Length.
It's tapered so I can get the diameters once I pick that lower up from the engraver.

Can the 45 acp upper be fit with a regular barrel nut? I would like to have one setup like my RRA 9mm with Moe handguards.

As a side note I have a CMMG 22 lr dedicated upper and it is possibly the most reliable 22 lr upper out there and the accuracy is very good, better than some bolt actions out there, now that is with ammo that it likes as with most 22's.

Steve............

Please disregard, I figured it out.

CMMG Guard + Stern Glock Block + RR =

Video

Picture

So I finally I got a chance to try my 9mm Guard setup again for the second time.
I'm using the Guard lower, Aero Precision 458 upper and RDIAS.  No carrier weight.
The first time out, I was using a JSCPS with the H2 weight equivalent and it kept locking the bolt back even though I had plenty of rounds in the mag.  Even tried holding down the bolt hold open during firing to stop that and then I had a lot short stroking.  Tried my 147 Gr reloads as well as factory and it didn't make a difference in the issues.

I then read all the posts here about having to go with a stock carbine buffer.  
So this time I tried that as well a JPSCS with standard weight.
I wasn't have it engage the BHO anymore but now I was having failures to eject.  I pulled the ejector spring and it was about an 1/8" shorter than a standard 556 ejector spring.  Replaced the ejector spring and that problem went away.
The JPCS standard weight was giving me light primer hits in full auto and wasn't as smooth as I had hoped.
The standard carbine buffer was working fine but also not as smooth as I hoped.
Also bear in mind that I brought a post sample MP5K out as my goal for smoothness.
I then switched to an old hydraulic Enidine buffer and it was pretty nice.  MP5K still a bit smoother but the Guard is getting really close.
I brought an A5 buffer tube and spring with me but forgot to bring my wrench so I couldn't swap out at the range.
I'm looking forward to trying the A5 out after seeing your results as my goals are similar to yours -  to get it SMG competition ready.  
I do have some custom tungsten carrier weights (5.1 and 6.8oz) that I use for 7.62x39 configurations that I'm going to try.
I have factory Vltor buffers as well as the complete Heavybuffers.com set.

I also have a custom delrin plug so I can use any carbine buffer with the A5 setup as seen in the picture below.
I'm hoping that may give me more options than messing with A5 specific buffers.



With that plug, I can try some of the buffers I have below...After seeing the noticeable difference the Hydraulic made, I'm hoping using the Hydraulic + 5.1 tungsten carrier weight + A5 tube + standard rifle spring = MP5 smooth.

That is awesome!
Looking at your picture, looks like you had to lower the mag block in the lower...which is to be expected with this setup.  
I'm assuming that doing that you are losing the BHO ability lowering the block right?

You are correct...I had to lower the block and lost BHO.   I think, however, I might be able to make it work.

Why was  it necessary to lower the block? How did you keep the block in place now? The set screws? I assume the mag release no longer holds it in place?

The Guard system requites the round to be presented at a lower height compared to the Colt-style blow back system.  I filed the slot to allow the mag catch to still function with the Stern block at a lower position in the mag well.  The release still 'locks' the block and keeps it from moving downward and the set screws limit its movement upward.

Late to the thead.. I too hope they offer at least a "builders" kit in 10mm also....

Any luck with testing?  curious as to your results.  I think the nonstandard "low shelf" lower (after dremelling down) has a little bit of a timing issue I need to fix, which could have effected some of the testing.

Who, me?

Looks like they changed from 1/2x36 thread to 1/2x28. .  I could of used what I already had originally.  Guess I will shorten and 3 lug, or have thread 1/2x28 so I can swap other suppressers without have to swap pistons everytime.  Time throw the 1/2x36 piston in the parts drawer...

Amphibian....and anyone else for that matter :)

While my modded Stern block worked fine with G19 mags, it did not like the 33 round Glock mags.  I was getting feed failures (the bullet was nose up and wedged in the barrel extension).  I moved the built in ramp of the Stern block down and it cycles dummy rounds just fine now...still need to shoot it.

