Yes, the factory A-Bolt trigger is adjustable, to a point. With my spring RCBS trigger gauge my A-Bolt triggers usually bottomed right above 4 lbs at the lowest setting. The 'Medium' Timney spring brings it down to 3 lbs or less. It also should be adjustable within a lower range too. I haven't adjusted a bunch once I put them in.
The factory A-Bolt trigger is not bad, as far as factory triggers go. That extra 1-1.5 lbs is noticeable though. If you buy the Timney spring 'kit', you get the medium and light spring. I use the lighter spring for my 'varmint' A-Bolts, or you could sell it. It's a relatively low cost & easy to do improvement.