This tool is the best way to prime, bar none. There just isn't another tool that does it as well, and effortlessly as this one. If you're not banging out 9mm, or 223, in massive quantities, then this is the tool you'll want to use. It's just a pleasure to prime with. That said, I do use it to prime 5.56, and some 9mm, before I turn to the progressive.If you have the Frankfort Arsenal Vibra Prime, or Hornady's new tube filler, then filling the tubes for the RCBS Auto Priming Toool is super fast too. No quite as fast as loading a hand primer tray, or Lee tray, but next best thing.If you've got a combo of new/tight primer pockets and hard primers, then this is also the tool you want to use.If you're new to reloading, then start with this tool. Why? Well you can prime on the press, but you'll have better feel and do it more effortlessly with this tool. I've got a single stage, a couple of turret presses, and a progressive press, and a couple of hand priming tools, and I use all of them to prime with for different brass/loads, but the I do the bulk of my priming with the RCBS Priming tool. It's just that good.**************************Some observations on use:It's best if this tool is level. If your bench isn't level, then you can level it with some shims. The reason it is best leveled is that gravity lets the ram move back down after the primer is inserted. If that ram is leaning to one side, it might catch the opening in the shell holder and hang up. So, leve the tool.Use a RCBS shell holder. Use any shell holder but give the shell holder opening a slight chamfer. That's the hole in the center of the shell holder and the chamfer should be on the opening as you look down into the shell holder. The reason for this is that you want the ram to drop down through the shell holder without hanging up, and sharp edges could make it hang up.You can modify for comfort, and convenience, by adding some cushioning or an extension. This will make the tool even more comfortable and effortless to use. I've tried several way, (bicycle cushion grips, soft tape, ...) but wound up using a schedule 40 pipe (the white ones at the hardware store, 1" I think, just look at the handle size) that extends the reach of the handle to where my hand wants to be. This way I can use the tool sitting down and have my arm resting on my chairs' arm rest, and I can push, mostly straight and down, to seat the primer. Ergonomics is important to me, as I sometimes prime 5.56 lots of 1,000+, to later load progressively. The excellent feel this priming tool gives, guaranteeing each primer seated properly, makes this extra step worthwhile. Plus this way I can charge powder, flare, check powder, seat the bullet and remove flare and not have a single speck of powder on the press when done. See picture.It's very easy to change from small to large primer rams, but it's also easy to put the wrong size ram when changing rams. So, if you're flipping primers, or the primers aren't inserting properly into the ram cup, then double check that you've got the correct size seater ram installed.