I built a standing rest a couple of years ago for our range.....stuck two 10' 4x4's into the ground about 3 feet deep and 30" apart, braced them apart with 4X4's at ground level, 4 feet up, and at the top. Spaced 3/4" holes 3" apart from 4' level to 6' level. Took a 24" length of 4" ABS pipe and put caps on both ends and then drilled the cap centers with 3/4" holes. Wrapped the ABS pipe with foam and carpet and banded and duct-taped it. Through this goes a 3 foot length of copper or steel pipe which is fed through the holes in the vertical 4x4's. ....The end result is a standing rifle rest, adjustable for height!
The pipe ends are held with bolts or cotter pins so they don't fall out. Cheap, easy, and works well, ...no elbows rests as they don't occur in the field! ...Just think of an "H" with the crosspiece adjustable!
Not sure where I saw this concept originally.

~Arctic~