|December - January 2001
Volume 36, Number
In its heyday, the Browning Model 71 in .348 Winchester was considered potent bear medicine. See page 34 for updated loads. Grizzly photo by Jeffrey Rich.
There may be a few shooters who can
look at themselves in the mirror and honestly say they are not interested in getting the
maximum out of their firearms. For the rest of us, at least from time to time, there is an
ongoing quest for horsepower. Most will seek that edge between a mild load and danger.
They are after that ethereal thing called maximum. Finding that edge is a combination of
art and science. Here are some tools that will help you make intelligent, safe decisions
while in search of maximum.
Before we can look for maximum, we
should not only define but also understand it. There are two ways to define the concept.
The first is purely scientific. Our Sporting Arms and Ammunition Manufacturers
Institute (SAAMI) sets standards for maximum pressure (sometimes arbitrarily) for each
cartridge. What the pressure actually is depends on the individual cartridge. Different
units can be used to measure this pressure, ranging from LUP (lead units of pressure), CUP
(copper units of pressure) or psi (pounds per square inch). I wont attempt to fully
describe the minutiae of each, for it is a very complex system. Basically the lead and
copper units measure the amount a little cylinder made of those materials is compressed
when the load is fired. The psi measurement is done electronically. Lead is used for lower
pressures, while copper functions at high pressures and psi works for all cartridges.
To give you a hint of the
complexity, if for example, a .30-06 is measured with copper and psi - simultaneously for
the same cartridge - the numbers and accepted standards are different, even though the
pressure is the same. Explaining this fully takes something akin to a Ph.D. The important
point here is that when you see vastly different pressure numbers, for the same cartridge,
especially from older to newer manuals, this is the reason. Pressure, represented in
electronic psi, is often a higher number than with other systems.
The other more broad, less
scientific and maybe more reasonable definition of maximum is a load that is safe and
reliable, one that wont hurt you or your gun. One that wont hurt your gun,
that is, while extracting all possible performance.
Maximum pressures as used by SAAMI
vary dramatically, depending on the type of cartridge. The numbers you see in manuals
represent average pressure, while SAAMI sets limits for maximum average and maximum
individual shot in the string. Beginning at the low end of the spectrum, we have shotshell
pressures. They vary from the lowest maximum of 11,000 psi (electronic) for the 10 gauge
through 13,500 psi for the .410, through the 12 gauge 3 1/2-inch at 14,000 psi. Yes, that
is correct. Those who pick the maximum number choose different ones for different gauges
and chamber lengths.
As we move up the pressure scale, we
find the various pistol and revolver cartridges. The lowest pressure that comes to mind is
for the .45 Colt, limited to 15,000 psi, followed by rounds like the .45 ACP and .38
Special that operate at just less than 20,000 psi, or CUP. (The two scales are almost
identical at these levels.) The top of the normal handgun list would be the .44 Magnum
with its pressure limited to 40,000 CUP and apparently 35,000 psi from Alliant. Rounds
like the .454 and .480 go even higher, right into the realm of highest rifle pressures.
When we look at rifles we see the
lowest pressure for the .45-70 in Trapdoor rifles at under 28,000 CUP, while
loads for the same cartridge rated for Ruger No. 1 rifles work at 50,000 CUP. When we
reach the high end, we find cartridges like the .300 Winchester Magnum with a limit of
55,000 CUP or 62,000 psi.
Please understand that none of the
numbers above are designed to represent absolute rules nor are they certainly the precise
SAAMI numbers. They are being used to illustrate a very important concept - within the
spectrum of firearms there is an extreme range of maximum pressure. What that means to us
reloaders is many of the concepts intended to allow us to: see, smell or touch maximum
pressure simply do not work. Actually, only the very highest limits can be reliably
discerned at home. That is, we can make reasonably reliable judgments about
the highest rifle pressures, but for others we are dependent on published data. We will
look at rifle pressure judgment in a moment, but now lets spend a little time
understanding the variety and variations in the data that is available.
The most complex reloading also has
the lowest pressure limits. Shotshell loads are wonderfully complicated and sophisticated.
