I made up 100 test rounds to try to find a good load for my M1 carbine and to try to come as close to Military Ballistics as possible. To do this I made up 10 rounds in 5 different powder charges using two different powders. I used random cases from the 1350 I had prepared. I also chose to us some 110gr Coated Lead Slugs I bought in a plastic bag at a recent gun show. I figured I only had 200 of them and since what I was looking for mostly was velocity they being the same wieght and basic shape as the other slugs I would be loading should get me real close. So I packup go to the Club and sight in the Carbine at 50 yards using some PMC 110gr FMJs I manage to get it about spot on within the accuracy I can muster using military peep sights. I put the first test rounds into the mag and rack the slide. The round won't go into battery. Holding the bolt open just a hair. So I pull the bolt and eject the round I check it out visually and see no problems. Same thing happens with the second round. Now I know the OAL lenght and slug diameter is spot on I checked them with my digital calipers. I drop the third round into the chamber and allow the bolt to slam into it. This time it goes into battery. I aim and fire. The rifle has a slightly louder report then the factory ammo and maybe a hair more recoil. The point of impact is about 3" above where I expect it to be. The next round having been stripped off the top of the magazine does not go into battery. So I hit the bolt charging handle with the meat of my hand. Not hard but hopefully enough to put the round into battery. No luck. I pull hard on the bolt lever and the slug remains stuck in the rifle while the case comes out with the bolt and of course flings 11grains of 2400 powder all over the breach. OK bullet is stuck in the barrel trip to the range is over. I come home push the bullet out of the barrel and see it has rifling marks on it!!!! I double check the OAL of the other bullets in the test batch all are spot on at 1.680" double check that in 3 books and against the PMC's OK thats not it. I then take a Raineer Coated Lead slug 110gr and seat it to the same depth and drop it into the chamber (NO POWDER) it drops in fully and then I put it in the top of the mag and rack the bolt. it strips and chambers to full battery perfectly!!!!! I then take one of the unused Gun show 110gr slugs and weigh it weight a hair under 110gr I weigh the Raineer slug weight a hair over 110gr I then lay them side by side and the little light bulb goes on over my head. See if you can tell why? Look at the ogive of the bullet on the right. See how it remains parallel for so close to the tip! I measured and the gunshow slug is .308" in diameter for .450" from the base. It was being shoved into the rifling when attempting to be chambered. In 43 years of reloading I had never run into this with a reload that was at published OAL. SO now I get to pull 98 slugs and dump some powder in the yard resize the brass and load up some proper shaped bullets. I guess my Carbine chamber throat must be in pretty good condition. Live and learn.