zaitcev
Member
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- Oct 14, 2016
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While that is true, the mass of the brass piece is rather insignificant.
Radial Delayed Blowback
- Thread starter Sgt_Mike1
- Start date
shoobe01
Member
1) Yes, "down load" is the term of art for loading fewer in a magazine than the rated capacity. "Down load by 2" is common for M16/M4, so the crosscheck is the same as for fully loaded then you can do the same thing no matter who loaded your mags.
2) Yes to much of the Thompson Blish lock: it was before really good analytical or observational methods. The lock absolutely works in principle and at higher pressures, etc. He just didn't do it right on the .45. I always wanted more to the story so we could find why he (apparently) didn't at least pull an Edison (or Dyson) and iterate a few dozen or hundred times. Say, drill the bolt out to lighten it and fire in a test fixture progressively, see when velocity gets too high. He'd have immediately noticed the lock isn't working, and adjusted it and regardless have better optimized the mass / spring for the bolt. Luck was in the end on his side.
3) Have been using a CMMG radial upper in IDPA and generally messing about for a while. I don't track except on my precision rifle, but got to be 1,000 rounds through it. Dead reliable (like an AR 15, and very much unlike the straight blowback Colt SMG, never need to clean it), feels to the shoulder the same as any pistol carbine, but splits are MUCH faster, so it works. A lot. Totally suggested.
2) Yes to much of the Thompson Blish lock: it was before really good analytical or observational methods. The lock absolutely works in principle and at higher pressures, etc. He just didn't do it right on the .45. I always wanted more to the story so we could find why he (apparently) didn't at least pull an Edison (or Dyson) and iterate a few dozen or hundred times. Say, drill the bolt out to lighten it and fire in a test fixture progressively, see when velocity gets too high. He'd have immediately noticed the lock isn't working, and adjusted it and regardless have better optimized the mass / spring for the bolt. Luck was in the end on his side.
3) Have been using a CMMG radial upper in IDPA and generally messing about for a while. I don't track except on my precision rifle, but got to be 1,000 rounds through it. Dead reliable (like an AR 15, and very much unlike the straight blowback Colt SMG, never need to clean it), feels to the shoulder the same as any pistol carbine, but splits are MUCH faster, so it works. A lot. Totally suggested.
lysanderxiii
Member
The R51 is not a delayed blow-back. It is fully locked.
The breech block moves back approximately 0.08" and stops on the locking shoulder. The initial movement imparts motion to the slide which moves another 0.08 to 0.10" before picking up the breech block out of the locking shoulder, then the pair move rearward to complete the cycle.
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Sgt_Mike1
Member
Jim Watson
Member
I have shot both 1928 and MiA1 Thompsons, unfortunately not on the same day.
I could not recall a difference in feel of operation.
Why is the breechbolt movement in a Remington Model 51 .080"?
Because that is the thickness of a .380 case head. No sidewall unsupported til the bullet is gone.
Lots of other gimmick guns in collections, not many in regular use.
I kind of like the primer setback Garand. Variously reported as obsoleted by more progressive powder or crimped primers.
I could not recall a difference in feel of operation.
Why is the breechbolt movement in a Remington Model 51 .080"?
Because that is the thickness of a .380 case head. No sidewall unsupported til the bullet is gone.
Lots of other gimmick guns in collections, not many in regular use.
I kind of like the primer setback Garand. Variously reported as obsoleted by more progressive powder or crimped primers.
Crosshair
Member
It's delayed blowback
If it's a "Locked Breech", then what unlocks it? The carrier? How did the carrier get its energy? From the initial "blowback" portion of the cycle. Hmmmm. Sounds like a blowback cycle that is getting mechanically delayed.
Hesitation Lock has always been considered a delayed blowback system from everything I've read about it. I suppose you could try to claim it is a gas-operated system, with the case as the piston, but that shirt just doesn't fit as good as the "Delayed Blowback" one.
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lysanderxiii
Member
It gets its energy to unlock the same place an M1911 gets its energy, from the motion of the slide.
The proof that it is a fully locked system is that if you remove the slide, and fire the pistol, the cartridge energy will still be contained. A delayed blow-back would require the mass of of slide to keep the energy contained.
The proof that it is a fully locked system is that if you remove the slide, and fire the pistol, the cartridge energy will still be contained. A delayed blow-back would require the mass of of slide to keep the energy contained.
zaitcev
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It's a scholastic conversation about the number of angels at the tip of a pin. The hesitation lock action combines characteristics of blowback and locked breech actions as you two just threw back and forth. Of course the cartridge bottom has to move, which is where the action gets its energy. Crowbar is right and you are flat out wrong on this. But beyond that, of course it's locked.
