So I've been working with all kinds of shooting bag fills as a matter of product R&D for a while now and I've seen what seems to work and what doesn't and managed to figure out a lot of the why.

Ultra-light fill is new in the market and there have been a few (very minor) teething issues but it strikes me that the complaints I see sparsely popping up about ultra-light fill are trivial gripes by people that didn't think their cunning plan all the way through and so they didn't use the product correctly and got unexpected results because of it. Most good (meaning they work well) bag fills are rigid and heavy as a result. Very few good fills are compressible or light weight. Without getting into areas of engineering that are obfuscated from Joe Sixpack by the curiously overcomplicated terminology there are a few tips I can pass along. Most people have never really played with the ultra-light fill options because they're only now just coming out on the market so I can see some tips there being helpful. Heavy fill has been out there (in the form of sand) since the beginning of time and people still do that wrong so I figure the whole area of shooting bag fill could use a little explanation.

Part of the problem is people typically just assume that they need to fill their bag to the same level it was before regardless of the specifications of the media. Basically, a lot of people don't know anything about materials selection but they know how much weight they're willing to carry. Complicating matters is, nobody that I can find publishes instructions on how to use their special magical media.

So, let's get at it. For this discussion we're not looking at the mass density (heaviness) of the fill but at the compressibility. Why ignore heaviness? Simple, you can get heavy fill that's compressible or not and you can get light fill that's compressible or not so, compressibility is the differentiating factor between them. Weight is just a selectable feature.

Hard fill pellets as used below is media that when you take one pellet and squeeze it between two fingers, it doesn't compress or change shape at all and if it does, the change is permanent and any springback is below the threshold of being noticed by the human eye (so < 2% springback). Hard fill is typified by materials like sand and extruded plastic cylinders, kitty litter, lead shot, hulled rice, dry corn, crushed corn cob, crushed walnut hulls, airsoft pellets and little girly clear pink plastic models of the Platonic solids.

Compressible fill is any fill that when you squeeze a particle of it, the particle either compresses or changes shape or both but when you relax the pressure the pellet resumes (partially or fully) its prior shape. Compressible fill comes in a lot of forms like shredded styrofoam, polyfill, buckwheat hulls, and the new BoxToBench Precision Ultra-Light Shooting Bag Fill. Almost without exception (almost), before the B2B fill came out all ultra light fills were subject to water infiltration. B2B's new fill changed the landscape so much that people need to learn how to use their tools all over again.

Hard (rigid, non-squishy) fill with coarse pellets: You want a full bag but not a tightly full bag. Excessive unfilled space will allow room for the pellets to move past each other reducing quality of lock-in and making the bag seem squirmy. Hard pellets should be smaller than 5mm (the smaller the better up to a point) and should not be regularly spherical. Hard pellets really benefit from an irregular catalog of non-round shapes to add angles and corners for better lock-in and stability under load. The lightest hard shelled media is still not that light. When you have a hard media bag done up with too little fill in the bag it'll seem that your POA moves around in steps after you've settled in. This is caused by pellets moving around and because of all the sharp angles involved it seems to jump around. When you have too much hard fill in it'll be hard to get the rifle to settle in in the first place and will be like shooting off a steel pipe.

Hard fill with fine pellets/granules: This is stuff like sand and #8 or finer lead shot. High density means it'll take more energy to move the fill around meaning it'll be more stable at smaller bag-fill percentages. The closer you get to the particle size of fine sand the more forgiving it'll be of decreasing bag fill percentages. Why? Well the more dense and fine something is the easier it'll make a steep angled pile that could support weight without a container. As particle size grows and mass density drops, the less able it is to form steeply angled piles and the more putting weight on top of such a pile destabilizes it. Want to test, try stacking basketballs into a cube without a container.

