An alternative to manual guns and the pneumatic ones, are electric battery units. I have the Ryobi model pictured below and I bought it to caulk 19 replacement windows in my home. Each window required 3 complete caulkings plus the caulk to set the window. I went through about 30 tubes of caulk.
I was invested in the Ryobi 18V series of power tools so this choice was easy for me. Other manufacturers also offer battery caulking guns.
The Ryobi gun, and I imagine others, offer a speed control separate from the trigger and an automatic speed "bump" to get the caulk started. Without the effort to squeeze a handle at a uniform rate, it is easy to concentrate on the travel speed of the gun to apply a uniform size of bead. I bought this figuring that after my window job I could just eBay it, but it was so useful I decided to keep it. That was a good decision- I have used it many times.
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