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Posted: 12/11/2016 2:45:13 PM EST
I do not own a gas delayed (gas retarded) pistol but have always been intrigued by them. How does the piston overcome the force trying to open the slide? I understand the gas pushes the piston forward, but the gas also pushes the the breech rearward. is the gas cylinder/chamber larger in diameter than the bore/chamber of the firearm, making the the gas volume displaced by the piston greater than the volume that would be created by the slide and empty shell rearwards?

What is the diameter of the piston/ gas cylinder for those who have access to them?

This is purely out of curiosity at this point.
Link Posted: 12/11/2016 4:17:09 PM EST
Link Posted: 12/11/2016 4:31:58 PM EST
I have seen the video before, what I am interested about, is how the slide stays in battery until pressure drops. My brain tells me that the larger piston, in this case, the brass and chamber would overpower the smaller piston moving an equal distance. Assuming the gas cylinder is a smaller diameter than the bore. Is the mass of the slide enough that the pistons job is to simply increase the time it takes to open?
Link Posted: 12/11/2016 7:43:24 PM EST
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Originally Posted By GriswoldGuns:
I have seen the video before, what I am interested about, is how the slide stays in battery until pressure drops. My brain tells me that the larger piston, in this case, the brass and chamber would overpower the smaller piston moving an equal distance. Assuming the gas cylinder is a smaller diameter than the bore. Is the mass of the slide enough that the pistons job is to simply increase the time it takes to open?
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Yes, the gas pressure just acts as a delay to the slide moving rearward.
Link Posted: 12/11/2016 8:05:30 PM EST
Those are good and interesting questions. Even though I have a CCP, I do not have the answers. Sidenote: Even though arfcom hates the CCP, I freaking love the thing. Highly reccomend it.
Link Posted: 12/11/2016 10:09:18 PM EST
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Originally Posted By Thorgrim:
Those are good and interesting questions. Even though I have a CCP, I do not have the answers. Sidenote: Even though arfcom hates the CCP, I freaking love the thing. Highly reccomend it.
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The reason that I ask them, is that I doodle up ideas when I am bored, and without revealing too much (on the .0087% chance that I actually do something with the idea), I had an interesting thought pop into my head today and needed more understanding of the gas retarded principle.

If you get a chance, could you tell me what the approximate diameter of the gas piston is on the CCP? I am just wondering what the ratio is for bore to cylinder.
Link Posted: 12/12/2016 1:11:24 PM EST
The ratio of the gas piston is dependent on the caliber of the gun.

When considering the action pressurized, the bullet is rapidly accelerating and gas pressure in the cartridge case is working against the breech face to push it back. With the piston pinned to the front an equal amount of PSI is encountered exerting force in the opposite direction. Gas pressure develops from the time of ignition, thru pushing the bullet out of the mouth of the cartridge, then uncovering the port as the base passes, at which time peak pressures occur. It's not instantaneous and is spread over fractions of a second until the bullet clears the muzzle, at which point the entire trapped volume can exhaust out the bore from both ends.

Therefore while the ratio might be of interest, the gas port diameter and it's location in the barrel is also critical to timing. It's not unlike the AR15. Since it's caliber dependent, and I suspect barrel length has it's impact, then a map of that for one cartridge may include an area where gas port diameter and gas cylinder diameter chart appropriate space in coordination with slide timing and it's cyclic rate.

What we see changing more often or not for the AR15 is port diameter and location. The internal piston sealed by the rings on the bolt remains static. This happens in Browning actions, the ramp angle on the barrel lug controls the timing of unlocking and at what speed it's done. S&W 3 Gen guns are reportedly using different ramp angles on standard make guns vs TSW which delay the action slightly more due to hotter loads or accuracy requirements. Now, compare that with the GI standard 1911 swinging link which is the same for any barrel length - I think that points out why the shorter actions are more problematic and why they suffer unreliability because they are locked into a fixed delay only suitable for a 5" barrel.

Since you asked. Just some crude observations.
Link Posted: 12/12/2016 1:28:05 PM EST
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Originally Posted By GriswoldGuns:
Is the mass of the slide enough that the pistons job is to simply increase the time it takes to open?
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Yes. The gas pressure slows down ("retards") the movement of the slide while the bullet is still in the barrel. As soon as the bullet exits the barrel gas pressure drops.
Link Posted: 12/12/2016 10:43:23 PM EST
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Originally Posted By tirod:
The ratio of the gas piston is dependent on the caliber of the gun.

When considering the action pressurized, the bullet is rapidly accelerating and gas pressure in the cartridge case is working against the breech face to push it back. With the piston pinned to the front an equal amount of PSI is encountered exerting force in the opposite direction. Gas pressure develops from the time of ignition, thru pushing the bullet out of the mouth of the cartridge, then uncovering the port as the base passes, at which time peak pressures occur. It's not instantaneous and is spread over fractions of a second until the bullet clears the muzzle, at which point the entire trapped volume can exhaust out the bore from both ends.

Therefore while the ratio might be of interest, the gas port diameter and it's location in the barrel is also critical to timing. It's not unlike the AR15. Since it's caliber dependent, and I suspect barrel length has it's impact, then a map of that for one cartridge may include an area where gas port diameter and gas cylinder diameter chart appropriate space in coordination with slide timing and it's cyclic rate.

