Limerick, without wanting to cause offence you asked people's opinions and thats what they gave.
You were upfront and honest about your past, fair play but with things like firearms I think there is a very thin line. Yes, you made a mistake, yes you took the punishment and served your time but some people don't agree that you should have a firearm certificate.
The best thing to do, if you really want one is apply and leave it to the discretion of whoever deals with them.