 they were not bucking the wind as good as the bc would suggest even though the drop was as expected.
     
  9. Pinkes

    Pinkes

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    Don't want to start a thing but...I'm shooting the 200smk with great success in my ftr rifle,2620fps.(couldn't find 200.20x in SA) With marginally stability SG of 1.34. And the kicker is its in a 11twist,at 4200ft altitude. BC i'm using for validated drop is G7 0.354
     
    Last edited: Dec 3, 2018
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  10. willbas

    willbas

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    I an trying the now I got a load with a 3 SD and need to confirm my setting depth and will test them out to 300 this weekend my use for my next 600 yard match in January. IMG_5636 (1024x683).jpg
     
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  11. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    Damon - I really like your thinking on this, but I have a question. Did you really mean to say they "have too much BC to be controllable"? What does that mean? There are plenty of bullets designed with higher BCs than a 200 gr 30 cal bullet, even the ones currently available. In my mind, poor performance has little to do with the BC per se. It has everything to do with a design flaw, which could mean a lot of things including where the Cg is located, boattail design, etc. Although those design issues may be influenced by the need/desire to keep the BC very high, to my mind that doesn't mean there is any theoretical upper limit to BC in a 30 cal bullet of any specific weight. It merely means that there is something about the bullet design that is not quite right given the rest of dimensional and physical characteristics of that bullet. In other words, I believe it should be possible with appropriate testing and design changes to keep the high BC, AND get rid of the fliers (inconsistent precision). Why would that not be true?

    Within a given caliber and weight class, such bullets are going to be longer by definition as BC is increased, thereby requiring faster twist rates. In the case of the Berger 90 VLD, there are no such issues with precision and grouping. With the exception of the Warner 198 gr Flatline bullet, the length of the Berger 90 VLD with respect to caliber ratio is much greater than any .308 bullet currently made. The Warner 198s only exceed this because they do not have lead core and therefore must be much longer for a given weight. Regardless, if extremely long and stable high BC .224 bullets currently exist, there shouldn't be any reason the same ratios cannot be reached with 30 cal lead core projectiles, and the 30 cal bullets currently available still have a long way to go. In my mind, the issues with precision observed with these longer 30 cal bullets are design problems that can be engineered out, rather than some inherent physical upper limit of BC that has been surpassed. What say you?
     
  12. damoncali

    damoncali Bullet Maker Site $$ Sponsor

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    I was using shorthand for “too much length”. Given a bullet length and reasonable design parameters, there is a limit to the BC you can cram into a jacket. Once you optimize BC for a given length (which will not be optimal for accuracy, given the same length constraint ), the only way to get more is to make the overall length longer. Berger has done a pretty good job at optimizing bullets for drag. That’s why I think Sierra went with an even longer bullet - they had to in order to materially improve on BC.

    But as we’re starting to see, the things you can do to reduce drag come at a cost in other areas - stability and precision.

    As for long .30 cals (scaled up Berger 90s if you will), I’d have to run some numbers on that. I’m not sure where the problem in doing so first shows up.
     
  13. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    I'm not sure where the boundary is either. However, a 90 VLD proportionally scaled up to 30 cal would be about 1.72" long. With the exception of the monolithic solid 198 Flatline bullet, no other 30 cal bullet in the ~200 gr weight class that I am aware of has reached that length. However, the Berger 230 Hybrid is getting close, and obviously has a much higher BC than the 200 gr weight class of bullets. With the extra 30 gr weight and alterations to various other bullet dimensions, the 230s are a very good and stable design, which again suggests to me the possibility that the upper BC limit may not have yet been reached for bullets in the 200 gr region. However, the more you try to improve the BC, perhaps the more consistent that every other aspect has to be so you don't end up with an unstable bullet.

