5.56 mm NATO caliber sniper rifle:

Pipe size 1 is 1.315 o.d.x 1.049 i.d. x .133 wall thickness in schedule 40.One could make a 5.56 mm sniper rifle by ordering a 5.56 mm blank barrel $51.99 & have a gunsmith chamber it with a reamer & then put the 1" o.d. barrel inside the 1.049" i.d. Pipe size 1 & tack weld pipe to barrel on the muzzle end. And then weld this threaded on one end Pipe/Barrel to the metal stock as BC Truck does in the Home made 410 shotgun video

Any gun where the US Govt has it number can be traced but this gun will have no number so when the martial law time comes when a Police SWAT team kick open doors you & your house will not be suspect and you less likely to be shot dead on the spot or sent to a FEMA camp to meet the guillotine. When this Gestapo leaves in their armored vehicle you will have available a powerful long range & accurate rifle.

BLACK POWDER MUZZLE LOADER-Ammo has become difficult to obtain & may become illegal & the penalty may be death if you are caught with it. As a back-up your weapon should have an adapter to use a black powder charge. Also you need to know how to reload once fired primers plus a bullet mold and a big supply of hard to obtain lead. You might have to melt down air gun pellets or get tire weights etc