Cheap and easy fix
Here’s what I learned about Stoeger coach guns. Early production firearms had fairly soft steel in the working parts. Stoegers are very popular with Cowboy Action Shooters because they’re decent shotguns at a reasonable price. The guns are used hard when shot on the clock, jerked open, slammed shut. So my problem of wear on moving parts making the firearm loose in the joints is not uncommon. A local cowboy action shooter and gunsmith told me that my issue with the gun coming open after the first shot was due to wear on the barrel lug. He suggested I gently tap the top of the lug to peen the metal back to a sharp edge. He said to take it slow and check frequently to be sure there was tension on the opening lever through out the arc of movement. So I took a small ball peen hammer, tapped the top of the lug maybe a dozen times. Checked it out, tapped it another dozen. It now locks up tight as a new gun. The fore end still rattled, so I put a thin layer of J B Weld on the hook portion of the latch on the barrel. Bingo. Everything’s snugged up. I test fired the gun, pulling down as hard as I could on the barrels. Didn’t come open. I'm happy.