Was interested in doing a lightweight 9mm build - 4.5" barrel and the smallest LWRC stock setup possible with skeletonized upper and lower.

I finished an 80% lower and was going to machine the skeleton myself, when I came across these F-1 setups that are already done.  Looks pretty much like what I had in my head.  At $499 a set they're not cheap, but neither is my time.

Anyone used one on a 9mm build?  If so, did the mag block work out ok with the lightened lower?  Any other issues?

With the bolt and heavy buffer you're never going to get an ultra light 9mm build.  My 5" with lwrc and DD lite rail is still 6.5 lbs and that's minus any optics.  Not a lightweight gun and I'm not sure you can get a blow back 9mm much lighter.

I concur.  I think basically no matter what, a 9mm AR based platform is going to be heavy.  You could look at some of the other platforms that use roller-lock or locked breach to really lighten up the load.

Thanks guys, I'll save the money on the receiver and just make it tiny.

Here is a picture of mine.  I wanted to keep it as minimalist as possible.  this is a 4,5 inch barrel.

What upper are you using?

HYRYSC

Cool looking build.  Who makes that stock?

Thanks

Kattman from Michigan

How are you going to get a short buffer up to weight? Maybe use an AR10 buffer or something?

I say "buffer" although 9mm ARs don't really have buffers, they're more just weighted spring guides. The weight is part of the reciprocating mass, as the diameter in the receiver is not large enough for a full weight 9mm blowback bolt.

What's the hand guard?

As far as buffer - there's an aftermarket U-2 that does the job.

I will be the first to say that is one beautiful piece. That said I would ask the question, why not go for a barrel that is just a bit longer. Why? Much better performance from a 9mm round. If you want a 4" barrel use a pistol. If you go out a bit with the barrel you will gain a lot of power from that round. I guess I am hard headed and look for performance over looks. A little more barrel will pay you back. But, we are all different in what appeals to us.

Your handy, dandy 9mm reference of 9mm barrel lengths. Different ammo, different improvements. Lots of physicals involved with powder burn rates, bullet weights, etc.

9mm Ballistics by the inch

As a bit of real world testing we took some 9mm 115gr. ammo out one day and tested it on an old water tank. In a pistol (4" or so barrel) the ammo would dent the water tank pretty good, but it would never penetrate it. Took the exact same ammo, same day, same tank and fired it out of my little TNW ASR with a longer barrel (16") and every round went through that tank. My buddy with me that day was amazed. I don't have all the answers on what is best but from real world testing I have seen much better power out of a little longer barrel. That fire you see out of those short barrels....that is wasted power that could have made your bullet have lots more energy. Try it  yourself. But, if looks are your priority, then don't bother, go for what looks good.

What are the grips? I know the adapter just was curious who makes the punisher

That is just a Anderson lightweight Sport upper.   I played around with some of other gee-whiz looking uppers, but I kept coming back to this one.  Plus it is uber cheap at under $40, so that was a plus too.  

I can't think of it right off the top of my head now, but I can PM you when I get home and check it out.  Really dig the looks of it and it feels really nice too.

You make excellent points for certain, but I have a Scorpion for better ballistics.  I built the little AR just for fun!

I am not for certain what the handguard is actually.  I saw it at a gun show and it was the shortest one they had, so I grabbed it. It is not a very high-quality piece, but it does the job until something else catches my fancy.

The grips are from amazon.com.  I just searched for "1911 punisher" and just scrolled through til something caught my eye.

I believe the stock is strike industries.

Yep, that's it!  Thanks.

Same exact boat.  I've got the Scorpion set up almost the same.  This little AR is just for shits and grins - maybe a show off piece for my 07/02.

5.5" shoots very nicely, even surprisingly out to 100 yards

Funny, I started to read and was going to quote baliistics by the inch to refute you (and then saw you referenced it).

I've always looked at the heavier rounds.  Does look like the lightweight (90g etc) gets a boost in velocity, but 115g (my standard plinking) only goes up by less than 10% from 5" to 18", heavier (subsonic) like 147g goes from 1007 to 1083 from 5" to 18".

I'd argue that there is no reason to go longer than 5" (although light, supersonic, bullets may benefit from a long barrel).

I reduced the weight somewhat on mine by replacing my Spikes ST-9X with this hydraulic buffer:

https://www.blitzkriegcomponents.com/ProductDetails.asp?ProductCode=AR15%2DKYNJP%2D9P

<rant>I have heard from more than one range-commando about how my little 9mm AR is useless (of course this is usually after they have asked to shoot it and I let them).  I think that most folks miss the point.  This is not a build for war, or the zombocalypse or whatever other fantasy that some folks might harbor.  I build this for two reasons:  #1, because I could and #2 because I wanted to.  If I were ever to go charging into a zombie infested city, a 9mm would probably be near the very bottom of my list of weapons to choose, only slightly above an atlatl.  If I did survive the initial plague outbreak, or EMP, or alien invasion, my loadout would closely resemble this:



Certainly not a little 9mm carbine.
</rant>

9mm carbines are fun, inexpensive to shoot and always attention getters at the range.  I think everyone should have a couple.

Note to the OP.  Build one or three.  I am certain that you will not regret it.  I know that I certainly don't!

Who does the grip adapter for 1911 grips?

Pearce Grips

What Optic is that? I think it is on a Seekins mount.
Thanks.

What optic is that??  I think it is a Seekins mount

The thing about 9mm velocity vs. barrel length is that is not only bullet weight dependent but also heavily affected by powder type.

I've loaded 115 grain rounds (under max load) that exceed 1600 fps from a 16" barrel

It is just a cheap little Black Spider Optics with the stock mount.  It has some features that I really like such as the auto-shutoff and automatic or manual brightness control but the FOV is very limited.  Doesn't really bother me much on this since its just a range toy, but I am still thinking of swapping it our for a T1 one of these days.