I suggest you go to a gun store or even to Walmart and see what they look like and how long and wide to make them. They usually have a zipper along the side so they open flat. A drawstring wouldn't work as well. And they need to be very thick. I would suggest 3 or 4 layers of batting. Also, a web handle for carrying.

I think the people that asked you to make the cases have no idea what's involved - they might be better off just going to a store and buying something appropriate.

I've learned - the hard way - that sometimes store-bought is just more practical AND economical in the longer run.

My DH is an avid hunter and his cases have to hold the rifles safe and for the rifle to be safe from others. He flies to hunting trips and his rifles goes on the plane too. The ones you make will be nice but not suitable safe gun storage at home when not in use if that will be the only case to store it.

If he just wants them for protection from scuffing when traveling they aren't hard to make. I made 2 for DH. I took the guns and laid them on the cutting table. I made them out of fleece since he just wanted them for protection when taking to the range. Basically I traced the shape of the gun then drew the lines straight to make a elongated triangle shape. Made a flap on the top that folds over and closes with Velcro.
DH is always asking me for strange things like upholstery for antique cars or tool bags for the truck. He doesn't complain about all I spend on my hobby so I figure I can make a few things for him.
good luck

IMHO, worn denim would make a great outside for this job.

As both a quilter and a gun owner, I agree completely that your BIL would be better off just going to a store and buying something appropriate. You have no idea of what the structure is, and the amount of padding needed, and where it's needed most, etc. I DO know all of these things, and I would never, ever, in a million years let anyone try to talk me into making a gun case. I'm not even sure you could get a home-made case onto an airplane; they're getting so strict about transporting guns. I just mailed one, and it had to be both in a gun case with sides that would tolerate at least 50# of pressure, and inside a box with appropriate padding in the box.

If you want to do something for your nephew, make him a nice "man" quilt, or something like that.

If he is transporting guns out of state, I'm not sure what he asked for is sufficient. If it is not out of state, he could wrap in any old blanket. You need way more info.

I've made several "cases" for my husband and a friend of his. I did the same as Pattypurple did and I made mine out of an old velour blanket. I put ties on each side at the end and when folded over, they could just tie it. They're really simple to sew up and if you're using practice pieces with batting I don't see why those wouldn't work for transporting. DH keeps his in those cases all the time. Good luck!!!

A big beach towel wraps a gun nicely. I have done socks for them with t shirt type fabrics

I made some for DH & DS's. I used camo flannel inside and out and two layers of cotton batting inside. . I copied the pattern of on of there store bought ones. I added Velcro to the long side so they could open and close them and handles to carry them with. I do not have pictures of them as boys are now living out of state and DH took his with him when he went to Wyoming for the summer. Made them about eight years ago and they still work perfect.