I'm not too sure what you mean here. Lowering the amount of shrapnel makes sense but if shrapnel is lowered what is it replaced with? Do you mean to say its replaced with items/stackables that you "normally"/abnormally get? In which case saying ,"it will NOT spawn extra stuff in loot" is misleading.
I will give you an example:
The tt you will get will be lowered, thus the filler (which on Caly is shrapnel)
If it costs you 3 PED to kill an atrox, you will get (in case of a 1x loot) 1 liver oil, some 10 hides and 1.98 ped tt shrapnel.
With a better DPP gun it will cost you 2.75 which will lower your shrapnel stack to 1.73. The difference will not be replaced.
Loot now is based on cost to kill, mostly, efficiency and looter having a direct impact on the amount (tt) you get back each kill.
What I mean with better DPP will not spawn extra stuff is that you will not get other stuff in those 1.73 left, after getting stackables...