I was shooting with a friend who offered to bring some rounds of .308. Before I noticed he had loaded and chambered a 7.62X39 by mistake. It is now wedged tight (live). I tried tapping it out with a dowell but it splintered and is now in the barrel as well. Worse yet, the rear pin wont release the upper receiver (only the front will release. Is there any fix? He is offering to replace the weapon but other than this its a great firearm.

you got the dowel stuck as well?
is the BCG back? or forward?

Dowell stuck BCG forward

IMHO. You should consult gunsmith. You are unable to separate upper and lower. On this style firearm using dowel thru barrel on closed b.c.g. will not typically release internals when in closed position. I have heard someone tell me (claim) a gunsmith resolved something similar before by removing barrel. I would not try it (let gunsmith) since it is ready with a live round.

My idea also, I have no idea why the upper wont come off, but I dont want to mess with it with the live round in it. Regardless, my buddy will replace it if its too damaged. I actually had this happen before when a friend brought ammo for my .223, but he got .222 instead. That was no problem except that the first round jammed and we recognized the issue right off the bat. Thanks for your opinion anyway.

By all means take it to a gunsmith and make sure he knows there is a live round in it.

I'm trying to visualize this. Maybe some one can explain it to me.

The .308 is according to SAMMI specs a larger cartridge then the 7.62X39
Longer, 2.015 compared to 1.528 case length.
2.490 compared to 2.17 overall length with projectile
diameter .4703 compared to .443 in.
with a length of 1.5598 compared to 1.1984 to the shoulder.
with a headspace of 1.634 compared to 1.252

OBTW the M&W 10 is .308 WIN/7.62x51

wouldn't the cartridge just be lose in the chamber if not fired and fall out if the bolt could be opened unless the ejector jammed it somehow.

Just seems that the problem he is having seems odd if I am correct except he can't get the bolt to open.

Correct me as I have to be wrong as he is having his problem.

__________________
Psalm 23:4

I agree with what the others have posted...
without INTIMATE knowledge of the workings of the rifle, let a gunsmith handle it.
I really doubt anything is damaged, sounds like the extractor has the rim and bolt forward, but not all the way... wood is alot softer than steel so no damage there.
personally I could free everything up, but I am very mechanically inclined and have a pretty good amount of knowledge of how everything goes together and functions, I have been in the "fix it" and the "make it work" business for a very long time.

good luck

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

I agree with the previous poster, it's almost a lead-pipe cinch that this issue isn't a stuck cartridge. For this issue to exist with a 7.62x39 in a 7.62x51 chamber, the problem is almost certainly with how the extractor has jammed against the misfit case. Secondly, for those of you who think that you can drive an unfired stuck cartridge out of any AR with the bolt lugs still engaged, you need to study-up a bit on mechanics. Think about it. The only way your gonna get the bolt to release is to turn the bolt first to release the lugs. If it would come out any other way, don't you think the 60,000 PSI when you fire it would become a major problem?