Um...sorry to bother everyone again......
Picked up a new gas tube for my AR (after getting the old front sight removed), and I'm ready to install it, but I'm running into two problems
1. The gas tube is an absolute pain in the ass to get in to the front sight block. it goes in a little bit then pretty much freezes solid. I even tried using a good lubricant on the end of the tube to try and get it to slide in, and it didn't do a thing. I'm sure I could eventually tap the thing in, but if it was misaligned the slightest bit w/ regards to the pin hole, there'd be no way in hell I'd be able to rotate the tube around, and it'd be even more of a beast to get the tube back out. Anyone have any tips/tricks on how to do this?
2. The rear of the tube is very rough when inserted into the carrier key. It'll go in, but never smoothly and sometimes it catches. Is it ok to just sand it down a touch?
While no gun-smith, here's my take on your problem.
First, who made the gas-tube? There are tons of junk AR15 parts out there which don't conform to mil-spec requirements. You should insist on using mil-spec parts, IMO. (best not to purchase parts based on the price or which is cheapest, but more so on the reputation of the seller, stick with those that require compliance w/ mil-spec standards, Bushmaster parts for example or Colt)
Second, it is okay to use the proper sized drill bit to ream the gas block by hand preferably (to which the point above also applys) out to the proper dimension, not to enlarge it, but ream it to remove burrs.
These same principles should apply to the gas-key which the tube fits into, reaming to remove burrs using the proper drill bit (done by hand again) or sanding the tube as you mention.
Stick with quality parts, if yours are then I'd say your on the right path and not out of line with your proposed mods.
added: while the gas-tube should not be loose, it should be able to be positioned using small pliers or vise grips, without damaging the tube (by having to grip the tube too tightly)
I just installed a new barrel and gas tube, had similar problem with the gas tube.
Gas tube would not go far enough into the FSB. I lightly reamed the FSB hole with an undersized drill bit; felt like it was removing rough spots rather than enlarging the hole. This helped, but for the final 1/16th inch I (very lightly) tapped the gas tube in from the other end using a wooden dowel and a hammer. Roll pin hole lined up fine.
SUCCESS!!!!! Reamed out the FSB and the carrier key, did a very light sanding job on the ends of the gas tube (maybe 10 seconds each side), and it went in. Popped on the PRI flip up, installed the RASII, and now she's ready for testing! Thanks for the advice guys, it really helped