Hi harmoniums.

IMO Shouldn't be too much of a problem - Neither of those two rifles are too difficult to licence (Just make sure neither of them are evil, bull-pup, or black!:rolleyes::D)

However, two particular items you'd have to watch out for on the application process:

1. Status of your residency - AFAIK One must be a resident of Ireland for 6 months prior to the granting of a FAC - Now, in your case, I'm sure that you are only temporarily working in the States and have indeed been resident in Ireland the whole time, whilst working overseas.;) If you have an Irish Driving Licence, Passport, and Utility bills showing this residency in Ireland, there should be no problems, if you're asked for proof, as that is the usual proof of identity and address.
2. You'll need to show "Good Reason" for these two firearms - If you're not a member of an authorised range or club, then you cannot use "target shooting" as your reason for owning the firearms. However, you may use them for vermin and pest control, in the case of the 10/22, and for foxes and deer etc. in the case of the 308 (Although is the 308 a wee bit overkill for a fox? The more experienced fox-culling lads will know more about this, but AFAIK the Gardai consider .220 and .223 sufficient calibres for fox.)

If you're going to be around a lot and would like to do a fair bit of target shooting, maybe consider joining an authorised range to allow you to do so whenever you want?

If you haven't done so already, have a very careful and thorough read of the Garda Commissioners Guidelines in conjunction with the FCA1 form itself.

Hope that's of some help.

dC