What you are describing has NOTHING to do with the load...it MIGHT be an artifact of the recoil...which is a mechanical problems somewhere, probably in the trigger, transfer bar...something is hanging up...
Next time you have a FTF, wait a minute or two, open the action and see what the primer indent looks like...then see if it will fire again...if it will, it is NOT the primer but the "ignition system"...the fired primer should look normal and the unfired primer should have less of an indent.
Something is slowing down the hammer fall or interfering with the hammer falling fully...the recoil is "readjusting" whatever is causing the FTF on the second go-round.
That is unless you have a bad batch of primers, the primer pocket is deep and the primer isn't getting seated so the anvil is firm against the bottom of the primer pocket...if the primer ISN'T seated all the way to the bottom and the hammer fall isn't strong enough to seat the primer AND fire it...or the firing pin isn't quite long enough or have enough inertial then FTF will drive you up the wall. All these things have happened to me at one time or another.
The best thing to do is strip the action...check each part of the ignition system to be sure it is functioning correctly, start over with a new box of primers, buy a CARBIDE primer pocket uniformer and work over the brass...check each item in a step by step way and eliminate them one by one...so you won't be chasing your tail. I would start with the gun, THEN check the ammo buy using at least two different brands of cases, and at least two, maybe three brands of primers...some primers have harder cups so a light strike caused by a slow hammer coupled with the intertia style firing pin can make you do bad things.
The Handi has an inertia type of firing pin so just about ANY hammer slow down or light strike, hard primer, or primer not seated deep enough can case FTF's.
And check things TWICE...I've worked on problems without finding a solution only to go back, recheck and find I didn't quite look hard enough or glossed over "something that couldn't possiblly case THAT problem" and have it jump up and give me the "red face".
Luck