As a base line, there is nothing, absolutely nothing, in the way of visible pressure signs
that will keep you out of trouble. If you see anything like sticky extraction, primers
actually flattened by pressure or other accepted pressure indicators, you are literally
miles above maximum. Put another way, if you see excess pressure in a shotshell load, be
very glad you are not looking at pieces of your gun instead. The only way to create safe,
reliable shotshell loads is to absolutely follow the printed recipes.
Why? Because, even apparently
insignificant changes in shotshells, ones that may make little or no difference in
metallic rounds, can send pressure into relative orbit. To illustrate this we take an
example from the Hodgdon Shotshell Manual. They loaded a specific recipe, basically a 1
1/8-ounce trap load, in five different hull brands. A Federal Gold Medal produced 1,200
fps and 10,400 psi. This is a perfectly normal, safe load. Then the same ingredients were
loaded in a Remington Premier hull. The velocity fell to 1,186 fps - telling us all is
well, except the pressure increased by almost 50 percent to 14,800 psi. Another recipe
might have just the opposite effect. Simply changing wads or primers can create the same
havoc. Of course, changing shot material from lead to steel is almost guaranteed to rip
your gun apart.
So, there is one and only one way to
get a good maximum shotshell load: follow the recipes in reputable loading manuals! This
is not bad news because the data for shotshells is far more complete, much more detailed
than we see for any metallic shell. If you search a little you can find a shotshell load
for virtually any component and application that can be safely used.
As we move forward into the various
handgun cartridges we are confronted by limitations similar to those from shotshells. Once
again there is very little we can see or measure that can give us a reliable indication of
maximum pressure. At the lower pressure levels, say those under 30,000 CUP, almost nothing
visual happens to the case or primer; and like shotshells, if you have tough extraction or
primers that look bad, you are far beyond safety.
As we move into the high-pressure
cartridges like the .44 Magnum, or beyond to the .454, that operates in the pressure realm
of magnum rifles, we find a double-edged sword, the classic good news and bad news. The
good news is that a revolver and modern revolver brass handle high pressure more
gracefully than any other firearm. Pressures that will begin to stick in a bolt action or
loosen primer pockets in a .300 Weatherby case are likely to behave as if they were
perfectly normal in a fine revolver. Behave, that is, until the pieces of hot steel begin
to fly. Thus, the bad news is that there is very little to tell us we are in trouble!
If you have a double-action
revolver, say a .357 or .44 Magnum, you may have to push hard on the ejector rod as you
pass maximum and move into the danger levels. The thinner cups on the pistol primers may
also begin to flatten considerably more than a normal or factory load. Handguns do not
exhibit the wild tendencies of shotguns, but once again we are essentially limited to
using the data in the manuals. Normally, you can safely substitute a cast lead bullet for
a jacketed one of the same weight, because the lead bullet usually generates less
There is another physical feature of handgun
bullets that changes pressure. The amount of bullet inside the case effectively changes
the case capacity. That is, if a bullet is seated more deeply, the gun actually thinks its
chamber is smaller and generates more pressure with the same load. Thus, bullets designed
to have a maximum amount of the bullet outside the case, like the LBT designs, usually
generate less pressure than a Keith shape. This is because more of the Keith protrudes
into the powder chamber.
Because the bullet variables are
rarely illustrated in the manuals, a reloader must be aware of bullet metal and design
changes. Most important is: Do not substitute a bullet that goes farther into the case in
a load that is listed as maximum. A chronograph is also a good indicator of
pressure. If you change bullets in the same recipe, be sure the velocity is not higher
than the known load. In almost every instance more velocity will equal more
As we move into the realm of high
pressure rifle cartridges, we at last have enough room, under the ceiling of maximum
pressure, to allow us to make intelligent judgments about the safety of our loads. Now we
have several seeable and feelable pressure indicators. The most
commonly used is a visual impression of primers. Unfortunately it is also the most
Flattened and cratered primers can
be due to excess pressure. But, slightly excess headspace is often the cause of flat
primers. They back out of the pocket on ignition, then when the powder lights it slams the
case head, with protruding primer, back against the breech face. The predictable result is
a very flat-looking primer. Cratered primers are usually caused by an ill fit between the
firing pin nose and its hole or by a weak firing pin spring. However, both of these visual
effects can be used as warning signs. The way they are useful is if they are not present
with factory or starting loads and then they become progressively more apparent as the
A more reliable indicator is
extraction force or bolt lift. Once again this is relative. To best use extraction force
as an indication of trouble, you must begin with loads that provide little, or no,
resistance to lift and extraction. Then, as you work up, if you feel some increasing force
needed to lift the bolt or worse need to tug or bang on the bolt after it is up, to pull
the case out, pressure is surely too high.
