Questions:
How are you priming your brass?
Press ?, what type press?
Hand primer tool ?
Bench mount primer tool?
Die mount primer tool?
etc....
The primer should start in easy enough, then just need constant medium pressure until it seats.
You should be able to "feel" the primer pushing into the primer pocket, then the pressure should go up as the primer is completely seated.
Pull brass out of shell holder and look and feel it. It should just be a "tad" under flush.
If so...You got'er done.
Look at factory loaded ammo primer depth as a guide.
If you feel a lot of pressure without any sensation of movement of the primer, STOP and look whats going on.
It could be upside down,sideways or wrong size primer, or the pocket may have been staked ie. military type brass.
If the primer is staked, you need a completely different process. (Ask us how when or if this happends )
100% MUST DO THIS.... Wear safety glasses at all times when handloading/reloading.
If a primer ignites while inserting it into the pocket, (You have safety glasses on at this point..RIGHT?)
It will POP kinda sharp and loud...but not as loud as a bullet being fired out of a pistol.
It will startle you..just be calm, walk outside and yell..!!! (Thats what I do...it helps )
99.9% of the time it will be a harmless pop. This has happened to me several times in many years.
Usually it's MY FAULT for not paying attention.
I have read that in a press mount primer system with a tube feed, that several of the primers had a chain reaction. This "could" be kinda bad.
But, I do not know of anyone this happened to in many many years.
I'm sure if all the conditions were perfect, it may happen.
Just don't dwell on it and get loading and enjoy the fruits of your labor.
After priming a bunch of them, it will seem perfectly normal to you.
Just practice and use safety procedures when loading.
Don2