I've been researching pistols with the intention of buying my first, I'm almost positive that what I want is a XDm model in the .40. However I primarily want to use and fire 9mm ammo. The .40 will be there mainly for: - fun (mixing up the ammo types) - so I can have a good pile of reasonably powerful ammunition without investing in large amounts of premium 9mm ammo - in case my tastes change or I feel I need the extra weight and force of the .40 - so I can take advantage of sales or price drops due to some massive surplus for either type of ammo as they come about. I intend on keeping this gun for a long time and I'm a young man so I imagine over I'll make a good chunk of this investment back. But, again, I do plan on making this a primarily 9mm handgun. So as someone new to all this, I was wondering if I could have some feedback on: 1. Is it reasonable to buy a .40 with the intention of using a changed-out barrel for most of its life? Besides gun dimensions/weight and the extra cost of equipment is there any possible disadvantage in using the .40 frame to primarily shoot 9mm rounds over just getting the 9mm frame? 2. The barrels I'm looking at (from Storm Lake barrels) have some options: -Extra length: does the stock holster accommodate the extra length of the barrel? Seems nice for a bit of extra power/accuracy. . .thoughts? Also this is a pre-requisite for: -Ported barrels: Do they have a use beyond cosmetics? What are they all about? -Threading. Silencers are illegal in my state, but in the event I moved or. . .something. . .as long as I'm getting an extra barrel this extra features seems like a "why not". . .sure straight up they're a little ugly but with the "thread protectors" available it seems they'd look pretty sharp. Anything further to note? 3. I've heard talk of setting the spring to 18. . .or something. I'm still not very gun-savvy what does this mean? Does it require another part, a separate spring component? If so is that easy to acquire/install? 4. Other thoughts? Thanks for any help!