I watched it and gave th video the first thumbs up.

I am still trying to dial in the 9mm setup.  I got really frustrated with making it reliable and slower so I tabled it for a while.  I recently ended up ordering one of the VLTOR pistol A5 extensions from midway and going to try some of the buffer combinations Amphibian recommends.  I have a spacer so with that in the back of the spring can try a myriad of carbine buffers I have with the longer A5 tube.  I also ordered the Kynshot/Blitzkrieg hydraulic and the Tub flat spring for the A5 to try.  My goal is to get it smooth or close to an MP5, reliable, and in the low 700 RPM's suppressed or not.  Basically as close to an MP5 as possible.

After reading Doctor_Evil's post on the rifle tube, A5 tube, carbine tubes as well as the various buffers and springs I did my own testing.  
I've got some pics I've put up here: http://c3junkie.com/?page_id=538
So I don't clutter up things too much here.  I need to put some notes on that link but for now my conclusion is that while I could get the RoF down in the 400's it was too bouncy at that RoF.  
I did some testing with the carbine buffer and came to the same conclusions as Doctor_Evil.
I really didn't want to use a rifle buffer tube as I like my collapsible stocks.  So decided to break out the A5 setup.  
I played with the A5 a few years ago and gave up on it since I found that in order for it be reliable in full auto 556 I had to increase the amount of gas I was running compared to a standard carbine buffer spring and H2 buffer and I didn't want to do that.

What I did figure out was that by chance I ordered a Blitzkrieg/Kynshot 9mm buffer and it just so happens that its compressed length is the same as an A5 buffer.
They should market it as such as now it gives A5 users another buffer option instead of just using the limited amount of A5 buffers out there or using a custom plug like I had made.

Below is pictured the length of an A5 buffer:


Now here is the Blitzkrieg/Kynshot 9mm buffer:


So under full compression, it is basically the same length as an A5 so you aren't going to damage your lower using this buffer in an A5 tube.
For reference here is the extended length:


Below is one of the strings I got with this setup.



This is using a standard 9mm Colt bolt weight which is what CMMG sells as the heaviest.  I also tried a custom tungsten weight and it was too heavy/bouncy for my liking.

I did have a few failures to eject and pulled the ejector spring and it seems to have compressed a little under a new one.  
I mentioned before this was really bad when I first shot the Guard and swapped it with a new one.  So this is the second time I'm doing this.  This time I installed a Sprinco enhanced extractor spring and curious to see if that fixes the issue.

I am now a fan of the Tubbs flat wire spring + A5 + Blitzkrieg/Kynshot buffer.

I have tested it in my goto 556 upper and surprisingly my gas settings didn't have to change like the last time I tested the A5 setup.  
I can easily pull singles (this is a 12.5 mid 556 setup) and I think it is smoother than before.  I was previously running either a white Sprinco spring or an H2 JPSCS setup.

BTW, the standard JPSCS setup was resulting in bolt bounce issues with my Guard and the H2 JPSCS was too heavy to function.

I have also tested the Tubbs flat wire spring + A5 + Blitzkrieg/Kynshot buffer combination in my 9mm belt fed FM9 and it has smoothed that out some and works great.
I also used the 308 Tubbs flat wire + A5 + Blitzkrieg/Kynshot buffer combination in my Shrike and it has also smoothed that out and I can easily pull singles out of that also.

Needed more work to run with the Glock 33rnd mags.

Video

Guard vs Banshee...... Which one do you like and why?

Such and awesome post with so much good news.  I had purchased the Kynshot 9mm hoping it would work b/c it appear to be the same size as the A5.  I'm really excited to try these set ups with my Shrike and my inbound 12.5 middy upper as well!
I've definitely had the failure to eject problems and I will try the Tubbs enhanced ejector spring to see if it helps.  Wondering if this is the weak spot in the new system?  Was you prior replacement a standard ejector spring?

