FWIW a friend in my volunteer fire department approached me at a meeting and said he had a problem.
He has a Howa 300 Win mag which he says fires factory ammo just fine. He then went to FL resize it and the rounds would not go back in chamber. He figured dies were bad so he got another set and same thing happened. He bought a third set and same thing happened.
I told him to bring rifle and ammo and brass down and we fired a round and ran them through my dies I have used for 30 years and same thing. Round would not allow bolt to close.
That only means one thing, a bad chamber job with not enough clearance on the shoulder. My match 300 Win Mag reamer has a tighter neck and min base dimension above the belt so I pulled his barrel, cut off threads and rethreaded it and put him a nice chamber in it and lo and behold all his sized cases went in just fine and he was up and running and a happy camper.
The bad news is that he has three sets of 300 Win Mag dies.
On the other hand I had a friend when I was at Picatinny and he said his M1A had problems. His bolt would unlock and everything comes to a stop. I told him to bring the rifle and loaded ammo in to work and I took it home for a looksee. Lo and behold it did exactly what he said. I ran his fired cases in my 308 dies and loaded his load/bullet combo and it worked just fine. Visually there was nothing about his sized cases that drew attention.
I told him to send the dies back to RCBS and tell them what happened. They sent him a new set of dies and they worked just fine.
Distinguished Rifleman High Power & Smallbore Prone
President's Hundred (Rifle) US Palma Teams(2)
US Dewar Team (2),4 Man Natl.Champ Team SB Prone
Cert Test Dir. Sm Arms and Ammo,Aberdeen Pr Ground, Firefighter I, AC4HT