To test the forward assist after assembling it, you can load a dummy round into the chamber, then push the forward assist to ensure it can fully engage the bolt. Cycle the charging handle, then push the forward assist again to verify that it remains engaged. Repeat this process a few times to ensure the forward assist functions smoothly and effectively.
Their is no NATO M4. NATO countries that use the M4 either contract the purchase or license the production.
The ar-15 uses this. you can't push the bolt forward manually, it goes forward with spring pressure. So, if it's dirty or doesn't close properly, they have an external "forward assist" that will bump it forward when you hit it.
The forward assist on an AR-15/M-16 style rifle forces the bolt forward. When you push the forward assist, it pushes against notches in the bolt carrier, which force the bolt to move forward and lock into the barrel extension even harder than it already is. It's used to silently close the bolt securely, and to make sure the bolt is in battery.
The M-16 Carbine or M4 use a 5.56x45 Nato round or the civilian version .223 Remington
Yes, although, personally, I'd think it a waste to replace an upper just for one with a forward assist.
Use the A4 or the M4
No
M4
SOPMOD is a kit issued to customise m4's for special operations, and more recently regular infantry use. It contains an array of attachments including IR laser pointers, silencers, ACOGs and reflex sights. Special operations use the M4A1 variant which is virtually the same as the regular M4 but has the ability to fire fully automatic.
Depends on intended use.
It depends on what sport you are talking about.