I really liked the Angstadt receiver, plus the CMMG MKG 45 but not the price tag. The RDB is something that really interests me since I shoot quite a bit of 45 Super out of 1911, M&P, and multiple S&W 625 revolvers.

So I decided to build my own AR-45 using both companies. So far I have a matched receiver set from angstadt arms. A 8" MKG barrel and bolt kit from CMMG. I used a PSA lower build kit with their EPT trigger and a SBA3 brace.

$354 Angstadt Arms Receiver Set
$321 CMMG MKG Barrel Bolt Kit
$170 PSA SBA3 EPT Lower Build Kit
$124 CMMG RML7 Handguard
$969 Total so far

Both companies said the same thing in response to my email asking if they would work together. "We haven't tested that upper/lower combination and can't guarantee fit, functionality, or reliability". I've seen other posts here from Macon recommending the Angstadt lower with his DI upper. So I figured if it works with a regular bolt carrier on his setup, it can't be far off with the CMMG bolt carrier.

So I quick threw the upper together with a barrel nut I had in a spare parts bin (still waiting for the handguard to come). Assemled the lower without the trigger so I could test hand cycling. It works fine with one exception..... the bolt lug between the 5 and 6 o'clock position slightly catches the very tip of the follower in the magazine or the rearward cycle. I'm going to try and shave it down a hair to see if it won't catch the bolt. As of now besides that it cycles fine by hand. LRBHO works as it should and all.

Just waiting on the handguard and need to decide on a flash hider/compensator too.



One question for you guys..... what spring and buffer should I be using with this setup? Seems like alot posted they are just using the standard carbine spring and buffer with the CMMG barrel and bolt kit.

That looks sweet, OP.  @Amphibian

Looks good. I have the same Angstadt lower and the 5" .45 RDB barrel from CMMG. Works great! I think you'll enjoy it a lot. I plan on getting the 10mm RDB setup from CMMG as well when funds allow so my lower will pull double duty between .45 and 10mm.

As far as the spring and buffer, CMMG's technical support recommended a standard carbine spring and an H buffer to me. I'm using a standard spring but am using the Kynshot hydraulic buffer which weights slightly more than an H buffer at 4.2oz (model# KYN-RB5000). I feel like it can actually go higher in weight on the buffer but haven't tried. Recoil felt a lot heavier/sharper with the standard H buffer in my testing compared to the hydraulic so I just stuck with the latter.

Is that hydraulic buffer a direct replacement for a standard buffer? (regardless of weight)

I've never used a hydraulic buffer but seems like alot of guys do on PCC in the AR platform.

So I took out my AR-45 build today for the first time. We ran around 500 rounds through it. A mixture of 230 gr Armscor ball and 200 gr berry's HP plated reloads in front of 8 gr Accurate #5. I had one failure to eject on the first shot with Glock factory mag. It stove piped and I think it might have possibly just been because of the first shot, not really sure why it did that??? It was factory 230 gr. The other two
were failure to feeds were the 200 gr HP. One from a SMG mag and one from a glock mag. Both HP caught the lugs and stuck. Otherwise it ran flawless. LRBHO worked every time on both Glock and SGM mags.



Now before I ran the gun, I shaved the very front pointy tip of the followers on all magazines. It was catching the lugs of the bolt. After I did that, it hand cycled with no catching. However you can see they were still scratching the bolt when fired. So I might take a little more off them. The Glock mags were fine, but the SGM mags were tight loading. You can see where it was slowly shaving off the stops on the mag from loading into the magwell.

So next thing I plan on doing is getting a Tubbs flat wire spring, and I'm going to start with a Kynshot RB5000 hydraulic buffer and possibly the CMMG tuning kit to add more weight to the bolt. I don't necessarily want to go with the A5 buffer just yet but I do have one (well a PA-10 buffer tube). I'll keep posting my results.

So far I'm very happy with the build. I haven't put a muzzle device on yet, just running a thread protector as of now. I might just put on a A2 birdcage or possibly make one like the CMMG SV out of 303 stainless.

You may have seen my posts raving about the 556 Tubb flat spring / A5 or PA10 buffer tube and Kynshot RB5007 hydraulic.
I use that in my 9mm and .40SW CMMG RDB configurations as well as many other rifle caliber configurations.

I personally think that if you don't want to change out the buffer tube and stick with carbine length to use the RB5005.

I have hydraulic info here: http://c3junkie.com/?page_id=430#hydraulic

I find the RB5000 to be too stiff and in effect, don't get as much benefit.

I don't have the .45 CMMG RDB setup but I do have a local buddy that does.  He is using the same 556 Tubb flat spring / A5 or PA10 buffer tube and Kynshot RB5007 hydraulic I use on a lot of configurations including his .45 CMMG RDB.  He is using a full auto lower and Rudy's mags and mag block and I shot it just a few days ago.  Very smooth and reliable.

The RB5005 is still listed as needing the 7 3/4" buffer tube though? Have you found that not necessary?

