Originally Posted by Falcon16
a 10rd will work great with a dropout a 15rd might be long enough it would interfere with grabbing at the knob to change out 12g's.
Regarding the 10rnd tube, this won't work very well; Regarding the 15 you're correct (although, wearing gloves, I've had no problems using a 15rnd tube and the dropout knob).
You can instal the 10rnd stock class feed with the dropout, but the stock class feed tube will be angled slightly down towards the stock class feed adapter (according to certain stock class runs this isn't "true" stock class, as feed tube is no longer horizontal, and you no longer have to rock/tilt the marker to chamber a ball).
The problem is that the stock class 10rnd feed cap will interfere with the dropout changer. There are feed risers and one piece stock class feed tubes with risers built into them that you can find, although I forget the names ATM. A 15rnd tube will work fine, in terms of its end cap clearing the dropout changer, but as was suggested turning the knob on the dropout changer can become difficult. See: CCI Dropout Changer Question
Of course, you can make your own riser, but that depends on your own know how, what you have available and your creativity. Unfortunetly I know of no step by step instructions on how to do this off the top of my head. I can't imagine they're all that difficult to make (i.e. you could probably do it with a dremel and drill no problem), but I wouldn't rather buy a stock class one piece feed specifically designed as such (I like things clean cut, tight and professional looking). See this for example of riser.
I've seen people mod their cap (how, without interfering with the feed gate, I can't imagine), but if everything stock you'll have an issue with the 10rnd feed cap and the dropout. Again, you will end up with your feed tube slightly angled and not perfectly horizontal (this could also put stress on feed tube threads/stock class feed tube adapter screw). Again, if you use a 15rnd tube, this won't be an issue as the feed tube cap will clear the dropout changer, but you might find it difficult to operate the dropout changer's knob. Without a riser, as you see, there are pluses and minuses either way.
See this: Opinions on the Pistol Phantom
On a slightly unrelated note, I also find the 15rnd tube a little long, even with a dropout changer. This is especially the case with my ghost. Anyways, I end up cutting down the feed tube to 12 or 13 balls, so I have a bit extra but the tube doesn't hit me in the goggles. Plus I never really have the need to have 15 balls, 10 is fine with me, plus the ability to top off once I've only got one or two left is definitely a plus.
EDIT: Here's a thread basically asking the same questions as you: Drop out & stock class feed ?'s
EDIT 2: You also can always get a forward facing (Sheridan style) adapter for your 10 or 15 rnd feed tube, which would make the issue of the feed tube cap getting in the way of the dropout changer irrelevant. And it would still be totally stock class under any definition I've heard of.
EDIT 3: Here is a feedtube that will provide clearance over dropout changer: Stripes Phantom Feed