Yes i experienced all same as menehir talked of. But nevertheless not bad.
But to be honest i find the HUD not so good . the original or even the carbonite HUD is better . the health bar restricts the vision. But the weapons work good.
Myself ive noticed mod weapons seem to work good in SP but in MP theyre buggy.
I think the answer for MP is to make the dc15 pistol the default 0 wep u spawn with and your mod weapon the secondary wep then when u switch wep the hud arms work good.