Halo 1 Pistol replace Brute PR help

[StalkerUKCG]

So im making a zanzibar mod were the brute PR is replaced by the halo 1 magnum (tombstone still legal) so iv replaced the model and the projectile but iv got a few problems

When shooting theres a shot with sound (pistol sound) then a muted sound.

The ammo counter at the top constantly has 4 shots bullets and 0 ammo (basically i need help with a HUD fix)

Iv added a 2x zoom but theres no "zoom HUD"

Id like to fix the power of the shots(3 shot kill) and correct the timing between each shot

A full tutorial would be appreciated and help alot of people ( i imagine) if anyone has the time

Also what steps would i take to replace the Sentinel beam with a Assault Rifle

IS it possible to add new weapons to maps or just edit existing ones ?