My New Pet Varminting Load:
MV 4650 fps!, BC 0.221!
M.L. (Mic) McPherson, December 2004
Synopsis: Contrary to what many of us have in the back of our minds as we choose and prepare our favorite varminting load, velocity is not everything. Other factors are important; these include: accuracy, barrel heating, recoil, and cost. However, for the sake of this discussion, the one other factor that is critical to the long-range varmint hunter is the ballistic efficiency of the bullet, which we commonly refer to as Ballistic Coefficient (BC). For hunting smaller species of vermin in the wide open West, BC can be just as important as muzzle velocity because what determines maximum useful range is not muzzle velocity but delivered velocity. Assuming best modern plastic tipped construction, varminting bullets will cease to expand violently when terminal velocity drops much below about 2000 fps. Hence, when looking for the ideal combination we need high muzzle velocity, high BC, and sufficient accuracy. When targets happen to be closer at hand, it is also useful that recoil be minimal — so we can see the impact; when targets are unusually plentiful, it is helpful that the combination does not generate excessive barrel heating — so we can keep on shooting without destroying the barrel.
I suspect that ever since the first nimrod discovered that it was possible to contain the explosion of blackpowder behind a rock in a wooden tube in order to project that rock with significant velocity in the general direction of some sort of target, one and all of his intellectual descendants has had one goal — more velocity! I will not fully address the velocity-versus-momentum argument here; rather, I will settle it with the following statement: So long as bullet terminal performance is adequate to the task, increased velocity is the proven solution for all real-world applications (some of those applications require limited velocity only because it has been proven impossible to make any bullet perform correctly with higher impact velocities); meanwhile, for the varmint hunter, velocity is king.
What we tend to forget when discussing or considering the muzzle velocity potential of various loads is the efficiency of the bullet at retaining velocity — Ballistic Coefficient (BC). So long as any selection of bullet types share the same diameter, nose and base profiles, BC is a linear function of mass. For any given type of bullet construction (materials and design) there also exists a practical minimum bullet mass for each caliber where bearing surface is sufficient to assure accuracy — it is infeasible to retain identical nose and tail profiles when bullet mass drops below a certain threshold. This is one reason the plastic tipped bullet design has changed varminting, it allows for significantly lighter bullets in each caliber to retain optimum nose profiles for a high BC. At the same time, it allows manufacturers to use one bullet instead of two for each basic design — the plastic tip encourages rapid expansion despite a relatively heavy jacket so the manufacturer can beef up jacket thickness and still see sufficient terminal performance when handloaders use the bullet in more mundane applications. Where, formerly, every manufacturer found it useful (or necessary) to offer two otherwise identical bullets, differing only in jacket thickness, in each varminting design, one significantly superior design now suffices.
Modern Limitations to Ideal Varminting
The classic example is the Nosler 22-caliber Ballistic Tip line. The 55-grain BT and the 40-grain BT have essentially identical nose profiles with sufficiently similar base profiles so that relative BC is almost exactly a mirror of relative mass. As demonstrated in an earlier Varmint Hunter magazine article, when we load each of these bullets in any size case using the best propellant and equal peak pressures, the lighter of these two bullets has a significant trajectory edge across the feasible range where explosive expansion is likely to occur, rendering ranging errors less critical; it also generates significantly less recoil, so that we can see impacts on the occasional close-range target. However, the lighter bullet does exhibit about 10% greater wind drift, so it might not be quite as useful for long shots on a gusty day. Generally, I have concluded, as have the folks at Nosler and many other shooters that the lighter bullet is king in this game.
Now, consider how we can improve upon performance of this bullet. With conventional materials, it is infeasible to reduce mass or improve BC by much, compared to what is already offered (particularly in the solid-based Nosler varminting bullet line) so all that we have left to consider is increasing muzzle velocity. However, keeping all other factors similar (gun weight, etc.) and assuming similar potential accuracy, unless we reduce bullet mass, any velocity increase will also increase recoil and barrel heating, which are both anathema to ideal varminting. So, we need lighter bullets and, if we intend to use conventional (affordable) materials, lighter bullets must be of smaller caliber. Whence the value of smaller-caliber chamberings.
While I certainly have no objection to the 19-caliber, the 20-caliber (5mm) is the default option for those who want to shoot the best available plastic-tipped modern varminting bullets. Hence, when my Superior Ballistics Inc partner (By Smalley) and I set out to create a smaller caliber varmint cartridge utilizing the patented and proven superior SMc ™ design, we had two likely options: 17- and 20-caliber.
Based upon his personal bad experiences with the 17-caliber, Smalley was completely uninterested in that option. Nevertheless, I built one such gun for my friend Jim Williamson and he is thrilled with that. That chambering is based upon a modified version of the 17 Mach IV and will launch the fine new Hornady 20-grain V-Max at velocities that will allow it to far outperform the original 17 Remington, 25-grain HP load! Recoil of the 17/23 SMc is not worth considering and barrel heating (especially when using moly-plated bullets) is a non-issue.
