It may affect accuracy a little bit but for most reloaders that's not really a concern. However it can be a problem when working with a primer tray or tube type priming tool.
The best way to avoid this is to have an adjustable tool and seat firmly until the primer stops. This will ensure that the second hammer strike will properly detonate the fully seated primer.
Preparation
In order for the primer coating to stick, the surface needs to be clean. This may require chemical etching and plasma treatment as well as sand blast cleaning.
Often primers can have stable secondary structures that remain above the annealing temperature of the reaction, binding to each other instead of the target DNA and resulting in non-specific amplification. A good primer design tool should be able to check for these and warn you of them.
Lyophilized primers should be dissolved in sterile milli-Q or TE grade water. The best ratio is 255 ul of a master stock to 10 pmol dilution to make a working solution. Make sure you aliquot and store working primer solutions to avoid repeated thawing and freezing of the solution. Check the quality of a primer solution by running it on a denaturing polyacrylamide gel to verify a single band. You can also run it through a sequence database to check for mismatches.
Safety
The most important safety precaution is to follow all reloading safety protocols, such as wearing safety glasses, securing your press in a vise, and ensuring the work area is clean and free of spilled powder and unused primers. Primers can be very dangerous if not handled correctly and discarded properly, so always use caution and care.
It is also very important to fully seat the primers in their pockets. If a primer isn't completely seated the impact from the firing pin can cause it to detonate. When a primer is completely seated the anvil leg of the primer will be indented into the primer pocket and there should be no to little bridge height between the primer anvil leg and the primer pocket indent.
It takes practice to be able to feel through the lever of the priming press whether the primer is starting into the pocket or not. This is why a lot of people get a seating depth indicator, because it makes the process much easier and more predictable.
Priming Tool
A good hand priming tool is a must-have for anyone who loads a lot of cases. A good one will give you the right amount of feel and work without wearing out your thumb
or hands.
If you do not fully seat your primers it will affect how hard your revolvers hammer strikes which in turn can affect accuracy. If you use a revolver, you need to rotate the cylinder a few times after seating each primer to make sure that it is not "high" and not hitting the firing pin too hard.
There are many bench-mounted priming tools on the market but they are often slow and lack the "feel" of a manual priming tool. The Hamilton CPS solves this issue by combining speed and precision into a single unit. It will quickly seat the first primer in the shell holder by feel and then you simply raise the top part of the tool until it no longer touches the seated primer.
Seating
The vast majority of misfires in handloaded ammunition come from primers not being seated to the bottom of the primer pocket. This is especially important in semi auto revolvers where the primer may be driven to a position where it contacts nothing but the firing pin anvil during the second hammer strike.
This is why some primers have hard primer cups – they are intended to be seated a little bit lower than the normal primer pocket for use in these types of firearms. There are also primers with harder cups designed to mimic the harder cups of military ammo.
Newer optically initiated metal, oxide and semiconductor primers are promising candidates to replace traditional heavy-metal percussive primers that pose safety risks in some military applications requiring high impact energies. These technologies are currently evolving outside of the public domain and will eventually be available for wider commercial application [2,3,4,5].