Since you'll be baking the highpoly on to the lowpoly you can certainly remove such details as Grooves or other Concave surfaces. You can also remove the vertical Beveled Lines of the magazine as they contribute very little to the Silhouette of the magazine, and once again, it's sufficient that your highpoly has this for baking purposes. See attachment-1.
Tip: What I usually do to save time on optimizing an object is... I model the low poly first with all quads, but those details that I know are going to be on the highpoly but not on the lowpoly, I will add those details using an extra EDIT POLY MODIFIER.
eg, My low poly magazine will be mostly flat on the sides with no Grooves and Ridges, but I will add an edit poly modifier on top and bevel or extrude the grooves on the modifier. Further more, I add another edit poly modifier and on this I add all the support loops/edges that the TURBO SMOOTH modifier needs. When done, I make a copy and name it Magazine_high for highpoly and Magazine_low for low poly. This way whenever you want to optimize and go back to your lowpoly, you can simply remove the Turbosmooth, and the Edit poly modifiers. Of course I will also further optimize the Lowpoly to avoid wastage.
If you need, I can attach my AK-47 max file here so that you can study the difference between both Highpoly and Lowpoly and get an idea of how it's optimized. A rule of thumb is to have close matching silhouette for both the HP and LP. So you can remove subtle details that can be achieved by Normal maps from the HP.