I'll check your post on your sight as well....great stuff Amphibian!

So the CMMG BCG for the banshee and guard use a firing pin spring in the 9mm's

But in the 45acp versions there is no firing pin spring ...., how come?

Yeah, I had a standard ejector spring in there after the OEM one was giving me issues.  If the Sprinco one has issues too, I'll try a Tubb's ejector spring.  I've run into some configurations that are hard on ejector springs for some reason.  I don't know why but my 5.45x39 setup in full auto kills them...or maybe that is just because I was 40 round mag dumps.  Strange as I will do 75 drum dumps in 7.62x39 with no ejector issues.

I'm going to try to get some ROF measurements with the Shrike and some other setups.

Anyone?

Are the 9mm BCG's/buffers lighter than the .45? Maybe they're concerned with bolt speed in the 9mm causing slamfires.

On my .45 DI AR, If I dropped a round in the chamber and dropped the bolt from the bolt stop, it would slamfire.

Cool, thanks for sharing.

I'll bet that that Stern company will make another model for this.  If these delayed radial bolts hold up, I imagine that blowbacks are gonna go the way of the dodo bird, and MP5s too.

Your vid?  Why are comment's disabled?

Please keep us updated as to what it takes to keep this running.

I hope to do something like this w/ one of those binary triggers on a SBR'd lower.

First I've heard of this.  I have both 45 and 9mm build-kits and both came with firing pin springs.  Seems strange they would take it out.  Have you asked CMMG?

No problem.  I've talked to Stern and they asked the mods I did to make the block work but revealed no further plans.

That is my vid, I have another with the 32 rounders.  That was one of the first videos I ever posted, not sure why I disabled comments.  I can enable if it would be fruitful.

I ended up need to move the 'ramp' in the block down after failure with the Glock 32rnd mags.  This meant filing away the aluminum under the ramp (just over a millimeter).  This eliminated the nose up jams I was experiencing.  It then ran 100% .

so you did this filing in addition to the block sitting lower in the mag well?

Do you have a measurement to share for much lower the block is to sit in the mag well, at least in your case?

Thanks so much.

Yes please.  And update on a 9mm bolt w/ slower geometry.  Funny that you can change the bolt lug angles w/o having to change the barrel ext lug angles??

SWEET!  So if a guy was using a mag block in a standard lower he could just use the same spring/buffer between this and a regular 5.56 AR upper??

Guys, using the stern, or other glock mag blocks, modded so everything sits a bit lower, is there a stop in any of these mag blocks that prevents over insertion of the mag?

I hear that in addition to the ejection port being opened up a bit, the guard upper receiver has stops to prevent over insertion of the mag?  Caliber specific??

If you use their Guard upper, wouldn't that be a way to index exactly where your magazine/mag block needs to sit in a standard lower receiver??  Serious question.

That is what I'm doing.  I have a factory Guard lower but also have modified a 9mm Hahn block to work with unmodified Colt mags as well as modified Suomi drums with Colt mags welded to them.
I'm using the A5 tube + Kynshot/Blitzkrieg hydraulic buffer + Tubb's flat wire spring on this as well as my 556 setups, 9mm belt fed, 7.62x39 and 5.45.

Guard buffer / spring testing: http://c3junkie.com/?page_id=538
Cheap alternative to the Vltor A5 buffer:http://c3junkie.com/?page_id=571

Over insertion is not done in the upper but the lower.  That is how my factory Guard lower is.

The Stem block has a stop built in (part of the feed ramp).

Does that buffer have sliding weights inside like a regular buffer, or is it just a solid mass like most 9mm buffers i believe?  If it has sliding weights inside, are the weights under spring tension like w/ the A5 buffers?

What I would like would be to use one spring (probably a Tubb) & one buffer with either a Guard or a gas operated 5.56 upper (w/ adjustable gas block). Wondering if this Kynshot 9mm buffer could work w/ either upper?

