quicksilver500

It'd be worth ditching 2.49b and going with the latest blender with Niftools available, I'm using version 3.2.2 right now and I can tell you it's one hell of an upgrade. The meshes 3.2.2 exports are a lot more performance friendly as well. Not only that but there are no issues on my end importing any vanilla weapon meshes. Other than that, the error message here can tell you a lot about what is causing the import error. There are certain properties and nifblocks that Blender can't import, no matter what version you're using. I'm not sure if there's a workaround for this as I'm not familiar with what's going on on a fundamental level, but I've found that blender has issues with Billboard nodes (as in your case) and nitristrips or shapes that have the NoLighting shader. Deleting blocks that have these properties from the source nif before you import them is the best option, as long as you're not trying to edit those blocks specifically. Thankfully these properties are usually only found on special effects applied to meshes, in your case the bilboard node is for the electrical effects inside the barrel of the Tesla Cannon. If you don't want to edit this part of the weapon you're in luck, you can simply delete it out of the base nif and import easy peasy. If you do want to edit this part of the mesh it's probably easiest to simply do it in Nifskope my scaling the vertices using the Transform function, more in depth editing than that will be more difficult unless you upgrade to a newer version of Blender and Niftools.

I'm no expert either, but I'm pretty sure you're not supposed to hold a pump action shotgun with the pump, as doing so will cause the recoil of the weapon to re-chamber it, which can be dangerous. Idk, but regardless, if you want to change it it should be easy enough to go into the G.E.C.K. and change the Handgrip option to something that is a little further down the stock. Hope that helps.

Solid Project has Sprint with a variable speed and AP reduction: https://www.nexusmods.com/newvegas/mods/63239/

Sounds good man, why don't you download the G.E.C.K. and give it a shot?