I finally realized that it might be a good idea to mount a scope on my AR. Unfortunately I have an A2 upper that doesn't have a rail. How simple of a task is it to swap out the upper receiver (with the same barrel, of course)? I understand that I'll need a vice, a grip for the upper (to hold it in the vice), the proper barrel nut wrench, and guages to recheck the headspace after everything is complete. I also know how to add a FF tube. With this in mind, would swapping uppers be a big deal?

Quoted: I finally realized that it might be a good idea to mount a scope on my AR. Unfortunately I have an A2 upper that doesn't have a rail. How simple of a task is it to swap out the upper receiver (with the same barrel, of course)? I understand that I'll need a vice, a grip for the upper (to hold it in the vice), the proper barrel nut wrench, and guages to recheck the headspace after everything is complete. I also know how to add a FF tube. With this in mind, would swapping uppers be a big deal?

Everything you need to know is tacked at the top of this forum.

You dont *need* headspace gauges... you are using the same barrel, and headspace is no altered by changing the upper receiver.

Not a big deal.  Sounds like you have a handle on it.

I've been told by one gunsmith that my headspace needs to be rechecked anyway if I add a float tube. Given that the bolt matches up with the lugs in the barrel, and the bolt + barrel are the same, I wondered why I'd need to do this. Is it because of the fact that the distance between the bolt and the barrel, after the bolt is forward, could change?

This has always been a point I've misunderstood, and I don't want to screw it up.

Yes it's easy. You don't need to worry about headspace.  You're using the same bolt and barrel extention so nothing is changing that would affect headspace.

I did this same thing last week. It was the first work I'd done on my AR.  It was not hard.  

I have a barrel vise so I used that to remove the barrel.  After rebarreling a few 60+ year old mausers removing the AR barrel was extremely easy.

The hardest part was removing the gas tube.  I the vise grips I was using kept slipping. Once I switched to a different pair it came right out.

I put a free float tube on mine so I had to remove the front sight.  It was a bit tricky pounding out the pins that hold the front sight block. Once I got the barrel supported in a way that would keep it from rolling to the side when I hammered the punch it worked fine.

You'll need an armorers 's wrench and a barrel vise or an action block.  I used a cheater bar (a 3 foot piece of pipe) but I could have done without it.

Quoted: I've been told by one gunsmith that my headspace needs to be rechecked anyway if I add a float tube. Given that the bolt matches up with the lugs in the barrel, and the bolt + barrel are the same, I wondered why I'd need to do this. Is it because of the fact that the distance between the bolt and the barrel, after the bolt is forward, could change? This has always been a point I've misunderstood, and I don't want to screw it up.

Sounds like a gunsmith.  They will always say to check it.....

However, you are correct.  With the same bolt and barrel... headspace does not change.  No matter what.  (except for wear over time.... but we are talking remove/replace)

Lets just say you swap receviers, and something is WAY outa spec on the new receiver.  Guess what?  Your bolt wont lock.  If it wont lock, it wont fire.  If it locks, your headspace is exactly the same as it was before.  Absolutely no need in this case.  You didnt change anything.

Quoted: You'll need an armorers 's wrench and a barrel vise or an action block.  I used a cheater bar (a 3 foot piece of pipe) but I could have done without it.

Get an action block to remove barrel nuts.  Using a barrel vise puts all the torque on the tiny barrel extension lug, and the upper receiver slot.  Good way to end up with a canted front sight.

Lets just say you swap receviers, and something is WAY outa spec on the new receiver. Guess what? Your bolt wont lock. If it wont lock, it wont fire. If it locks, your headspace is exactly the same as it was before. Absolutely no need in this case. You didnt change anything.

Heh. Good point. Thanks for your advice.

The front sight base is different on an A3, and you can't easily switch Front sight bases.

You need an F stamped Sight base for the proper zeroability.  you're better off buying a complete upper, Son.

Quoted: The front sight base is different on an A3, and you can't easily switch Front sight bases. You need an F stamped Sight base for the proper zeroability.  you're better off buying a complete upper, Son.

WTF?  Who is talking about changing out FSB's?

Quoted: Quoted: The front sight base is different on an A3, and you can't easily switch Front sight bases. You need an F stamped Sight base for the proper zeroability.  you're better off buying a complete upper, Son. WTF?  Who is talking about changing out FSB's?

If you change the upper receiver from A2 to A3, and want the use of the carry handle peep sight, you need the F stamped Front sight base.  

The Front sight bases are different on A3's.  If you happen to have one, you might find an F stamped on the left side.  I don't know the exact height difference, but I'm anal about details and want 100% compatibility on my guns.

If he isn't using Irons anymore then it's not an issue.

Quoted: Quoted: Quoted: The front sight base is different on an A3, and you can't easily switch Front sight bases. You need an F stamped Sight base for the proper zeroability.  you're better off buying a complete upper, Son. WTF?  Who is talking about changing out FSB's? If you change the upper receiver from A2 to A3, and want the use of the carry handle peep sight, you need the F stamped Front sight base.   The Front sight bases are different on A3's.  If you happen to have one, you might find an F stamped on the left side. If he isn't using Irons anymore then it's not an issue.

Pretty sure thats only true for Colts.

I order Bushmaster barrels all the time for rifles, put them on A3's with carry handles/BUIS, and A2's, and have never had an issue, like you speak of.

Quoted: Pretty sure thats only true for Colts.

Could be.

If you do run into that issue you can get an extended front sight post from Bushmaster.  Hell of allot easier than replacing the whole sight base.

Sight post

CD

if the post is steel, i can see no reason why you cant braze a brass bead on the end and file to fit. it would be better to see with the peep sight.

You know, I get a lot of mileage out of my current A2, and it's got a lot of mileage left to go thus far. I guess I'll just wait until my next rifle to get an ACOG/A3 setup. I'll just assemble it myself :)

I've been told by one gunsmith that my headspace needs to be rechecked anyway if I add a float tube. Given that the bolt matches up with the lugs in the barrel, and the bolt + barrel are the same, I wondered why I'd need to do this.

Because this "gunsmith" does not understand the AR-15 design.  Adding a float tube, changing receivers, changing bolt carriers (not the bolt, just carrier), none of these have any effect on headspace.

Quoted: if the post is steel, i can see no reason why you cant braze a brass bead on the end and file to fit. it would be better to see with the peep sight.

Or maybe just replace the rear app with a notch!