Carbine pop-off
I've seen similar problems...first check and make sure the spring that holds the barrel band on is still square at the contact point, and set at the right height to engage the band, ...that the point on the band it engages is square, ...and tighten the barrel band screw down tight. Make sure the metal tabs on the handguard are firmly attached to the guard and parallel to the barrel not bent or flexible. If it's still popping off the wooden handguard may either been compressed and oil-soaked enough that the wood has collapsed under the band, or it may be an aftermarket handguard and not the right length for your carbine.
The cheapest parts to replace in sequence would be the retainer spring first, handguard second, barrel band third.
Hope that works...the M-1 is great fun with either 15 or 30 round mag...possibly the most fun small rifle you can buy. Only the SKS in my collection comes close, and it's heavier to carry and holds fewer rounds.
Paperpunchr
"While the bitter parties stifle every voice that warns of war,
Every man should have a rifle and have cartridges in store."
---Henry Lawson, Australian Poet.