Right - so Jeremy said he had opened a new box of ammunition. Thanks for that. :D
Now I'll read the rest of your post. 
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EP were satisfied that Jeremy had opened up a new box of 50 new bullets, on evening of 6th August 1985, because they only found 30 bullets on the kitchen worktop; 29 loose ones tipped out onto the worktop, and a solitary bullet, still in the ammunition box, along with the plastic wrapper next to the ammunition on the kitchen worktop, and that 25 bullets had been fired during the incident - since a new box of ammunition only contained 50 bullets, and twenty were missing, EP knew that five additional bullets used in the shootings originated from some other source, and they accepted that there must have been, and was, five bullets already in the gun before Jeremy started to load new bullets in from the new box of ammunition on the evening of 6th August 1985...
EP did not only accept Jeremy's word for it, they had hard facts to back up what he told them...
These five bullets which were already in the ammunition magazine, had all previously been loaded into the ammunition magazine, and removed, and been replaced, as a result of non use of the loaded rifle on a previous occasion, when the weapon may have been taken out with a view to shoot vermin around the farm, or a spot of target shooting, and any bullets in the gun had been taken out and out to one side, until the next time, the gun was taken out with a view to using it for similar or the same reasons...
EP spoke to Jeremy at length about what would normally happen if he had taken the gun out with a view to shooting it, and he had not used it, and Jeremy told them that there was one of two things that might happen, (1) he would remove bullets from the guns ammunition magazine, or he would simply remove the magazine clip from the weapon, detaching it from the gun, so that it could not be fired, unless bullets were added back into the ammunition magazine, or the ammunition clip with the bullets in, was clipped back onto the weapon...
EP were satisfied that the five bullets which had already been preloaded into the weapons ammunition magazine, could have been loaded twice into it, and fired once from it...
Furthermore, they were also satisfied that Jeremy had loaded new bullets into the ammunition magazine, from the new box of 50...
EP had reason to suspect, or doubt that the twenty (20) new bullets taken from the new box of ammunition, had been loaded more than once into the ammunition magazine, and EP accepted that all the bullets which had single magazine marks upon them, were in fact the 20 new bullets taken out of the box, at some stage, between evening of 6th, and morning of 7th August 1985...