460 rowland suppressed - mac10 clone DIY delayed blowback

[Hannibalbarca]

After some thought I’ve changed my mind about going with the Glock 21 as my platform due to concerns with durability of the polymer frame.
I’m now really considering instead getting a mac10 clone such as the vmac45 or a master pierce arms, leaning towards the vmac nickel plated, in combination with the buffer tube adapter for the brace, thread adapter or have it threaded to .578, and a better side charging handle. Will still be using the 28 oz suppressor. Also, if I did have someone make a thread adapter or find one, would it be fine to mount a suppressor to it? The thread adapter is thread unto the barrel but it would be to the rear and not the tip of the barrel, would I be asking for baffle strikes with that?
This will again fire 45 super loaded to 460 rowland specs, so 1550 FPS 180 grain jhp from a 5 inch barrel.
Also the accuracy as well, not really familiar with the mac10 in regards to accuracy, all things being equal, to say a Glock or 1911.


I have my concerns, such as the durability, parts availability, what recoil spring to use, rounds feeding(bolt velocity) and the DB suppressed from blow back Guns..
Would be interested in someone doing a DB test using a suppressed Glock 9mm and 10mm vs a blow back ar with the same barrel length.

Looks like I’m going need to make the bolt heavier. Tungsten inserts perhaps?

[propeine]

After some thought I’ve changed my mind about going with the Glock 21 as my platform due to concerns with durability of the polymer frame.
I’m now really considering instead getting a mac10 clone such as the vmac45 or a master pierce arms, leaning towards the vmac nickel plated, in combination with the buffer tube adapter for the brace, thread adapter or have it threaded to .578, and a better side charging handle. Will still be using the 28 oz suppressor. Also, if I did have someone make a thread adapter or find one, would it be fine to mount a suppressor to it? The thread adapter is thread unto the barrel but it would be to the rear and not the tip of the barrel, would I be asking for baffle strikes with that?
This will again fire 45 super loaded to 460 rowland specs, so 1550 FPS 180 grain jhp from a 5 inch barrel.
Also the accuracy as well, not really familiar with the mac10 in regards to accuracy, all things being equal, to say a Glock or 1911.


I have my concerns, such as the durability, parts availability, what recoil spring to use, rounds feeding(bolt velocity) and the DB suppressed from blow back Guns..
Would be interested in someone doing a DB test using a suppressed Glock 9mm and 10mm vs a blow back ar with the same barrel length.

Looks like I’m going need to make the bolt heavier. Tungsten inserts perhaps?

Why don't you just build/buy a DI gun and be done with it? All this craziness around trying to control bolt velocity for a REALLY hot pistol round could be solved with using a locked breach gun. The heavy bolt won't be pleasant to shoot. Call Macon Armory, or maybe even that new rotary breach from CMMG would be better.

[fishman]

That's what I was thinking.
Buy a cmmg mkg45. Ream out the chamber to 460rowland. Put the heaviest action tuning weight in the carrier. Put a heavy 9mm buffer in there.

Maybe modify a 7.62x39 bolt and do a DI upper on a pistol mag lower.

[Hannibalbarca]

After some thought I’ve changed my mind about going with the Glock 21 as my platform due to concerns with durability of the polymer frame.
I’m now really considering instead getting a mac10 clone such as the vmac45 or a master pierce arms, leaning towards the vmac nickel plated, in combination with the buffer tube adapter for the brace, thread adapter or have it threaded to .578, and a better side charging handle. Will still be using the 28 oz suppressor. Also, if I did have someone make a thread adapter or find one, would it be fine to mount a suppressor to it? The thread adapter is thread unto the barrel but it would be to the rear and not the tip of the barrel, would I be asking for baffle strikes with that?
This will again fire 45 super loaded to 460 rowland specs, so 1550 FPS 180 grain jhp from a 5 inch barrel.
Also the accuracy as well, not really familiar with the mac10 in regards to accuracy, all things being equal, to say a Glock or 1911.


