I suspect withdrawal of the variation is what they are after - and no I'm not going to withdraw it
As for the arguments for the caliber - they were well documented in a summary attached to the application
I started to reiterate those arguments to the FEO when he rang all those weeks ago
He stopped me saying that he'd never fired a rifle in his life so had no idea what I was talking about
He also questioned why folk such as he were being asked to make such judgments of behalf of the the Dept when they (he) clearly had no expertise to call upon
So you have a situation which is not uncommon where the FEO isn't experienced, doesn't know what to do. He may well prefer it to go away, more than likely he is just putting it off. Its a normal human response. Not ideal, pita for you but is complaining going to help him deal with it or just make the situation worse??
I think you can go to the front of the queue if you can turn these situations into something easy for them to deal with rather than being the hard one in the pile.
I agree with the comments above, you should have written communications not really because you then have an audit trail that helps your complaint, but because you can make your case in a way that survives the phone call. So if the FEO did not get it, then they can at least pick over your case later on, copy bits directly into their forms and go show it to the people who do understand. Email is best, it comes across as less pompous and more immediate. You can leave a message that will be picked up and you can craft your pitch without the FEO interrupting. The you can have a bit of a thread bouncing back and forward. Keep it short and simple, don't assume they can pick out the important bits, just give them the important bits. Don't confuse them
Maybe this is a bit obvious, so apologies about grannies and eggs etc but basically what they need to put in their internal forms are :
what do you want - rifle, cal, ammo, can and permissions
where - everywhere please because I am experienced and therefore get invitations to do stuff all over the place kind of thing
why - it will do x, but importantly why the other things you own are inadequate to perform the same task.
The last bit is really the important bit. Imaging him standing in front of his boss who says "but he has a 308 why isn't it enough". If you can give him that answer then it becomes easy.
Its not ideal, it would be nice if these departments were fully staffed with highly experienced individuals but we have to find ways to make the world work as it is.
If it has been running on for a while then you have the opportunity to email the FEO and tell him you (!) have obviously not explained the need properly so if he can give you an idea of the issues with your request then you can have a stab at giving him some clearer explanations. So he tells you his (his bosses ?) issues and you can then give him the answers. All by email so he doesn't have to remember them.
If all that does not work then at least you have a trail you can use to argue the case in another way.