Tonight I acquired an AR in .260 Remington, built on what appears to be a matched SI Defense upper and lower set. They fit together nice and snug. I knew the man who put this gun together and unfortunately he's no longer around. I had thought he built the gun on Aero Precision receivers, but I obviously misremembered.

So what about SI Defense? I can't recall the last time I ever read or heard the name.

A .260 AR would be sweet! Not much that it wouldn't be good for here in TX. How much does it weigh bare?

A bit heavy at 8-3/4 pounds. I'm exploring handguards as I don't care for what's on it, but not because of weight...I may change the buttstock as well.

It's gonna be my daytime piggy killer. I figure it'll reach out as far as I can see so it'll wear a conventional optic.

https://falkordefense.com/

Those Falkor Defense AR rifles are stupid heavy. The 6.5CM is 10.25 lbs! Add a scope base, scope, full 10 rd mag, sling and you're lugging around a 12lb. log.

That's the main reason I've never owned a large framed AR before. I want to take a little weight off IF I can do it economically. It has a composite PRI handguard on it now and I don't like it even if it weighed half an ounce. Not sure I'll keep the buttstock as well. The barrel is a Lilja and I know it shoots, so it stays, weight be damned. It's probably gonna weigh ten pounds or better all ready to rock no matter what I do, so I'll just have to get used to it.

You might look at the fore end and Mission First Tactical minimalist stock that POF use.

Yep. But that was the answer to the Op's question.

SI --> Falcor

Yes it is, thank you. Any other relevant info or discussion is welcome too.

I don't have any other info, but do remember the name SI from back in the day. A snug fit lower and upper means they put some work into it.
You're in a better position to let the forum know how it shoots.

It should be ready for its first handloads soon. Here it is in its [almost] final form. I shaved a little weight off with the new Odin Works handguard and the Magpul fixed stock and am down to 8.4 pounds bare-assed naked. Soon a Geissele SSA-E trigger will arrive to replace the Rock River NM 2-stage currently installed. The barrel is a Lilja 1:8 of about 19-1/2 inches and I fully expect MOA performance or better even though I won't need that for slaughtering Central Texas piggies. I think I'll scope it with a Super Slam 3-15x50 duplex with illuminated dot...that should be perfect for an all-around dawn-to-dusk hunting rifle. I've selected 120-grain Ballistic Tips and will be loading my first trial loads in the next few days...I'm sure they'll work out fine.

For full darkness I have a couple of less powerful alternatives equipped with thermal scopes. I'm fully covered now, for sure!

Nice rifle. The Lilja won't disappoint...nice grouping ahead!

Took it out this morning and it did not go well.

The rifle was built by my neighbor about ten years ago. The guy was generally pretty good with his hands but I think he took advice from the wrong people more often than he realized. I remember there were issues with the rifle after it was built, and I guess the whole thing just slid to the back burner and never was addressed. I didn't realize that there were still problems with it.

I had feeding issues all morning. I had to chamber the first round of each magazine manually, then insert the mag. I was using the P-Mags that my neighbor always favored and did not have the single ASC mag with me...I think the P-Mags may be part of the issue. Also, a bit of the feedramp profile of the barrel extension is a bit proud and may be catching the nose of the bullets. Overgassing seems to be an issue...ejected brass flies to about the 2 o'clock position. All the while I was wondering why the bolt catch would not work, and a while ago I discovered that the gun has the wrong buffer in it. It is not only probably too light at 2.95 ounces, but it is too long (3-1/4") and won't allow the bolt full travel in the buffer tube. I have an Odin Works adjustable .308 Carbine buffer on the way. Maybe, just MAYBE that will cure the feeding problems...but for the doubt I also ordered a couple more mags. I've never been a P-Mag fan.

The trial handloads I fired were not so good...everything was looking too hot (and some undoubtedly WAS too hot), and the feeding difficulties were very distracting. There was actually a few positive signs, but I wasn't really in the game this morning. After analysis of my velocities I've made some adjustments and will try again in a week or three.

I'll get this thing ironed out, one bug at a time. I expect it to shoot bugholes.

Is the RRA trigger for sale? I'm always looking for deals on more of them at reasonable prices. They are pretty dang good triggers. Have won quite a few matches with them.

Sure. Send me a PM. Or I'll send you one.

Check the gas block alignment while you're at it.

Good looking rig and I’m sure when you get the bugs worked out it will be a great piggy killer.

Consider installing one of the new Arkin LW 4-16 scopes. I just ordered one for my RRA that’s a bit on the heavy side too. I’m ok with the weight for that one.

I received my new buffer today. I unpacked it and installed it anticipating the feel of a fully functional rifle only to be disappointed AGAIN. I should have anticipated this knowing full well that my neighbor assembled the gun with the wrong buffer...naturally it had the wrong spring, too. Fully compressed it was too long to allow the bolt to travel fully rearward in the buffer tube, so off on a search for information I go. I found a ton of bad advice (imagine that, on the internet!), then when I ran into good info it was not too difficult to identify it as truth.

