I know nothing about putting handguards on an AR, but would it be possible to fit a Troy TRX handguard on a Spikes ST-15? The thing that i am unsure of is how to get it past the front sight post? Sorry if this is a stupid question, thanks in advance for your knowledge.

You have quite a few options.  



1.  (easiest).  Buy a drop in battlerail.  These are non free floating, but easy to install.  

2. Remove FSB, install free float rail, reinstall FSB.  The 7.2 inch version should be the right length.  I would imagine you just have some taper pins to remove on the FSB.  Its a bit of a pain, but certainly not impossible.  Then you have to reattach the FSB.



3.  (If you want a longer rail).  You can cut the ears of the FSB, and turn it into a low profile gas block.  Then you are free to get a rail any length you want.

Do you think someone with no AR experience could remove the FSB and reinstall it properly? Also, what method would you recommend for cutting the ears off? Hacksaw?

Unless you have an overwhelming need for a free-float rail, you should consider this (http://www.bravocompanyusa.com/Troy-Ind-Tactical-Free-Float-Mid-Length-p/troy%20mrf%20di%209.htm).  Easy & not expensive.

http://troyind.com/%20/battlerails/troy-battlerail-trx-extreme-m7-7-6

This is the one i want.

The rail you listed above is too long.  You need a 7.2 inch handguard assuming a carbine length gas system.





To remove the FSB, you would need a plastic block to support the FSB, and give the pins a good whack with a hammer and punch.


Also, the barrel nut for the TRX is different than a standard nut.  So you need a vice, upper vice block, torque wrench, and a AR wrench to remove the barrel nut.  Then you have to install your Troy barrel nut, but they are kind enough to give you a wrench when you buy the rail.





Then you still need to reinstall everything.  Its not difficult, but you would need to have a few tools.
If you did want to cut the ears of the FSB, a dremmel would be your best option, but you still have to swap barrel nuts.





In short, unless you really really want free floating, go with the drop in option.



I personally went with a different option.  I built a second AR, so I could have one with a TRX rail.  No disassembly required!