Never heard of anyone having trouble filling a bucket of any common material and lifting it, but sand can get heavy when damp. I know my LA 243 can lift a heaping bucket of moist clay or dirt. A heaping bucket of 3/4" wet gravel was no problem for my BX either. Keep in mind that mine is the 2360, not the 1870. That's my "real world" experience.
Looks like the LA 203 can do about 410 lb at max. height, by spec, so a full bucket of sand might push the limits at full height. If damp sand is around 115 lb per cubic foot on average, and your bucket holds 4.2 cu ft, you might have to grab a little less than a full bucket, if you are loading trailers. You should have less trouble if you're not lifting it very high, like when transporting around the yard to spread in certain areas. Either way, you need heavy counterweight on the back, because the back end will bounce and leave the ground.