Thinking about a 9mm AR upper...

[338Shooter]

Do you know anything about Spike's ST-T2 heavy buffer (4.3 oz) with the 9mm buffer spacer:

http://www.spikestactical.com/new/z/stt2-heavy-buffer-st9bs-combo-p-235.html

If you want the ability to swap calibers without carrying extra buffers around it is a good option. i would get the ST-9X if you were gonna run a dedicated 9mm setup for the money though. Spikes doesn't sell them anymore, but you can find them. AIM Surplus has a couple in stock. I've been happy with my RRA 9mm buffer and wolf extra power spring.

 

[NikatKimber]

Wait, you just said you wouldn't want the ST-9X a minute ago??

 

[338Shooter]

I wouldn't switch my gun to it. I'd run one on a dedicated 9mm build if I was gonna drop $50 on the buffer alone.

 

[NikatKimber]

Gotcha. Can you run anything other than 9mm with the RRA 9mm buffer? Or is it dedicated too?

 

[Perplexed]

Since I already use the same lower for two different rifle calibers (5.45x39 and 7.62x39), I'd probably go for the ST-T2 buffer combo so I can switch out three different uppers. I know I can always get another lower, but a complete one is more pricey than I care for, and I don't mind the effort in switching out uppers. Thanks for the comments, Dustin.

 

[Ignored Member]

Since I already use the same lower for two different rifle calibers (5.45x39 and 7.62x39), I'd probably go for the ST-T2 buffer combo so I can switch out three different uppers. I know I can always get another lower, but a complete one is more pricey than I care for, and I don't mind the effort in switching out uppers. Thanks for the comments, Dustin.

You could get the lower one piece at a time. That's what I did, and it worked out great cause I could buy 1 part per paycheck and not cry over how much I spent.

 

[NikatKimber]

Not as much as you might think.

Surplus Arms & Ammo Stripped Lower @ $59.95

Spike's Tactical AR15 LPK @ $63

AR 6-Pos Stock (ComSpec) Kit @ $34.95

Total = $157.90

 

[MBB]

So I'm jumping in now as this is interesting to me. I hope I don't slow things down too much.

So why the need for a ramped bolt?

And exactly what needs to happen to switch between 9mm and another caliber upper using the same lower and retaining all AR functionality like bolt hold open?

 

[NikatKimber]

Bottom loading mag block for lower compatibility, and a heavy buffer. Some buffers are too light for 9mm, some are too heavy for .223 (or too long). Still working on that one.

The ramped bolt is so it will function with a standard hammer. The RRA (non ramped) 9mm bolt carrier requires the RRA 9mm hammer.

 

[MBB]

How does the bottom loading mag block attach to the mag well?

So there are buffers that will work for both 9mm and .223 interchangeably?

Thanks for info on the hammer/bolt compatibility.

If building a 9mm upper, does one need a 9mm specific upper receiver?