So far in this series of articles, we’ve considered the following as having a direct or indirect impact on the performance of our handloads: 1) The nature of smokeless gunpowder; 2) Handloading manuals; 3) The handloader; and 4) The rifle barrel.
This time we’ll have a look at :
5) Ambient temperature and how it affects the burn rate of rifle propellant, and
6) Pressure limits and psi “under the curve”.
AMBIENT TEMPERATURE: This is simply a term making reference to how hot or cold the temperature might be of the environment in which a shot or shots might be taken. It also takes into account how warm or “hot” the rifle’s barrel might be from multiple shots at a range, or rapid fire at an animal or animals as in groundhog hunting. At the beginning of this series, I mentioned a friend who left his ammo sitting on a table in an opened container on a hot day in brilliant sunlight. His first shot locked the action of his .270 Winchester even though it was a “book load” that he’d previously used without incident.
So, yes, factory or handloads can be “heated up” by some of the above mentioned physical conditions. We have no control over the fabrication of factory ammo, of course. But usually the product from manufacturers is “mild” enough to withstand African conditions at high noon — with ambient temps of 120*F, and even though some of that ammo might have been left unattended in bright sunlight conditions. Manufacturers can’t afford to expose themselves to potential litigations! Of course, that usually means that the same ammo, if used in certain parts of North America and Europe, might not be up to par if used on a larger animal at 250 meters and -17.5*C (275 yards and -0*F). All of that would be due to the nature of gunpowder being affected by ambient temperatures. That same, of course, applies to handloads. Perhaps not to the same degree, but on the other hand, maybe to an increased degree. We don’t know until we do some handloading of the same amount of the same powder and components (bullet, primer and case) in the same rifle under diverse conditions of outdoor temperatures.
A few years ago another moose hunt took me to the same region of Northern Ontario where I’d shot a bull a few years earlier. On the former occasion I used my .340 Wby. On the latter, I toted my CZ550 in .458 WM loaded with the 350gr Barnes TSX over a near max load of RL-7 for an MV of 2700 fps. A backup was my .300 WM that was never carried while hunting — it stayed behind in the trailer. But the .458 was toted daily for a week without any inkling of how that load might perform at near freezing temps. While there were lots of sign of moose activity, we never caught up with one. Sometime after returning home in mid-October, I went to the range to check the sight-in of that rifle and load as I still had time for some local bear hunting. I also chronographed them. I was astonished that they fell several inches below point-of-aim and chronographed at least 100 fps less than when tested several times in late summer! For some handloaders, who rarely shoot large game, or game beyond 150 yards, their response might be “So what!”. But on a moose hunt at 1600 kms (1000 miles) from home, where potential shots might be to 400 yards, or more, a couple inches low at 200 would mean over a foot low at 300 and about three-feet low at 400!
I switched to another powder, H4198, which is one of Hodgdon’s EXTREME powders. One year later the .458 plus the 350gr TSX at 2750 fps performed as expected on a good black bear. To this day, the 350 TSX combined with H4198 in my Ruger #1 in .45-70 LT (long throat) has never changed POI or MV due to ambient conditions.
There are better powders now, with regard to temperature sensitivity, than those we used to rely on. I’ve used “tons of” RL-7 in the past in my .45-70s. But the last can was given to someone else. There are better today.
However, excessive heat is still an enemy. When the cartridge case with powder inside is over-heated by the rifle barrel or other ambient conditions, excessive psi MAY be created if the load was safely put together in October as a “max load” with temps at or near +10*C (50*F) and used in a spring bear hunt in mid-June with unusual high temps of +30*C (85*F).It happens! MAX LOADS should be tested in hot weather, not cool. I have been disappointed with RL-15 in my 9.3 X 62 in that regard, but not with RL-17 which has not only given better performance all around, but also in regard to temp stability it has proven to be very stable and reliable.
So regarding ambient temps and its effect on gunpowder burn rate, some are much better than others. It is vitally important to find the best ones.
Bottom line: when gunpowder in a cartridge is heated by a hot barrel, or other conditions, the burn rate of that powder might well be altered to a faster burn rate. That would be the same as loading the cartridge with an equivalent load of a faster burning powder. By how much, we don’t know. And it’s not predictable. So even a pioneer or adventurous spirit should pay heed to facts relative to the use of rifle propellant. What are those facts? Rifle propellant seems to have a mind of it’s own under particular conditions. And it is not always foreseen.
