The previous 2 parts of this theme should be read to have a complete understanding of the following.
In Part 3 we will continue with the condition of a rifle’s bore to understand how that may affect the flight path and ultimate BC of a particular bullet fired from a specific rifle.
So far, we have considered the value of a chronograph in telling us:
1) The truth about actual muzzle velocity.
2) Standard deviation and extreme spread of a given load (also factory ammo), as well as the effects of temperature variances.
3) What powders to keep on hand and use.
4) The actual ballistic coefficient (BC) of a particular bullet fired from a personal rifle at a known MV.
This last advantage (4) of using a chronograph was Part 2 of the current series, and from where this theme is currently continued.
In the last article, I went into some detail in describing how a chronograph could be useful in telling us the actual BC of a bullet fired from a particular rifle at a known muzzle velocity (MV). The various factors that influence BC were mentioned, including the external conditions of environment. The physical conditions of actual MV and the rifle’s bore are huge factors as well. We will deal with those separately for convenience sake, but the one greatly affects the other in final results.
Muzzle Velocity: At least three (3) major bullet manufacturers give 3 different BC ratings to all their bullets depending on MV. Those are Sierra, Lyman and GS Custom. The BC ratings are designated for LOW, MEDIUM and FAST with an actual BC rating for each bullet within those categories. And we can’t assume that the BC will be greater at LOW than at FAST for example. There are too many other factors involved. Why Barnes tested their 350gr TSX in .458-cal. in a #1 Ruger in .45-70 ONLY is an unfathomable mystery, especially at such a LOW velocity at 81% load density! It made no sense whatsoever, especially when it is a very tough bullet intended for the magnum Big Bores! As I’ve somewhat vociferously complained here and in my manual on the .458 Win Mag, as well as to Barnes, it gives a very bad impression of the value of that bullet for any range beyond about 200 yards. Enough said, but please read my former blog.
(These 350gr TSX’s were fired at 2470 fps from my Ruger No.1 in .45-70 IMP and retrieved from the 100 yd berm. They expanded very well and held onto most of their initial weight.)
At Barnes’ 2139 fps from a #1 Ruger, plus their environmental conditions, .271 BC may have been their results, though they upgraded it to .278 BC sometime after I complained. I tested under conditions more “normal” for my hunting environment at an MV of 2470 fps. Then later, it was used in hunting from my CZ550 in .458 WM at an MV of 2750 fps, but I didn’t test the BC at that MV. The point is: actual MV affects BC.
Using relatively low velocity loads for a particular bullet designed for “reaching out there”, will likely give a poor result in actual BC. Why? Because the bullet will start to lose its stability — and hence it’s intended BC — at a range too far. Trajectory can often be compensated for but not bullet stability if MV is too slow.
I’ve a friend and correspondent, Bob Fritz, who has been a life-long competitive match shooter champion at 600 yards, as well as a big game hunter in N.A. and Africa, who has informed me that if you stand off to one side at 200 yards and hear a bullet pass that is whistling it’s because the bullet is unstable, likely due to the condition of the bore or travelling too slowly. Also, at long range impact the point of the bullet will be tipping upward. All of which is an indication of the BC promised not being realized.
CONDITION OF THE RIFLE’S BORE:
I’ve mentioned that not only throat erosion but bore condition affects a bullet’s stability and therefore it’s flight pattern and BC. If we know its MV and flight path (trajectory) we can calculate its actual BC. A chronograph can tell us it’s MV.
As pointed out, an oversized bore or a worn bore will produce an unstable bullet, sometimes to the extent of making neat keyholes! That’s not the bullet’s fault!
And, a bullet too long for the rate of twist of the rifling will be unstable — and useless for target shooting or hunting. So, a bullet too slow or too long will affect BC as well as the many other external conditions afore mentioned.
FIFTHLY, A CHRONOGRAPH CAN TELL US THE ACTUAL INCREASE OR DECREASE IN MV per 1gr increments in powder charge and suggest the concomitant increase/decrease in psi.
(From 2613 to 2634 fps for example)
Reloading manuals have traditionally presented neat little packages of predetermined increases and decreases in MV’s as though that could be calculated… in fact that was the way that many did it. But in the experience of the average handloader, if it actually happened the way it “was supposed to according to the book”, it would be regarded as a miracle.