You guys really need to duke out if Benelli B76 is inertial locked or delayed blowback.
lysanderxiii
Member
Well, according J. D. Pedersen, it is a locked breech system, he says so in his patent, and if any one should to know, it would be the inventor, not some guy on the internet.
The definition of a blow-back, or inertia lock is the mass of the bolt is what contains the energy of cartridge, ergo, if you remove a large part of the mass, the energy becomes uncontained.
With the Pedersen pistol design, you can remove the mass of the slide, about 80% of the mass, and the energy of the cartridge is still safety contained, it isn't a blow-back, period.
Demi-human
maybe likes firearms a little bit…
Blish thought his was locked too.
Said a guy on the internet, to a guy on the internet…
But I think we’re all being cavalier with the term “locked”.
And straying from the topic for the worst reason, academic.
Regardless the whys, things work or they don’t.
And the Radial Delay looks to work as well as the Browning Tilt does in a pistol, and better than a Blowback does in a AR.
I have discovered I can build a 45 Auto AR, with Glock mags, and a different company’s barrel, that will feel as nice as my other ARs, and I can tune it with buffer and carrier weight to my handloads.
Those bolt and barrel kits are looking even better!
someguy2800
Member
The R51 operates as a blowback for 2mm of travel and then is firmly locked as a tilting bolt mechanism like a FAL, BAR, ect…. It is most definitely a locked breach pistol because just pushing on the bolt face will not unlock it. It requires the slide moving rearward to unlock it.
A delayed blowback will open just by pushing on the bolt face but has mechanical advantage of some sort that must be overcome to open.
A delayed blowback will open just by pushing on the bolt face but has mechanical advantage of some sort that must be overcome to open.
lysanderxiii
Member
Actually, the patent for the "Blish lock" does not use the word "locked", but "restrained"Blish thought his was locked too.
Said a guy on the internet, to a guy on the internet…
And remember, patents are written by lawyers, so the choice of words means something about what the inventor thought . . .
Demi-human
maybe likes firearms a little bit…
And we continue to stray…
“Depends on what “is” is…” -Wild Bill C.
Bumping in the hopes of another range report on the Radial Delayed AR.
“Depends on what “is” is…” -Wild Bill C.
Bumping in the hopes of another range report on the Radial Delayed AR.
adcoch1
Member
Correct me if I'm wrong, but doesn't this thing just have shorter locking lugs on an AR bolt, and the 1mm or so of brass movement just initially bumps the bolt and carrier into motion for that 1mm or so, causing the bolt carrier to bounce back and rotate/unlock the bolt? Normally I am really perceptive about mechanical things, but I've never seen one of these in person...
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Sgt_Mike1
Member
Adcoch1 I'm not sure that the locking lugs are shorter. But here is what I have noticed by photos. CMMG seems to be out of stock of parts which means yours truly can't order parts to just look at or measure to validate.
Bolt - the back of the lugs have been chamfered to a point that the rear of the lugs do not present a flat surface allow considerably less locking surface than the 5.56 lugs would provide. The bolt is completely missing the gas rings
Bolt Carrier - the bolt retaining pin head is rounded as well as the cam path seems to be altered to cause the bolt to unlock with a greater ease.
Barrel Extension - (see my earlier post I showed a picture) the feed ramp has been altered to facilitate the 9mm round
but the majority of your post yes Like you I haven't put one in my hand but I think you are correct in the basic operation.
Bolt - the back of the lugs have been chamfered to a point that the rear of the lugs do not present a flat surface allow considerably less locking surface than the 5.56 lugs would provide. The bolt is completely missing the gas rings
Bolt Carrier - the bolt retaining pin head is rounded as well as the cam path seems to be altered to cause the bolt to unlock with a greater ease.
Barrel Extension - (see my earlier post I showed a picture) the feed ramp has been altered to facilitate the 9mm round
but the majority of your post yes Like you I haven't put one in my hand but I think you are correct in the basic operation.
greyling22
Member
I'll be honest, I read the first few posts then started skimming when the thread wandered. I have cmmg rdb 9mm upper I built over in the safe. Is it worth getting out and taking specific pictures, or has that moment passed? It does shoot a lot softer than either the ar9 or the cz scorpion I had. I did have some issues with the ejector spring, but a shorter stiffer spring from cmmg seems to have solved the problem.
Demi-human
maybe likes firearms a little bit…
Absolutely! I’m especially interested in the bolt and upper raceway(?) channels. I’m not clear if I need a CMMG upper receiver, or if it is merely suggested.
greyling22
Member
I just bought the barrel and bolt combo, used a cheap aero or Anderson upper, and some endomags in an Anderson lower.
