There are a dozen mistakes a person can make reloading ammo. But only one that makes guns come apart. And that is too much powder or too much of the wrong powder. There are some basic things a person can do to make sure that issue does not cause a Kaboom. Here are some suggestions>
1. Never have but one powder on your work or reloading area at one time. If you are reloading a pistol then only your W296 or H110 or Unique or whatever powder you plan on using are near your reloading spot. Same with bullets. I have 200 grain and 250 grain I am loading into the 454. Only the proper one is nearby while loading.
2. Make absolutely sure of the amount of the chosen powder is what you plan. Always look it up in a reloading manual, and check a second source. I suggest you go ahead and write down on a piece of paper what the load is going to be. I have been reloading since 1972 and had no Kabooms yet. Two days ago I loaded some 454. I wrote the formula on a piece of paper that will go in the box with the reloads. These are light loads. It reads like this:
454 Jan 7,2022
Hornady 240 Mag XTP
CCI SRP
Unique 14.6 grains, 1.6 cc
COL 1.745
Plan is for 1,600 fps in Rossi 92
So while I am loading, that paper is laying there reminding what I am loading.
3. Double check every powder charge. In my small load I only loaded 40 rounds as a test round for moderate loads. I used the little Lee Dipper instead of a powder measure. The charge fills about 75% of the case so I cannot get a double charge because it would run out of the case. Never the less, I still look inside every case to make sure the powder level seems right.
4, Immediately upon checking the powder level, I stick the bullet in it so no more powder could get into the case. If I am loading something like 30-06 where I may use the powder measure and cannot easily see inside the case, I add the powder and put the charged case into a cartridge block. Once the block is full, usually 50 rounds, I take a flashlight and look down into every case. I keep a cheap LED tiny light on my reload bench.
5. Powder selection. Most people believe that the powder is going to be the most accurate and safe when the case is as close to 100% full as it can be, that way it is not laying in different positions each time the rifle is fired. So, select a powder that is 70-100% filling. Many manuals like the Nosler manual will show you exactly how much of the case is filled. When you have a case that is more than 50% filled, then you cannot double charge a case without seeing the second charge spill over. Your biggest risk is a double charge.
6. Probably as important as anything is to not have interruptions or other people in and out while you are reloading. Somebody moving a powder around might cause you to pick up the wrong one. Then of course no drinking when reloading and just common sense safety things like that. Also, there is never anything wrong with using a checklist and keeping a log. You will want a log anyway so you know what did and did not work for a particular gun. I make comments in my little log, like "good accuracy-1 inch groups". I have one for Trail Boss the wimpy powder, that says, "too hot at this level", and others like "great light level load". The 454 that I loaded recently will have comments in the log about accuracy and velocity and recoil.
7. The last thing is select a loading recipe that is near the bottom of the load in the manuals. Most books will give you starting and max loads, like 50.0 grains, 52.0 grains and 54.0 grains. When you choose the hottest load you know you are approaching the danger zone, so start low and work up, that way you do not start with that fear.
Anyway, just go slow, pay attention and enjoy creating your own much cheaper which will let you shoot about 3 times more.
And enjoy the process.