From 27 years of using a CHrony, here are some basic tenets I’ve come to accept about handloads:
1) Don’t assume anything.
2) Let the chronograph tell you what’s happening.
3) In cases from .30-06 size and up, 1/2gr increments in powder charge mean little to nothing until you are at max or nearly so.
4) At certain stages, 1-grain increments may show little or no increase in MV. As a matter of actual fact, it IS possible that a 1-grain increase will show a DECREASE in MV! At another point in DEVELOPMENT of a load, a 1-grain increase may show a huge increase in MV. And that may be only at 85% load density. A huge increase doesn’t NECESSARILY imply “Back off. you’ve gone too far!” A favorite load of 68grs of a particular powder gave very good and accurate results. But I “felt” it was possible to go a couple of grains more. One grain more (69grs) and the MV became erratic and blew the accuracy to an unacceptable point. Should I continue? I had already loaded 3 with 70grs, so I decided to give them a try. It was near miraculous! The group tightened to sub-moa and gave an MV well above expectations. It has since become my hunting load and shows consistent performance.
5) 2 grains under max is NOT NECESSARILY the “most accurate” as many seem to claim. There are again too may variables to make such a claim. As a matter of fact, most modern cartridges are loaded “hot” from the factories. And they wouldn’t do that if they would be inaccurate. Plus, I’ve OFTEN found max loads to be the MOST accurate. And, by “max” I’m not referring to original standards for century-old cartridges in modern bolt actions of falling block-actions such as a Ruger No.1. But rather, safe standards as indicated by those same rifles being chambered in modern magnums.
(This 1/2″ group was shot at 100 yds over a three week period; one shot per week. It was a maximum 180gr load from my .300 WM)
6) And all of the above assumes that the best powder for the application is being applied.
7) Only a chronograph can tell us what is really happening in load development.
8) In hunting loads — and all loads that I actually use are for big-game hunting purposes — I aim for MOA, but will accept 1 and 1/4″ if that’s the best I can achieve with the load I want to use based on other parameters. The bullet is first, MV is second and accuracy is third in my set of criteria for an acceptable hunting load. Only a chronograph can tell me the truth of bullet speed.
Why not just go “by the book”?
Which book are we talking about? There are many and they don’t all agree! In fact, sometimes for particular cartridges any similarities seem to be entirely coincidental! Early on, I learned that Hornady and Lyman, for example, seemed to be working on different planets when it came to CUP claims for the same basic loads for a Ruger No.1 in .45-70! Lyman made more sense to me and I went with them as to a basic claim for CUP. And they were right! Then, I talked with the head guy at Speer (at the time) and he endorsed my reasoning and claims even though their standards for a .45-70 were more traditional. The same happened with Accurate, who tested my load for the Ruger No.1 in .45-70.
9) So I guess the last and perhaps the most important thing a chronograph has taught me is to depend on experience and common sense, and less on “the book”.
But for the neophyte my advice is : DEPEND ON “THE BOOK” but compare it with your chronograph!
When I started to handload about three decades ago, a .30-06 was my rifle of choice. I had a simple LEE hand tool. At a gunshop that I often frequented, the subject of handloads for a .30-06 came up. A big guy behind the counter, younger than I, seemed to know some things about reloads for a .30-06… “Load it with IMR 4350 to the rim.Level it with a credit card, stuff in a 180gr and you’re good to go”! Sound advice? His point was: You just can’t get too much IMR 4350 into a .30-06 case for a 180gr to harm self or rifle. Maybe he was right! But I don’t know that as it was never tried in my personal experience of making handloads for two .30-06’s! But I do know that such advise is sane for particular cartridges, powders, primers and bullets… in specific rifles! “But that’s a compressed load!” You betcha!
My last advice is: learn from books and others you trust. Then learn from personal experience AND YOUR CHRONOGRAPH!
In addition to those five things a chronograph can tell us, there are at least a couple more:
Sixth: when you have arrived at a BALANCED LOAD, and
Seventh: The perfect REDUCED LOAD.
All that, and maybe more, next time…