Came across a stripped A2 upper today...had to get it...

So I yanked the A2 upper off of my first AR back in the mid 90s because I wanted something more "modern". Now that I have built a few "modern" ARs, I've been wanting to build a KISS A2 and almost regret ever cannibalizing my first AR. I've actually been frequenting this A2 area for a while, just haven't posted yet. Well, today I came across an A2 upper locally for $50 so I had to buy it. The guy told me that he had pulled it off of a preban bushmaster. It has a "FK" mark so I think it is a FN make per another thread here. However, it also has a "NT" stamped above the front take down pin hole which I don't what it means. I have a question for the group...This upper does not have M4 feed ramps but I would imagine that the barrel I put on it will have the M4 ramps (haven't decided between 14.5 carbine or 20 riffle)...do I need to stick with a "non-feed ramp barrel" or is it ok to go with a newer barrel? Also, have any of you ever used a dremel to make the ramps since they are pretty subtle (I know it may be taboo to suggest that)?

m4 ramps in the barrel will be ok..some people have grinded the ramps in the upper, but it should work fine without them..

^^this. It will be fine... if you have ramps in the upper and not the barrel (the reverse) it can cause a ledge that would catch the tip of the bullet.

This is what I thought, thanks. Just looking at it and using simple logic, it seems that it wouldn't be a problem in the combo that I might use.

Now to decide whether to go 14.5 or 20"....decisions, decisions.

I have another question...

I've seen a couple "A2 variants" in the pic thread with a "F" marked FSB. I am assuming that would make it difficult to properly sight it and take away elevation from the rear sight...?

Interested in hearing the answer to this as well. Been considering grabbing one of the PSA 20" uppers, and swapping out the receiver for an A2 i've had stashed for a year or two...

If you have the option (ie, you haven't bought the FSB yet), then you should get the "correct" FSB for the receiver. Non F-Marked for A2 receivers, F marked for flat tops.

My 20" A2 started as an A4 from Delton. Although I can't see a distinct F on the FSB (but all of the cast marks on this particular FSB are pretty illegible), I've assumed that it is F marked since it came from the factory with a flat top receiver. I had no elevation issues when sighting this in. (ETA: it's currently at Delton because the FSB is canted in relation to the receiver, when I get it back from Delton I will measure the FSB to determine if it is or is not F marked)

On my carbine however, I ordered a non F-marked FSB and temporarily built it up with a flat top receiver. I had to back the front post way out to get it to zero. If I was planning on keeping that receiver, I would have switched it to an F marked FSB. However, I just sent the barrel out to ADCO to be cut/pinned, and I bought an A2 upper for it. I'm planning on turning this one into a BHD-ish carbine.

Long story short, YMMV with F and non F-Marked FSB's. It is less of an issue on the longer sight radius of a 20", but if you haven't bought the parts yet, buy the "correct" ones.

To my limited understanding, an A2 upper receiver that is marked " FK is for Fabrique Nationale or FN. Below is a picture of the upper assembly of my FN M16A2 clone. Now own two of these and both have the FK = FN / Kaiser Aluminum forge code. As of late, I've encountered A2 uppers attributed to Bushmaster that have all assorted markings on them. Looks as if Bushmaster may have been out there buying up old military contract overruns from various forging houses.

Nice build. However he is referring to the "F" marked front sight base. Not receiver forge codes.

1. Get a barrel with rifle ramps or M4 ramps and don't carve up your receiver with a Dremel.

2. Get a standard (non-F) FSB

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