Mine shoots 450fps on duster with 0.20g BBs. My testing last year was when hot, used propane, 0.36g had horrible accuracy at short range (out to 100ft) and past that they just didn't have enough hop up to get them past 150ft. This WAS in fact before I learned about getting the graphite off the BBs, so maybe uncoated 0.36g would work better with less hop up (no graphite residue on the hop up, causing reduced friction, making the shooter put too much hop up to compensate, causes more problems for the accuracy/consistency).
Something to keep in mind, every BB shot out of your gun will get straight out to X distance before the velocity drops off and the hop up takes over creating lift. The lighter the BB, the sooner that point arrives (due to the light wieght not having enough mass to carry energy through air resistance). The heavier the BB is, the farther it'll carry before the hop up takes over from the velocity. Kinda hard to explain, but there is a sweet spot that you can picture, where the backspin overcomes the velocity and carries on for a while.
As far as 0.29g BBs go, yes, they are kinda light, especially for 500fps guns, but if the hop up is set right, you can get an easy 200ft out of it in mild wind before the BB drops off. But, at least the 0.29g SGM BBs are so consistantly made that they will do pretty much the same thing every time, where as Digicon/Straight BBs won't (due to the way they are manufactured.) I spent all last year ripping off 0.30g and 0.36g BBs (and some 0.43g) and got fed up with watching them go this way, that way and the other way. Some were at 9" pie tins at 100% (my KSC Glock 19 can do the same on those pie tins at that range using 0.30g BBs, but that's forgivable, IT'S A GBB!!!
), BBs would fly off to one side or the other, or go a bit high or hit. In December I bought a couple boxes of what I call "Match Grade Ammo", 0.29g SGM, and at longer ranges find it's consistant as, well, Special K. Will get some more games in this year, all of them using the SGM ammo, and get back on just how much better my CA M24 (and my KJW M700) is using them.
In the end, you want to make your sniper rifle as consistant as possible. Everyone does what they can to acheive that consistancy, but some think "Pfft, 0.29g SGM ammo, 500 per box and the same price as 1000 Straight 0.XXg BBs? Ya right, I'm sticking with the cheaper ones and will just make my rifle consistant!" Trust me, the road of fine tuning is long and frustrating enough as it is, spend the extra cash on quality ammo, save yourself the hassle. If it takes you 3-4 BBs made by Straight to hit your target, it might have taken you 1-2 shots using the SGM. There's your savings in the long run. At least you are in the US, it won't cost you $25 per 500 rounds of SGM. Unlike me up here. Hehe
BTw, have you floated your barrel yet? And have you done anything with the striker spring adjustment yet? Do both, the gun should settle in. First few months, my KJW M700 would shoot CD sized groups at 30ft. After a lot of shooting for fun, the groups went down to 10 shot dime sized groups at 30ft. Dry swab your inner barrel every couple mags (mine will group larger, dry patch down the barrel with the rod, it's back to shooting tight), use VERY little oil in your mags (oil sprays into the chamber, makes the hop up a bit slippery and doesn't work right) and keep gas in your mags all the time, not full, but some.
Sorry, mind wandered and took my fingers with it, I wrote a novel! (Ya, some will say, same old, same old.)