This was taken from a Facebook group so may help here..... the guy in question that asked the original question to royal mail runs a reputable company up north.
With a recent reply from Royal Mail, there has been some measure of success when it comes to knowing who to post your RIFs with.
Here's the reply I received last week:
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"Dear Mr Liggat
Thank you for contacting Royal Mail,
There are no restrictions on insurance sending airsoft guns through Royal Mail. Although we do have specific packaging guidelines .Please find below: Guns for sporting use
(Guns intended for sporting purposes - including Section 1 and Section 2 firearms, low-powered air weapons and their component parts - may be sent in compliance with UK law subject to any applicable controls on the possession or export of firearms)
UK destinations: Yes
International destinations: Yes
Follow these packaging guidelines: Use 1st Class as the minimum service. The sender’s name and address must be clearly visible on the outer packaging.
All items are subject to screening and a delay may be incurred if an item is deemed as suspect and sent for further checking. In order to work with Royal Mail to find any such items compliant, the non-pressurised cylinder should not be attached to the gun so we can clearly see the item is compliant. This is only relevant to guns that are acceptable in our network according to our ‘Guns for Sporting Use’ guidelines.
Canisters must not be attached or contained in gun."
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So basically:
-1st class or greater -Senders info must be clearly visible -No pressurised containers and gas mags must be empty of gas -All magazines must be out of the gun -Insurance IS valid -Maximum size = Medium Parcel (see below)
The only restriction not mentioned in the reply is that the parcel must not exceed the 'Medium' sizing restrictions or it will go with Parcel Force and essentially not be insured.
To be sent through the RM, the parcel must not exceed 20Kg with maximum dimensions of 610mm x 460mm x 460mm.
This may mean that you have to disassemble the RIF and send it in a box other than the one it came with. I'm sure it's obvious that this is preferable to sending it with no insurance.
It's also worth noting that you DO NOT specifically need to tell them it's a RIF (but do not lie if they ask). There's no label etc that they need to put on the box. They usually will ask you what's inside so if it's your first time sending something, it can be helpful to take along their prohibited items list so you can show them it's definitely allowed
Hopefully this clears things up