Or I guess it doesn't matter since it isn't traveling the distance of the 308 round. I see it is the same length as the RB5000 buffer.

RB5005 and RB5000 are both for carbine length tubes....the RB5005 is around 5lbs to compress while the RB5000 is around 10lbs.

Which do you think I'll benefit better from shoot hot 45 and 45 Super loads?

It seems like the 1.2 ounces more of weight and the hair more of compression weight (assuming it is in valving) could be enough to really make the difference.

The lightweight and heavier compression of the RB5000 seems to be what probably makes it a wash.

If you go back and read the link I put on my website, you'll see why I don't like any of the stiff hydraulics.  However as mentioned I don't have the 45 CMMG but my buddy does.  I brought all my buffers out for him to try and he came to the same conclusion I did.  There are a lot variables.  Maybe it will work well for the hot 45 loads you speak of.

I did read your page.... actually several of them.

I didn't type it out right so I think you miss understood. What I meant in the second paragraph it seems like the RB5015HD with the touch heavier weight and compression seems like the sweet spot between the RB5005 and RB5000.

And I meant seems like the low weight yet even heavier yet RB5000 is probably what makes it a wash as in to stiff and almost acts like a standard buffer.

The 5015HD is an A5 length buffer.  I tried it once for my .40SW CMMG setup and didn't like it.  I went back to the RB5007 but used my spring loaded tungsten weight in the carrier...
Ran it in a SMG match today actually....400 rounds full auto suppressed with no malfunctions and pretty smooth.

I wonder if has to do with the 9mm being a bit more snappy. Although I've never shot a 40 S&W.

I ordered the RB5005 and a Tubb's flat wire. I'm going to try that first and see how it is before I swap out the buffer tube and go the heavy route with the HD 9mm buffer. I'll post my results.

Thanks for all your help and guidance amphibian!

So the kynshot RB5005 buffer showed up today. Looks like a extremely quality buffer. I can't wait to test it out. The Tubbs flat wire should be hear Monday.

Also made a mag block to work on the upper. I always liked these with my regular AR's.

I think I forgot to elaborate on my response to this.  What I was trying to say which I've posted before is to not think too much of the weights when it comes to the hydraulics.  I've done testing where an H3 buffer (5.3 oz) and even an H2 buffer (4.5 oz) was too heavy for a specific configuration and thinking no way that the Kynshot RB5007 at 5.9 oz would work and it would work just fine.  I presume that it has something to do with the hydraulics not having as much of the 'dead blow' hammer affect as the typical mechanical buffers.

I am going to explore possibly lower the mag catch just a hair.

On a side note went out today to test the buffer combo reccomended by Amphibian. While I can't say I felt much of a reduction in recoil, the firearm operated much much smoother. Absolutely no "twang" whatsoever. Ran another 500 rounds through and without one single malfunction. Using the two Glock mags, and I'm now up to size SGM tactical mags. They all work excellent. I was so extremely happy not to have a single malfunction on the second outing after having three the first time out.

This gun is so much fun to shoot it is ridiculous. I've have two more Angstadt Arms matched receiver sets on the work bench to build. One will be a 5" and I think I'm going to build another 8" and SBR the receiver.

On another note I met three range nazi's today.

I love shooting in the steel pit. It's definitely fun and a good time. We have two pits at the local club. One for rimfire and one for pistol cartridges. The sign clearly states pistol cartridges only, rifles and shotguns prohibited.

The first guy comes over and says you can't shoot that rifle here. I politely proceeded to tell him it isn't a rifle it is a pistol caliber carbine. He said ok and walked away.

20 minutes later two men show up. One guy gets out and comes down and starts picking up brass. He asked if I kept mine and I said yes. He said I always ask before I take them. I said thanks and I appreciate that.

He proceeds to tell me I hope you're ready cause here comes my brother and he's gonna yell at you. So here comes this older fella with a orange vest on that says range officer. He says you can't shoot that rifle here. I said it isn't a rifle it is a pistol caliber carbine. He said do you hold it like a pistol. I can if you want me to.... then he goes on to say guys like you ruin it for everyone. You're destroying the steel targets and the concrete wall. I wasn't arguing with this guys after I tried to explain three times it wasn't a rifle. I said if you don't want AR pistols or pistols that can be shouldered you need to post a sign because I'm following the rules. Oh well every party has a pooper!

@Mad-Machinist what height should I be looking for on the rim above the case pocket on the bolt face?

We shot our first competition this weekend, was actually a practice run to test out everyone's setups which worked in our favor.

We had numerous problems loading a loaded magazine into a closed bolt. Different magazines, even glock mags, loaded to capacity or not. This is all leading me to believe the mag catch needs lowered. The firearm ran flawless besides this issue. We've never had this problem at the range but I've never been pressured to load it in a hurry either.

That might be something I'll have to look at as well although idk how it would work with the cmmg bolt.

There are stops cut into the lower receiver and they are sharp. They dig in hard especially if you bang the bottom of the mag. It just digs into the molded plastic stop.