You will find that it varies pretty dramatically.  I know guys running 100gr bullets with slow powders, guys running 147's with fast powders, and everything in between.  I have been using a 124gr FMJ over 4.0gr of Titegroup, which I know makes PF out of a handgun, so it should do so out of my 5" comped, pinned and welded barrel.  My girlfriend and I both have been shooting 8" CMMG radial delayed blowback based SBR's using this same load.   I have shot everything from 147gr over 3.7gr of N320, 115gr over 5.5gr of Power Pistol to 147's over N350, as well as my 124gr over 4.0gr of Titegroup load out of 3 different uppers using this Maxim buffer and all have been cycling reliably.

Thanks for the reply
My PCC load is subminor out of a pistol, I guess I’ll find out whenever I get it in

This would solve the charging effort neatly:

https://www.ar15.com/forums/general/Why-no-electric-piston-charging-handle-yet-/5-2656354/

Was back at the range today with three different lower setups to pit against one another.

1)
Carbine 7" buffer tube(std)
Maxim RDB
9mm bolt with weight removed

2)
Vltor A5 7-3/4" buffer tube
6oz 9mm buffer
1-Kynshot 2.5oz spacer/weight
Wilson Combat flat-wire buffer spring
Faxon 9mm bolt

3)
JRC 8.5" carbine buffer tube
Kyhshot RB5007 buffer
2-Kynshot 2.5oz spacer/weights
Wilson Combat flat-wire buffer spring
Faxon 9mm bolt

The upper used had a 5" barrel and an NFA side-charger receiver.

Ammo was WCC 124gr +P.

#1 was definitely the winner and #3 was a close second. The lower with the RDB seems to be settling in and getting smoother every time I take it out. Charging seems to be getting easier, but then I could just be getting used to it. #3 is a considerable improvement over #2, as it should be, but just not as soft or smooth as #1.

The Maxin RDB was installed without a buffer detent so that it just touches the bolt upon closing the receivers. I have not tried any other variation, such as tighter or looser.

As much as I like the GRS, the Maxim setup is proving to be the best. @Droppoint deserves many kudos for its development, but it's hard to beat a delayed blow-back setup that works. YMMV

ETA: I am going to try the 115gr ammo in a 16" barrel to see if it will make the action work as it should. If it does, the thing ought to be really soft shooting.

This is great info.  Thanks for the testing.  Looking forward to comparing against my CMMG RDB.

Question I have is with 100 power factor ammo will it help and work to the potential like with +P ammo or not function as it seems to be non-tunable out side of preloading

It didn't work well with 115gr ball. I had many stove pipes where the fired case was stuck in the ejection port, there was a new round in the chamber, but the hammer wasn't cocked. I have no idea how that compares to 100 power factor ammo, but the RDS doesn't appear to like lower powered ammo to function at its best, at least not for me.

100pf is really light but pretty common for Steel Challenge. My SC load is a 95gr at 1,025fps so just under that and it runs very well with a properly tuned Scheels.

Thanks for the putting all this together!  The GRS and Maxim operate under very different principles, so I would fully expect mechanical delayed systems to be better at mitigating felt recoil.  Since I don't make any money off the GRS, I don't have any skin in the game, so no worries here!  

IMHO the difference in the charging effort (10lbs. vs 32lbs.) makes the GRS better from an "everyman/woman" perspective, while the RDB will be better for serious competitors.  If the RDB was easier to charge, I'd put it in all my guns and toss the GRS in a heartbeat.  The RDB is a simpler install, self contained, and works very well after the initial chambering.

The ability, and provided instructions on how, to tune the Scheels seems like a more developed system.

Is there any way to tune the RDB? I didn't see anything on the website, and there apparently doesn't seem to be much in the way of info that arrives with the product, but those with hands on could probably confirm if there's any way to adjust it to your firearm and load.

