Brit,
If you don't know where to begin, then that's because you are trying to write it sentence by sentence, instead of building a "framework" first, and then filling it in.
When you build a house, you don't start at one corner, and then build a finished structure one foot at a time. You lay out a big rectangle, you build the foundation on that rectangle, and then you put up the frame walls to subdivide it into pieces. After you do this, you go back and finish the walls, room by room, by putting on the sheathing or drywall.
Layout for your book? Easy.
First Chapter: A Brief History of Parker Hale.
Second Chapter: Parket Hale's firsts modern Bolt Action Sporter: The Model "X"
Third Chapter: The Model "Y", successor to the Model "X".
Fourth Chapter: The Model "Z", successor to the Model "Y"
Etc.
I think you can see how this would work. Just draw up an outline of the chapters, going Model by Model. If there are submodels within the main models, then just divide the Chapters into subsections, based on the submodels.
A final chapter would be "Interesting and Odd Variants by Parker Hale."
Once your outline is laid out, you just start at the beginning, and fill it in. Limit the book to bolt action sporters only, or otherwise you will be overwhelmed and never get anything done. Once you write the bolt action book, you can always add a "Section 2", and cover (in the same manner) some other type of PH rifle.
All in all, pretty easy old Chap. Write in short and simple declaratory sentences, avoiding the passive tense whenever possible.
Personally, I think your posts have been very well written, and more than a few of them could have served as chapters of a book.
Guess I high-jacked this topic, but maybe it will lead to a nice book.
Best, Mannyrock