Mac roller delay?

[rybread]

You guys are full of ideas I love it! The roller delay would be behind the sear, so there would be drag at the start and end of the bolt stroke, allowing the full force of the bolt spring to be applied once it was forward of the rollers. I’m only looking for a delay sufficient to prevent bolt follow (if necessary) I could just lengthen the bolt channel/ stroke distance but even though I’m looking to mount this thing, I don’t want it to be comical novelty length!

 

[sniperdoc]

Have you considered using something like the Blish Device? It SHOULD be much simpler to make, and if done correctly, it would accomplish the same effect. Since it would not require any frame mods, if it doesn't work, take it out.

 

[Gaujo]

I had read that the Blish principal, at least as it was applied in the Thompson, had been disproven.

https://www.popularmechanics.com/military/weapons/a25414/tommy-gun-thompson-submachine/

"There was just one problem: Scientifically, the Blish Principle of metal adhesion does not exist. In reality, the effect Blish was seeing was that his lock merely added mass to the gun's bolt, which, in a blowback gun, simply slows the travel of the bolt. People figured this out during World War II, and British troops using Thompsons frequently removed the Blish lock. Later, when the Thompson was simplified to create the M1, the Blish lock was also abandoned."

 

[tlrgsxr]

I believe the B&T P26 uses a spring loaded ball and socket like the OP is referring to.

Here’s pics...
https://www.ar15.com/forums/Armory/BandT-9mm-Carbine-APC9/48-423440/?page=17

 

[sniperdoc]

I had read that the Blish principal, at least as it was applied in the Thompson, had been disproven.

https://www.popularmechanics.com/military/weapons/a25414/tommy-gun-thompson-submachine/

"There was just one problem: Scientifically, the Blish Principle of metal adhesion does not exist. In reality, the effect Blish was seeing was that his lock merely added mass to the gun's bolt, which, in a blowback gun, simply slows the travel of the bolt. People figured this out during World War II, and British troops using Thompsons frequently removed the Blish lock. Later, when the Thompson was simplified to create the M1, the Blish lock was also abandoned."

Yes, the Blish Device in the Thompson was unsuccessful

However, AFAIK, it was never tested in any other weapon, therefore the concept was not invalid

If the device were to be modified into a properly dimensioned curved shape and hardened into a spring which the bolt would have to deform (flatten) to travel over, it should slow the bolt.

 

[A&S Conversions]

It is my understanding that the Blish Lock principle only works under high pressure. I don't know as the pressure of .45 ACP is high enough to cause the adhesion of the dissimilar metals. Through testing Savage found that the extra machine time making the Blish parts and modifications of the receiver was not worth the time compared to a heavy squared off bolt. So Savage created the M1 version of the Thompson.

Scott

 

[sniperdoc]

It is my understanding that the Blish Lock principle only works under high pressure. I don't know as the pressure of .45 ACP is high enough to cause the adhesion of the dissimilar metals. Through testing Savage found that the extra machine time making the Blish parts and modifications of the receiver was not worth the time compared to a heavy squared off bolt. So Savage created the M1 version of the Thompson.

Scott

SAAMI lists standard 45ACP as 21,000 PSI, 12ga at 11,500. Since the Adhesion (only) method did not work at almost 2× pressure, there is no reason to assume it would work for 12ga.

 

[sniperdoc]

Maybe I need to elaborate more on my "Blish Lock" idea.
I used that term simply because it is the closest AFAIK to what I have in mind, but it does not completely or accurately describe my thought.
My idea is:
A piece of Spring Steel (the Device), shaped like a " ) ", whose Ends shall rest against the Attachment Point(s) which shall be located either the inside bottom of the Frame, the underside of the Upper, either (or both) sides of either of the above, or a combination of any or all.
The Curved Surface shall, at a certain point, be in contact with the Bolt in both Rearward and Forward motion of the Bolt.
The tolerances between the Device(s), the Attachment Point(s), and the Bolt shall be tight enough to cause the Device to deform (flatten) due to the pressure created by the pressure caused by the Bolt pressing the Device against the Attachment Point(s), thus impeding, and slowing, the velocity of the Bolt.

 

[slimshady]

SAAMI lists standard 45ACP as 21,000 PSI, 12ga at 11,500. Since the Adhesion (only) method did not work at almost 2× pressure, there is no reason to assume it would work for 12ga.

You're forgetting that chamber pressure is only part of the equation. The "SI" in PSI stands for square inch. The pressure exerted against the bolt is not the chamber pressure, it is the chamber pressure times the area of the rear of the case. A .22 LR has a max pressure of around 24,500 or so, well over 2X the pressure in a 12 gauge. People with suppressed .22 Ruger MKI/II/II/IV pistols use their thumb as a slide lock to hold the bolt closed for an extra quiet shot with no ill effects. The results from trying to hold a Remington 870 closed with the bolt locking block removed would likely not be as benign despite the much lower pressure...