I have my concerns, such as the durability, parts availability, what recoil spring to use, rounds feeding(bolt velocity) and the DB suppressed from blow back Guns..
Would be interested in someone doing a DB test using a suppressed Glock 9mm and 10mm vs a blow back ar with the same barrel length.

Looks like I’m going need to make the bolt heavier. Tungsten inserts perhaps?

Why don't you just build/buy a DI gun and be done with it? All this craziness around trying to control bolt velocity for a REALLY hot pistol round could be solved with using a locked breach gun. The heavy bolt won't be pleasant to shoot. Call Macon Armory, or maybe even that new rotary breach from CMMG would be better.

Cost and also size.

[Hannibalbarca]

I had an idea today.
What I converted it to a delayed blowback action?
My idea for this is to mill out a half circle recess in the bolt that corresponds to a half circle lug. This half circle lug would be on an L shaped piece of steel that’s welded up to the receiver. The half circle lug would be a ball bearing cut in half and welded to this L shaped beam of steel. For the bolt to come back it has to overcome the tension and friction of this lug.

[Hannibalbarca]

Someone on a different forum suggest direct gas impingement delayed blowback
Drilling a port in the barrel, making a custom gas block and having it direct gas towards the bolt and push it forward.

[DKDravis]

H&K did just that with the P7 pistols in 9mm kurz and 9 mm Para

They had to add some kind of "fluting" to the inside of the chamber to help the case to stick at the point of highest chamber pressure.
(At least thats the explanation I seem to remember reading 20 yers ago) The H&K Roller-lockers has the same kind of "chamber flutes")

I used to shoot a "sports" version of the P7 "grip-squeeze cocker" quite a lot, it was quite accurate.

[Hannibalbarca]

H&K did just that with the P7 pistols in 9mm kurz and 9 mm Para

They had to add some kind of "fluting" to the inside of the chamber to help the case to stick at the point of highest chamber pressure.
(At least thats the explanation I seem to remember reading 20 yers ago) The H&K Roller-lockers has the same kind of "chamber flutes")

I used to shoot a "sports" version of the P7 "grip-squeeze cocker" quite a lot, it was quite accurate.

Fluted chambers do help but I think it also leads to greater isn't instances of case ruptures since they stick to the chamber better.
Also for the delayed system, I bet the gas block would need to be very thin to fit into a Mac10 and also long.
The gas tube portion of the block would also need to be angled to hit the bolt.
I wonder, though, would it work if the gas block directed has towards the top of the bolt? Say you drill a horizontal hole in the bolt and a vertical one to where the two meet. You then drill a veritical hole from the top of the bolt and plug it with a steel cylinder piece.
The gas goes directly into the hole in the bolt and travels down the horizontal hole, wouldn't exit the front of the bolt since it's plugged.

Not sure if this would have the same effect as directly hitting the bolt but would definitely be easier to do in regards to clearance and machining.

[propeine]

Wrong...the flutes float the case with gas to AID extraction not to delay it. Seacamp pistols used a ring in the chamber to delay it.

On the P7 the gas is holding the slide shut with a piston not pushing the slide rearward. There is nowhere to put a rod of sufficient diameter on a MAC that can be large enough to resist the forces involved.

Gas delayed blowback according to Bender (long time member/SOT here for you newer guys) blows a ton of s--t back in your face when suppressed.

[fishman]

The flutes in a roller gun are parallel to the bore and help the case NOT stick. Some guns have flutes perpendicular to the bore that make the cases stick and delay the action. I assume you're referring to the latter with your mention of the p7.

Edit: prop beat me to it

[Hannibalbarca]

Wrong...the flutes float the case with gas to AID extraction not to delay it. Seacamp pistols used a ring in the chamber to delay it.

On the P7 the gas is holding the slide shut with a piston not pushing the slide rearward. There is nowhere to put a rod of sufficient diameter on a MAC that can be large enough to resist the forces involved.

Gas delayed blowback according to Bender (long time member/SOT here for you newer guys) blows a ton of s--t back in your face when suppressed.