On that note, I got my LevAR charging handle yesterday.  It works great but kind of awkward to use.  Like using a right sided charging handle.....ala AK..  Reach over on the right side with your left hand to charge.  This is all assuming you are right handed and don't want to use your right hand to charge.  It is more narrow than my Armageddon Tactical charging handle so less surface area if you want to use it without the lever action.  
I tested with no pre-load so worst case scenario.
It has to start out in the position shown below and then stays perpendicular to the bore's axis when you apply rearward force to the handle.

Do you have to hit the latch on the left side of the charging handle or does the right side large handle work like an ambi style charging handle?

Nope

Noice!  I have one on order, coming from Dack Outdoors - super price - $56 - but they take about 30 days to get product to your door.

Now we just need to convince Maxim or Springfield to make the same exact handle, but mirror-image so charging is with the LEFT hand.  I'm not holding my breath.

ETA: This is going to work much better with slick-sided uppers, too. My uppers are all AR-15 and have the forward assist in the way.

It really just sounds like a reciprocating right side charging handle bolted directly to the bolt or bolt carrier would be the simplest answer and give non-Sinisters the most leverage.  You're giving up a dust cover and marginally weakening the upper.

Most 115 ball is right around 125pf from a pistol, I think. 100pf won’t run right in some handguns, stock. Your 124+p is probably around 135pf-145pf from a full-size pistol.

PF is mass in grains times velocity in fps, divided by 1,000. I’m not trying to insult anyone, just wanted to provide some reference to the group, in case someone doesn’t speak PF.

The LevAR (pictured above) has a camming system that acts as a force multiplier to increase the operator's leverage and "pop" the bolt free for the first 1/4" or so.  Should be perfect to get most people past that 32lb. "wall" of the mechanical delay.

Video of operation near the bottom of this page: https://store.springfield-armory.com/levar-ratcheting-charging-handle/

Saw that.  That will help, but you're still at an awkward angle unless you dismount the rifle.

Stoner wanted to seal the action and allow use right or left-handed, but he wasn't trying to run a roller delay action in the stock.  

So I am assuming there was not enough energy to complete the firing cycle and short stroking. I have been using the Taccom MDRS and it is extremely tunable.  From a operational standpoint, if the delay comes from a mechanical system or a magnetic system, I cannot see the difference between the two.  But I may be missing something.

Thanks

OK, I went there...



Here are the spring stats.  These may not be 100% accurate, but should be relatively close:

Length: 9.5"
Wire diameter: 0.045"
Active coils: 38.5
Coil diameter: 0.45"
9 lbs. pressure at 4-1/16" compression (bolt in battery, no pressure on buffer, assembled resting state)
15 lbs. pressure at 7-5/16" (compressed to full bolt rearward)

By these measurements, spring performance is slightly more than a Sprinco Red.  This is more than 9mm blowback needs, but may be necessary for proper operation of the mechanical delay.

LOL...I just took the pictures below this AM.  
I was wondering how much the reciprocating mass is:


I also have the JP SCS tuning kit and the springs fit fine.  So I can mess with those and was also thinking I could maybe use a weak inner spring and use in conjunction with a flat spring.


I was already planning on testing the factory setup for a baseline then messing with the springs and also making a new buffer to extend the stroke to the max.  I'm measuring about .690" before the guide rod hits the firing pin.  I'm thinking I can get away with a custom buffer that is .5" shorter.  Yes, I know this may increase the chances of having the malfunction where a spent case gets behind the ejector but I don't care.  If it doesn't work I can always put the stock buffer back.

@Amphibian
Looking at your pic, there seems to be a significant difference in length between the JP and the Maxim. Anticipating any problems from that or is the pic deceiving?

Some of those JP springs seem weaker even though the OAL is longer.  I need to get a spring testing setup like @Droppoint did.  There are always wire clippers if necessary but I'm hoping not to have to go that route.

DUDE!  I was just looking at the JP SCS spring kits!  Glad you have them, now I don't need to buy them all and try trial-and-error!  PLEASE let me know if they work and how well.

I was just measuring the reciprocating mass - the roller cup, bearings, and collar extension.  Got a reciprocating mass of about 4.3oz.

