A shotgun should be cleaned after a day shooting before being locked in the gun safe. A rifle is cleaned less often.
A rifle needs more cleaning than a shotgun. Fouling of the barrel harms accuracy. A shotgun is smoothbore in contrast and doesn't rely on accuracy. A rifle should be cleaned after every use if you want to keep it in good condition.
Depending on the firing system of the weapon (different rifles use different systems) some will jam more often than others from dirt and the like. The M-16 will Jam from less dirt than an AK-47 will because the M-16 directs the gasses (and thus also particles) into the bolt carrier directly. Other considerations are things like how tight the parts are because the tighter the more interference from foreign matter. You still want to clean it because the accuracy will be harmed even though it will still fire. The parts need oiling as well.
If you are going to use the 525 daily you could get away with cleaning it every few days not daily. If it is going to sit a while you clean and oil it. If it sits a while the grime is going to harden and cause problems and the barrel will be fouled as well.
Jeremy wanted the gun to kill the family it seems, certainly that is how the police presented the purchase. There is no evidence of it being used that much let alone daily. The exterior looked new according to AP. That being the case he probably would not have cared about cleaning it though he should have. If he considered it a prized possession he would have probably been different and he woudl have cleaned it. I always clean my rifles after use, I don't want my barrels messed up.
AP didn't mention if jamming though, nor mentioned it being cleaned before put away though. It is possible that the dirt and grime from the murders (including possibly blood) combined with that already present and solidified to the point that it caused a problem that did not exist at the time of the murders. The bashing of the weapon into Nevill also could damage things to an extent.
I tend to think that the problems with the weapon resulted from the murders combined with previous noncleaning and didn't surface during the course of the murders. There certainly is no evidence to indicate it happened during the murders. 10-11 shots were fired in the master bedroom in the initial shooting. If it had jammed fewer shots woudl have been fired before Nevill got away and in fact Nevill would have had a chance to try to jump the killer before more damage was done. There is no indication of that at all.
The killer was also able to pour 8 bullets into the boys without an issue. These were the main actions. 4 into Nevill as passed out and then 2 into Sheila were not that many in a row.
It would be an attractive argument to say the gun would have jammed, Sheila would not know how to clear a jam and would have been subdued but I see little way to say a jam had to happen or did happen based on the evidence. Jamming 2 times in 100 rounds is a lot but there is still a lot of rounds fired before a jam will happen. You can fire 25 in a row without a jam several times despite that high failure rate. An ordinary failure rate is one in ever few thousand shots so you can see how high that is and yet it still doesn't mean a jam frequent enough to mean it had to happen during the murders. In the meantime that jamming was after the weapon was not cleaned from the murders and used to bash someone severely so th eproblems likely don't predate but post date the murders.
