FWIW: CMMG 9mm Rotary Delayed Blowback Buffer Weight Comparison
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- เผยแพร่เมื่อ 2 ต.ค. 2024
- Just some random footage I had on hand with the CMMG 9mm Rotary Delayed Blowback AR15 upper with a JP SCSS silent captured spring system and a 5.4oz 9mm carbine buffer. For what it's worth...
Full description of the system: • Rotary Delayed Blowbac...
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Banshee
Resolute
AR-15
FWIW, just tested a new CMMG 8" radial delayed upper this week and ran reliably with 115 gr ammo using both a standard buffer, H2, and H2 plus sprinco blue spring. On that last combo you could definitely feel the bcg slowing down but still locked back on an empty mag.
Use to practice on the SA80A1 with a 22LR conversion kit on a 25m range, it was also a great way to teach marksmanship principles.
I can't wait until you tune this enough to be competition reliable.
I wonder how the tuning would be unique from gun to gun.
A 9mm AR looks so incredibly fun. The last firearm I ever shot was in November 2018 with a 16" barrel SIG MPX. Very gentle shooting and every hole poked was enjoyable.
9mm AR's are fun, if sometimes wonky. I don't know of one that hasn't required some tuning. Mine sure did. AR-10 buffer spring, hydraulic buffer and SS hammer and trigger pins. I really need to chop the barrel and Form 1 it as an SBR. 16" is too long for 9x19mm.
I helped my dad get a PSA 12" AR9 pistol a few years ago. It was pretty good, but I found that some ammo nosedived into the feed ramp, which had a sharp edge. I put a little more radius on it, and it has been flawless since.
The ejection pattern was interesting - It looked like two forward, one back. Not sure what causes that.
Its common in the regular 9mm ar blowbacks.
I love how with those converted mags, it looks like you somehow accidentally shoved 9mm into a standard AR and it just kept working
I think it would be a good idea to get the weights CMMG produces for their RDB guns and give those a try. They were designed specifically for their system, so they ought to do the trick a little more precisely.
I have this system in the three available barrel lengths...the 16, 8 and 5 inch ones. the 16" is actually more like 12" since it was cut down with a lightweight extension welded to make overall 16". With the longer (16) one I run an H2-equivalent Armaspec captured buffer, and it's been completely reliable. But with the two shorter barrels I'd get cycling and ejection issues with that weight. Also some hammer-follow which made it like full-auto. Maybe because of less dwell/backpressure, but the shorter barrels run better with the carbine-weight equivalent. Seems they're more reliably cycling fully back. In the beginning I would get the crushed ejection spring and replaced with extra power. But when just expending cases manually, it doesn't toss out the round or empty case like a .223's. Ejection with 9mm primarily seems to be just 'knocking' the cases out when rearward travel stops under fire/cycling.
I will try an H1 again with the shorties, but am prepared to just stick with a carbine weight for those.
The last time I asked a question it went on a bit so hear goes again - does the extra barrell lengths velocity give you any real distance increase that is noticeably better?
Extra distance is not a relevant concern for PCC competition. For me, it's the ability to have a long forend that counts, so I can grip the rifle right out where I want to.
Ballistically, yes up to a point longer barrel length equals increased performance, whether rifle or pistol. This "sweet spot" varies from not only ctg to ctg but also load. Today there are loads specifically designed for short barrel guns (mostly handguns less than 4 inches, but notably 300 blk for pdw class weapons). Likewise shortening the bbl can drastically decrease the performance and range, most notably on rifle ctgs. Using the AR as a example, the gun originally had a 20 in bbl, going to an 11 in barrel not only limited the range and energy, but changed the performance of the mechanics of the gun, hence all the different gas and buffer systems.
Realistically, as far as range, not much. 16" 9mm's will run about 150-200fps faster than a 9mm pistol, but that's not really enough to make serious difference in effective range. 9mm bullets (like most handgun bullets) have low ballistic coefficients and as a result most people really don't consider effective past 50-100 yards.
115gn factory gives me about 1400 fps from 16" of barrel. But it's really not a concern of mine.
@@BlokeontheRange
Noice. Maybe later on a video with hotter loads?
Buy a Cozad active buffer. It's like a hydraulic buffer but uses a spring instead of hydraulic fluid. And is the best buffer in my opinion.
👍 für den Algorithmus
Give a follow up if you test more.
Of course! :)
If and when I come into money, Karl's, Ian's and your videos on the matter will be my bible for upgrade and maintenance of a WWDS2020.
I have an idea why the ejection pattern is inconsistent. I think its because of the different position of the buffer weights in the buffer. Let me try to explain. In my opinion the bolt system og the Banshee works like the Famas or G3. The pressure of the gases in the barrel are forcing the casing back against the bolt face, do to the angled surface of the locking lugs the bolt moves backwards and rotates, this rotating movement is transmitted to the cam pin and the cam pin is translating this movement to the bolt carrier and because the bolt carrier is resting against the buffer the buffer is forced to move to. In my opinion bolt carrier and buffer are accelerated by the Banshee like the bolt carrier of G3 and Famas.