Again there are reasons for false
indications. Once I was working with a very high-performance rifle. All was fine, then
things changed. After I turned the bolt up, the cases almost refused to budge from the
chamber, with the same loads that had worked perfectly only hours earlier. No, the chamber
was not bulged. A new case worked perfectly, but after it had been fired it would stick on
the second loading. When I reached the hair-pulling state of confusion, I saw it. As I
sized the cases, a tiny crack appeared in the lower inch of the full-length die. The die
had cracked and was not resizing the bottom of the case. Each time it was a force fit in
the chamber. A new die cured the problem.
Bolt lift can also lie. If the bolt
face is not square with the chamber, or it is rough, you will feel artificially high
resistance. However, it will be high for even factory ammunition.
There is one reasonably reliable way
to judge near-maximum and over-maximum pressure levels. This is case head measurement.
There are a few rules you must follow to get reliable results and some variables you must
First, you must have a high-quality,
extremely accurate micrometer. No vernier caliper has the potential. While the best
digital vernier calipers may read to .0001 inch, their stated accuracy is only .001 inch.
To correctly monitor pressure we must be accurate to less than one half of the verniers
potential. The best tool for the job is a digital micrometer and even better is one called
a blade micrometer. The blade micrometer has thin blade anvils instead of the
normal round ones. It makes it much easier to measure the thin, solid section on the
cases. A fine, standard digital mic costs between $100 and $200, while a blade mic is much
The measuring device must be
accurate in tenths (one ten-thousandth of an inch). The reason for this is
that .0005 inch, or one-half of one-thousandth of an inch, increase in case head diameter
indicates extreme maximum, almost dangerous pressure. Also, understand that you must
measure the solid brass head, not the expansion ring. Your measurement must be made just
in front of the rim or extractor cut and on the back one-third of a belt. Finally, you
must measure each individual case before and after each firing, and you must measure the
same place on each case.
To get accurate results you should
measure over a specific place on the headstamp. For instance, I use the WW on a Winchester
case, aligning that stamp with the anvil on the micrometer. Next, I zero the
micrometer on each case and repeat the measurement at least three times before I fire the
round. That is, set the mic on the case and zero, then open and reset. You must be getting
a reading each time that is on zero or not more than plus or minus .00005 inch away from
zero. This number is the limit of the micrometers scale. It is important to
understand that this kind of precision measurement takes practice and a certain skill
level. You must be able to get repeatable measurements, or your test results can be
invalid and dangerous.
Opinions differ about the kind of
case that yields accurate results. Some sources suggest it is only good to use an unfired
case. I do not agree, because often a factory load will move the case head considerably.
In my opinion, once the case has been fired, it settles down and becomes a reliable
If you are working with cartridges
with a high maximum pressure, those with 50,000 CUP or higher, case head expansion of less
than .0005 inch usually means safe pressure. My most important premise is that cartridge
brass varies, and that cartridge brass is the weak link in the system. If that brass is
not flowing, if the velocity is not higher than recommended in the manuals with the same
powder and bullet weight, your load is probably okay. Soft brass may flow at lower
pressures and velocities than indicated in the load tables. This means that a maximum
load, in those cases, is lower than it would be in a stronger case. If the load is moving
the brass more than the indicated .0005 inch, regardless of other factors, the load is too
Before we move on to indications of
dangerous pressure, ones that figuratively or literally slap you in the face, there is one
that is an intermediate indicator. This one may indicate you are over the top, or very
near it. Loose primer pockets are telling a story. By loose, I mean when you seat a new
primer little or no resistance is felt. In worst cases you can actually push the primer in
with your thumb.
