When a new projectile enters the reloading market, it’s a pretty big deal. It’s always exciting to see innovation coupled with precision, and performance. The GameChanger Bullets, a new offering in the tipped GameKing bullet line, are touted as the “…perfect blend of exceptional Ballistic Coefficients (BC), Accuracy, and Deadly Terminal Performance on tough wild game.” The bullets feature a synthetic tip for smoother chambering, improved flight and better expansion on target (game) impact. The open pocket design below the poly-tip further expands the lead core, while the precisely engineered jacket wall concentricity makes for an incredibly accurate bullet.
Tuned ogive for industry-leading BC.
Boat tail design creates stable flight and accuracy.
Open pocket (Hollow Point) expands lead core instantly on impact.
When it comes to the release of new projectiles, reloading data can be difficult to find. We’ve obtained some load data from the ballisticians at Sierra for select calibers. For more calibers not listed, please contact Sierra for assistance! The load data provided is to be used to their exact specifications.
Improving longer-range accuracy has a lot to with consistent bullet velocities. First comes understanding it! Here’s a start on it… KEEP READING
It’s springtime (finally) and one of the things on your list might be working up a load for a new rifle, or new bullet. I’ve talked about testing processes and procedures, and also some about those bullets, and especially those with higher ballistic coefficients. The more aerodynamic bullet, by itself, is no guarantee of a smaller group (and whether you’re shooting one shot or 20 shots, you’re always shooting a group…).
To make the “magic” of a high-BC bullet come to life, they all need to be arriving at the destination at really close to the same speed. On target, that’s all about elevation consistency. It’s pretty commonly accepted among long-range competitive shooters that points losses come more from errant high and low impacts than from missed wind calls. High-BC bullets traveling at more consistent speeds reduces dispersions in all directions. But only if they’re traveling at consistent velocities!
The first step to improving velocity consistency is getting a good way to measure it. That there would be a chronograph. Nowadays especially, there are a number of simple-to-use and inexpensive chronographs available, that are accurate. Some have more features, which mostly revolve around providing printouts, digital records, and calculations, but what matters most (to me at least) is one that lets me easily read the velocity of each shot.
So. What’s next is understanding the terms associated with this area of data-gathering.
“Standard deviation” (SD) is the most common measure of shot-to-shot consistency. It reflects on the SD reflects on the anticipated consistency of bullet velocities (some number of recorded velocities). The “standard” part reflects on a sort of an average of the rounds tested.
[Phrases like “sort of” upset mathematically-oriented folks, so here’s the actual definition: SD is the square root of the mean of the squares of the deviations. More in a bit.]
I pay less attention than many to standard deviation because: I don’t think standard deviation is near as important as is the “range,” which is the lowest and highest speeds recorded. Another that matters is “extreme spread,” which, by definition, is the difference between this shot and the next shot. I watch the speed on each shot. I compare this one to the next one and to the last one, and, as said, find the highest and the lowest.
Why? Well because that’s how I shoot tournament rounds. This one, then another, and another. A low velocity difference means that the accuracy of my judgment of my own wind call has some support.
A load that exhibits a low SD is not automatically going to group small, just because a low SD. I’ve had Benchrest competitors tell me that sometimes their best groups don’t come with a low-SD load, but do not apply that to greater distance! At 100 yards a bullet’s time of flight and speed loss are both so relatively small that even what some might call a big variation in bullet velocities (+/-25 fps or so) isn’t going to harm a group, not even the tiny groups it takes to be competitive in that sport. On downrange, though, it really starts to matter. (And keep in mind that “it” is a reference to velocity consistency, whether denoted by SD or otherwise.)
For an example from my notes: Sierra 190gr .308 MatchKing. Its 2600 fps muzzle velocity becomes 2450 at 100 yards and 1750 at 600 yards. (These numbers are rounded but serve for a example.)
If we’re working with a just awful 100 fps muzzle velocity change, that means one bullet goes out at 2550 and the next leaves at 2650, in the worst-case. The first drifts about 28 inches (let’s make it a constant full-value 10-mph wind to keep it simple) and the next slides 26 inches. But! Drop… That is THE factor, and here’s where inconsistent velocities really hurt. With this 190, drop amounts over a 100 fps range are about three times as great as drift amounts. This bullet at 2600 muzzle velocity hits 5-6 inches higher or lower for each 50 fps muzzle velocity difference. That’s going to cost on target, big time. And it gets way, way (way) worse at 1000 yards. Velocity-caused errors compound on top of “normal” group dispersion (which would be group size given perfect velocity consistency). Now, it’s unusual for a wind to be full-value and dead constant, so on-target left and right displacement is even relatively less — but elevation displacement is consistent regardless.
So, my 100 fps example is extreme, but half of that, or a quarter of that, still blows up a score, or an important hit on a target.
