A bit about using the pneumatic guns.... Fresh mixed sealant will flow much quicker than you think, based on the tip's opening...
A small hole won't flow a lot, but lets you have finer control over placement. A large hole will flow lots more sealant, but can get messy quickly. As work time nears it's limit, the sealant won't flow as well, and may require you to open the tip up a little more.
For doing fillets along seams, cut the tip at about a 45 degree angle, and flow the sealant as you push the tip along the seam. It will fill the gaps way better and can result in less mess and cleanup. Where you can't push, you can pull, but you may have to work the sealant in with a small, smooth tool, or with your fingertip wetted with some lightly soapy water.
For cap sealing fasteners, a 90 degree cut generally works the best. It takes some practice to get it down to a quick and clean application.
A shop trick on using the longer nozzles, ( 6" or so), is if you need to work some weird angles, before you fill them with sealant, you can use some heat from a lighter or decent heat gun to soften them and bend them as necessary.
If you want a sharp line to run the sealant edge to, a quality masking tape works well, just allow the sealant to set up for a few minutes before you start pulling the tape. Pull it away from the wet sealant at either vertical from the surface, or fold it back on itself and pull at an angle....like you would with taping an edge for paint.
Last thing is wear clothes you aren't afraid of ruining. No matter how careful you are, at some point you will get some on you and your clothes. It will clean off off of you, but forget trying to get it completely out of your clothes.
Don't forget that you can get sealants in various work lives, so that's a way to help cut the costs. Plan for enough work with the life you select and the volume to mix and that way you can minimize waste.
Almost forgot....Let off the trigger a bit before you want the sealant to stop flowing....It doesn't quit instantly!!!!!!