By John Bibby
Reloading rifle cases is much more complicated than reloading pistol cases.
There can be more complication in reloading for rifle as there are very few belted pistol cases and straight-wall cases are a bit easier to deal with (most pistol rounds). That being said, loading a bottleneck 5.56 (rifle round) is no more difficult and arguably easier than loading a bottleneck .357 Sig round.
The basics are still the same, load the proper powder in the proper amount, use the correct primer, seat the bullet properly. Admittedly, there is a step of lubrication with any bottleneck case that does not occur with straight-wall cases. Both rifle and pistol use straight wall cases 9mm or 444 Marlin. The same thing with the above-mentioned bottleneck cases.
Being a little over or a little under with the powder measurement can be catastrophic in rifle cases.
The loads that are published by reputable companies like Hornady, Lyman, Hodgdon, Sierra or any other big name in the industry are not absolute limits before catastrophic events happen. If a given rifle cartridge (say 5.56) has a range of 22-26 grains of a particular powder, that does not mean that 26.3 grains will cause a gun to explode. It means the same limit for repeated firing of that round is roughly at 26 grains. Your rifle, ambient temperature and repeated overloading “may” cause premature wear. This premature wear may cause a catastrophic failure in the future. Most rifle manufactures, build their guns to be able to handle 50% excess in pressure at least ONCE. As always stay within safe limits, but an occasional bump over is not going to cause an explosion, or the bolt through your face.
In contrast, some pistol powders have almost no spread between the lowest and highest powder amount. The .380 ACP is a great example of this. With a certain powder the minimum is 4.0 grains, and the maximum is 4.4 grains. Here we are looking at a very small window of acceptable, not to mention many powder measures cannot reliably throw tighter than 0.10 grains. This means setting the powder measure at 4.0 will get a significant number of powder charges at 3.9 grains. The same thing with a measure set at 4.4, producing many loads at 4.5 grains. Again, neither of these is likely to be catastrophic, but the percentage increase in under/over pressure is much more significant here with 0.10 grain of overage than with the 0.30 overage in the rifle example.
Loading cartridges at maximum pressure is risky. Downloading is always safer.
In the rifle 5.56 example above, if the statement means to load no higher than 25.6 grains, then the statement is correct. If, however, the statement is taken to mean loading in the 18-21 grain range is much safer than loading between 22-26 grains, that is completely wrong.
Depending on the powder and percentage of case fill, temperature, as well as angle of the cartridge at discharge; significant reduction in powder weights can create a very dangerous situation. When powder does completely cover the primer, there is a chance for delayed ignition/detonation. Normally a powder has a burn rate which is relied on for proper pressure regulation. In situations of low powder volume to case size, the powder can detonate instead of igniting. This means all the powder burns at once and creates a very strong over-pressure situation. This is much more likely to cause a catastrophic event, than a slight excess of powder. This not an uncommon occurrence when people attempt to create their own (from scratch) subsonic recipes.
Loading for maximum pressure provides the most accurate load.
This is almost never true. In most rifle cartridges there are at least two accuracy nodes. One is usually approximately 3% below maximum velocity. In a 3000-fps cartridge, that would be roughly 100 fps slower than max. There also tends to be a slower node that is around 10% below peak velocity. In the same cartridge, we would likely see nodes at +/- 50 fps of 2700 fps and +/- 50 fps of 3000 fps. This will vary by powder choice as well as percentage of fill for that powder in the given cartridge. In my experience, running an 86-94% load density seems to provide for best accuracy with many powders.
Very few rifle cartridges/powders provide the best accuracy/precision over a compressed load.
Velocity of a given load never changes.
Many people believe, if you produce your pet load for 6.5 Creedmoor and you do it faithfully and precisely, your velocity will be exactly the same each time you pull the trigger.
I have done some extremely great load work and have created loads with single digit standard deviations. Essentially meaning each trigger pull the velocity varied by significantly less than 10 fps. That takes a TON of work and is super awesome when it happens. Even when you are focusing on that it doesn’t always work. In comparison, factory rifle ammo is doing really well to vary by no more than 25 fps per trigger pull, and a better assumption would be 50 fps in either direction of the mean velocity.
On top of that, all powders are temperature sensitive. Some like the Hodgdon Extreme series, is significantly less affected by changes in temperature. They are still affected. A load developed in 65-degree temperatures, hits 2950 fps and is quite accurate. That same load on a hot (95 degree) day in August may well hit 3010 fps and not shoot nearly as tight of groups. In contrast, on a cold January day (24 degrees) the same loaded batch may produce velocities closer to 2850 fps.
Some competitors, up or download their cartridges based on temperature testing to insure they are hitting their most precise velocity.