Now the movable buffer weights come into play. In case #1 the weights are located towards the fort, they are moved as soon as the bolt carrier is moving and their inertia is added to the total weight of the accelerated mass. But in case #2 the weights are located in the rear. As soon as the bolt carrier is moving, the inertia of the buffer weights is keeping them in place. Therefore their mass in not count into the mass of the accelerated mass. Effectively you are firing a weapon with a bolt only kept shut by its masses inertia but the mass in slightly changing with each shot, because of the differing position of the buffer weights.
The first solution that came to my mind was to fix the puffer weights in place, but this will be dangerous, because this prevents them from doing their work, preventing dangerous bolt bounce. Blow back operations are very prone to this phenomenon.
A better solution would be to install a weak spring, nearly strong enough to overcome the friction in their own travel. This can cause a more consisted ejection pattern, because the weights would be in the same position at each shot.
To test this theory one only have to hold the barrel to the ground after each shot and shake is slightly, to move the buffer weights in their forward position.
Nice theory, except... neither the JP SCSS nor the 5.4oz carbine buffer used has movable buffer weights
Hmm, I'm not seeing anything here. We'll, not noticing but I like and comment because of the who know who rhythm.
Bloke off subject question, but what did the British army think of the M1/M2 carbine ?
That looks disappointingly snappy.
Hi, any updates of what works best for 9mm 16" RDB, do you have to get a longer buffer tube like A5 or Tubb wire if not using JP system ?
Fixed it with a Tubb ejector spring: th-cam.com/video/AZsz3v_SLTE/w-d-xo.html
I'm using the JP system with the standard spring and weights, which should correspond to a standard carbine buffer and spring.
did you have that extra weight inside bolt carrier? Mine came without it (whole rifle) and in standard configuration accuracy and consistency of ejection were very poor. It got better when I put that extra weight in.
Then chopped that barrel to 12", put on 15" inch hand guard and suppressor just for looks.
Nope. Any idea where I can get the extra weight? I did notice a couple of lateral holes at the back of the carrier, and I presume that that's what those are for.
@@BlokeontheRange CMMG sells them, although I apologize for not knowing if they can ship to you directly. However, if you have access to a machine shop, it's fairly simple to make a weight to fit in the carrier with minimal lathe time. You don't even need to incorporate the pin that interfaces with the holes in the rear of the carrier since when the rifle is assembled the buffer will keep the weight in place.
Another thing to keep in mind is that the carrier weight is incompatible with the JP SCS since it takes up the space where the SCS's guide rod needs to go. Hope this helps!
Why you didnt do the "Grip Clamp C" Style?
Because Bloke is British and he keeps to his training likely including lifting his pinky finger when drinking his tea (I'll have to check for this in any video where he's drinking tea) 😀
What spring did you use with the 5.4 oz?
The one that came with it in a set.
Have you considered using a high speed camera to look at just how much delay the system is giving the gun?
Yes, but don't have one unfortunately
@bloke My old samsung s8 has a high speed video option. It isn't easy to use because of the short recording duration, but I was able to get video of a poorly made mpk5 clone that failed to eject.
My assumption is a lot of people have newer phones than me and newer phones have more features.
Was there a change in felt recoil or the recoil impulse?
Yes, difficult to quantify, but it does change.
I use a carbine buffer and haven't noticed any irregular ejection issues. Makes me curious what is up with yours, might have been the JP setup.
I'll make another vid explaining it, but it was the ejector spring which was soft. Now replaced with a David Tubb one, and it ran over 200 rounds with the SP SCSS without a hiccup (but had a jam with a 5.4oz buffer)
@@BlokeontheRange huh go figure, I'll have to keep an eye out for that on mine.
My working theory is that due to the short cartridge case and the barrel extension, there's a "sweet zone" of ejector power and bolt velocity: too strong an ejector and not enough bolt velocity risks the case knocking the barrel extension on the way out and dropping, too weak an ejector and too much bolt velocity risks the case being ejected weakly and getting caught by the bolt. I don't have high speed video to confirm or deny, it's my educated-best-guess based on what I've observed.
@@BlokeontheRange that makes a lot of sense to approach it that way.
I do wonder if the timing of the radial system is a little fast out the 16" barrel, pressures are held a little longer in a pcc. An extra power buffer spring would help slow down the radial action in the pcc upper.
I only say that because I have very consistent ejection out of the 8" upper I have. My brass comes out surprisingly clean for a "blowback" too, are yours covered in soot?
If so, I would lean toward early unlocking (for lack of a better term). Blowback systems are pretty finicky with timing.
JP reckons that with their SCSS buffer system, the lightest weight and the heaviest spring (15-100) are the best combination. Mine's running so peachy with the standard spring though that I do not to want to tempt fate!
I do have some sooting on the cases, yes. And I've heard from my tame gunsmith that he's never heard of troubles with any of the 8" builds he's done (he's never done a 16), and I suspect I put rather more rounds down in any case!
Unusual to see a long barrelled 9 mm
It's a US made one, so 16" is the minimum barrel length without a tax stamp or making it a "pistol". Quite common for competition use too, cos it lets you reach out if you've got long arms.
It's gonna sound sarcastic and pointed, but I'm serious. You could call CMMG and say, "Hey I'm a big youtuber and I've done videos with gun jesus, plz fix my gun." My assumption is they'd send you one of the better made, hand picked units they sent off to influencers.
If I were in the US, maybe that would work... It's rather more complicated being in Switzerland!
That's really throwing them forward