First comes safety. If the load is too hot or too light, the signs will be readily apparent. If the rounds are overloaded, it will show most of the time. One mild sign might be a shiny ejector mark on the case head. As a rule they are not dangerous, but it will wear out the brass quicker.
Hot loads wear out a gun more quickly, and except in narrow circumstances, are not necessary. A good example is the 220 Swift. I load mine to about 100 feet per second below the absolute max. The accuracy is great and the groundhogs never notice the difference, but the rifle and brass does. Hot loads will enlarge the primer pocket, which will render it useless; this is not always a reliable indication of excessive pressure, though it should be considered.
Other causes may be a soft primer, sharp firing pin or sticky extraction. If you have a sticky extraction and your chamber is clean and not bulged in any way, you have excessive pressure that is approaching the danger zone, especially in older guns. This is a good time to stop, pull the bullets, check and probably reduce the load.
When you get to the point of blowing primers and excessively hard extractions, then you are courting disaster if you continue to shoot them. The cause could be too much or the wrong type of powder, or even the wrong type of bullets. If you think you put in too much powder, check to make sure you didn’t set your scales wrong when you measured back at the shop. It’s a simple mistake but it happens, which is why it is so important to focus totally on the job at hand. Some of the powder labels look very similar; this is why you should only keep one powder on hand at a time during reloading.
Loads that are too light are inconsistent and probably won’t shoot accurately. A really light load may leave a bullet in the barrel. If you are not sure if the bullet left the barrel, safely check it out before shooting again. If there is a bullet lodged in the barrel, do not try to shoot it out by pulling the trigger again. This is very dangerous, and at the very least will ruin the barrel.
If the ammo has a different sound every time you shoot, you might have a hangfire, which can also be caused by a load that is too light. What happens is the powder isn’t evenly distributed within the case and does not burn at an instantaneous rate. It will burn slowly or irregularly, hence the hangfire. Old ammo can also cause a hangfire and should be discarded, but you can save the bullet. If you think you have a hangfire, keep the action closed for at least 30 seconds. The powder could also be unstable due to poor storage conditions.
Naturally, you want to see how accurate your ammo is. Since there are a lot of things that affect accuracy, don’t panic if your ammo is all over the target. Causes may range from loose scope mounts to poor bedding. If you have an accuracy issue, check out everything else first, including the shooter. If the ammo was loaded correctly, then it should be at least fairly accurate. Keep in mind different guns like different loads, so you may have to try a few different combinations to get the accuracy you want.
Using a bullet that isn’t designed for a gun’s rifling is a common mistake. An example would be using a heavy 80- to 100-grain bullet in a .223 rifle with a slow-rifling twist. The bullet won’t stabilize no matter what you do.
If you are able to achieve a 1- to 2-inch minute of angle at 100 yards with a bolt-action rifle, you are right where you need to be. Handguns will vary, but a decent gun and ammo combination should be able to achieve a 3- to 5-inch group at 25 yards, provided the shooter does their part.
So, if you have the desired accuracy and velocity without loads that are too hot, you have arrived. You should keep records of all of your loads, both good and bad. Keeping notes on bad loads should prevent you from repeating them somewhere down the road.
Another good way to test your ammo is to chronograph it. That way you can see and not guess at the velocity, plus you can test it against manufactured ammo of the same bullet weight to see how your ammo stacks up against the factory fodder. Caution! You might get your feelings hurt. Modern factory loads have improved a lot over the last 20 years or so. They are very accurate and consistent and will be as good as custom-loaded ammo; this is especially true with some custom hunting loads.
During the course of my work, I shoot a decent amount of factory ammo and very seldom does it not perform as advertised. The downside to factory-made ammo is the cost, and there may be a problem getting it on a timely basis.
You will get a really great feeling when you have crafted your own product that performs well, rather than having to buy it from a store. Another one of the many advantages to rolling your own is the ability to make ammo for obsolete guns. Shotguns, as well, can benefit from reloaded ammo. I took down a bear with a Lightfield slug that I handloaded. If you take an animal with your loads, this is a special type of satisfaction and there are very few things that will match it. ASJ