Demi-human
maybe likes firearms a little bit…
This is what I was hoping to do as well. But with Glock mags. Not that the CMMG MKG lowers aren’t nice, but I like to mix and match.
Thank you for the information, @greyling22 .
It’s appreciated!
greyling22
Member
Here you go. I have the cmmg 9mm bolt next to a stag left hand but otherwise regular 223 bolt. They switch sides a couple times, so one is not always on the left. The cmmg has the 45° cuts on the locking lugs, the weird scalloped part of the gas key, and a slightly different profile at the end of the bolt carrier. I think it is designed that way so weights can be inserted inside of it.
Demi-human
maybe likes firearms a little bit…
A gentleman and scholar, Greyling.
Thank you very much!
Now I’m off to investigate another aspect of this PCC that I won’t muddy these waters with.
Thank you very much!
Now I’m off to investigate another aspect of this PCC that I won’t muddy these waters with.
adcoch1
Member
So it appears they are retarding (delaying) blowback by making the blowback basically un thread the bolt from the extension under recoil. Makes me wonder if a regular AR bolt would lock in this barrel extension. Interesting design idea. And should make the carrier mass a lot less critical.
Thanks for the pictures @greyling22 !
Thanks for the pictures @greyling22 !
adcoch1
Member
I'd bet the modified gas key is to keep these carriers from accidentally being dropped in a regular AR...
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Sgt_Mike1
Member
CMMG MKG = Glock mags , MK9 = colt/uzi style magazine. Which doesn't make any difference until your ordering a magazine. to misuse a model number in this conversation means nothing . Both work Great .
I'm drifting a bit, but it IS ONLY for background information NOT discussion, or to muddy the waters as to Why I started this thread to discuss the RDB while gaining a understanding of this system.
I've owned the CMMG MK9 (dedicated lower) 3.5" barrel and the Rock River (using magwell conversion) 5" barrel versions both setup for the Colt/uzi setup. My son conned me outta the Rock River and I still have the CMMG. Both have performed flawlessly with ASC, Colt, Rock River, Promag magazines. Sub (158gr) and super (90-115gr) types of ammo no difference in reliability .
Assisted a friend (Army buddy we both retired within months of each other) in his build, the hardest part was explaining the rule of thumb , 18 - 21 ozs total weight. In traditional blowback the buffer and bolt should weigh combined between those values as a starting point. He was steadfast set on a 16" barrel and using a poly receiver. Everything was going well until he got carried away firing as fast he could, sounding akin to full auto (even though I was telling him NOT to do so until everything was Ironed out) using mixed ammo. Bolt bounce finally got him on his third and last magazine change. Causing a similar to a out of battery firing. Resulted in completely destroying the Poly lower receiver in the magwell area. Nothing else except his pride and lower was damaged. He decided a dedicated receiver was what he really wanted, he obtained a MKG by mistake, runs flawless after we tuned his buffer weight.
That last part is what caused me to create this thread as the RDB system is completely different, not requiring heavy buffers etc to function. Also chances of Bolt bounce is greatly reduced if not eliminated. As it very well may be easier to tune for other calibers such as .30 luger (plinking) or 22 TCM (varmint dispatching). Even without the thread I had the thought that this would be a more advantageous system. Now back to the thread at hand.
I can't thank Greyling enough for the side by side photos as well as his input.
Actually that scalloped area looks to be there to allow the round head bolt retaining pin to be removed in assembly / disassembly. I looked at photos of a regular ar15 BCG (non stag) close up and the cam path is clearly different from a visual appearance. Now could a normal square head cam pin be used? I think I recall a FAQ on CMMG website saying so but they recommend the round one. Obviously they shortened the gas key to prevent damage to a standard AR gas tube if the bolt was switched it being solid i'm sure has a greater mass than a gas key but can't confirm until weighed.
according to another forum it has been reported that 5.7 bolt which is dimensional the same as a 5.56 except the bolt face dia. worked and converted the firearm into a single shot as the back of the lugs was not chamfered in the RDB barrel.
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someguy2800
Member
The parts will fit in any upper, however you may have ejection issues if you use a mil spec upper with a dust cover. The reason CMMG recomends using their upper is because they mill the ejection port a little larger. I went over this with them in emails when I could not get mine to work and they sent me a dimensioned drawing of how they mill the front half of the port larger and I did it by hand with a die grinder. Mine still didn't work afterward, but that's another story.
I tried it on mine when I had it out of curiosity and a normal bolt would go in the barrel extension and go into battery. I should have tried firing it with a 9mm but I didn't. The bolt face might not be quite big enough. Would be a neat way to make a single shot 9mm for shooting suppressed.
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