I wasn’t thinking of using a rod, I was thinking of using a direct gas impingement system.
There would be thin gas block on the barrel and a port would be drilled into the barrel. The gas block also has an integral gas tube that’s angled upward since it couldn’t be the same height as the bolt since it would hit the bolt, so it needs to be angled upward for the gas to hit the bolt.
The gas would hit the front of the bolt, probaboy to the right since there’s mor e surface area to use there.
I would mill out a shallow circular pocket in this area for more surface area to push off as well.

Although maybe you could make the gas block be right over the chamber and have a rod positioned in the block(it would ride in the block) and permantly attached to the bolt. It would ride through the gas block when the bolt reciprocated back. The block would need to be extended to beyond the chamber for the barrel port though but there won’t be as much issue with clearance in regards to the bolt snd gas block.
The gas would push the rod forward, delaying the action and when the bolt travels back the rod travels with it snd through the gas block.

I really should look at vmac or MPA Mac clone in person first. I’d be able to tell then how much room there is for the delay system. Don’t think any of my local shops have anything as niche as that though.

[DKDravis]

@ the P7 Gas delayed blowback:

I remembered it wrongly -- the flutes in the P7 chambers are there to ensure that the case is "released" - my bad --

As I remember he P7 mechanism the gas vent is just forward of the chamber, and directs gas onto a piston that in effect holds the chamber closed until the pressure drops (when the bullet leaves the barrel)

I do not know the MAC-10 construction, so I could not comment on how this principel coulde be used here in a practical way.

[fishman]

What a neat concept. I never knew there were guns using this system.

[propeine]

Wrong...the flutes float the case with gas to AID extraction not to delay it. Seacamp pistols used a ring in the chamber to delay it.

On the P7 the gas is holding the slide shut with a piston not pushing the slide rearward. There is nowhere to put a rod of sufficient diameter on a MAC that can be large enough to resist the forces involved.

Gas delayed blowback according to Bender (long time member/SOT here for you newer guys) blows a ton of s--t back in your face when suppressed.

I wasn’t thinking of using a rod, I was thinking of using a direct gas impingement system.
There would be thin gas block on the barrel and a port would be drilled into the barrel. The gas block also has an integral gas tube that’s angled upward since it couldn’t be the same height as the bolt since it would hit the bolt, so it needs to be angled upward for the gas to hit the bolt.
The gas would hit the front of the bolt, probaboy to the right since there’s mor e surface area to use there.
I would mill out a shallow circular pocket in this area for more surface area to push off as well.

Although maybe you could make the gas block be right over the chamber and have a rod positioned in the block(it would ride in the block) and permantly attached to the bolt. It would ride through the gas block when the bolt reciprocated back. The block would need to be extended to beyond the chamber for the barrel port though but there won’t be as much issue with clearance in regards to the bolt snd gas block.
The gas would push the rod forward, delaying the action and when the bolt travels back the rod travels with it snd through the gas block.

I really should look at vmac or MPA Mac clone in person first. I’d be able to tell then how much room there is for the delay system. Don’t think any of my local shops have anything as niche as that though.

What holds the bolt shut? You're adding energy to a system that needs less energy. MACs aren't locked breach

Unless you're still talking about the P7 style system. Now you need a big rod to resist the tension forces imparted by the bolt thrust.
40,000 * .225*.225*3.14 = 6,350lb of bolt thrust (these are rough numbers)

Lets say you're using 110ksi yield material (Q&T 4140) and want a factor of safety of 2
55000 * r * r * 3.14 = 6350
r= .192
D = .384 so a bit bigger than 3/8" to resist the bolt thrust. Thats not even counting the flanged surface you'll need to push against since your rod is coming from the rear.

I've spent a lot of time on PCC stuff. Not in this caliber but the concepts are the same regardless just the sizing is different.

What is your end goal here. A size restriction? Put the recoil spring somewhere else on an AR platform and get rid of the buffer tube.
https://www.ar15.com/forums/ar-15/Foldi ... /4-666635/

Weight restriction? MACs are heavy as hell because of the giant bolt and you're going to need an even more giant bolt

Cost restriction? MPA is the same cost as a Glock. You should be able to build an upper for that cost.

