Author Topic: "Ported" piston mod?  (Read 2587 times)

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Offline czgunner

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"Ported" piston mod?
« on: June 24, 2024, 07:45:34 PM »
Has anybody attempted to drill/mill a port in a piston to bleed off gas for suppressed use? Yes, I know somebody is selling this.

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Offline RSR

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Re: "Ported" piston mod?
« Reply #1 on: June 27, 2024, 07:28:13 AM »
We had someone here who was playing around with that, but don't know if it went anywhere.  I think he ultimately drilled, tapped, and put a set screw into the gas block instead.

He or another found there were different piston shapes/profiles, and went that route to tweak IIRC.  You could probably also reprofile the piston head (convex, smaller diameter for foremost section, etc.) of any surplus piston as well...  Just know you'll need to remove chrome first if working off a surplus one.

*And I think the ported piston being sold is snake oil.  Like exhaust on a vehicle, most restrictive point only one that matters...  So that 1/8" or smaller port in neck/shaft, not the size of hole (~1/4+" in the face is what affects [and if anything the large cup in face collects more gas and more pressure than it would otherwise; cup may delay but doesn't arrest the force of gasses...]).  Things that matter like smaller diameter, shape of piston face, etc., deflect energy off the piston, not collect and focus it...

One thing I'd do first, is to ensure that you're running all new springs throughout -- recoil, striker, bolt return springs.  And I would think you could probably fab a double layer bolt return spring as well for suppressor use, another spring internal of the OEM one...  Nowhere else really supports spring mods, unless you just bend your own w/ more loops or add a recoil buffer/spacer at the recoil or striker spring's rear (I think the now-discontinued Canada-made recoil buffer is behind striker IIRC, but would need to double-check that).

Offline RSR

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Re: "Ported" piston mod?
« Reply #2 on: June 27, 2024, 07:45:02 AM »
Remember that the gas block has vents integral, so anything affecting piston force instead of adjusting gas reaching the piston, only has a half inch or so of recoil time before forces begin to equalize and piston returns to battery. 

Why recoil on the Vz58 is often described as snappy -- lot of energy transmitted over short period of time...

In addition to springs, you could also try adding mass to piston or bolt carrier, though both present longer term reliability challenges.  Maybe try clamping a weight to the charging handle?   

Regardless, I do think adjustable gas block or piston design like KNS that can bleed off more gas than a pinhole mod is the way to go.

Offline czgunner

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Re: "Ported" piston mod?
« Reply #3 on: June 27, 2024, 01:33:04 PM »
Thanks for the input RSR.

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Offline MeatAxe

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Re: "Ported" piston mod?
« Reply #4 on: June 27, 2024, 02:11:08 PM »
Remember that the gas block has vents integral, so anything affecting piston force instead of adjusting gas reaching the piston, only has a half inch or so of recoil time before forces begin to equalize and piston returns to battery. 

Why recoil on the Vz58 is often described as snappy -- lot of energy transmitted over short period of time...

In addition to springs, you could also try adding mass to piston or bolt carrier, though both present longer term reliability challenges.  Maybe try clamping a weight to the charging handle?   

Regardless, I do think adjustable gas block or piston design like KNS that can bleed off more gas than a pinhole mod is the way to go.

Apparently, KNS has had a design in the works for the Vz58 gas system. Hope they release it soon. Looks like their multi-adjustable “Czech Valve” for the Bren 2 is the best solution for that gun’s cycling issues.

Offline czgunner

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Re: "Ported" piston mod?
« Reply #5 on: June 27, 2024, 02:29:09 PM »
Remember that the gas block has vents integral, so anything affecting piston force instead of adjusting gas reaching the piston, only has a half inch or so of recoil time before forces begin to equalize and piston returns to battery. 

Why recoil on the Vz58 is often described as snappy -- lot of energy transmitted over short period of time...

In addition to springs, you could also try adding mass to piston or bolt carrier, though both present longer term reliability challenges.  Maybe try clamping a weight to the charging handle?   

Regardless, I do think adjustable gas block or piston design like KNS that can bleed off more gas than a pinhole mod is the way to go.

Apparently, KNS has had a design in the works for the Vz58 gas system. Hope they release it soon. Looks like their multi-adjustable “Czech Valve” for the Bren 2 is the best solution for that gun’s cycling issues.
Yeah, I email KNS every 6 months asking about it. I try to get other VZ owners to do the same.

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Offline RSR

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Re: "Ported" piston mod?
« Reply #6 on: June 29, 2024, 05:11:52 PM »
Thanks for the input RSR.

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You bet -- another option would be to play around with dremeling grooves or similar on the piston's perimeter.  Since they're easier to fully swap out on the Vz58 than AK, could get surplus and play around w/ that route.

I would thing mirroring any grooves at least 180* would be needed, though splitting them into 4 at 90* might be better than 2 at 180*...   Can probably do some calculations with respect to area of piston face and adjust groove depth as a percentage of total area, sizing groove depth and width in line with calculations... 

I don't fully understand KNS's system, but I think that's what it's trying to do with respect to allowing more gas to bypass the piston both internally and around the perimeter of the piston face.  AKs do however have their pistons move further to the rear than Vz58s since moving the full length of the bolt carrier; whereas, I'd ballpark Vz58's pistons at no more than 1/2, and maybe only more than 1/3, of the total distance traveled vs. the AK.

Point being and having thought a little further, I think AKs and their long-stroke gas systems are more conducive to piston tuning than a short stroke gun like a Vz58 -- and that might be why the only Gas Regulators I see for short stroke systems by KNS are CZ Bren and FN SCAR gas valves, and not pistons...