Buy a MANUAL 510 so you will get the totally sealed threaded end
I don't like cart+atty either but atty+drip tip for dripping is great for testing juices and with a manual battery it is safe to do that. And I usually use Boge cartos on my 510 - you have to buy the standard resistance ones, not the ones that say LR or Low Resistance nor HV. With the manual battery you are also safe from killing your battery if a carto leaks.
being able to drip is great for testing juices because you don't want to fill up a blank carto with a juice then find out you don't like it.
And I love the PCC at NoSMokeVA.com - it fits standard 510 batteries including manuals and can hold 2 batteries (one charging slot and one plain slot) and if you take one carto condom off it can hold 6 cartos. I usually take the mouth-end condom off and set them mouth-end down.
I vape both standard manual KR808D-1 and 510 so I charge 2 batteries of each overnight as well as the PCC. The PCC can't charge a KR808D-1 battery but a standard KR8 battery will fit threaded end up in the front battery slot. And I put my spare 510 battery int he charging slot threaded end down. And some alternate cartos for each in the slots. And I also have two complete ecigs outside the PCC. And juices in my pocket - that is my setup for going to work.
There are very few prefilled cartos for 510 but lots of blanks.
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Re Riva - yeah they've been out of the Deluxe carto set at Liberty-Flights.com. remember to click the 20% off on the front page. I bought the Riva 510 Lite Bundle and then got a Riva 901 cone there too - the 901 cone is the one they must use in the Riva carto kit they are out of (because they are out of boge cartos). I just tested the 901 cone - it fits the Riva 510, it is shorter, and the hole fits over a carto. And get a buttong protector here on this Ego page
http://www.liberty-flights.com/product.asp?id=41