Re: AR15 carbine buffer parts?
Don't cause yourself extra headaches when you're building your first AR. Get all standard milspec parts to start with (which doesn't necessarily include the buffer tube). Make sure the gun works in the standard configuration before you start f-ing with it.
In terms of getting a fancy stock at first--spend that $100 on 300 rounds of ammo and one more day at the range. Seriously. Spend your money on practice and training. That is what makes you useful to yourself and your family--not whether you have a standard stock or a fancier one.
As for milspec vs commercial buffer tubes, the milspecs are smaller in diameter and a bit stronger. If you can get one, great, but there is no difference in how they actually work in real life. It is really hard to bend a buffer tube. Just make sure to match your buffer tube dia to your stock.
In terms of buffer and spring--some guns don't run well with all ammos when using heavy buffers and or springs. Most of your cheap practice ammo, like Wolf and brown bear, is loaded way weaker than your 5.56 spec ammo. It might not cycle that gun with the heavy buffer and heavy spring. I like my gun to run with everything. Of course, I'd rather practice 30% more for the same money and use cheaper ammo sometimes, but more importantly if SHTF, do you really want to be worrying that your gun only works with 3 brands of ammo? No. You want your rifle to work with everything--whether you bought that sweet Black Hills shit, or whether you're using someone else's junk Wolf ammo. Your rifle is useless if it doesn't fire each time you pull the trigger.
You can always spend ten bucks and get an H-buffer later, or a heavier spring later, if you want. I use them, but only once I know a gun runs fine stock, and with the different types of ammo I want it to.
