Push the receiver pins back into place. Collapse the stock fully and pogo it. To pogo the rifle, hold it vertically by the handguards with one hand and grasp the charging handle with the other. Bang the buttstock on the ground while pulling firmly on the charging handle. You may have to bang it pretty hard. Pogo the rifle until the round extracts, or the extractor rips the rim off. If the round extracts, you can carefully clear the barrel of the dowel with a solid cleaning rod. Toss the rod down the bore and let the weight & momentum do the work. DO NOT BANG ON IT WITH A HAMMER! DO NOT USE A WOODEN DOWEL!
If the rim tears off, separate the upper from the lower and take it to a gunsmith.
Once you get the bolt open, you can lock it back, knock both receiver pins out and remove the upper.
This is why banging on a rod with a hammer to knock a stuck case is a bad idea. Instead, toss a solid cleaning rod or a 12 inch piece drill rod down the bore and let the weight & momentum do the work