As too whether or not it would work (Blish) I have no idea. The Blish idea that two surfaces "lock together" under high pressure has been pretty much debunked, but the mechanical disadvantage of having to push an inclined locking piece up a ramp is similar to the principle of the rollers in an HK. Essentially a delayed blowback system. Ian @ forgotten weapons did a vid on the 30-06 rifle Thompson entered into the US rifle trials and apparently the thing ejected empties so hard they stuck in wood!

https://www.youtube.com/watch?v=EMO4o4yANpY

Are you trying to delay opening of the bolt, or simply slow the bolt once it has opened to reduce the rate of fire in FA? If the latter why not a buffer arrangement that acts like the delay mech in the Skorpion? Hook at rear of receiver, bolt hits buffer and hook engages bolt. Pnuematic screen door closer type mech in buffer keeps hook engaged until forward bolt travel has pulled against the hook long enough for the plunger in the "door closer" to travel far enough to allow the hook to pivot away.

 

[rybread]

This is only regarding a potential need to slow down a bolt slightly in what is the equivalent of a max-31 length upper. It may not be necessary, but I like having a few options if needed.

 

[bruh44]

I know an MP5 style upper was made as an M-16 upper years ago. If I recall what I was told about it was there were ATF hang ups and the cost to build was far too high.

 

[rybread]

I know an MP5 style upper was made as an M-16 upper years ago. If I recall what I was told about it was there were ATF hang ups and the cost to build was far too high.

Yes- because, as previously noted that upper was made from what is considered the receiver for those types of guns.. just to add more confusion it varies by firearm!

 

[A&S Conversions]

I know an MP5 style upper was made as an M-16 upper years ago. If I recall what I was told about it was there were ATF hang ups and the cost to build was far too high.

Because of how the "upper" was designed and built, the FATD considered the "upper" a firearm. Adding a firearm to a registered machinegun means one too many firearms firing automatically. As far as cost, the roller delayed system needs very close tolerance, very hard heat treated parts. So manufacturing costs will be higher. I think that there is a very limited market, but a market nonetheless.

The roller delayed system is still considered by many to be the premier system for submachineguns. The roller delayed system would be adaptable to the Tenko adapter system. Currently CMMG has a radial delayed blowback system that does work with the Tenko adapter. There is plenty of discussion of the CMMG system on a AR specific board.

Just a simple custom detent pin can be 10 times the cost of the off the shelf part. So the more customized and complex the part is it can raise the cost to hundreds of times the cost of the off the shelf part. I think that there have been some very cool ideas suggested. The biggest issue would be the cost of implementing those concepts.

Scott
Manager A&S Conversions L.L.C.

 

[Fishman]

Would being open bolt affect the function of a roller lock? It seems like it would slow down the bolt coming in to strike the ammunition and potentially causing it to fail to sufficiently strike the primer. It seems like you would have to strengthen the string to overcome this additional resistance to the bolt coming home.

Yes, that would be a potential problem. We discussed this topic on silencerTalk. A gas delayed blowback, or a chamber ring delayed blowback would be very easy to implement on a mac upper.

 

[rybread]

So I’ve digested all this and I’m going to test a far more simpler solution I have in mind. Same concept as roller delay, but a much simpler approach. Like a slow ROF solution for about $12 vs. $800+

Just waiting for 4, $3 parts to arrive in the mail, then I’ll put it together to see if it will be feasible.

 

[rybread]

Yes, that would be a potential problem. We discussed this topic on silencerTalk. A gas delayed blowback, or a chamber ring delayed blowback would be very easy to implement on a mac upper.

The problem cited above is theoretically applying the resistance in the wrong place. The resistance should only be applied at the very start & end of the bolt cycle to arrest initial acceleration & the recoil impulse. When the bolt is stripping the next round and striking the primer, it is not under any additional resistance from my proposed device.

 

[rhouston8]

I had read that the Blish principal, at least as it was applied in the Thompson, had been disproven.

https://www.popularmechanics.com/military/weapons/a25414/tommy-gun-thompson-submachine/

"There was just one problem: Scientifically, the Blish Principle of metal adhesion does not exist. In reality, the effect Blish was seeing was that his lock merely added mass to the gun's bolt, which, in a blowback gun, simply slows the travel of the bolt. People figured this out during World War II, and British troops using Thompsons frequently removed the Blish lock. Later, when the Thompson was simplified to create the M1, the Blish lock was also abandoned."

hah. thanks Gaujo...learn something every day . I didnt know that about the Blish Lock. Funny.

 

[rybread]

My industrial strength parts arrived today. I could stack all 4 on a dime, they are so small. I’ll be drilling a bit tonight and possibly visiting the range tomorrow to test my garage made slow fire upper.

 

[sniperdoc]

I bet they cost a hell of a lot more than 4 for a Dime!
Let us know how the Range Test goes.

 

[rybread]

I got one of the 4 installed. It required a little more clearance so I had to drill a bigger hole in the opposite side and hit it with a wide bit. It seems to work- there was tension, enough that I couldn't push the bolt through- but when I pushed the upper down to the table, back plate first, it slammed home. Photos to follow.