[TheWho]

No problems when:
Setting default model then changing to custom arms.

This doesn't work:
Setting default model then changing to custom arms then changing to custom model.
In this case the arms will overlap again.

nvm, you snippet works without overlapping

Important note:
You have to have a game_player_equip with atleast one weapon eg.: weapon_knife to make it work.
That's why franc thought he fixed it, in some map this entity isn't implemented.
We have two options, whether to spawn the player a weapon and remove it or loop for game_player_equip and remove the ent and recreate it with a weapon.

And I'm not using a timer, I use 20 delayed frames.
Shout out to KissLick's stock:

PHP Code:

stock RequestFrame2(RequestFrameCallback:func, framesAhead = 1, any:data = 0)
{
    if (framesAhead < 1)
        return;

    if (framesAhead == 1) {
        RequestFrame(func, data);
    } else {
        new Handle:pack = CreateDataPack();
#if SOURCEMOD_V_MAJOR >= 1 && SOURCEMOD_V_MINOR >= 7
        WritePackFunction(pack, func);
#else
        WritePackCell(pack, func);
#endif
        WritePackCell(pack, framesAhead);
        WritePackCell(pack, data);

        RequestFrame(RequestFrame2_CallBack, pack);
    }
}

public RequestFrame2_CallBack(any:pack)
{
    ResetPack(Handle:pack);
#if SOURCEMOD_V_MAJOR >= 1 && SOURCEMOD_V_MINOR >= 7
    new RequestFrameCallback:func = RequestFrameCallback:ReadPackFunction(Handle:pack);
#else
    new RequestFrameCallback:func = RequestFrameCallback:ReadPackCell(Handle:pack);
#endif
    new framesAhead = ReadPackCell(Handle:pack) - 1;
    new data = ReadPackCell(Handle:pack);
    CloseHandle(Handle:pack);

    RequestFrame2(func, framesAhead, data);
}