I just realized something today, something I have never read or seen anywhere to date.
We all know there are several minicons who become decent weapons. Some of them include a standard 4mm "handle"... but others don't, such as Armada Gunbarrel and his repaints, and Armada Terradive and his repaints. Thise can unfortunately only be used by TFs with a minicon port.
However, while converting some various rifles from knockoffs to work with Classics as spare weapons, I discovered that a double-ended connector from LEGO Techniqs and related kits (like Bionicles) not only fit nicely in the hand of a Classics figure, they also fit perfectly in the port on a minicon!
Here's a pic to show what I mean:

And in the pic below are two types of the connector I'm talking about - the one on the left has the hollow end on both sides, the one on the right has the hollow end on one side and a ridged cross-section post on the other:

The one on the left works best, as the slight ridge around the end gives it a snug fit in a TF's hand. The one on the right doesn't fit as well, and thus pivots around and tilts towards the ground at any chance it gets.