Compressible fill pellets: You want a little space but not too much left in the bag. You want 10% of your bag's capacity to be air space but not much (or any) more. Too full of a bag will lead to a springy/bouncy bag instead of a solid rest. Too little fill will cause you to always be fighting media flow which will appear to be a continuously variable POA. Your cross hair will appear to slowly move across the target instead of staying in one place or orbiting a particular spot as the media continually moves around. If you have too much in the bag your cross hairs will appear to bounce. You only need a small amount of compressibility in a soft media. It doesn't need to be very soft and excessive softness will lead to bounciness.

Compressible fill with small pellets/granules: Similar to hard fill, the smaller the pellet size the more stable, up to a point but only up to a point. That point is calculated by knowing the diameter of pellets, their actual 3D shape and their compressibility as well as the surface coefficient of friction of the pellets. Compressible pellets throw a curve ball into the simple rule of thumb we can use with hard fill because unlike hard pellets, compressible pellets can increase the amount of friction applied to neighbor particles under load by deforming from their original shape and conforming to a common shape with their neighbor particles. As an example on a pair of spheres or cylinders (or indeed almost any convex curved 3d shape) in direct physical contact another particle just like it you only have 2 extremely small points of contact. When you compress a spehere you get an oblate (flattened) spheroid which means there's a potentially HUGE amount of surface area that can now apply friction to neighbor particles. The same applies to cylinders and other convex curved 3d shapes.

These are full of B2B's ultra-light fill. Notice they're not bulging and it looks like I could have gotten them a little fuller? Well I could have but it would ruin the effectiveness.


A factory rigid-fill bag stuffed almost but just short of all the to the gills.


Getting your bag-fill fill ratio wrong will super not help you no matter what fill you choose.
Choosing the wrong media will only add or remove weight from your load-out. It should not affect performance if used correctly.

I have a back injury which limits me to 15 pounds. I have a couple bags filled with pet store Walnut hulls.

mine is filled with rice

I did not read your novel

I read your novel. I appreciate you going into depth on the subject. I've used rice, corncob media, and sand, but right now I'm using airsoft bbs and they're working reasonably well. They're pretty light and stay more or less in place.

Headlines aren't news. Laziness is loss.

A couple old socks filled with rice and tied off work fine for me. If I ever expect to be shooting in wet environments I'll likely make up a sock full of airsoft BB's.

Popcorn works pretty damn good for me.

Plastic beads, rice, sand will work shooting from a bench. The stuff he is talking about is super light weight . Shooting PRS or anything where weight/performance matters is where this material shines. I bought a small amount to start (4 liters) and after seeing how light and how well it works, I ordered 16 liters more. It's not the cheapest stuff but, I would much rather carry bags made with this fill material while out hunting than a bag filled with some.of the heavier fill mentioned.
I was really surprised just how light this stuff is. I think the cloth  material I used for the bags weighs more than the fill.

Weight hardly matters in PRS.  Guys are shooting 25+ rifles now.  I tried some of the git-lite fill and i wouldn't switch to it over the heavy fill in my Game Changer.  I think it has great application for hunting and stuff but prefer the added mass for a positional shooting bag.

Good to know. I can t shoot PRS due to working every weekend . Just thought why carry extra weight when it's not necessary.

I usually recommend this stuff here in the shooting bags rear bags I make. Weight seems to be just right.

I have used some of the ultra-lite stuff from the OP and for a hunting application, it would work fine. For bench rest though or any extended periods of shooting, I didn't like it.

This is with the ultra-lite fill from the op, great combo for rucking through the woods, but not for recoil management.

Too bad, lots of matches in OH

Oh, I know. My brother and nephew both shoot PRS. I took them to Rayners years ago for their first try at long range shooting. My nephew did really good for his first time out and my brother was great at stringing expletives together. Quiet creative really.
The nephew is doing really good in PRS. If you shoot the matches I'm sure you know them.

I ordered the Box-to-bench filler, and it's basically weightless, which is perfect for a LR shooter who is weight conscious.

This was perfect for the bag I'm making, which attaches to the rucksack I just built for a friend.