Why should the shop pay for the shipping? They didn't build the gun. H&R did.

If you have a beef with someone paying for shipping it should be with H&R and not the shop. Too dang many people think that the local shop should foot the bill for anything that goes wrong with a product that they sell.

I know what you are going to say. They sell the products and they should stand behind the products that they sell. Well, if they manufactured the products that they sell then I would agree. The local shop could simply stop selling the inexpensive guns and sell only shotguns that cost $1000 or more so that if something does go wrong with one they would have enough of a profit to offset the rare problem with a gun.

Assuming you purchased the USH in walnut it should have come in somewhere around $250 and the shop made about $40 - $50 bucks on your purchase. And now you want them to foot the bill for sending the gun back and their profit goes down by about $15.

Do you think a shop can stay in business operating like this?

You purchased an inexpensive firearm and as with nearly everything sold these days you get what you pay for. The shop didn't force you to purchase it.