PRESSURE LIMITS AND PSI “UNDER THE CURVE”:
Maximum average (peak) pressure (MAP), for rifle cartridges designed and fabricated in the USA, has been set by SAAMI (Sporting Arms and Ammunition Manufacturer’s Institute). SAAMI represents various companies which have agreed to certain standards for determination of psi in small arms. Yet, not all companies involved in production of rifles or products related thereto are members. But the standards set obviously have a safety factor built in. Formerly, CUP (Copper Units Pressure) was used to measure pressure. Today, PSI (Piezo) is deemed more accurate and therefore used by SAAMI and most other manufacturers. In many cases the Piezo number is about 20% more than the CUP number while the actual pressure is the same. For instance, the SAAMI standard for MAP in .30-06 used to be 50,000 CUP. Today it is 60,000 PSI, the actual pressure being the same. For some cartridges they are equal or nearly so. Due to the .45-70 Springfield being an ancient cartridge, with relatively weak actions in it’s original form, the CUP standard is 28,000 CUP and now 28,000 PSI (piezo). That, of course, belies the fact that most modern rifles in .45-70 can handle pressures to 40,000 PSI, and the Ruger #1 in .45-70 to around 60,000+ PSI. Standard rifle cartridges based on the .30-06 case have a SAAMI limit of between 60,000 and 62,000 PSI. Magnum cartridges, including some of the more recent ones and Weatherby have pressure limits to 65,000 psi (Weatherby to 66,100 psi). Such numbers are arbitrary of course. In most, it’s the brass case that determines actual pressure limits. Tests have been conducted that reveals that some brands of .45-70 brass can quite easily handle 70,000 psi without failure. That, of course, can’t be published as a current standard because there are many relic .45-70s still in operation. And, it’s likely that lever actions in general couldn’t handle (for very long) that level of pressure either.
But we are speaking (writing) about MAP, and PEAK PSI, not merely of max pressure — whatever that means. This is difficult to get a handle on because (again) of so many variables. Unless we have access to a professional lab where all of our loads could be tested, we are relatively still in the dark or “flying blind” so to speak. That’s why we refer to manuals despite their anomalies! Better than “flying blind” I suppose. Yet there are ways and means of determining if our loads are safe. And even writers and pros use them. What are they?
Micrometer measurement: This is what I use, and what some notables of the past used if a lab wasn’t handy. Even SPEER’s older manuals gave details in this regard. The expansion of the case head is measured after the second, third, fourth firing, etc., to determine what the brass deflection might be after the initial firing of a new case. The same new brass case, with the same load, will expand (deflect) more in some chambers than others because all chambers for the same rifle cartridge may be closer to SAAMI specs than others that may be larger. So don’t expect the same load fired in two different rifles to show the exact same results. And don’t expect factory ammo to be the best guide for starting this process, either, as much of it is on purpose underloaded, as explained above. I start with new brass for handloads, whatever the brand might be. For my .45-70s it is always Remington nickel plated. The primer pockets on these have never expanded regardless of what the pressure might be. I throw them out when they become work-hardened and begin to show cracks or splits at the mouth.
For hunting purposes, I only use new brass or once fired after my hunting load has been firmly established.
Starting with a load that looks like (after thirty-six years as a handloader) it might be a good place to begin, I measure the case expansion at the head (about 1/8″ (4 mm) in front of the slight groove between the rim and beginning of the case body of a .45-70 case, for example. A record of that is kept in my handloading notes as a reference point. As the load is increased by 1/2 to 1 grain increments, case head is always measured by a micrometer (not a caliper) and recorded. When a good, or what appears maximum, load is reached, that is recorded for further/future reference. Keep in mind that every rifle is somewhat unique in this regard. The “idea” that a deflection of 0.0005″, after the first firing, is max for a “standard” case as in .308 Winchester, and 0.001″ is max for a “magnum” case has no scientific basis because, as pointed out, some brass cases are softer than others and some chambers are “larger” than others. But I do keep record, as mentioned, of what APPEARS to be a safe maximum based on OTHER evidence (which follows).
Case Extraction and Appearance: Again, every rifle is a rule unto itself. Some bolt-actions cock on opening while others cock on closing the action. Some are “rough” and others “buttery smooth”. We need to become familiar with the action of our rifles regardless of type: bolt, lever, doubles or singles before we ever shoot them. Some break actions use ejectors (I had one in .45-70) and others extractors only (I’ve also had those). Lever actions tend to have less “camming” power than bolts. In Marlins, for example, it’s very easy to detect when “enough is enough”. With bolts a lot depends on the smoothness or roughness of the chamber. We need to become familiar with such details of our rifles. One of my NEF single-shots in .45-70 would eject the cartridge case with such force and speed I needed to be careful not to get wacked in the head by flying brass — BUT, I much preferred that to trying to extract a fired case with gloves on in January weather when it poked it’s head a mere 1/4″ from the breech! But case extraction and appearance are important clues as to pressure in spite of some anomalies.
(These are Hornady 9.3 X 62 brass. Two have been once-fired with a max hunting load of RL-17, resized and primer seated, ready for the same hunting load. The other is a never-fired case with the same primer. Hint: it’s not the “best looking” one! It’s actually the one in the center. Left-click on photo for enlargement. Click return arrow for return to text.)