[propeine]

What a neat concept. I never knew there were guns using this system.

yup P7 are awesome. They get hot after a couple of magazines though. Not surprising when the "gas block" is right above your left hand.

[fishman]

Now you need a big rod to resist the tension forces imparted by the bolt thrust.
40,000 * .225*.225*3.14 = 6,350lb of bolt thrust (these are rough numbers)

Be careful calculating bolt thrust around here. Some people get really upset.

He won't need the rod to be able to withstand the full 6300lbs. If there's 6300 pushing on of end and (for example) 3500 lbs pushing on the other. It will only need to withstand 3500 pounds of tension. This 3500 would be dictated by the pressure in the piston chamber and the size of the piston.

[propeine]

Now you need a big rod to resist the tension forces imparted by the bolt thrust.
40,000 * .225*.225*3.14 = 6,350lb of bolt thrust (these are rough numbers)

Be careful calculating bolt thrust around here. Some people get really upset.

He won't need the rod to be able to withstand the full 6300lbs. If there's 6300 pushing on of end and (for example) 3500 lbs pushing on the other. It will only need to withstand 3500 pounds of tension. This 3500 would be dictated by the pressure in the piston chamber and the size of the piston.

It is the internet. I expect people to get pissy.

It would open then! Need to withstand the 6300lb minus any friction/stiction from the chamber while the case is expanded. The thrust on the piston is pushing forward remember?

[fishman]

It doesn't need to completely counteract the bolt thrust. Even a partial resistance will delay the action. Isn't that the core concept here? If the piston completely counteracts the bolt thrust then the gun won't cycle at all

[propeine]

It doesn't need to completely counteract the bolt thrust. Even a partial resistance will delay the action. Isn't that the core concept here? If the piston completely counteracts the bolt thrust then the gun won't cycle at all

It cycles once the pressure on the piston drops. After the bullet leaves the barrel.

<iframe width="1280" height="720" src="https://www.youtube.com/embed/Wqll5aPJZHM" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

Watch that in really slow motion. Muzzle blast occurs at the same time or slightly before the slide begins to move. If the slide tried to move beforehand it would likely rip the extractor groove off or pull the case head right apart. That is part of the reason for the flutes because it still begins moving before pressure has subsided fully.

[fishman]

Id need to see much higher frame rate footage before I was convinced.

Id imagine footage of a blowback 380 or a highpoint would look the same. It APPEARS as if the slide doesnt move until the bullet leaves, but that's not the case with blowback guns.

Edit: yep. Just as I suspected. https://youtu.be/a5V9BfUtFP0

How would the pressure in the piston cylinder ever drop lower than the pressure in the barrel if the gasses have to vent back through the barrel to escape? Does the piston cylinder have ports to atmosphere that aren't shown in the above diagram?

Based on the diagram and the sequence of operation as I understand it, the slide isnt ever locked, its just slowed. Is this not the case?

[propeine]

Id need to see much higher frame rate footage before I was convinced.

Id imagine footage of a blowback 380 or a highpoint would look the same. It APPEARS as if the slide doesnt move until the bullet leaves, but that's not the case with blowback guns.

Edit: yep. Just as I suspected. https://youtu.be/a5V9BfUtFP0

How would the pressure in the piston cylinder ever drop lower than the pressure in the barrel if the gasses have to vent back through the barrel to escape? Does the piston cylinder have ports to atmosphere that aren't shown in the above diagram?

Based on the diagram and the sequence of operation as I understand it, the slide isnt ever locked, its just slowed. Is this not the case?

Nope no ports in the piston although there is bound to be some leakage. You're also correct that the slide isn't ever locked. Gas delayed blowback is the technical term. The piston area does however fill immediately after the projectile leaves the case. Pressure would be the highest in the first 1-2" of barrel then gradually fall both while the bullet is in the barrel and then drastically after it left as well. The piston is only 7mm in diameter not 9mm so presumably there is a balance there and at some point the piston pressure may still be higher but the residual in the bore is able to overcome the piston's resistance to movement. Inertia is all that is keeping things in place for the first 1-2" of bullet travel or so I suspect.

[fishman]

So how doable is implementing this on a mac, or even a blowback AR.