So what’s a tolerable SD? 12. There have been, rest assured, much calculation to lead up to that answer. That’s the SD that “doesn’t matter” to accuracy, meaning it’s not going to be the leading factor in a miss. It’s more than I’ll accept for a tournament load, but for those I’m looking for an extreme spread never more than 10 fps (the range might be higher, but now we’re just mincing terms). More later…
The information in this article is from Glen’s newest book, Top-Grade Ammo, available HEREat Midsouth. Also check HEREfor more information about this and other publications from Zediker Publishing.
Tips that help take bullet jump out of the accuracy equation. Find out how!
Last time I shared some insight about bullet “jump,” and specifically with respect to the viability of setting up a “zero-jump” chamber/ammo combination.
To hit the highlights: Jump is the gap the bullet must traverse when it leaves the case neck to engage the lands or rifling. Generally, best (and better) accuracy comes with this gap is reduced to a minimum amount, or at the least reduced. Better is better.
To go farther into this topic, it’s worthwhile to move the bullet around, seating it more or less deeply (nearer or farther from the lands at rest) to maximize accuracy. Clearly, there’s a limit on cartridge overall length if the rounds have to fit into a magazine box so they can feed right. In NRA High Power Rifle competition, the AR15 pilots are specifically not allowed to have the rounds feed from the magazine in semi-auto mode; each round must be loaded into the chamber one at a time for the “slow-fire” segments, which includes the 600-yard event. That means competitive High Power shooters using AR-platform rifles are free to move the extra-long 80+ grain .224-caliber bullets out to near or on the lands when chambered. That doesn’t really matter but it explains the popular “Wylde” chamber we tend to use. It’s got a long enough throat to free more case volume and also provide a bigger “expansion chamber” for burning propellant gases, but it’s not as long as a NATO-spec so should perform better with bullets that do have to be loaded deeply in enough to fit the magazine box. Something like a Sierra 80gr or 82gr Berger won’t usually shoot worth a flip loaded to mag-length. That bullet, and others similar, are simply too dang long for a .223 Remington case. A huge amount of the bullet swallows up the case interior.
The best defense against ever worrying over jump, meaning whether you’re getting good accuracy regardless of the amount of bullet jump (well, at least within reason…) is bullet choice. Specifically, a tangent-profile bullet with a conservative ogive. Recollecting from some materials I did a while back, a “secant” profile is a sharper taper-in from bullet body to bullet tip; a tangent is a smoother transition. Secants, more or less, have a “shoulder” indicating a more abrupt taper rather than a smooth arc. For examples: true VLD (very low drag) and the Hornady A-Max are secant.
Bullets with relatively shorter nosecones and relatively longer bearing areas (length of the bullet that’s in contact with the rifling) are likewise more tolerant of jump.
There’s been a trend for many years now toward creating bullets with higher ballistic coefficients. Worthwhile pursuit! Only issue is that when a bullet design features better aerodynamics, the features of that are, yep, longer nosecones with shallower angles. The ogive (what I’ve been more descriptively calling the nosecone because it’s easier to picture) usually is expressed in calibers. Technically it’s “calibers of ogive,” and that’s the ogive radius divided by the caliber. To me it’s easier to picture looking at the “other side” of the equation: the arc that scribes the profile in multiples of the bullet’s caliber. So, a 7- to 8-caliber ogive is a tighter circle (more rounded profile) than a 12- or 15-caliber ogive. Most of the “high-BC” profiles use a 15, some more. In other words, they’re stilettos.
I’m kind of breaking this down farther and faster than exercising good technical care in covering this topic should warrant, but: comparing both same-weight and same-caliber bullets, the longer it is the more sensitive it’s going to be to jump.
I have shot way too many high-X-count 300-yard cleans with bullets jumping 0.030+ inches to say that it’s not possible to have good accuracy unless jump is minimal. I admit that’s only a 1 moa group. I’m also using what some makers call a “length-tolerant” bullet, and specifically that’s a 77gr Sierra Matchking, and the same goes for a Nosler 77 or Hornady 75 HPBT (not A-Max). It’s the bullet form, not just its weight, that has the strongest influence on all this.
So, do you have to abandon better ballistics to attain better accuracy? Maybe. At least to a point. With the smaller calibers, which don’t have other advantages larger calibers have simply by virtue of weight and sectional density, there tends to be an effectively greater discrepancy between the lighter and heavier (again, it’s really shorter and longer) bullet ballistic performances.
A rifle with a generous-length magazine box provides greater jump-reduction via loaded round architecture. If there’s enough room, a bullet can be scooted out to the limit of the space within the box.
As always, well at least usually, there are tools! Get them and use them. A gage “set” from Hornady is well advised. There are others similar. I’ve been using their LNL Overall Length Gage and Bullet Comparator for many years and receive needed results. The first tool indicates the seating depth that touches the lands, and the second provides more reliable and accurate means to measure and record it.
