I'm seeing very little info on Spike's Tactical uppers since 2010-2012, and using the forum's search tool didn't yield any matches because it disallows apostrophes.

I'll be onto my third upper receiver for the 9mm pistol build next week...  The first had to go back due to the bolt being incompatible with my Spike's Colt-style lower (upper was bought as a bundle, so had to return everything as one), and the second (an 8.6 oz billet) from a different company had a slot too tight for the charging handle to go in all the way.  Both were slick sides.

Hopefully, the replacement for #2 works out fine, but if not, I'll probably give the Spike's slick side upper a try.  It ought to be a good match for my lower; maybe I'll order it regardless and have two options for this and another build.  It was out of stock at JBO when I was making a replacement choice on #1 and ordering a barrel/handguard, but is back in stock now.

https://www.joeboboutfitters.com/Spike-s-Tactical-Slick-Side-Upper-Receiver-Forge-p/sp-sft56m4.htm

They don't specify the weight, but Spike's shows it as a mere 5.9 oz on their site:

https://www.spikestactical.com/collections/upper-parts/products/uppers-stripped-uppers-m4-no-provision-upper?variant=32733928908

Both are shown as part #SFT56M4.  Can a forged upper really be that light?  And are there any drawbacks in terms of precision or durability, especially if it's subjected to more recoil with a blowback system?  Spike's has a good reputation, so I can't imagine they would risk it on an inferior product.  I just haven't seen much else approach it, and these indicate the previous (?) version w/ deflector & dust cover was 7.2 to 7.3 oz, which supports the newer lighter figure:

http://ar15armory.com/forums/topic/144225-is-physics-playing-a-trick-on-me-stripped-upper-weights/
https://www.youtube.com/watch?v=Q72GQGU5XPw

So, Spike's seems to be making uppers significantly lighter than much of the competition, which is doubly odd because their Colt-style lower is a tank at 13.9 oz partially assembled.

p.s.  From Spike's page:  "If you are looking for down and dirty lightweight, this is for you."  It's tough to read between the lines as to whether that means no-nonsense rugged, or a bit rough around the edges.

Why not ask Tom himself in his industry section?
He is usually quite responsive to questions.

@badazzar15

Spikes is GTG. I almost got their slick side upper for my last build but wanted the FA and dust cover in the end. Good company and top quality, up there with BCM, LMT and Colt IMO.

OP don't get me wrong I like spikes - all of my lowers are spikes but save yourself the coin and get the Aero upper

That's like someone asking you if you're the best at something...you'd rather let someone else answer that for you.  Surely, there are dozens if not hundreds of people here who have bought the product and have an opinion of it.

Okay, you've definitely got me curious.  What is it you don't like about the Spike's uppers?  Or is it just that the Aero uppers are cheaper and thus better value?  (Wouldn't the same apply to the Aero lowers?)  At around $50, I have considered them, but without the forward assist, the deflector bulge bothers me.  They don't make a true slick side, as far as I can tell.

Pretty much the opposite of what I'm looking for.  :)   Your assessment matches my opinion of them.  I'm just confused how they can offer something of top tier quality at significantly lower weight and/or lower prices than the competition, unless some compromises have been made.  Wouldn't everyone else machine off a rather massive 2 oz if there are no drawbacks?  Obviously, I'd like to believe it's legit because I'd like to buy it, but it just doesn't seem to add up.

This is what I was referring to when I suggested you ask Tom.

I'll run it by him tomorrow if an answer is still needed by then.  I've spoken with Mark via email previously, but haven't "met" Tom yet other than looking through their Industry forum just now.

I bought one of their slick side uppers from AIM. Used it for a 7.62x39 SBR “build”. Great upper, I have already bought a second one for another build. Honestly I just like the look of no forward assist. It’s a quality piece.

That's reassuring, thanks!  Did it seem as uber-light as advertised?

Edit:  It looks like AIM carries the older (?) version mentioned in the first post.

https://www.aimsurplus.com/product.aspx?item=XSTSFT55M4

That's got the dust cover and deflector, and weighs 7.26 oz.  It claims to be 1.5 oz lighter from removal of the forward assist, and mid-8 oz does appear to be milspec territory, but it sounds like that's their standard machining, not whatever has gone into the 5.9 oz version.

I took Ditch-Tiger's advice and ran it by Spike's in their Industry forum, and...crickets.

https://www.ar15.com/forums/industry/question-about-your-slick-side-upper-and-problem-with-my-your-Colt-style-lower/282-285531/

I asked JBO and they don't have the weight info in their system, so I went with the last resort and asked Spike's directly via email.  They responded immediately, confirming the 5.9 oz listing.  They haven't yet responded to two proddings as to whether there are any durability or precision concerns with that low of a weight, however.  I still have a hard time believing they would put the product out there and risk their reputation if it's not good to go, but it's weird that it's so tough to get an answer.

And...I got a response from them that they're confident in the build quality despite the light weight, so it's a go.