DirectX: Rotating my mesh with first person camera

[TomTheFox]

Hey guys, I really need some expertise here. I'm developing a game engine in DirectX and all is going smoothly -- however, what may seem like a very simple problem I just cannot for the life of me find out. My engine imports .X mesh's and is able to place them anywhere on the map, rotate them, scale them, etc, with a CMeshInstance and CWorldTransform class. My engine renders BSP tree maps with collision detection/gravity/physics and the like, and I can place objects anywhere, and when the player runs over them he/she can collect them/use them. In this instance, the player picks up an AK47. Now, obviously I'd like to display that AK47.
Screenshot: https://drive.google.com/open?id=189hiJJKe8UXu0Q-a2gxilmtQG-0uzGE9

Problem is, I cannot for the life of me figure out how to keep the rifle aimed relative to the player's direction (vCamDir). If I turn to the right, i'll stare right into the gun or beyond it. I don't really have a camera class for the BSP scene, I simply use input from the mouse to determine Pitch/Yaw/Roll with

D3DXMatrixRotationYawPitchRoll(&matRot,
0,
D3DXToRadian(g_fSpinY),
-D3DXToRadian(g_fSpinX)); /*But this won't work with the mesh, but creates a perfect first person camera for the BSP scene*/

My Meshes are loaded as follows:

m_pMeshes[2].SetXPosition(vGunPos.x);
m_pMeshes[2].SetYPosition(vGunPos.y);
m_pMeshes[2].SetZPosition(vGunPos.z);
//....
m_pMeshes[2].Render(); //Render AK47

I can use m_pMeshes[2].RotateX(), RotateY(), RotateRel(), etc, but I simply cannot find a relationship between my mouse spin variables (which are determined by dx and dy vars from obtaining the mouse coords).

How can I keep the mesh/rifle rotating with the player? I have a D3DXVERTEX3 for the players direction, a vertex for position, etc, but I just don't know what math I should use to achieve this. And I am *not* using sprites with alpha blending to *pretend* there's a rifle in the bottom screen :P I want to use a real mesh.

The rifle's mesh rotation is handled by the following function:
m_pMeshes[2].RotateAbs(vGunRotate.x, vGunRotate.y, vGunRotate.z);

I mean I even wrote a function to mimic how I'm viewing my BSP scene just to get *some* kind of handle on the rifle's rotation/axis(obviously this is not used in conjunction with any other rotation function):
m_pMeshes[2].YawPitchRoll(
0, // Yaw around the y-axis, in radians
-D3DXToRadian(g_fSpinY*10), // Pitch around the x-axis, in radians
D3DXToRadian(g_fSpinX*10)); // Roll around the z-axis, in radians)

But to no avail. I move the mouse and the rifle spins out of control having a seizure.
Here is a screenshot of when I move the player via the mouse just a tad: https://drive.google.com/open?id=1o-YJ4YTeO5KqCAxkYtZ_T2hil4UynVdm
(I changed the FVF format for the texture coordinates so you could see better in this particular screenshot, irrelevant to the problem)

ANY help would be appreciated. And I thought this would be easy. I need you seasoned pro's on this one. Thanks!

[mbozzi]

To me, the screenshots hint that you're using the wrong coordinate basis for the rotation.