Sorry for the delay,
Gator,I'm just an interested shooter.
In your post you are describing what I understand to be Variable Practice.Whereas in Random Practice one changes skills on each rep,in Variable Practice one changes the same skill's parameters.For example,on each rep one could vary the range to the target and/or the number of shots fired.Practicing the same drill repeatedly is known as Constant Practice
Variable Practice makes the execution of the skill more robust because it is practiced in a wide variety of contexts.To extend the math analogy:now we practice solving 8x7,8x2,8x11 etc.
Random practice improves the ON DEMAND execution of the skill by spacing reps of a skill enough for "forgetting" to occur.Back to math:we will practice 8x4 then 3x6,9x5,7x7,2x1...by the time we practice 8x4 again,we have to summon up the solution,not just parrot it.Both Random and Variable have their place.
Contextual Interference (C.I)
Blocked/Random and Constant/Variable practice schemes fall along a continuum called Contextual Interference.C.I. describes the interference with learning caused by changing skills or parameters.As noted earlier,this interference actually improves learning.
C.I. can be modulated: beginning at the low end,there is Blocked/Constant.I think it would be safe to say that this is how most of us practice.We practice a Block of the same drills using the same parameters until we are satisfied.Then a new drill or a new skill is practiced.
1)Draw and fire 2 shots at 7 yards freestyle for 10 reps
2)Draw and fire 3 shots at 10 yards strong hand only for 10 reps
3)At high ready,switch to weak hand only and fire 1 shot at 15 yards for 10 reps
At the highest level of C.I. there is Random/Variable.Here ,on every rep you would change the skill set being practiced-and you would vary the parameters each time a skill set was practiced.
1)Draw and fire 2 shots at 7 yards freestyle
2)Draw and fire 3 shots at 10 yards strong hand only
3)At high ready,switch to weak hand only and fire 1 shot at 15 yards
4)Draw and fire 3 shots at 12 yards freestyle
5)Draw and fire 1 shot strong hand only at 5 yards
6)At high ready,switch to weak hand only and fire 2 shots at 8 yards
Etcetera.
XRe,
The best way I have found to design practices using C.I. is to write down the skills that you need to practice.Then, for each skill,list the parameters you will use it in,i.e., freestyle prone at 50?Yeah.Weak hand only at 50?Nah.
Skill Examples:
Shooting on the move
Freestyle
Strong hand only
Weak hand only
Reloads
Parameter Examples:
Distance to target,target difficulty,no shoots,movement
Number of Shots
Par times
Starting positions(Draw,gun in hand, gun on table)
Prioritize skills and parameters(Saul Kirsch has an excellent template in Thinking Practical Shooting) and then make a list of interleaved drills.Base the list on available time/ammo and there you have it.Modulate the amount of C.I. to avoid burnout.
Sometimes you gotta plink

.
Deliberate Practice
K.Anders Ericsson coined this term in his studies on expertise.He studied musicians and chess players at various skill levels and found marked qualitative and quantitative differences in the way that experts practice.Briefly,given a similar amount of practice time,experts spent more time actually practicing,practiced outside their comfort zone,and attacked weaknesses.
This is not an easy way to practice.It requires planning a session thoroughly,and you are committing to that plan.It is best done alone,because a bit of concentration is involved.You must accept lower practice performance or face enormous frustration(remember,you are only getting 1 chance at a drill:ichi-Go,ichi-E

)
It is not fun and relaxing.At all.At the end of one session that involved movement in all directions;swingers and multiples;and shooting freestyle, strong-and weak hand only;my nervous system felt ...stretched out.The quality of mindfulness and attention required is tiring.
References
These are the most useful I've found
Motor Learning and Performance by Richard Schmidt
Motor Learning by Richard Magill
Skill Acquisition in Sport edited by Williams and Hodges
Motor Learning and Control for Practitioners by Cheryl Coker(probably most concise and accessible)
The Road To Excellence edited by K.Anders Ericsson
Expert Performance in Sports edited by Starkes and Ericsson
Attention and Motor Skill Learning by Gabriele Wulf
Hugh