If you begin with a case that has a
tight primer pocket, fire it and find the pocket is loose from one shot, the pressure is
very high. This kind of pressure will probably show up between .001 and .003 inch head
expansion on the micrometer - or, from two to six times too much. This load almost blew
the primer, almost put you in big trouble. A more subtle kind of pocket expansion may
occur after several firings. That is, the pocket grows progressively larger, a little bit
at a time, shot after shot. This is probably not dangerous. It simply means you are right
on the edge.
If I am loading for a high intensity
rifle cartridge and the pockets are okay for three shots or more, I am comfortable with
the load. If you have a case, or batch of cases, that prime very easily, it is time for
them to join the junk pile. Their useful life is behind them.
There are other indicators of
extreme pressure, dangerous pressure, that must not be ignored. These show up without a
micrometer. If you see a shiny place appear on the case head where the extractor cut, or
ejector pinhole, is in the bolt face, you are nudging serious trouble.
If the primer leaks, indicated by
soot on the case head around the edge of the primer, the load is shouting at you to back
off. A blown primer, where you get a big gas leak and the primer is out of, or falls out
of, the fired case, is kissing the grim reaper. When you blow a primer and you and your
rifle are still blood free and in one piece, be sure to thank the necessary gods and the
The tools above are offered for several basic
purposes. First, because loading data varies considerably, it allows you to have a
hands-on approach in determining the true maximum load in your rifle. It is not intended
to exceed the maximum loads in the books but, in reality, to determine which maximum is
maximum. The loading data in most of our manuals is very good, very safe. So good in fact,
that it is easy to be lulled into a false sense of security, lulled into believing that
even the maximum loads are always safe in every firearm.
Always and every are dangerous
words. Here is an example of a very experienced reloader who was nearly badly bitten by
blindly believing a load that had been good in five .257 Weatherbys would be fine in the
sixth. The load was the maximum listed in the powder manufacturers manual. It was
great, with plenty of speed and lots of accuracy. Most important, it demonstrated
absolutely no signs of excess pressure. The experienced reloader was very busy, too busy
to work up a load.
He was about to take a friend
antelope hunting, so he simply instructed the would-be antelope hunter to assemble some
ammunition with the known load. Our expert stopped by the loading bench to be sure all
components, weights and bullets were correct. They were. Then he sent the hunter to the
bench to zero the new, out-of-the-box Weatherby Accu Mark .257 Weatherby. There were three
shots, then the shooter reappeared with the three fired cases and a very quizzical look on
Every primer pocket was black and
huge. The shooter instinctively knew something was wrong but had such deep and implicit
trust in the expert that he fired two more shots, simply believing the expert could not be
wrong. Well, I was wrong, dangerously wrong. Aside from being wonderfully strong, that
particular Weatherby had a tight barrel and throat that pitched the pressure into orbit.
No, all maximum loads are not safe in every gun - just like the manuals tell us!
Beyond normal caution and
consideration for variations in factory arms, there is the question of cartridges/calibers
for which there is no certified loading data. If you are an advanced reloader
and are working with a new or wildcat cartridge, one without precise data from a pressure
gun, you become solely responsible for generating safe loads. With the micrometer and
other indicators you should be able to arrive at a safe, sane maximum load for your rifle.
With the understanding of some of
the pressure indicators available to us, it is time to address the question/dilemma of why
loading data varies so much. That is, if you consult loading manuals A, B and C for the
same cartridge, using the same bullet weight and the same powder, you will probably find
the maximum load varies several grains.
There are a multitude of reasons. If
we use the most professional laboratories as a base line, we begin to get an idea of the
complexity of ballistics. They use pressure guns, generally a universal
receiver that accepts large diameter barrels. These barrels are made by a few highly
qualified barrel makers to very strict tolerances of bore, groove and chamber. The numbers
are specified by SAAMI. So, each lab has barrels that are made the same, as
close as machining tolerances will allow. They then calibrate that barrel,
using a very special lot of reference ammunition. This ammunition is loaded in
one lot, tested and stored in controlled conditions. Thus, each barrel receives a
correction factor that zeroes the barrel relative to the reference ammunition.
Now, they can begin shooting with unknown ammunition.
For the moment we assume that if
each lab fired the same ammunition in their barrel, that is same powder, primer and
bullet, they would see the same pressure. This is essentially true. However, if they
change primers or, even more significant, powder lots, differences can occur.