The leade, which, again, is the transition to the lands and determined by the chambering reamer (or throating reamer if custom-done) does influence tolerance for jump. The shallower the angle the better, but, that’s a two-edged issue. Take a commonly-used 3-degree leade and make it a more preferable 1.5-degree leade and that takes way on more than double the distance (length of cut) to attain. Again, when there’s a magazine getting in the way of bullet seating depth flexibility, a shallower leade eases transition into the barrel bore for a jumping bullet, but also increases jump. There are some cartridges, like David Tubb’s 6XC, that were designed specifically to “perfect” all these relationships: magazine-mandated cartridge overall length, bullet choice, and leade in, and it’s one reason it owns the records it does. Otherwise, it’s often a compromise… But don’t compromise accuracy for anything. A smaller group is, in the long run, the best defense against both wind and distance when it comes to hitting a target. Reliable feedback equals correct adjustments.
Getting a handle on improving long-range accuracy has a lot of to do with understanding the importance of consistent bullet velocities. Here’s a start toward that…
There’s one more thing (seemingly, there’s always one more thing…) that’s important to accuracy at extended distance. I’ll say “extended distance” is anything over 300 yards. That is bullet velocity consistency.
I’ve said in these pages before that a good shooter will lose more points to elevation than to wind. This next explains that a might more.
First, and the first step, is getting and using a chronograph. It doesn’t have to be a zoot-capri model, and nowadays that’s a fortunate bonus because there are a number of inexpensive chronographs available that are entirely accurate.
“Standard deviation” (SD) is probably the most commonly used measure of bullet velocity consistency. SD reflects on the consistency of velocity readings taken over a number of shots. “Standard” reflects on a sort of an average of the rounds tested.
[Math folks don’t use phrases like “sort of” when describing numbers and can provide tickier definitions of SD and the means to calculate it. Here it is: it’s the square root of the mean of the squares of the deviations. Actually harder to say than it is to calculate.]
Steady Wins the Race
Standard deviation is not the only measure, and I don’t even think it’s the right one, let alone the most important, but it’s no doubt the most popular way to talk about ballistically consistent bullet performance. I don’t think standard deviation is near as important as is the “range,” which is the lowest and highest speeds recorded. Some who write and talk about it call that “extreme spread,” but if we want to get picky over terms (and ballisticians, card-carrying and self-styled, tend to get right touchy over such formalities) extreme spread is the difference between this shot and the next shot.
I watch the speed on every shot. I compare this one to the next one and to the last one, and, as said, find the highest and the lowest.
There is no saying that a load that exhibits low standard deviation is going to group small, just because of that. Any Benchrest competitor will tell of experiences whereby “screamer” groups came with high SDs and hideous groups with low SDs (“high” and “hideous” by their standards, still pretty small for the most of us). But, at 100 yards the bullet’s time of flight and speed loss are both so relatively small that variation in bullet velocities isn’t going to harm a group, and, yes, not even the tiny groups it takes to be competitive in that sport. On downrange, though, there is going to be a relatively greater effect on shot placement, right? Yes and no. Drift and drop are influenced. There is a relatively greater effect in ultimate displacement of elevation, more next. Based on drift allowance it probably does not.
To put an example on it, let’s say we’re shooting a Sierra® 190gr .308 MatchKing. Its 2600 fps muzzle velocity becomes 2450 at 100 yards and 1750 at 600 yards. (All these numbers are rounded examples, and examples only.)
If we’re working with a truly hideous inconsistency of 100 fps, say, that means one bullet goes out at 2550 and the next leaves at 2650 in a worst-case event. The first bullet tracks across about 28 inches (constant full-value 10-mph wind to keep it simple) and the next moves sideways 26 inches. Figuring drift on 2600 fps means it’s two inches off, one inch per shot.
Drop, which means elevation, is a (the) factor, and here’s where poor SDs bite. With this Sierra® 190, drop amounts over a 100 fps range are about three times as great as drift amounts. A vertically-centered bullet at 2600 fps hits about 5-6 inches higher or lower at each 50 fps muzzle velocity difference. That’s enough to blow up a score to elevation. And it gets way, way on worse at 1000. Keep always in mind that velocity-induced errors are compounding “normal” group dispersion. And, in reality and as discussed before, it’s unusual in a competitive shooting venue for a wind to be full-value, so the on-target lateral displacement is even relatively less — but the elevation displacement is consistent.
The next-to-the-bottom line, then, is that poor SDs don’t hurt in the wind as much as they do on the elevation. The bottom-line, then, is back to the start: don’t shoot a load with inconsistent speeds. It’s flat not (ever) necessary.
So what’s a tolerable SD? 12. That’s the SD that “doesn’t matter” to accuracy. More later…
MATH: For Them That Wants It If you have no electronic gadgetry to help, calculate SD like so: add all the velocities recorded together and divide them by however many there were to get a mean. Subtract that mean number from each single velocity recorded to get a deviation from the mean. Square each of those (eliminates the negative numbers that ultimately would cancel out and return a “0”). Add the squares together and find the mean of the squares by dividing again by the number of numbers. Then find the square root of that and that’s the standard deviation figure, which is “a” standard deviation, by the way.
This article is adapted from Glen’s book, Handloading For Competition, available at Midsouth HERE. For more information on that and other books by Glen, visit ZedikerPublishing.com