@amphibian

Look for spring testers people have built or sell for 1911 recoil springs.  One of those, just a little longer, should work perfectly for the JPSCS sized springs.

This is all very cool and I'm excited because this is the sort of "drop in" style of solution that many of us are hoping for.

So it looks like the guide rod is the equivalent of the locking piece in the H&K system? In order to tune the system, you would need to grind a new guide rod?
The pics/videos show the bearings are pretty dry, but I would have expected them to be packed with a little grease (or maybe I'm just used to looking other mechanisms where bearings are packed with grease).

I noticed that the system seems to "jump" forward a little bit in the slow motion footage that Droppoint posted. I wonder if affixing the back of the guide rod through the drain hole in the receiver extension would smooth that out at all?
I do like Amphibian's idea of trimming down the urethane bumper a little bit to increase the stroke length. Would it be possible to replace that bumper with a hard rubber stopper (like a drain plug from the hardware store) or would the rubber bulge and bind against the spring coils too much?
Or perhaps sticking the system in an A5 receiver extension with a hard rubber spacer at the back of the tube could help lengthen the "moment" before the bearing mechanism is overcome and smooth out the recoil impulse that way?

I'm guessing that bolt bounce is mostly a non-issue since the bearing lock up appears to be quite stout. Once the front part of the system pops forward, the bolt would have to bounce hard enough to overcome the bearings again.

Thanks for sharing the pics and the outcome of your testing and tinkering. It's a huge service to the community!

I still haven't had a chance to shoot mine.  Hopefully tomorrow.  Been raining a lot here in FL and I go to an outdoor range.
I did make a custom 'bumper' last night:
The stock one is 1" long and mine is 1/2".  You can maybe go another .200" or so and then you risk the guide rod impacting the back of the firing pin.
Optimally, you want the inertia to run out to so it never impacts but I doubt that will happen with this setup.

I don’t have one, so I may be mistaken, but as I see it from a previous post: The MP5 trunnion recesses analogous the recoil spring guide recess, the MP5 LP angles to the conical angled surface of the large rear weight, the MP5 carrier to the large rear weight, and the MP5 rollers to the bearings.

So, to tune the system ala HK locking piece change, one would change the conical angle on the inner front surface of the large rear weight.

Mine had grease on the bearings.

Droppoint, was there grease on your bearings/

Not Droppoint, but mine were greased also, for another example.

Yes - I cleaned them off for the pictures and put bearing grease back on them for reassembly.

FWIW, I asked Maxim what to lube the system with and they said to use Lucas Extreme Duty Gun Grease, but that was not to be considered an "official endorsement".

Stupid and probably expensive thought, but couldn’t someone mill the collar back to a straight cone, then have keyway fit raceways for the bearings so you can change the angle of engagement, Ala HK roller keys?

Probably pointless and expensive but curious on customization.

Special thanks to @CJoFL for coming out to help me with taking the high speed video and running some of the configurations below in full auto.
I will try to work on processing the videos later.
For now wanted to post our findings.


What I found disappointing was configuration 1 and 2 were both relatively loud with the Maxim RDB system.  #2 is an integral blowback setup so not like I can use the CMMG RDB system with that barrel/suppressor.  I should have brought all the parts for  @Droppoint's GRS.  I'm sure that system was not loud with my CT9KS when I tested with the GRS before and I never tried it with my integral but I'm sure it would be fine since I've never had the integral hurt my ears on my old blowback setups.
CJofFL and I couldn't tell the difference in suppression between my tuned CMMG RDB or the MP5.  Both are excellent and very quiet with the CT9KS.

I tried with the stock Maxim RDB setup with no preloading.  I also tested with my custom 'bumper' I posted earlier.   That worked fine and also dropped the cyclic rate.
Stock setup below.
]

Custom buffer below.


We noticed that I should have made my delrin spacer a tad longer as the spring is going solid height before hitting my delrin spacer.   I measured .086 gap clearance.

