AR15 remove semi-automatic system

[Not_A_Llama]

This has been done before - you will gain a little velocity, which will help with inaccurate distance measurements, but there is not really a gain in mechanical accuracy. You will also have the bolt rifle shooter's problem of breaking position to cycle the gun (I can hear the groaning already from the bolt gun cultists).

You should also know that it can be more difficult to cycle the action manually than you might imagine.

The easiest way is to get an adjustable gas block, and turn it off. Pretty much all semi-auto guns need gas tuning anyway, so this is a good investment. I recommend only the Superlative Arms gas block.
A side-charging upper will make this much easier. The gun becomes a straight-pull bolt action.
You could use a setscrew in the gas port or the front sight base to block gas.
You can also look at the pump action and straight-pull rifles from Troy.