    To that end, the longer you are willing to make a bullet of specified weight and caliber, the higher you can push the BC. However, one of the most obvious ways to do that is to lengthen the nose and shorten the bearing surface, and that is likely where potential stability issues or other undesirable side effects of having a really short bearing surface such as balloting can come into play. So my question would be how far can a computer-aided design program realistically go in terms of actually predicting the upper limit? In other words, for a given bullet length, how good are these programs at predicting optimal boattail/bearing surface/nose lengths, Cgs, meplat diameters, etc.? Can they even do that at all? Or are they better at providing close to optimal dimensions for maybe one or two aspects of a bullet, given a few other set aspects such as OAL, bearing surface, and weight, for example? Just curios what are the limitations with regard to in silico bullet design.

    I can imagine that it might be possible to push the BC slightly higher than it currently is in the 200 gr class of 30 cal bullets, but it seems like to do that will require not lengthening the nose and/or not shortening the bearing surface by as much as has been done recently with some bullets that seem to be difficult to tune. That in and of itself does imply there is a finite upper BC limit within a given weight class/caliber bullet (of course, that is assuming no unforeseen disruptive technology advances). I'm mainly interested in whether a computer can do an essentially perfect job of designing the "optimal" BC bullet, or if so close to the margin, much of the design would need to be done by hand. Obviously, rigorous testing/validation would be required in either event.

    Edited to add: along the same line, would it be possible to plug the dimensions of currently existing designs into a program and possibly determine why they might be slightly unstable, or at least, very difficult to tune consistently?
     
    Last edited: Dec 6, 2018
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  14. damoncali

    damoncali Bullet Maker Site $$ Sponsor

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    I'm not sure what the deal is with 1.7" long .30s - I just haven't looked into them. I can't really comment on the manufacturing issues making a jacketed bullet that long either. I just don't have the experience.

    What I can say is there was a lot of work done by the BRL and other agencies - both here and by our allies that resulted in some pretty pragmatic software that can figure these problems out. McCoy's McDrag is a good one that gives reasonably accurate results. Most people know it as the BASIC program that you can download from JBM. It's cumbersome to use - you have to manually type in parameters and read the output. What I did was take the math behind it and re-write the software in a modern language so that I can iterate over thousands of combinations of parameters - different ogive lengths, meplat diameters, Rt/R values, boattail anlges, boattail lengths. This gets to a pretty good idea of what the maximum attainable BCs are. There is some judgement required (mainly the minimum bearing surface you're willing to tolerate and manufacturing limitations on meplat diameter), but one you settle on those, you can iterate over quite a few designs and get an idea of which ones are near optimal.

    There's also a program he wrote called Intlift, which was based off a program written by Morris and adapted to small arms by McCoy. Between McDrag and Intlift, you can get a pretty good prediction of the aerodynamic coefficients required to calculate drag, stability, and a factor that I call "jump sensitivity" simply because I'm not sure if it has a proper name. I first ran across it in a study done by Bob McCoy on the accuracy of 5.56mm ammunition. It's not terribly clever, but it was one of those "why didn't I think of that" type of things.

    In any case, it's a number not unlike BC that gives you an indication of a bullet's accuracy potential and is dependent on basically the same factors as stability. The difference is that you want a low jump sensitivity, not a high one. Jump sensitivity does not paint the entire picture of a bullet's accuracy however. It's just the bullet's sensitivity to aerodynamic jump induced by tipping at launch, which is one of the larger factors in overall accurac. It does not account for how easy it is to make a bullet fly without an initial yaw, for example. (You could make very low jump sensitivity bullet that is very inaccurate by reducing the bearing surface to zero, for example). But I've found that it's a pretty good indicator for reasonably designed bullets, and I've gotten a good correlation between group size and jump sensitivity by varying core weight in my 180s, for example.