We were going to test the weakest JP spring but it has the same .046" wire gauge diameter and being longer, it goes solid height sooner and I don't feel like cutting coils since we were thinking maybe we should go with an even stronger spring to keep the bolt closed longer making it quieter but then it will be even harder to rack the bolt.

I also feel like it got easier to charge but like others mentioned, maybe I am just imaging things.

Bottom line for me, the number one requirement for me is suppression and IMHO, it is worse.  I think even my old straight blowback setups I don't shoot anymore suppress better than the Maxim RDB.  Droppoint's GRS is a great improvement over that.
I already mentioned my tuned CMMG RDB is on par with my MP5 in smoothness and suppression.

IMHO, if you don't care about suppression and the additional charging force, the Maxim RDB is very smooth and a great drop solution.

So I'm back to waiting on the MEAN Arms bearing delay.....

So it looks like the Maxim unit is a no-go for the full-auto guys.  Too bad, as the MEAN Arms bolt is starting to look like vaporware.

Thank you for the usual superb write-up.

When is someone going to throw the Maxim RDB behind a CMMG RDB?  I'm curious if it will function!

Actually, I think a good FA use case for it would be with a Colt DOE upper.  Very nice looking upper.  I'm always torn with that setup as it looks so good and I want to suppress it but then it kills the value and 'correctness' so I just do anything.  I do have a friend that has one.
Here is the non-suppressed cyclic rates:


3 round burst:


With my custom bumper it came out to a pretty nice rate:


3 round burst, notice as mentioned in the beginning of the video that my custom delrin spacer isn't glued or press fitted so it is sitting in front of the custom steel washer I made.  So it actually isn't bottoming out which I think is impressive.


I am going to make a new Delrin spacer and undersize it so I can press fit it in place and also make it slightly longer to prevent the spring from going solid height.

Uh...yeah...I could have done that yesterday...forgot.

I had hoped the benefit of the Maxim to the masses would be to allow an AR9 to suppress like a Mp5 with its somewhat similar roller/bearing delay. Dead Air once posted about the development of the Wolfman and how the AR9 was 9-10 dbs louder than the MP5 at the ear with each platform being at the extreme ends of the loudest/quietest suppressor hosts. The Maxim might narrow the gap, but it was still unpleasant to my sensitive ears and Amphibian's less sensitive ears too. In contrast, Amphibian's, albeit heavily customized, CMMG and MP5 were both very comfortable without hearing protection. That's applies to a CT9KS on all 3 and the Maxim with integral.

Doh, I forgot about the 'Maxim RDB behind a CMMG RDB' test too

ETA: It was interesting to note, and can be seen in the hi speed video above: when the large rear weight is forced rearward, it actually yanks the small forward piece rearward separating it from the carrier briefly. It reminds me of the descriptions of the forceful extraction on the MP5/G3 with the carrier forced rearward, traveling at a much greater speed than the bolt head until yanking the bolt head with it.

Too bad he just guessed that the delay would help with suppression and didn't actually test it.
I thought the same thing too but was disappointed and @CJofFL was there as well for some consensus.

Anyone else able to share suppressed impressions?

That is disappointing but thanks for saving me a little $$$

Sounds like the delay is coming too late in the cycle.  So since you have a much light reciprocating mass it's moving faster initially, causing increased port pop.

True...but I think the amount of reciprocating mass is irrelevant.  The amount of mechanical delay isn't enough.
The MP5 for example has very little reciprocating mass compared to this...unless you are referring to the mass of the Maxim unit itself?

Irrelevant to the entire cycle yes, but if the delay is coming too late, then it's not irrelevant to the initial opening of the bolt.

So I mentioned I didn't have any preload to give it the most mechanical advantage, maybe we have should tried to get a little preload in there just to make sure it was contacting the bolt.

Just to be devil's advocate, maybe working suppressed wasn't in the engineering parameters for the RDB.

You are correct and they don't mention it at all on their website.  My bad for assuming that since the company also makes suppressors that this product would help with suppressor usage.  Again no instructions and waiting for some more feedback as I didn't adjust for preload.

I'd definitely be interested to see if that helps with suppression.