Long story short, I have one from not long after they hit the market I think - never used until now. Built with an undetermined lower parts kit for most of the small parts; Larue MBT trigger and a Colt carbine receiver extension. (Father passed, it was something he had that I had to rescue from NY - I replaced the "mil spec" trigger in it, and replaced the commercial-spec carbine receiver extension with a Colt mil-spec dimension one)

Basically, I'm getting intermittent failure to feeds; rounds just hang up before even climbing the feed ramp. Not sure if it's hitting on the bottom lip of the upper, or what. Random magazines. What's weird is reloading the same mag to the same round count and it won't have issues. The upper itself is a Colt factory 6960 upper; I haven't had it on another lower yet to see if it's the lower or the upper. Hopefully next weekend I'll get that chance.

This was with brass M855, Wolf steel-cased, and Hornady commercial loaded ammo. With both an H and H2 buffer. I don't remember if I used any Pmags with it, but it's happened with Surefeed E2s as well as a bunch of other aluminum GI mags (Duramag, Brownells, D&H, ...all the usual suspects)

Anyway - the only things I can think of is it's possible the upper's having issues, or the lower's out of spec in some way. Maybe the mag is being seated too low, maybe it's off dimensionally, I just don't know. It doesn't seem LRB is making them anymore and as I recall they were pretty cheap when they were being made...

Were they known to have some dimensional issues, or have other issues? Really hoping it's a lower issue and not an upper one

Had one a decade ago, worked great.  Sold it at some point.

Lrb has a great reputation. They make forged m14 recovers that are considered to be the best in the game. Their staff is top notch, at lease it was when I bought mine.

While I don't have their ar receiver, I would not hesitate for one minute to buy one.

That's just it - they didn't actually make their AR receivers; they were subcontracted out. They were rollmarked LRB, but the manufacturer was JV Precision in Connecticut.

So ... Get a basic lower (Anderson, PSA, etc.), transfer the parts, and try it?

That's my plan - I was asking if there were known issues with these though - if there were, it'd make discarding it a lot easier. Otherwise it's a case of "maybe it's not the lower" which opens up a whole new can of problems. I was trying to verify the lower first.

It’s not the lower.

I have more than one LRB lower, never any issues. I’ve had them for years.

Sadly I think you're right...I had it apart to clean it, and for shiggles decided to drag a punch up and down the feed ramps. I think either the RE is machined wrong, or the upper has an issue...either way, there's a noticable gap/ledge between the RE's feed ramp and the receiver's feed ramp; the RE sits a little higher. So you can run the punch up the reciever feed ramp and it'll hit a flat ledge...a very small one, but one nonetheless. It's not a smooth transition from the receiver to the extension. My two 6921 uppers on the other hand, smooth from top to bottom. Oh well, back to Colt it goes.

JVP also machines LRB's M14SA receivers. Quality operation.

Like the lower left pic?

No, not nearly like that, more like the ramps weren't milled down far enough. There's a slight ledge, enough for the tip of the nose to hit it and just flat stop which is what I suspect it's doing..

I have a few builds with the LRB lowers, no issues.

FWIW - I sent the upper back to Colt for warranty work - none of my other uppers (including home built ones) have any kind of a ledge or hitch when running a pencil or punch up the feed ramps from the transition from the upper receiver's ramps to the barrel's ramps. Hopefully that gets back in early January (the guy I spoke to at Colt said at the end if the year they shut down for a couple of weeks, so there's going to be a delay)