What we see changing more often or not for the AR15 is port diameter and location. The internal piston sealed by the rings on the bolt remains static. This happens in Browning actions, the ramp angle on the barrel lug controls the timing of unlocking and at what speed it's done. S&W 3 Gen guns are reportedly using different ramp angles on standard make guns vs TSW which delay the action slightly more due to hotter loads or accuracy requirements. Now, compare that with the GI standard 1911 swinging link which is the same for any barrel length - I think that points out why the shorter actions are more problematic and why they suffer unreliability because they are locked into a fixed delay only suitable for a 5" barrel.

Since you asked. Just some crude observations.
View Quote



This is getting closer to what I am trying to understand.

To my knowledge, the gas port has to be near/touching the mouth of the case in order to start building pressure in it as soon as possible or the action would start to go out of battery before there was resistance.

For simplicity sake, lets say all examples are for a 9mm, since that's what the CCP and P7 are.

To break it down to a more basic level, my question involves different size gas chambers for lighter actions and or different barrels. For example, we know that on the Walther CCP, that we have a constant weight for the slide and a constant diameter of the gas chamber, but if the slide weight was reduced by half, would the diameter of the gas cylinder have to be increased by some amount? My thinking says yes; the reduced weight (inertia) of the slide would require greater force to keep it closed for the same amount of time.

What would need to be done to counter the longer dwell time of the bullet in a longer barrel? Would increasing gas chamber size be required? Gas port size?


Another hypothetical that I just now came up with:
If we take a firearm that had a larger gas cylinder and piston than the bore, would it lock the breech until pressure was gone? Say the piston displaces 3cu inches but the volume created by opening the action is only 2cu inches, regardless of action weight or springs and given a sufficient gas port, would it act like a locked breech while firing?
Link Posted: 12/13/2016 1:01:12 AM EST
You guys are overthinking this.

The Nazis developed the action. There's a point of diminishing returns with it. That's why they went to the roller-locked system. The gas is actually bled out during the process. That's the "delay." When the bullet leaves the barrel, the pressure drops completely and the slide cycles full speed. So basically, the slide goes slow for a millisecond and then goes fast to cycle the gun. It is never "bottled up." The trick is to slow it down enough for it to function without blowing up.

It works for smaller calibers because the size of the piston and the volume of the chamber have to be proportional to the volume of gases and the size of the bullet. HK made a .45 P7, but it never worked well and they had to make lots of modifications.
Link Posted: 12/13/2016 6:18:25 AM EST
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Originally Posted By Leonidas777:
You guys are overthinking this.

The Nazis developed the action. There's a point of diminishing returns with it. That's why they went to the roller-locked system. The gas is actually bled out during the process. That's the "delay." When the bullet leaves the barrel, the pressure drops completely and the slide cycles full speed. So basically, the slide goes slow for a millisecond and then goes fast to cycle the gun. It is never "bottled up." The trick is to slow it down enough for it to function without blowing up.

It works for smaller calibers because the size of the piston and the volume of the chamber have to be proportional to the volume of gases and the size of the bullet. HK made a .45 P7, but it never worked well and they had to make lots of modifications.
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This is more or less what I am trying to understand. More specifically, the formula for understanding this.

Also wondering how it would work using something like 5.7x28 or 7.62x25.
Link Posted: 12/13/2016 8:13:35 AM EST
Link Posted: 12/13/2016 11:10:08 PM EST
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Originally Posted By GriswoldGuns:


This is more or less what I am trying to understand. More specifically, the formula for understanding this.

Also wondering how it would work using something like 5.7x28 or 7.62x25.
View Quote



I'm not an engineer, so I can't give you specific formulas. I will say I've been told that this is fairly basic stuff for an engineer. The problem is finding someone willing to do it. Also, I should add that companies like Walther and HK probably have proprietary methods of figuring out what works and what doesn't. This is as much art as science. Materials are a huge factor.

If you're thinking about your own design, this is a hard road to go down. The Browning linkless design is popular because it's cheap to manufacture and extremely forgiving.

Link Posted: 12/17/2016 4:44:52 AM EST
The gas on the piston is making the slide 'heavier', by helping it resist movement. The slide would still move, just slower than if it were unassisted.

It is ok for the slide or bolt to come back during firing, the problem is if it goes too far too soon.
Link Posted: 12/20/2016 11:58:23 PM EST
Don't forget friction. Its a huge factor as the case expands against the chamber wall. In fact, some blow-backs use irregularities in the chamber to hold the case in position a little longer but they are usually .380, 9x18 and smaller calibers. So, if you don't take that into consideration in the calculation the resulting gas pressure delay system will be too powerful and will result in short-cycling. That's the reason the piston diameter is smaller than the chamber diameter - equal would be too big.
Link Posted: 12/21/2016 3:27:07 PM EST
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Originally Posted By Thorgrim:
Those are good and interesting questions. Even though I have a CCP, I do not have the answers. Sidenote: Even though arfcom hates the CCP, I freaking love the thing. Highly reccomend it.
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What sort of ammo do you use in the CCP? Jacketed, plated, or what?

Thanks
Link Posted: 12/21/2016 3:47:10 PM EST
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Originally Posted By Seanquigley:
This videos shows
https://www.youtube.com/watch?v=coLytAnGgpo
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Let's try this again.
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