Some of the more innocent handloaders look at the figures in one of the numerous reloading manuals on the market and see a certain powder charge with a certain bullet weight in a given cartridge listed as MAXIMUM. Their reaction is shock, horror and they dive for cover. Evidently, they think that if 1/2gn. more powder is used than this MAXIMUM load the rifle will blow up with a frightful bang, rip the shooter into myriad ragged pieces and, scatter blood, flesh, bone fragments and hot bits of shrapnel all over the countryside.
Actually, things aren’t quite that extreme. In fact, a maximum load is a predicted maximum powder charge, and while it can be an overload, it’s not quite as dangerous as many reloaders imagine it to be. In recent years the people who compile reloading manuals have erred on the side of caution and reduced their maximum loads - something many handloaders have noticed and commented on. However, this was done for a perfectly good reason. Too many handloaders looked at the data, were impressed by the velocity of the maximum load and set out to work up from there. Of course, they struck trouble with excessive pressure right from the start. This was incentive enough to have maximum loads reduced slightly. If you were to check an old manual you are likely to find a reduction of at least 2 grains between the old and current maximum charges.
This doesn’t mean, however, that it’s safe to start with a maximum load when you commence working up data - you definitely should not! Maximum powder charges are listed as the likely level where you can expect your loads to top out. They are intended to give an indication of when to stop adding powder. Despite being slightly reduced, all maximum charges should be treated with respect and once you reach that point, you should proceed with the utmost caution, even if the fired cases and rifle don’t show any signs of excessive pressure.
Maximum loads are not carved in stone. They can’t be because of all the variables. Just how much powder can be used in a certain calibre with a particular bullet weight depends on a great many factors; the type of action, the make of case, the type of rifling, the rifling twist, the bore and groove diameter, the throat length of the chamber, the primer, the hardness of the bullet, the amount of bearing surface it has, and so on.
Some makes of cases are heavier, due to having thicker brass and hold less powder than others, hence they will show pressure signs quicker. At least one make of magnum primer designed especially for heavy charges of slow-to-ignite powder, increases pressure if used with smaller amounts of easily ignited powder.
Bullets with hard jackets and cores and considerable bearing surface can increase pressure by up to 8,000 p.s.i. Bullets that are seated out so that they are jammed into the lands at the “lede” raise pressures by about the same amount, enough to expand primer pockets and cause gas leaks. Bullets seated so deep that loading density is increased can raise pressure by about 2,000 p.s.i, but are not as critical as those jammed into the rifling.
Chambers with long throats cut so the bullet has to make a considerable jump before it engraves the rifling result in lower pressures - and also less velocity.
Always bear in mind that cartridge cases that are thicker, have less capacity, and will give the same pressure and velocity with less powder than another make of case which has more powder capacity and thinner brass.
Some actions are capable of handling more pressure than others. The brass case is the weak link, and actions that support the case with the steel of the chamber or the recessed bolt face clear up to the extractor groove will handle more pressure than actions that do not.
Actions that enclose the case with steel to the extractor groove are the Model 98 Mauser, the Ruger M77 MK II, Weatherby Mark V, the post 64-Model 70, the Dakota 76, and the Model 110 Savage. The Model 1903 Springfield, the Classic Model 70 and the 1917 Enfield all use a coned breech that leaves a little of the case sticking out. But with good modern brass, all of these actions are safe with pressures running up to 60,000 p.s.i as shown by the fact that they were used for thousands of hot 7mm and .30 calibre magnum rifles. The new Classic Winchester Model 70 is chambered for the Winchester Short Magnums which are loaded to mean pressures of about 63,000 p.s.i.
In this modern day and age, all the ammunition companies together with makers of bullets and cases and propellant powders have equipment for taking pressures and velocities. Most of them put out manuals containing data for handloaders. These manuals usually give such valuable details as the make of case, the make of primer, the make of the bullet, the length of the barrel, the pitch of the rifling, and the maximum cartridge overall length. They also list the maximum case length and the trim-to length.
Very few list any pressure data. Norma did years ago, but in any case it would be irrelevant because of all the variables that exist. It would be a fluke if their listed load produced the same pressure and velocity in your your rifle with different components to what the manual listed.
Another thing for the handloader to remember, is that if the load he settles on gives easy extraction and he can reload his cases from 10 to 30 times without primer pockets becoming enlarged, that load is safe in his rifle with the components he used.
On the other hand, if his cases are hard to extract and after three or four loadings he finds that primers slip into the primer pockets with little or no pressure, the load he is using is too hot no matter what the maximum is supposed to be. If he gets primer leaks or a blown primer, he has definitely exceeded the maximum charge for his rifle.
Load development a.k.a “working up a load” might be defined as the detailed execution of the planning of a handload for a specific purpose. This includes a fair amount of experimenting and testing to ensure that the load is safe. You should begin with a powder charge below the listed maximum and work step by step upwards until the desired specification for the projected load is achieved, or until it becomes obvious that it cannot be achieved safely with the selected components.
If the handloader has a micrometer, he should measure the solid head of his cartridges before and after firing and compare the measurements. On rimless cases, the reading is taken on the case head immediately forward of the extraction groove, and on belted cases the head forward of and adjacent to the belt. These are the most favoured locations. On rimmed cases, the head just in front of the rim is the diameter most often used.
All cases expand noticeably in these areas on first firing, whether with factory loads or handloads, so this technique cannot be used on this firing. That first firing will expand the case to match the dimensions of the chamber in which it has been fired and any further expansion on subsequent shots is a sure indication of very high chamber pressures.
