Hi Joe!  Welcome and “Just the facts…”  First with “excuse me”, but you may well have your answer before you!  Wrong magazine.  Before going into any convoluted research exercises or worse, messing with the rifle itself beyond good cleaning, seems to me you need to try the functioning with the correct magazine.  Possibly to sell that .284 mag with a bit extra $ to purchase the .308 magazine.  Your mismatch mag likely more valuable than .308. – Just a thought from definite non-gunsmith! 

Finally, Joe, the fact… I never experience such problems with my Model 88 and the proper .308 Mag! (Humor alert!) 

Good Luck & Best!  

John

I had one years ago in .243 that did that a couple of times.  Both times were while sighting in a scope, using sandbag rests.  Both times it fired only twice even though there were more rounds in the magazine, so it was not a total runaway.  I think that in a good solid rest, concentrating on crosshairs and trigger pull, I might have caused the second shot by not gripping the rifle firmly.  A recoil bounce.  I know that when I held the grip firmly, and pulled the rifle back into my shoulder, I could not make it double.

I don’t know what the “rate of fire” is when this happens, but it is faster than anything I fired in the Army.

Good luck, and I hope you figure it out.

POE

I have been collecting the model 100 for many years and I have hunted with one since 1965. I never have had the double fire issue with any of mine nor have I ever had a firing pin failure. Two issues I have had with these fine SA rifles are failure to extract and failure to eject, both are separate issues and both have always been resolved with a deep cleaning.

Semi Auto sporting rifles such as the 100 are not normally heavily fired and most of these are basically deer and big game rifles. No offence to deer hunters but most are not usually gun buffs knowledgeable about the inner workings of these SA actions. Safe to say that most hunters will use their rifles for the hunting season and give it a basic cleaning before placing it back on the rack or in the safe. Basic meaning clean the bore and wipe it down but rarely ever is the action removed from the stock where the real cleaning begins. I have done the firing pin recall on all 7 of my 100s and it is not a simple task but well worth the time because I got to see where the issues arise from. Dirty gas tubes, sludge build up in the chamber and locking lugs and old and dirty grease that has dried in the extractors and ejectors. Cheap, usually military type of ammo is also a culprit. At the neck of the chamber I find a burn ring where the bullet enters the lands and grooves, blow back I suspect, and this causes the case to stick and the extractor to be overridden. After I address all the dirt and dried grease my guns function flawlessly. My original 100 I bought new back in 1965 and have hunted with every year since probably does not have 300 rounds fired through it. I have a few that might not have more than 20 rounds fired since new and even they were dirty inside. I can’t stress the need to clean and the need to use the proper oils enough and very sparingly. Oils attract dirt and debris and that clogs up the works.

Olin/Winchester is still honoring the firing pin recall to this day on guns that are now 50-64 years old and it is a rather tedious process but still an active recall.

Guns being deep cleaned and new and old firing pins. The cracked stock shows how NOT to do things.

I was browsing eBay for Model 100 related items and came across this leaflet.

I find it interesting that Winchester actually provided instructions/explanation about the potential “doubling”.

I wonder if other semi-automatic models had a similar warning leaflet.