    That's where things get tricky and require some judgement. If you increase BC, you increase jump sensitivity, and neither is necessarily a linear change (with whatever factor you're considering). So at some point you have to choose a design that balances out the drag characteristics with the inherent accuracy potential of a bullet given the spin it's going to require (and the spin rates that are available for purchase - it does no good to design a bullet that's ideal for an 10.7 twist). If memory serves, a bullet made with a 1.4 inch jacket (so, about 1.440" long, give or take), maxes out BC at *roughly* .330ish. (Don't quote me on that - I'm going off memory here). But that is far from the most accurate bullet you can make of the same length jacket.

    And none of this even touches the reality of what it would take to launch a 1.7" thirty at a reasonable velocity. So that's also a consideration. It could be that the long .224/2.43s get away with some things that .308s can't simply because they don't have to contend with the same recoil. Just speculating.

    Edit: I would also be concerned about the bullet's structural integrity at 1.7". That's not only going to have a lot of spin, but it may require a fair amount of bearing surface and possibly a long barrel to take full advantage, which can lead to a lot of heat. I've never heard of a commercially available 1.7" jacket before, so who knows. I'm sure someone has tried it.
     
    Last edited: Dec 6, 2018
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  15. damoncali

    damoncali Bullet Maker Site $$ Sponsor

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    This is a good question. I don't know how to make an "easy to tune bullet" outside of the conventional wisdom (tangent good, secant bad), which I don't think is the whole story anyhow. There are too many good shooting VLDs out there to write off the secant ogive as "hard to tune". But then, there are also quite a few benchrest guys who really get into this stuff and tell me secants are harder to tune, and I'm not willing to discount their collective experience either.

    I think aggressive secants (most "tangent" long range bullets are actually mild secants, according to Litz's measurements) might get a bit of a bad name simply because when VLDs were introduced, they were on the long side of available bullets, and for the reasons I gave in the above post, they're less accurate than the shorter, lighter bullets shot out of slower twists. BUT - compared to today's heavy BC monsters, a VLD actually can have a desirable weight distribution, and can be *more* accurate than some of the highly drag-optimized bullets (which might have less aggressively pointed ogives and more weight in the nose).

    My suspicion is that "tunability" has to do with a bullet's tendency to tip, and is influenced by chamber configuration and whatever mystery mechanism that causes seating depth to matter. But I don't really know. To be honest, I haven't found that any bullet is significantly easier or harder to tune at F Class levels of accuracy. Some shoot better than others, but I find you still need to dial in seating depth and charge weight somewhat tightly to get the best out of a bullet. Benchrest may be different.

    Stability is also hard to nail down. You can get a pretty good Sg from the programs I mentioned above, but the Miller approximation of those same equations is pretty good. At least for boattail bullets - it starts to get a little iffy with flat base bullets. I recreated the Miller data from his primary sources and it's a bit more spotty for the flat base bullets, but still surprisingly (to me at least) good. But Sd is much, much harder to pin down. I'm not sure there is a pragmatic way to work through that other than by testing. Applied Ballistics seems to be doing work in this area, at least indirectly if not directly (I don't have any special knowledge of their current efforts). And even that is tough and expensive.

    There is engineering literature out there that gets into some of these issues. I'm currently searching for more information on the impact of geometry on a bullet's yaw limit cycle. I think if we can eliminate that, we can see a significant (but small) improvement in realized BC (as opposed to idealized). All I'm aware of currently are some studies on boattail angle and trailing edge radius. I would love to see some information on boattail length, or ogive configuration, but I've not found anything yet.
     
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  16. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    I see, thanks. So there would have to be significant $$$ in a 1.7" 200 gr 30 cal bullet for anyone to ever go that far. I wasn't even to the point of thinking about available jackets, cores, etc., merely curious about what might be the highest BC attainable. As far as your estimate of 0.330 for a 1.44" bullet, assuming you are remembering that value correctly, well, we're already there. The 200-20X bullet runs in the neighborhood of 1.50" long, with a box BC of 0.328. Of the two longer 200 gr offerings I am aware of that are reputed to be difficult to tune consistently, the one I have actual measurements for is in the 1.58" length range. Perhaps we are already at (or very close) to the upper limit. If so, that's a shame, because, you know, when it comes to BC, it's like a drug...I always want more...More...MORE!!! LOL. I guess I'll just have to be satisfied with what I have.
     
