I've used reloads but have only shot at weekly league shoots a few times. The one match I watched it looked like all the shooters used factory loads. The boxes I saw were all Winchester Xtra-lites or Low noise/Low recoil or were Remington STS loads. That makes sense as those are the slickest hulls available and are the least likely to hang up, especially when new. Those hulls are also the ones recommended by Briley for use in their sub-gauge tubes as they don't stick. That would be a fairly important reason to use factory loads in competition.
As for your reloading light loads, you will need to get pressures over 10,000 psi to get clean burns with the faster burning powders. That gets harder and harder to do as shot weight decreases. There is just not enough resistance to do so in a 12 ga. I'm not aware of a powder available to the public that is clean burning in such an application. I load 7/8 oz for that reason as it is possible to get a relatively clean burn without a lot of recoil or expense.
