Here are the four 7 shot cylinders I have purchased so far, all dialed in and functional.
1) This one is from Custom3Dnerf on Ebay - overall this is my favorite cylinder. The only thing I had to do to get it to work was sand down the outer diameter of the cylinder - it rubbed slightly on the body, causing issues with rotation. It has full length barrels - and the barrels are very tight fitting. This is something I prefer for performance upgrades - the darts really pop out of the cylinder. If you leave your ARs intact, this is the cylinder for you. I installed this in the "ULTIMATE" NERF Hammershot mod I am selling. Note that the full length barrels mean you can't use Whistlers, old (large head) suction darts or Dart Tag darts - not that this is a real loss at all.
2) This one was from Etsy - it has multiple rotation issues and took the most work to get it to function properly; short drive sprocket, drive sprocket opening too large, drive sprocket “stop” is located too far back, the cylinder doesn’t fit tightly, front piece floats freely, adding to loose fit. Cylinder was too large and rubbed against body. I gave the guy feedback and he said he was going to improve it. I sanded it down, filed the drive teeth, added material to the inside of the drive sprocket, added a solid spacer inside to keep the front piece from floating - and then finally swapped the entire drive sprocket from another cylinder. It works great now after a bunch of work - but I wouldn’t recommend it to anyone in it’s current design. This cylinder does allow use of intact AR.
3) This is the Chinese cylinder from Ebay that runs for 28 bucks. As mentioned briefly before - the barrels are a bit loose, requiring “newer” darts for a good fit. I had to sand down the rear edges of the barrel openings - they would catch on the foam gasket and eventually pulled it off completely. After sanding these edges down it works great. As stated in the ad - if you rotate the cylinder when primed, you’ll break the teeth on the drive sprocket. (Realistically, who does that anyway? I have never rotated a primed cylinder, so I am not too worried about it) This cylinder allows use of intact AR.
4) This is the latest one from OutofDarts on Etsy - probably the highest overall quality of all cylinders. This is the only cylinder so far that is truly “drag and drop” with no work required. Reinforced drive sprocket allows rotation when primed - the flattest rear cylinder surface of all cylinders so far – and BEVELED rear openings on the barrels themselves, eliminating the foam gasket issue. This cylinder does require AR removal – it simply won’t work with the AR intact. This is due to the completely open rear barrel opening - which gives full air flow for removed ARs. If this cylinder allowed use with AR it would be my favorite. If you prefer to remove your AR, this is the cylinder for you. (I use this one in my Sweet Revenge)
Lastly - if you do want to leave your AR intact on the cylinders that allow it, be sure to bend the AR tab upward as depicted below. This is required so that the tab does not slip into the dead space (hole) in the middle of each dart. If you don’t bend this tab up, every once in a while when firing you’ll get a misfire or "weak fire" due to the AR tab not being depressed.
The misfires using an AR happen for two reasons -- first, the original (stock) Hammershot cylinder has the posts and support intact - so that the AR tab can never slip into the dead space in each dart. Secondly, on all 7 shot Hammershot cylinders the barrels themselves are spaced slightly farther out than the original 5 barrels, in order to fit all 7 -- this means that the AR tab is actually positioned closer to the dead space center (hole) in each dart, and more likely to slip into that space or not be fully depressed.