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  17. damoncali

    damoncali Bullet Maker Site $$ Sponsor

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    Yeah, like I said, Berger has done a very good job optimizing bullets for drag. There are probably a few minor gains that could still be made on some bullets, but that Litz character knows what he’s doing. I think the next evolution in target bullets will be to get more consistent BCs. It seems like there is more to do there. BC wise, the 200.20x is close to as good as you can get for a bullet that size.
     
  18. Bart B.

    Bart B.

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    Regarding the quality of a given caliber bullets as their length increases.

    When my friend broke the 35 year old 1000 yard record at the 1970 National Matches with a borrowed 7mm Rem Mag using a new 168-gr. Sierra match bullet, rifles so chambered flew out of gun shops. But really good accuracy seldom happened with Sierra's new 28 caliber HPMK bullet. Jacket material used in those record setting bullets were from a few hundred prototypes made with a left over roll of copper that was extremely uniform in metallurgy properties.

    It was several years before good copper was plentiful to make those 28 caliber long bullets as uniform as similar 30 caliber ones.
     
  19. D.Stone

    D.Stone

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    Well I took them out to a mile today. They do seem to be accurate. I don't know if I would consider them F-Class accurate because I am shooting at steel which is more forgiving.

    41.7 gr H4895
    3.130 OAL
    2620fps.

    Today was fairly cold for the Southeast, and the Berger calculator is giving me a stability rating of 1.35...which is not good. My calibrated G1 BC was .670 from 835 yards to 1350 yards. I was able to get my 3rd shot on the 1 mile target which I think is a 24 inch by 24 inch square. Shooting a 20x40 IPSC at 1350 yards was pretty trivial as well; I had a much easier time than the guy next to me using a 6.5 Creedmoor. (That also has something to do with shooter skill.)

    I don't think that anybody that is happy with their FTR load with the 200.20x bullet is going to go jump on these. The BC advantage is there if I am reading the number right. The one redeeming quality of these bullets is that they are better suited to rifles that are already optimized for average match bullets like 155s or 175s; I'm not sure if that can be said about the 200.20x bullet. I'm probably going to load up a bunch of these again tonight because lobbing them really far is a lot of fun, and I can shoot it all day.
     
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  20. Laurie

    Laurie

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    People maybe now have access to a new tool in determining this BC v LR stability balance - electronic targets giving terminal speeds and ES/SD data for strings. There is a thread somewhere on the forum that followed the use of Silver Mountain e-targets at Lodi for the US FCNs in 2017, their first major event outing in the USA I believe, and it has a very interesting post from a competitor who used both 223 and 308. Having suffered problems with his 308 he had to switch mid-tournament to 223 and found that despite starting with very similar ES values at the muzzle for the cartridges that the 223 terminal speeds ES at 1,000 (shooting 90s IIRC, but cannot be 100% certain on that) was double that of the 308. This struck me forcibly at the time as significant in that the 223 with 90s is known for elevation fliers at long ranges and there has long been a suspicion that these bullets' stability lack 100% consistency so that a small minority generate different levels of drag from their fellows. The e-target data appeared to support that hypothesis.

    So ..... if there are doubts about whether some bullets 'work' at 1,000, I would suspect that similar problems could well show up on the e-targets' retained speed ES / SD sizes. If all 20 rounds in a match are recorded as being within the same size of range as those from bullets known to be very stable and consistent LR performers, that would suggest that any problems they have are not as a result of variable stability. Any increase in yaw, precession etc should increase drag / reduce terminal speed.

    Of course, if every bullet were to suffer the same amount of yaw and increased drag, the terminal speed ES could still be apparently satisfactory. However, given mutters about some models behaving inconsistently that outcome seems very unlikely, and even if it did apply, the effective average BC would be affected across the board.
     

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