in order to use a 306 with an Empire drip shield, the only way I know (and I have one of these set-ups on a REO Grand as we speak) is to use a 510 to 510 unsealed adaptor/extender...here:
510-510 Adapter (Unsealed)
...along with this specific drip tip:
Delrin 306 XL Drip Tip
this drip tip will fit over a 306 and allow you to slide the drip shield right over it. Although it does restrict you from using the tip of your choice, it makes the REO very pocket friendly while using a 306..it absolutely will not leak.
Another alternative is to use this:
306 to 510 Drip Tip Adapter - Avid Vaper
this will slip over a 306 and allow you to use any 510 drip tip you choose..there is no need for a 510 to 510 extender, as a drip shield will not fit over this and you will not need the added length...basically a way to use any 510 tip you want but not as leakproof as using a drip shield..there are folks who will advise against using adaptors as shorting out your atty is a bit more likely with the extra piece, and I think there is definitely some merit to this. I personally have never had a problem though. I happen to really like the leakproofiness the drip shield can offer. I use drip shields with both the 306 and 510 attys, but not always..lol. .hope this helps.