I was pessimistic about OP's mac plans but this could be the path to success. Even in a 9mm mac or AR this could be very valuable allowing bolt carrier weight to be greatly reduced.

[propeine]

So how doable is implementing this on a mac, or even a blowback AR.

I was pessimistic about OP's mac plans but this could be the path to success. Even in a 9mm mac or AR this could be very valuable allowing bolt carrier weight to be greatly reduced.

go read through my 9mm upper concept thread on that other forum. It takes a lot of space because you're controlling a bolt that is behind the barrel, not a slide that is near the front. On an AR there isn't enough room for even a very large handguard. I played with stuff for over a year to varying degrees of success. Then I built an MP5 because it just works. Unfortunately that isn't an option for 460 rowland although I have seen a CETME cut up to be turned into 45ACP so with enough skill...

https://www.troupsystems.com/product/hk ... rsion-kit/

http://www.weaponeer.net/forum/forum_posts.asp?TID=6756

[fishman]

Just do a normal long stroke piston AR setup except instead of porting the gas to the front side of the piston, port it to the rear side. Put the gas block and piston as close to the chamber as you can.

[Hannibalbarca]

Wrong...the flutes float the case with gas to AID extraction not to delay it. Seacamp pistols used a ring in the chamber to delay it.

On the P7 the gas is holding the slide shut with a piston not pushing the slide rearward. There is nowhere to put a rod of sufficient diameter on a MAC that can be large enough to resist the forces involved.

Gas delayed blowback according to Bender (long time member/SOT here for you newer guys) blows a ton of s--t back in your face when suppressed.

I wasn’t thinking of using a rod, I was thinking of using a direct gas impingement system.
There would be thin gas block on the barrel and a port would be drilled into the barrel. The gas block also has an integral gas tube that’s angled upward since it couldn’t be the same height as the bolt since it would hit the bolt, so it needs to be angled upward for the gas to hit the bolt.
The gas would hit the front of the bolt, probaboy to the right since there’s mor e surface area to use there.
I would mill out a shallow circular pocket in this area for more surface area to push off as well.

Although maybe you could make the gas block be right over the chamber and have a rod positioned in the block(it would ride in the block) and permantly attached to the bolt. It would ride through the gas block when the bolt reciprocated back. The block would need to be extended to beyond the chamber for the barrel port though but there won’t be as much issue with clearance in regards to the bolt snd gas block.
The gas would push the rod forward, delaying the action and when the bolt travels back the rod travels with it snd through the gas block.

I really should look at vmac or MPA Mac clone in person first. I’d be able to tell then how much room there is for the delay system. Don’t think any of my local shops have anything as niche as that though.

What holds the bolt shut? You're adding energy to a system that needs less energy. MACs aren't locked breach

Unless you're still talking about the P7 style system. Now you need a big rod to resist the tension forces imparted by the bolt thrust.
40,000 * .225*.225*3.14 = 6,350lb of bolt thrust (these are rough numbers)

Lets say you're using 110ksi yield material (Q&T 4140) and want a factor of safety of 2
55000 * r * r * 3.14 = 6350
r= .192
D = .384 so a bit bigger than 3/8" to resist the bolt thrust. Thats not even counting the flanged surface you'll need to push against since your rod is coming from the rear.

I've spent a lot of time on PCC stuff. Not in this caliber but the concepts are the same regardless just the sizing is different.

What is your end goal here. A size restriction? Put the recoil spring somewhere else on an AR platform and get rid of the buffer tube.
https://www.ar15.com/forums/ar-15/Foldi ... /4-666635/

Weight restriction? MACs are heavy as hell because of the giant bolt and you're going to need an even more giant bolt

Cost restriction? MPA is the same cost as a Glock. You should be able to build an upper for that cost.

Again, the only thing the gas(no rod here) will do is slow down the cycling of the bolt to keep pressures at safe levels when the case is extracted so that I don’t have a case rupture or best the gun up too much.
I thought about the rod method a bit more and since the gas blow would need to be open ended for the rod to travel through the gas would just escape to the other open side and not act on this rod(piston).