Primer Pockets: Not primers, but the pockets in which they are seated are also important clues to safe and sane pressures or, on the other hand, excessive psi. Once more, a lot of this also depends on the “softness” or “hardness” of the brass case when new. Some lots are too soft to begin with, so unless we have a reference point for the same cartridge in the same rifle that tells us that this particular lot is soft compared to others, we may be “up a creek without a paddle”. For another example relating to my first Ruger #1 in .45-70. My first .45-70 was an 1895 Marlin, so I didn’t learn very much about what brand of cases were best in handling pressure as I never pushed that rifle beyond about 30,000 psi. They all seemed to work about the same, and I bought what was available in either Remington or Winchester(never mixing them of course for the same batch of loads). It wasn’t until that first Ruger #1 that I discovered that Federal nickle-plated brass would not handle the psi of the Remingtons. The pockets would expand enough that black soot appeared around the edge of the pocket, and when they were re-sized, primers would seat with hardly any pressure at all — they would almost fall into place. They would not handle 60,000 psi whereas the Remingtons would go well past that without any problems at all. In fact, that particular load (tested for me in the USA by a powder company) could be fired 10 times with the primer pockets remaining tight as if new. After 10 X I’d throw them into the garbage. Primer pockets are definite clues as to where we are in a particular load’s pressure.
Primers are not for a number of reasons which are mentioned in just about all reloading guides. Chief among them is the hardness factor of the metal cup containing the primer mix.
Load Stability and Reliability: I look for and settle on loads with an extreme spread of no more than 20 fps, and often less than that. Also, not merely as a goal but in actual fact any load must show consistency and reliability from season to season and year to year for it to become a hunting load that I not only will publish or recommend to others but rely on personally. And all of that takes into account the potential variations in gun barrels, lots of powder, ambient conditions, primers and bullets used.
(That’s the CZ550 in .458 WM mentioned in the text.)
There’s one other matter I must mention, however. The notion often suggested in reloading books, and passed around as common “truth”, that a “max load” (whatever that is) minus a couple grains of propellant most often gives best accuracy and overall results. I can only speak of my personal experience, of course. But based on many years of handloading most common magnums, and some high pressure non-magnums, I’ve rarely found that idea to hold water. My most accurate loads in 7mm magnums, .300 magnums, the .340 WBY and .458 Win Mag, plus a number of .45-70s have been absolute “top” loads — I’m speaking of sub-moa with consistency and extreme spread. Of course, like everyone else, I have my “off” days in which moa or sub-moa isn’t always possible, but that has always been my fault, not the fault of a particular load. My goal for EVERY load that I use in the field is MOA, or better. Why? Because it gives great confidence, not only due to the accuracy factor but because I know that rifle load can be depended on under ALL conditions to perform as expected or wanted in ballistics as well as precision.
PSI “UNDER THE CURVE”
This is an expression having reference to the fact that following peak pressure it begins rather rapidly to decline all the way to the muzzle, as previously mentioned. In a graph it would not be a straight line but a descending curve that is rather steep at its beginning but levelling out more as the muzzle is approached. The less steep that curve is the higher the pressure will remain drawing near to bullet exit from the muzzle. In other words, it is typical of a slower powder to not peak as quickly but to maintain relatively high pressure throughout that curve (That’s why, for instance, that I can get such excellent performance from RL-17, compared to RL-15, from my 9.3 X 62). A faster powder may reach the same peak psi but will fall from it much more quickly. It will not maintain the same pressure on the base of the bullet as will the optimum slower powder, giving less than optimum results in muzzle velocity. That assumes, of course, that the shooter WANTS optimum results in bullet energy, flatness of trajectory and accuracy down range in a hunting context. It also assumes that he/she has discovered the “right” gunpowder that will consistently accomplish all that. And that is not to say that “the right” powder will be discovered by asking that question on an Internet forum. Recently, someone asked about the “right” (best) gunpowder for the .30-06 in using big game bullets of 150 to 180gr. 90 plus percent recommended IMR4350 since they had used it for decades. That’s where I started when I began handloading my first .30-06 — with IMR4350 thirty-six years ago! But do those who recommend IMR4350 today mean to say that nothing as good or better has come along since then?
QUICK LOAD (QL)
A good friend has provided support for me in the development of handloads for my 9.3 X 63. I’ve sent him the data of several loads that appear safe. He plugs that data into QL, including barrel length and COL, and then sends me a printout that not only provides PEAK PSI but a full graph including the pressure curve from start to muzzle. The limit I aim for is 64,000 peak psi, same as the .338 WM. So, he cuts everything off just below that number. QL is no guarantee, but it does provide, along with other “signs”, a confirmation. I’ve greatly appreciated his help in this regard. If you can’t afford your own but have a friend with QL, he may be able to help you also.
All for now…
More to come.