As a way of testing I cut an AR15 carbine spring to a length that would allow the bolt to be locked back. With the buffer set up with maximum optional weight it still will not chamber a round by operation of the bolt catch/release (although it seems to come pretty close) but it does seem to do okay when the charging handle is pulled all the way back and released. The new spring may tie up the loose ends here. I hope so...I can't [yet] imagine what else I'll need to replace. I think the only additional change that might be necessary would be an adjustable gas block but I'd rather avoid that if possible. We'll see.

So now I am waiting on a small collection of AR-308 buffer springs.

^^^^^^
Masarcoppersolidpoo...


Shunned
Unaccepted
Irrelevant
86,d too many times to even count

I’d really consider just taking the thing apart and starting over with proper assembly.

That's pretty much where we've gone with it. The only parts that have not been removed are the ejection port door, the mag catch, the bolt catch, and the take-down pins. Those all function as advertised. The one major component I cannot positively identify is the BCG...but I knew the guy who built it so well I could predict what he'd do in situations with about 97.8% accuracy and based on that I know it's a high quality bolt & carrier, but there are no markings. Maybe I should weigh it to compare to what's typically used and make sure I have the buffer weight in the ballpark. If that's where it needs to be then I think the new buffer spring will have it hitting on all eight.

Update:

Things are getting much better.

I replaced the buffer and spring and that corrected two problems---one being that the BCG would not travel far enough into the buffer tube for the bolt catch to operate, and the other being that the rifle would not feed correctly. Oddly enough, or maybe not so odd is the fact that the P-mags now seem to work reliably whereas the ASC mags appear to be complete pieces of schidt. This runs counter to my experience with ASC mags for 6.5 Grendel and 6mm AR, which is the reason I tried the ASC magazines for this rifle. If there's a fix for the ASCs I'd like to know. I am a fan of mags that work, but I'd much rather they be made of metal than any polymer. Yes, I AM pretty much a luddite at times.

What has NOT worked [completely] thus far is the Odin Works buffer which I set up for its maximum weight (4.6 oz. as received). The rifle now feeds, chambers, locks, fires, unlocks, extracts, cocks, and ejects (again, seemingly reliably) but ejection is too vigorous with brass bouncing off the deflector and traveling in the 2 o'clock direction. At least it's not smashing one side of the case mouth flat anymore, but I want the ejection to be correct. I have an additional tungsten weight for the buffer on the way which will bring the buffer weight up to about 5.6 ounces. Hopefully that will be all I need, but there may be an adjustable gas block in my future.

More good news...my first handloads were a bust with almost everything being too hot, owing to the fact that I was experimenting with powders for which I had no published data for my chosen bullet in the .260 Rem. Between sheer nervousness and all the functional failures I experienced on that day, nothing good was accomplished other than finding out quite a few things that would not work and which therefore were taken off the table. When I shot a couple of days ago (Sunday) it was a completely different story. I had a total of 16 different handloads using five different powders. All groups were five shots fired at 100 yards, and of those 16 different loads 9 of them turned in sub-MOA performance. Several of those were under 3/4 inch.

So...I will declare (and I hope not prematurely) that this rifle is a winner in the making, and all I have to do is tame the ejection. Hopefully the cure won't induce some other malady, sending me in circles.

I think I'm gonna love this rifle.

Update to the update...I received my extra tungsten weight today and installed it in the buffer. I fired one test round to check ejection, and the empty flew in the 3 o'clock direction. I'll take that and run.

Some guy on the youtube says that the set screw that holds the plug screw secure on these adjustable buffers won't stay put. I'll be watching for that. I have several types of threadlockers available should that become necessary.

I'd say this rifle is ready to rock, and it's going hunting with me very soon. I may fire a couple of ten-round groups at some point to satisfy my curiosity. I think the rifle will hold MOA for ten rounds, and even twice in a row...but I'm not sure the shooter is up to it. I've fired good groups with ARs and I've fired not-so-good groups with ARs, and I really can't tell (almost always) when I've done something right or something wrong. I don't know whether I'll ever be comfortable with the ergonomics, but I do know I can kill stuff with one.

Last update...the rifle shoots like a dream. It gets credit for three of five hogs killed over the weekend, and it never missed a lick. The total would likely be much higher if my night gun (the 6.8 this time, my 6 AR stayed in its case) had been feeding correctly...gotta look into that, but the 6.8 accounted for two pigs anyway.

All I need now is for Magwell Ind. to come out with the Brass Goat for large frame ARs.

Truth is, I'm getting these crazy ideas that I don't need an AR15 at all for hunting and I might need to do a QD thermal on the .260. I'm also beginning to wonder if there's such a thing as a stationary goal post.