So... Framing nailers...... someone want to educate me on the significance of 21° Angle versus a 28° Angle?
Unlike what was stated above, I must point out that there is a big difference in the angle, and it is not just the angle that the gun fits in (which is the least important difference).
The angle is determined by how the nails are stacked in the strip.
In 28° nails, the shanks of the nails are all next to each other in the strip. In order to allow one nail shank to lie next to the next, they originally clipped the heads of the nails to a "D" shape. That had code compliance issues, so you can now get nails with offset heads, that still have an "O" shaped head, but work in the clipped head style nailers.
This arrangement just happens to stack at 28°. They can be held together with wires, or paper tape. Some nailers prefer wires. Some prefer the paper. Get the one that your nailer is supposed to use.
In 21° nailers, the head of one nail butts up against the shank of the next. Plastic spacer strips keep the shanks apart to make this arrangement work.
These always use full round head nails, with centered heads. I find that I get hit a lot with chunks of plastic, so with my new nail gun, I find that I tend to turn my head as I pull the trigger. This is something I never did with my paper collated nails.