Anyone know how feasible it would be to fill sparring/training

You mean for falling on? Not a good idea, you're gonna need a metric dickload of sand to make them thick enough and with that much sand you might be able to drag them across the floor but definitely not lift.
As to how, you could open up a seam and just pour it in there I guess.

Sand is not a good impact absorber in comparison to foam. Falling on it hurts.

>>1197904
this

foe that size just use a mattress maybe.

Broke 2 ribs falling off a quad bike at the beach, sand is pretty much concrete from above 1m, or going faster then walking speed.

>>1198037
No matter how much ``wrestling'' you might do on a mattress, I doubt one would hold up to the rough 'n tumble of MMA.

>>1197904
This. Aikido instructor said they thought it would.be fun to have a class.at.the.beach one day. Everyone was sore and bruised as fuck

>>1198063
yeah of course, besides "wrestling" i used to practice judo falls and throws on a mattress. not actual matches of course.

>>1198071
i cant imagine doing that at one od my local beaches. they renovated the club rooms recently so theirs sandstone pieces scattered all over

>>1197789
>how feasible it would be to try to move a sand filled sparring mat that weighs 460 pounds?

5 foot x 8 foot x 1.375 in thick mat = 4.6 cuft
sand weighs from 90 lb. per cubic foot to 130 lb. per cubic foot.

>>1198382
Math for the win.
+1