Well I ordered a short FF RAS and it's on its way. I have looked at the instructions for installation shown here:
www.knightarmco.com/faq.htm The pdf file given in the link doesn't have any text and doesn't really go into any detail. From looking at the instructions though, I think I have a pretty good idea on the basics of what I need to do, but would like some additional insight from anyone who has experience with installing one of these handguards.
I should mention that I am already half the way there. I have already removed the front sight base and the barrel. I was a bit anxious about getting the front sight base off, but it actually went fairly smooth. I kept the gas tube attached to the FSB since the instructions show that they need to be attached when the FSB is reinstalled. Had one person hold the barrel with the front sight resting on a rubber mallet head and used a 3/8" brass punch to knock the taper pins loose. Took about 5 good whacks on each pin, but they came out and the ends didn't get mushroomed so I should be able to reuse the pins. Have read using a steel punch can deform the pins as well as leave pretty good gouges on the FSB, so I am pretty glad I bought the brass punch.
Actually, I was really surprised this step of the process went as easy as it did, have read multiple horror stories on this site on getting those pins to move. This was a Colt barrel though, so maybe that did help some, have heard that on Bushmaster barrels the pins can be much more difficult to remove.
One thing I did notice is that the brass punch left some brass marks on the FSB and they have been somewhat difficult to remove, even with Barnes CR-10 copper cleaner. I think it would have been a good idea to have put a decent coat of CLP on the FSB beforehand so that any brass marks left on the FSB would have a layer of CLP underneath them to ease removal.
Once the pins were out, I had to tap on the FSB with a rubber mallet to initially free it from the barrel since it was press fitted on fairly decently. Then I just removed the barrel nut and the barrel and now I am currently waiting for the handguard to show up so I can install it.
So not that I am ready to install the new barrel nut, is there anything I should be aware of? Hopefully, the barrel nut will index well so I don't have to really torque it. I have an upper receiver vice block and improved barrel wrench on the way from Bushmaster. I also went ahead and forked over the cash for the moly-slide paste for the barrel threads, didn't cost that much and figure I may want to remove all this stuff down the road, which the paste should make easier to do. I am currently not planning on using a torque wrench, but I can get one from a friend if necessary. I figure I will just hand tighten the barrel nut and then use the wrench to index the nut to the next gas tube hole. Have read about installing the carrier and using a spare gas tube to help index the barrel nut.
Question 1: If indexing the nut does prove difficult and I have to really crank on it, is it ok to go over 80 ft-lb spec? I don't think I want to be down in the 30 ft-lb range since the use of a forward grip will add some torque to the handguards, and I have read that the handguard ring is tightened in the reverse direction to the barrel nut and may cause it to come loose.
Once the barrel nut is on and indexed, next comes installing the index pins, handguard, and handguard ring.
Question 2: Does the FSB/gas tube combo need to be installed before the handguard ring is tightened down? If so, is it just to make sure that the barrel nut does not come out of alignment with the gas tube hole in the receiver?
I have read that getting the top rail of the handguard perfectly inline with the upper receiver rail can be tricky. I was thinking of attaching my removable carry handle or ARMS #35QD mount to the both the receiver and handguard to keep them in line as I tighten down the handguard ring. Hopefully there will be enough clearance for the strap wrench to fit between, I guess I will see when I get the parts.
Question 3: If there is not enough clearance, are there any other tips anyone could provide to get the handguard and receiver perfectly aligned?
Question 4: Should I use the moly paste on the handguard threads? Any downsides to doing this?
At this point, the only thing left is to reinstall the taper pins.
Question 5: Is there any pitfalls I need to be aware of in getting the FSB back on and the pins back in? Before I removed the pins, I noticed that they stuck out about the same amount on each side, so I figure I will just pound on them until they are in that configuration.
Well that is about it, if anyone is still reading this long-winded post, I would really appreciate any guidance one could offer. Thanks.