Installing a 5.7-28 upper on one of my AR15's

[57FNLover]

Before I buy or install a FN upper on one of my AR15's, I need to know if it is necessary to change the buffer and spring.
Anyone done this conversion?
If so, where did you order the buffer & spring?

[MrSlippyFist]

The upper should come with a buffer and spring, a buffer at the very least. Someone correct me if I'm wrong.

[Kerberos]

Yep, the upper comes with a buffer. OP, I'm going to list my used AR57 16" upper in the next week.

[Ulwembu]

I bought one last October. It comes with a carbine buffer, no spring. I ordered the rifle buffer seperately as I shoot with a rifle stock.

[57FNLover]

Where are you getting these uppers?

[Ulwembu]

One of the sellers is Copes Distributing. I've got good experiences with these guys.

[paberglund]

http://www.heavybuffers.com/ar15carbine.html

I put one of the 9mm-QT Buffer - 11.5 ounces - $125 (comes with stiff spring) in mine, but that was to compensate for the longer barrel I bought for it (28"). I will say that the heavier buffers causes the cases to come out of the gun shaped more uniformly with less deformation than with the "factory" buffer and spring.

I got my AR-57 upper through Blackheart International for $600 - the cheapest I could find it on the web and they are still at that price (I just checked).

[Ulwembu]

Copes is selling them for $ 575.00

Interesting about the buffer. I've got the rifle buffer by Aero Precision in mine with a standard rifle spring. That one weighs 233.5 gram. Your's is about a 100 gram heavier. Might this also work for the 16" version? Don't you feel more movement in the rifle?

[paberglund]

Even better price - everyone should have an AR-57 upper!

I think I'm right on the edge of blowback vs spring/buffer - I had one factory round that didn't cycle properly after I put in the buffer and spring. If I understand the mechanics of the 5.7 reading the material on this site, the pressure spikes quickly so the barrel length may not be a factor. I have read that you need a heavier buffer if you are using a silencer, but I don't recall the exact reason.

It's got a definite thunk-a when it cycles - I'll have to try the regular buffer/spring to see what the difference is.