It may be that the recoil spring case installed in the front of the barrel housing is in backwards. The part is a spring retainer that encircles the barrel inside the barrel jacket. One end of it is slightly smaller in diameter than the other. That smaller diameter end goes in first, towards the breech in reassembly and retains one of the two recoil springs within it.
The smaller diameter end being the same diameter as the barrel is often assembled the wrong way with the small diameter out as it appears to be a simple spacer to be placed over the end of the barrel.
Assembled incorrectly, the rifle will fire, but the action will not be allowed to recoil far enough for the bolt to unlock and open so you get a failure to eject.
Manual operation of the bolt with the part incorrectly assembled will give no hint of a problem.
You can see if it is assembled wrong by pushing a cleaning rod down the bore and aginst the bolt by hand.
If it is assembled incorrectly, you should only be able to push the bolt and barrel assembly backward a little more than an inch. It will take some force to do so.
If assembled correctly you should (with some muscle!) be able to push the bolt/barrel back almost to the full rear of the receiver ejection port. The bolt wont unlatch doing this manually, but you can get it to by holding the bolt/barrel at that full rearward position and then pushing the bolt handle backwards about an additional 1/4" to unlatch it and the barrel will recoil forward,,the bolt continueing back.
If the barrel does not fly forward of it's own spring power when the bolt is unlatched in the above exercise,,a worn or broken bolt lock may be the problem. It can cause maulfunctions in extraction and ejection.
Other things to look at are the extractor itself. They are sometimes brittle and can break the hook off the tip causeing extraction problems. The top of the bolt where the extractor is secured into in a groove sometimes cracks and gives the extractor excess room to move around and not get a secure hold on rounds upon extraction.
Sometimes the wrong caliber extractor has been replaced in a rifle. They are different and will cause problems.
Lastly, a chamber that is rusted or damaged will cause problems in extraction. A stuck caseing that is removed with primitive tools sometimes leaves gouges and nicks in the metal that the new rounds cling onto when fired and won't extract smoothly.
Don't attempt to dissassemble the barrel jacket assembly w/o some detailed instructions & pics. A couple of specialized tools or at least some very carefully made ones are best used to get the barrel nut and jacket bushing apart. The springs are under heavy compression inside. Be very carefull when disassembling.
The Model 8 and 81 are great rifles in my opinion. Out dated for sure but they have a certain class about them. I have a late (1933 mfg) Model 8 in 32Rem that I'm currently putting back in shape and upgrading the wood. An FN Mod 1900 would be nice find!