Case head expansion after firing is the handloader’s key to acceptable pressures in his reloads. If the mike shows the cartridge case head has expanded by as much as .001” then that pressure is excessive for that shot in that gun. Some experts claim that even .0005” is too much, but by my rule of thumb this is the outside limit of permissable expansion. I always try to keep my working loads under .0001” expansion, and recommend this as a sensible limit for the average handloader. What it all boils down to is: if the mike shows measurable head expansion, then brass is beginning to flow because the pressure is too high. This is a sure indication that it is time to reduce the powder charge.
If, as we shoot a series of pressure loads, and check each increased powder charge with the mike, no pressure signs appear, the next heaviest charges are fired, and so on through the series. On a rare occasion, it may be that no sign of excessive pressure shows up even when you reach the listed maximum load. You may even be able to exceed the maximum charge weight recommendation in your manual with safety. But this only means that your particular rifle has a chamber dimensionally larger than standard, which makes it more tolerant of those maximum charges than the test gun used to compile the handbook data. Most loads are tested in a barrel with minimum dimensions which is attached to a universal receiver, but some ammomakers, like Norma for instance, take pressures using factory rifles.
This business of published velocity figures also needs some interpretation. Almost all rifles for standard centrefire big- game rifles are now furnished with 22-inch barrels, and rifles for the belted magnums are furnished with 24-inch barrels. But velocity figures published by the riflemakers are generally taken in 24-inch barrels if the cartridges are in the .270-.30-06 class and in 26-inch barrels if they are in the magnum class. One notable anomaly is the .30-30 Winchester as most of the arms for it are carbines and there will be a loss of at least 150fps in their stubby 20-inch barrels. This means, of course, that in the carbines it will
not be possible to duplicate the published velocities.
Reloading manuals list barrel lengths, but bulletmaking Hornady lists 6mm Remington data taken in a 22-inch barrel while their .243 data is taken in a 24-inch barrel. Every few weeks I get a letter from a reader complaining about how the velocity of his handload is not as high as what is listed in his manual. Alas, it not always possible to duplicate manual velocities, even when the same components are used. This is because of the variations we discussed previously, and too, his rifle may have a different barrel length and chamber dimensions. Factory ballistic tables should also be taken with a large grain of salt.
One ballistics lab experimented by shooting Remington factory ammo in a 6mm Remington rifle which had the barrel docked after every string. With the 100gn bullet, velocity was 3176 fps in the 26-inch length, 3084 fps in the 24-inch, 2997 fps in 22- inches, and 2955 fps in 20-inches. This translates into a loss per inch, not of the oft quoted 25 fps but more like to 45 fps!
Gun nuts love to argue about the performance of various cartridges and use as the basis for their arguments factory published data on muzzle velocity, retained velocity, energy, and bullet drop. This is about as futile as arguing with a little man who wasn’t there, because much data is based on figures for muzzle velocity obtained in a barrel length not furnished in factory rifles. And there’s the same difference with handloads using different bullets and different lots of powder.
All this is neither here nor there as far as the hunter who reloads is concerned. He should forget all about squeezing an extra 100 foot-seconds out of his handloads.It won’t make much difference to a deer whether the bullet that smacks into him has left the barrel at 3000 or at 3200. If it lands in a vital area, he’s a dead deer.
How much does an extra 100 fps gain you in flatness of trajectory? Not much! For example, take the Hornady 95gn SST driven at 3200fps and 3100fps with both loads zeroed at 200 metres. The difference in drop is only about 12mm, and the difference in energy delivered at 300 metres is barely 80 ft/lb.
Hot loads then, don’t flatten the trajectory enough to worry about but they do exact a penalty in shorter case and barrel life. Hardly a fair trade, wouldn’t you agree?
Comparing factory drop figures to your handload because they have the same velocity is a waste of time. I’ve found that they do not agree with bullet drop I get on the range. And when I check the velocity of factory ammo on a chronograph I find that in my rifle anyway, the delivered velocity does not always live up to advance notices. The only way to find out how effective your handload is and get valid figures is to chronograph it and then shoot it at various ranges.
A lot of rifle and bullet effectiveness lies in the head of the shooter. If he is a true believer then Old Betsy is going to reap death and destruction. A mate of mine uses a 7mm Rem. Mag. with the 150gn bullet on deer. Deadliest outfit he ever owned, he tells me. He swears by it and can’t see how I can shoot deer with a lousy .270 Winchester. I’d hate to disillusion him, but when he left his rifle with me for safe keeping while he went overseas, I snuck it out to the range and chronographed it. The muzzle velocity of the particular load he uses clocked just 2880fps. With a bullet of the same weight and somewhat superior ballistic coefficient in a Marlin XL 7 .270 Winchester with a 22-inch barrel I get over 50 fps more velocity than he does in his rifle.
He has read the figures, and he believes them. Because he believes them has unbounded faith in his rifle and reload. Because of this faith he shoots his rifle well, and because he shoots it well, it kills well. But if he ever found out that his pet load in his favourite rifle was giving him 220 fps less velocity than he thought he was getting, he would be devastated and his rifle would be certainly be ruined. So it’s going to remain my deep dark secret.
This article was first published in Sporting Shooter, December 2011
This short clip from the Discovery Channel's 'How Stuff Works' show takes an interesting look at how bullets are made in the Sierra factory.