I use an A5 extension with an A5H2 buffer for my M16 lower.  I run a 8" Guard upper for 9mm and 10.5" Noveske Switchblock for the 5.56.  Both run great in semi or FA.  I haven't tried the 9mm suppressed, yet.

does a suppressor affect the action of a (delayed) blowback really?

I assume it will increase the pressure like any other operating system, hence CMMG's Action Tuning Kit.

Hmm, I had the understanding that blowback firearms were not sensitive to either barrel legnth or having a suppressor mounted as everything that drives the action occuurs in the first few inches of barrel.  Maybe i was wrong or this does t apply to this radial delayed system

Your understanding is a misunderstanding.  I'll give you an example.  The M11-380 submachine gun is an open bolt, fixed firing pin, simple blowback operated gun, that employs advanced primer ignition. The Lage MAX11A1 is a rate of fire (ROF) reduction upper for the M11-380 submachine gun. The Lage MAX11A1 is a .380 ACP upper that drops the M11-380 ROF by around 50% give or take depending on ammo and the like.  The Lage MAX11A1 has a reciprocating mass of about 22 oz. compared to the standard reciprocating mass of about 12 oz.  The standard M11-380 barrel length is just over 5 in.  To get the MAX11A1 to operate, Lage had to extend the barrel length to 8 3/8 in. so that sufficient back pressure could develop before the bullet leaves the barrel.

As for the CMMG radial delay system (their terminology), I suggest you ask CMMG directly.  I believe they have their contact information at their Forum in the Industry Section.

Best of luck with whatever you decide to pursue.

MHO, YMMV, etc.

Thanks for helping me out.

Also  Good to know that max makes an upoer for 380 mac11

I just returned my M11/9 to stock (removed the Lage upper) and I love it like this.  So fast and fun!

Do you have a .380 Mac?

nope I gots no FA, but I likes the idea of a 380 SMG, seems like a perfect chambering for it, probably a lot easier to control than similar in 9?

"bolt specifically made for slower rate of fire"
+1 on that for sale!

Anyone know if switching to a standard ejector spring fixes most of the ejection/stovepipe issues?  Did anyone end up trying the Tubbs?  I'm getting ready to do a replacement tonight, prepping for the Ohio match this weekend.

I'm embarrassed (but also now very happy) that I've just learned about the Guard. I've got a Glock QC10 SBR lower and a standard blowback upper that runs OK but the sheer mass slinging around has made it not as enjoyable to shoot. I'm so desperately looking for an enjoyable PCC to shoot that checks all the right "boxes" but it seems they all fall short somewhere. I'm a huge fan of the AR platform so if I can get a smoother shooting system with good reliability and LRBHO, less weight, and preserve the ergonomics that make the platform so great, then this may be a real winner.

I'm going to order a kit and I'll try and keep the post updated with my findings and experiences with compatibility in a non CMMG lower. Though I'm not as resourceful as some of you gentlemen in here.

From going over the thread quickly myself I have the impression that lower kiss made for low back uppers may not have the correct magazine position for the guard.

I got the same impression though as most things like this it seems "murky". I ordered the barrel and bolt today but got an email from CMMG saying barrels are 4-6 weeks out.

Hopefully when I get mine in I can provide pictures/feedback on any issues and we can try and work through them together.

I switched to a Tubbs ejector/extractor spring set and for that shooting session that day it went well.  The next time I went out, I was having ejection/extraction issues again.  I bought a second 9mm BCG barrel combo and noticed the 2nd Guard extractor and ejector springs were a lot stronger than my first 9mm Guard bolt.  I did a complete BCG swap with the newer one and it was 100%.  So I pulled the Tubbs ejector/extractor spring set out and put in a stronger ejector/extractor springs I had laying around that felt close to what my 2nd Guard felt like and it is running 100% again.

However, I know two other guys running the Tubbs ejector/extractor spring set and they both are running fine.  So who knows.