Nevertheless, both Smalley and I were more interested in a 20-caliber, which is far more similar to a 22-caliber than it is to a 17-caliber — 20-caliber bullets have 83% of the cross-sectional area of 22-caliber bullets while 17-caliber bullets have only 71% of the cross-sectional area of 20-caliber bullets and only 59% of the cross-sectional area of 22-caliber bullets.
Based upon this, I made the argument that the 20-caliber was worth pursuing. My basic belief was that if it was possible to make good 22-caliber barrels then making good 20-caliber barrels should not be a problem and that fouling should be only marginally worse in the 20-caliber. With newer and cleaner propellants and with moly-plated bullets useful 20-caliber chamberings seemed likely to be feasible.
Two critical factors drove this project to reality. First, the readily available 6mm Norma BR, an existing commercial case that was essentially ideal for conversion to 5mm with the SMc design. Second, other wildcatting and commercial developments were driving the availability of 20-caliber bullets. A third factor is no small matter, that conversion of Norma made 6mm Norma BR cases is so easy that anyone can do it in one or two steps! (due to different annealing, Lapua cases are not so easy to convert).
With our previous experiences in converting cases into 22-caliber, 6mm, 6.5mm and 30-caliber being akin to pure torture, we were both anxious for any conversion that was just simply simple! — the 5mm/35 SMc fulfilled that dream.
Summer of 2004, on our way to and from the Varmint Hunter’s Jamboree, Smalley and I, sported three 5mm chambered rifles, two in 5mm/35 SMc guns and one in the intellectual predecessor of those, the 5mm VarmintMaster (same basic design excepting a hemispherical shoulder rather than an elliptical shoulder with significantly greater usable capacity but a shorter neck, which likely significantly reduces barrel life). While varminting on that trip, we shot the 30-grain Berger LTB, loaded to about 4600 fps; the 32-grain and 33-grain Hornady V-Max, loaded to about 4500 fps; and the 40-grain Hornady V-Max, loaded to about 4200 fps in these guns. We fired around 700 rounds and we killed an inordinate number of prairie vermin with shots ranging from about 50 yards to about 500 yards and under all manner of conditions from dead calm to, hold on the second fence post to the left, with occasionally stronger gusts.
We were thrilled to note three surprising things about these 5mm SMc guns. First, all kills within about 350 yards were simply spectacular. We noted that all three bullets performed similarly in this regard and that typical center-of-mass hits resulted in something that we had not seen before — the target would balloon to the maximum elastic limit, pause at that size and shape and then disintegrate. Rather spectacular, to say the least.
I have coined a term for this effect: The Blowfish Special. Owing to the mental image this term engenders (from memory) I like this name so much that I have considered renaming the 5mm VarmintMaster as the 5mm BFS. Smalley has noted that one has to be sick to get a kick out of such things. Because our fellow shooter at the time, Jim Ricord, was laughing hysterically after observing this effect for the first time, I noted that Smalley and I are both sick and that, evidently, we are in good company.
Second, recoil was in a different class from what we had seen with high performance 22s. For example, Jim Ricord, used his new Savage Low Profile 223 that, excepting chambering and bore size was identical from butt pad to scope to muzzle crown with the 5/35 chambered Savage that I was shooting. Moreover, his load launched a 40-grain Nosler BT at about 3900 fps using a stiff charge of BenchMark. My load launched the 40-grain Hornady V-Max at about 4250 fps using a few more grains of the same propellant. Hence, my 5/35 chambered gun launched the same mass bullet using a heavier charge of the same propellant to significantly greater muzzle velocity; nevertheless, we compared those two guns and we all agreed that his 223 chambered gun kicked harder — in the sense of sight picture disturbance — it was easier to see impacts at close range when firing the SMc chambered gun!
This would seem to be an impossible result until one considers that what disturbs the sight picture the most is initial gun recoil — that recoil that occurs in response to initial bullet and unburned propellant acceleration into the bore. Because the SMc design does a better job of trapping unburned propellant in the case, with these particular loads, less total mass (bullet plus unburned propellant) initially accelerates into the bore in the SMc gun. Hence, initial rearward gun acceleration (when the gun is least tied to shooter and so he is least able to control gun movement) was comparatively reduced with the SMc.
Third, that despite a noteworthy performance edge, the 5/35 generated no more barrel heating than the 223 did. Again, this is a direct result of SMc design efficiency, more energy is converted into bullet velocity and less into barrel heating, which is a very good thing indeed.
