What you are talking about is the USMC M Series of sniper rifles, which started off as a Parkerized, wood stocked Remington 0, .8
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The quickest way to learn and
answer your question is by enrolling in an auto technology school, school, or sometimes called Vo-Tech school. The administration office people should be able to answer your questions and give you an idea of their recommended courses for your quest. If you have day job, they may offer night classes for the DIY maintenance and some type repairs so you get an idea of the tools you'll need to accomplish. For an adult starting at ground zero like you indicate, it may be overwhelming for awhile to fully grasp and comprehend the rapidly advancing technologies. So maybe first you should answer if you already know how to replace a burned out light bulb before going to a school for advice. If you always go to gas stations that have attendants to fill your tank, probably not your cup of tea.