units on density in FEMAP

[jargon5]

Does anyone know how to reconcile the units on density when using FEMAP and using lbf, inches, secs as the base units (this allows for psi to be inputed for stresses)? The Nastran Techs say to divide by the density, which is in units of lbf/in^3 by 386.4 (converting ft and gravity), yet when I do this the units of my hand calcs don't work out. Let me explain:
-I have density in the form of:lbf/in^3
-And I want to get density in the form of: lbm/in^3 (avoiding slug units since I don't have slugs in my pressure units)
-In other words, I have Force/Volume, and I want Mass/Volume.
-Using F = ma, I recognize that I need to divide by acceleration, or gravity, to get the mass. Yet, the units don't work. Below is the breakdown:

1) I first divide density by gravity of 32.2 ft/s^2. Now, I have units of (lbf*sec^2)/(32.2*ft*in^3)
2)I recognize that I need to covert the feet to inches so I divide by 12. My units are now: (lbf*sec^2)/(386.4*in^4)
3) I recognize that 1 slug =(1bf*sec^2)/ft
4) Also, 1 lbf = 32.2 lbm*ft/s^2

Yet, by using either 3) or 4), I don't end up with lbm/in^3. Have I missed something here? This is pretty basic units conversion, so I must have missed something. I have run tests on small coupons to verify that the 386.4 is the right conversion number, and it checks out.

 

[jargon5]

The answer to this question can be found at the comparison icon on NE/Nastran's website. You need to login first, and then go to support-knowledge-comparison-effects of wtmass parameter.

The end all conclusion is not to divide by 386.34 in the density value input, but to change the wtmass parameter by 386.4 for dynamic data. This explains why my units for the density were not working out. Nonetheless, it is essentially the same result.