I acquired a couple of these JSA Tactical ("Like" them on Facebook, JSA Tactical) rear sand/bean/airsoft 6mm pellet bags about a month ago. They have since become my go-to bags for my sniper matches with the ORA here at Base Borden's Mons Range.

They come in small, medium, and large sizes. Have a look; pictured UNDER the rear of my HS Precision stocked Surgeon 591 .260 Rem build is the SMALL rear bag.
Now this next picture shows the Medium bag standing UP to give lots and lots of support whenever your rifle's rear end is over 6 inches from the mat/deck/ground.
Check out the MOLLE strap/sewing on the long side of the 'can' or cylinder shaped rear bag! Very thoughtful....

LIKES:
What I really like is the 1000 Denier cordura material that they use. Different camo colours/patterns available, but the digital theme is my fav.
I particularly like the 2 dimensions used, one on the flat part of the "can" shaped cylinder gives me support for low heights when my rear buttstock hovers above the ground, and when I need more height when say, the bipod legs are extended, then I just stand that little bag up on it's end.
I also like the density of fill that the JSA Tactical makers top up their bags. NOT too stiff so that you cannot get the squeeze for raising and lowering your sniper rig, and NOT too soft so that your really gotta squeeze to get any decent level of support.
I did not get any hand cramps/ cramping action throughout the entire day. Even Ryan of Funker Tactical seemed to like this set up.
I also like the strap on the side of the cylinder shaped bag, a quick carabiner or snap link will help the rapid packing up and deployment of the shooting position. And there is another strap across the diameter of the bottom of the can... I think I might just slide a "Grimlock" on there just for rapid attachability on the shooting ruck/3 day pack/assault pack.
I am loving the 6mm airsoft beads over the old standard 'sand bag' fill. The advantage of the 6mm airsoft pellets is that they don't absorb water when shooting or competing in the rainy conditions. I need all the help I can get. I'm not getting younger.
DISLIKES:
Okay, the stitching at the very bottom of the "Can" shaped cylinder where the beads were filled needed some re-inforcement; looks to me like they set their sewing machine to 5 stitches per inch. Doubling the number of stitches would seem stronger, BUT here's the cautious side... or the benefit of the doubt....
Some of you users/expert shooters out there might wanna stuff some more beads to 'tighten' the bead fill 'tension' inside the bag. And I figured the 5 stitches per inch closure would allow quick stitch 'picking' to remove them stitches and then add more beads followed up by a rapid pass on your sewing machine.
Hey, that can work for me.
Another problem with the camo coloured rear bags is that when you are in a hurry, you can easily / accidentally leave the bag rolling around in the tall grass. OOOps!
And that's why I like an aluminum snap link or some sort of webbing trailer for quick pack attachment. 
Final Word:
I love these bags and I'm gonna be carrying them to my Sniper Clinics and matches! For most of your bench needs, the SMALL baby is what you need. I had to extend my bipod (Harris BR Swivel 6"-9") legs and I discovered that the SMALL bag stood on its end worked for me.
I don't think the MEDIUM bag will work for you unless you are using a taller bipod or your rear buttstock geometry may warrant that MEDIUM height. Maybe you might find yourself in taller grass or ambushing coyotes in some grass, who knows?
JSA Tactical makes a LARGE bag, but I would save that for situations when a bipod is not needed, bench resting maybe, hunting gophers off the hood of yer pickup truck? Sometimes it's handier with the LARGE bag snap linked and web straped to a small bag for rapid setup while hunting gophers in the back of yer pickup truck bed, I learned this from you Alberta gopher hunters a few years back.
Hope this makes sense and leads you to happier precision shooting success!
Buy what works for you and your game. In my case, I want stuff to make me look KOOL because the "look cool value" is super fun.
OH, BTW, JSA Tactical is working on all kinds of modern camo patterns/colours/fabrics. They can be very innovative in this department.
Cheers all!
Barney

They come in small, medium, and large sizes. Have a look; pictured UNDER the rear of my HS Precision stocked Surgeon 591 .260 Rem build is the SMALL rear bag.
Now this next picture shows the Medium bag standing UP to give lots and lots of support whenever your rifle's rear end is over 6 inches from the mat/deck/ground.
Check out the MOLLE strap/sewing on the long side of the 'can' or cylinder shaped rear bag! Very thoughtful....

LIKES:
What I really like is the 1000 Denier cordura material that they use. Different camo colours/patterns available, but the digital theme is my fav.
I particularly like the 2 dimensions used, one on the flat part of the "can" shaped cylinder gives me support for low heights when my rear buttstock hovers above the ground, and when I need more height when say, the bipod legs are extended, then I just stand that little bag up on it's end.
I also like the density of fill that the JSA Tactical makers top up their bags. NOT too stiff so that you cannot get the squeeze for raising and lowering your sniper rig, and NOT too soft so that your really gotta squeeze to get any decent level of support.
I did not get any hand cramps/ cramping action throughout the entire day. Even Ryan of Funker Tactical seemed to like this set up.
I also like the strap on the side of the cylinder shaped bag, a quick carabiner or snap link will help the rapid packing up and deployment of the shooting position. And there is another strap across the diameter of the bottom of the can... I think I might just slide a "Grimlock" on there just for rapid attachability on the shooting ruck/3 day pack/assault pack.
I am loving the 6mm airsoft beads over the old standard 'sand bag' fill. The advantage of the 6mm airsoft pellets is that they don't absorb water when shooting or competing in the rainy conditions. I need all the help I can get. I'm not getting younger.
DISLIKES:
Okay, the stitching at the very bottom of the "Can" shaped cylinder where the beads were filled needed some re-inforcement; looks to me like they set their sewing machine to 5 stitches per inch. Doubling the number of stitches would seem stronger, BUT here's the cautious side... or the benefit of the doubt....
Some of you users/expert shooters out there might wanna stuff some more beads to 'tighten' the bead fill 'tension' inside the bag. And I figured the 5 stitches per inch closure would allow quick stitch 'picking' to remove them stitches and then add more beads followed up by a rapid pass on your sewing machine.
Hey, that can work for me.
Another problem with the camo coloured rear bags is that when you are in a hurry, you can easily / accidentally leave the bag rolling around in the tall grass. OOOps!

Final Word:
I love these bags and I'm gonna be carrying them to my Sniper Clinics and matches! For most of your bench needs, the SMALL baby is what you need. I had to extend my bipod (Harris BR Swivel 6"-9") legs and I discovered that the SMALL bag stood on its end worked for me.
I don't think the MEDIUM bag will work for you unless you are using a taller bipod or your rear buttstock geometry may warrant that MEDIUM height. Maybe you might find yourself in taller grass or ambushing coyotes in some grass, who knows?
JSA Tactical makes a LARGE bag, but I would save that for situations when a bipod is not needed, bench resting maybe, hunting gophers off the hood of yer pickup truck? Sometimes it's handier with the LARGE bag snap linked and web straped to a small bag for rapid setup while hunting gophers in the back of yer pickup truck bed, I learned this from you Alberta gopher hunters a few years back.
Hope this makes sense and leads you to happier precision shooting success!

Buy what works for you and your game. In my case, I want stuff to make me look KOOL because the "look cool value" is super fun.

OH, BTW, JSA Tactical is working on all kinds of modern camo patterns/colours/fabrics. They can be very innovative in this department.
Cheers all!
Barney
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