As the probable 300lb swinger in question,
300 Kettlebell Swings
From the few videos that I have seen with loads of 300 bls, none of them looked good.
So, a 300 lb Kettlebell Swing is quetionable.
Contreras' Swing with 203 lbs/92 kg is something that I cannot endorse
This take us back to...
Strength Training Percentages
Power Output is best displayed with certain Training Percentage Loads.
Examples
1)Traditional Strength Training Exercises
Power with these exercises (Squats, Bench Press, Deadlifts) are between 48-62% of 1 Repetition Max.
2) Olympic Lift Movements
Power is optimally displayed with loads of 70-80% of 1 Retition Max.
3) Kettlebell Swings
It difficult to perform a 1 Reptiton Max Kettlebell Swing.
Thus, the Training Percentage based on Body Weight appear provide the guidelines.
The Push Band
The Push Band provide more accurate feedback on the Power Output in a Kettlebell Swing.
Power Factor
Over 10 years ago, I purchased the Power Factor to determing Power Output.
It is comparative to Bathroom Scales. As with Bathroom scales it provides you with a fairly accurate reading with a small plus/minus factor of error.
The Power Factor worked well for measuring measuring the Power Output of Traditional Strength movments.
Great Demonstration of Heavy Kettlebell Swings
The Poster Children for them are...
1) Al Ciampa performing Kettlebell Swings with a 92kgs/203 lbs.
I posted Ciampa Swing with this but the video has dissappeared.
2) Anna's Heavy 68kg/150 lb Swing
Anna deftly handles a kettlebell 10lbs less than her bodyweight. Well done!!
www.youtube.com
Anna provides a great demonstration on Heavy Kettlebell Swing.
It is going into my library of Training Information.
Go try some heavy overweighted swings without thinking too hard about how high an intentionally overloaded swing is gonna go, then try out your normal weight swings again, they'll probably be easier.
Overloaded Swings
The loading in this movement fall more into Maxium Strength Training; the load is too heavy for Power Development.
Post Activation Potentiation Training. PAP
This is the the method that you elucing to.
The PAP Protocol eccentrially Super Sets a Strength Movement with a Power and/or Speed Movement.
When a fairly Heavy Movement is performed first, followed by a Power and/or Speed Movement; greater force is produced in the Power and/or Speed Movement.
The Strength Movement needs to be fairly heavy but not not too heavy. If it too heavy it dampens or negate the ablity to produce force in a Powser and/or Speed Movement.
A Rest Period between the Strength Movement and Power and/or Speed Movement of more than a minute, ensure greatet force Production.