The surprising velocity potential of the relatively small 5/35 case (equivalent to 35 grains of water usable capacity, which is comparatively similar to the 22-250, in terms of cross-sectional bore area to case volume), this chambering leaves little to be desired in the performance area. In order to achieve a useful increase in performance, it would be necessary to significantly increase usable capacity (for example, the 20-250, which has about 20% more usable capacity). The problem with that approach is that it also significantly increases recoil and barrel heating while monumentally decreasing useful barrel life. Hence, we are satisfied that the 5/35 is just about ideal in terms of performance-versus-costs.
For this reason, the only way to generate a worthwhile increase in performance using the 5mm bore is to use a bullet with a higher BC. Enter the new Sierra 20-caliber BlitzKings in 32- and 39-grain weights. Sierra did a fine job of combining an efficient shape with the proven plastic-tipped design. Its new bullets have worthwhile BC advantages over the fine Hornady offerings. The BC advantage of these Sierra bullets is about 10%, which means that when these are launched at the same velocity, the Sierra bullets will travel about 10% farther to deliver the same impact velocity. Hence explosive useful range is increased by about 10%, which is no small improvement. If the 32-grain Hornady V-Max will deliver explosive performance at 400 yards, then the 32-grain Sierra BK will do so at about 450 yards! (The above analysis is based upon the unproven but reasonable assumption that jacket thickness and core materials are reasonably similar.)
However, the issue is accuracy. While I had never been able to get the 32-grain Hornady to shoot as accurately as the 40-grain Hornady does, when launched at top-end 5/35 velocities, I was able to achieve sufficient accuracy to assure hits to at least 400 yards when I did my job and when conditions were favorable. Hence, the 32-grain Hornady was my preference because it generated significantly less recoil and it shot flatter (recall the above-noted Nosler 40- and 55-grain, 22-caliber comparisons).
So, when Sierra announced their new 20-caliber bullets, I was most interested in the 32-grain version, for the same reasons. However, preliminary testing with these new bullets in a 1/12 twist barrel of proven accuracy potential demonstrated that the lighter Sierra bullet was evidently not up to the stresses imposed by launches in excess of about 4400 fps. While, the 39-grain bullet showed exemplary accuracy — I am confident I can find a combination that achieves 4200 fps with five-shot groups consistently in the 4s or even better — the 32-grain bullet produced patterns — groups in the 1½ MOA range were the best I could do.
For this reason, I was most anxious to test the 32-grain Sierra in the 1/16 Pac-Nor barrel that Chris Dichter had send me. This twist will not stabilize any bullet heavier than about 33 grains but it is reported to work well with lighter bullets, which are what I am most interested in.
To date, I have only been to the range twice with this barrel to test loads using the 32-grain Sierra in the 5/35 but the results are encouraging. The load that looks most promising is a top-end BenchMark charge with the bullet seated about 0.020-inch off the rifling. Muzzle velocity exceeds 4650 fps with a standard deviation hovering near 10! Accuracy of the one five-shot, 100-yard test load at this overall length was well under 0.4 inch, on centers. Other loads tested at similar lengths provided sufficient accuracy so that I am encouraged that I can probably find a combination that will routinely beat the one-half MOA standard, which I consider to be sufficient for a 400-yard prairie vermin combination.
I expect to continue to tinker with OAL and primer choice, while looking to improve accuracy. However, even if this load proves to be the best possible combination (seems unlikely), I already will have a load that is a step above my former top choice, the 40-grain Nosler BT launched at 4400 fps from a Savage 22-250 (BenchMark again!).
Until Nosler introduces their version of a lightweight 5mm varminting pill, it looks as if the 32-grain Sierra may well be the most efficient such option. The hypothetical (for now) Nosler bullet should be about 30 grains and it could well have a slightly higher BC than the Sierra 32-grain BK. The reason this is feasible is that Nosler uses a solid-base design with a thicker jacket near the base of the bullet shank. Because gilding metal is significantly less dense than typical core alloys, the solid base and thicker jacket walls increases bullet length (for any given bullet mass). Hence, Nosler can offer a lighter bullet with a longer nose (higher BC) and still have a sufficiently long bearing surface to provide requisite accuracy potential.
An added bonus of the solid base design is increased toughness against chamber pressure and chambering misalignment; hence, these bullets tend to be a bit easier to make shoot well in any given gun — the Nosler design is more forgiving. Finally, it is very likely that any such bullet will shoot just fine in the standard 1/12 twist that is the default standard for the 20-caliber bore.
The downside is that inevitably, Nosler bullets are a bit more expensive so those on a budget may prefer the Sierra or the Hornady. While the Sierra has the BC edge over the Hornady bullet, by a useful margin, some guns may not shoot the Sierra as accurately as the Hornady and that could be a deciding factor. Meanwhile, to my lights, the 32-grain BK is the new King of the Hill.