The "tilt test" is done with the rifle completely stripped of everything but the bolt, op rod, and gas system.
Stock, trigger unit, and recoil spring is off.
The rifle is tilted at a 45 degree angle and the action should open all the way from gravity.
Tilt forward 45 degrees and the action should close.
The test to determine if the rifle has a problem is to shoot the rifle. If it fires, extracts and ejects, and reloads properly, there's no problem.
If it's short stroking, first replace the recoil spring with a USGI specification spring. NO EXTRA POWER.
In the M1 the spring is not just a recoil spring, it powers the entire action and it requires a specification spring. A bad spring or a non-GI spec spring can cause all sorts of odd problems.
Buy a new USGI spec spring from Fulton Armory or Orion 7 Enterprises. They make new production spec springs.
Next GREASE the rifle.
In the M1 oil is used to prevent rust. The lubricant is grease. There's online charts showing where to grease, or buy a GI manual.
If the rifle still has trouble, look for a gas leak.
Places to check are to make sure the gas cylinder lock screw is down tight and that the valve in the screw is sealing properly. A loose screw or weak spring in the valve or some grit stuck under the valve may hold it open and leak. Any problems with the screw.... replace it.
Look for excess soot from firing around the gas cylinder and barrel indicating a leak. There'll normally be some sooting present.
Have the gas cylinder and gas piston head gaged to insure they're a proper fit with each other.
Check the gas port in the barrel to insure it's not rusted or clogged, and make sure the port is properly centered in the opening of the gas cylinder.
DO NOT start digging into the gas port and damage or open it up. Use a brass wire to clean only if the port is clogged.
Buy an M3-A1 Combination Tool, and use the chamber brush to thoroughly scrub the chamber. Inspect for rust, rings or bulges, or other damage.