Now, the big variable enters the
picture. Bullets are very different, different that is from brand to brand within the same
weight. A soft bullet with a short bearing surface will usually show less pressure (and
often velocity) than a hard, long bullet like the Barnes X-Bullet. Further,
pressure is influenced by seating depth of that individual bullet.
Then there is another grand variable
- each company has different views of what maximum pressure should be. Some,
quite frankly, are more afraid of their lawyers than others and print softer
loads. As the wild cards get wilder, some makers of loading manuals do not use sophisticated pressure guns. Some use strain
gauges, a test that is scientifically marginal at very best. Without SAAMI-spec barrels,
reference ammunition and correction factors all bets are off. And, in the not too distant
past, complete loading manuals were published, by big companies, without any formal
pressure testing equipment at all.
Last, but not least, there is the
transition from lead and copper crushers to electronic piezo (psi) testing equipment. As
mentioned earlier this new equipment is like viewing pressure through a very different
Then, it is fair to ask, who can we
believe? In a way we can bring this whole conversation full circle. Who can we believe?
Well, actually, all of them and none of them, at the same time. Once we see the variables,
under very controlled scientific conditions, imagine what goes on by the time the lead,
primers and powders reach us. Few pay attention to primer lots and not many more notice
powder lots. Then, powder gains or loses moisture, throwing its actual energy content per
weight out of kilter.
Next, enter our very random barrels
and chambers. The good news here is that normally a production barrel and chamber will be
bigger than the minimum SAAMI barrel used by the laboratories. Thus, our guns
will usually generate lower pressure (with the same ammunition) than the test barrel. We
can normally use most published (from the major manuals) data. To do this, you must use
the same bullet, powder and primer. Then, you can apply the tests I have offered to be
sure you are okay.
Always follow the advice given with
the individual loading data regarding starting loads and work-up procedure. Last, but not
least, you be the final safeguard and responsible party. Watch the signs, double check and
listen to your rifle.
As a conclusion, I thought it would
be fun to look at some loading data, going back as far as we can, while still having
similar powders, to see just how much, or little, data has changed over almost 50 years. I
began with the Lyman Ideal Handbook No. 39 (1953) and ended with the latest Hodgdon,
Number 27, published in 1998. The former was probably
produced without formal pressure apparatus and with the relatively crude chronographs of
the day, the latter with the most sophisticated piezo-electronic pressure setup and
laboratory quality chronographs.
I wanted to see cartridges that were
not influenced by the military, therefore did not use the .30-06. Also, I wanted
relatively high-performance rounds for rifles. The two that appear in the early Ideal data
are the .270 Winchester and .300 H&H. This data predates the .300 and 7mm magnums. For
the same reasons we will look at the .357 Magnum revolver round also. I selected the load
that gave the highest velocity for any given bullet weight, comparing the same powders,
old and new, and then picked the highest velocity load available today, with any powder.
As we look at the numbers in the
table, a few thoughts surface. First, contrary to popular belief the data is not being
softened in modern times. Within these examples and many others, manuals
today, with the sophisticated equipment, are giving us just as much as did the old Ideal.
Further, with the improvement in powders, translating into slower burning rates, the good
old days of high velocity are really right now. Way back when, when 4350 was the slow
powder, even the midcapacity rounds like the .270 WCF wanted slower fuel. Now with the
advent of H-4831, IMR-7828 and Alliant Reloder 22, pressure/velocity relationships are
better than ever.
Of course, we should give credit
where due, to the grand masters who created the old manuals. By and large they did so
by the seat of their pants without great laboratory equipment. Instead they
used perhaps a micrometer, skill, experience, common sense and good judgment - tools that
are becoming very rare today. That the computer era equals the old days is not remarkable;
that the old days equaled the computer certainly is worthy of our respect.
In conclusion, the laws of physics are alive
and well. Firearms must obey them and so should we reloaders. We have great data
available, and every reloader should own several reloading manuals to have the full
spectrum before him. When you search for a maximum load, begin by seeking data for the
same bullet (weight and brand) you intend to use. Follow the data closely and watch for
any indications of excess pressure. Have fun, be careful, and oh, by the way, the last few
feet per second really do not matter.