[TommyG]

I have a 2nd gen 18 in RFB. I adjusted the gas regulator as per Kel-tec manual. Wound up with 15 clicks to bottom with bolt locked back. All is well.
Now I installed my SilencerCo Saker suppressor and with Gas cap almost removed, the bolt locked back. I then called Kel-tec and they told be that there was a Suppressor piston available for $50. I received piston and noticed that it was different as to even having a tit on piston face for spring to go over. Invoice stated RFB-162 Suppressor Piston 2nd Gen. After installing this piston I still get lock back when gas cap is almost removed. This piston seems to over gas more than old piston. I tried to attach photo of old and new piston but not sure if it worked. Question is, should procedure for setting gas be same for suppressor with bolt lock back then 2 clicks closed.

 

[TommyG]

Additional Photos of suppressor pistons

 

[MightyHunter]

TommyG. Very interesting and informative. I have a AAC SR7 suppressor waiting for the tax stamp and was thinking about ordering a suppressor piston for my RFB gen 2. I am at 12 clicks from bottom for lock back with my 150 grain SST bullets. I may wait and see if my stock piston will do the job. If not I can always order a suppressor piston. Your stock piston looks exactly like mine.

 

[BlakeHanson]

After installing this piston I still get lock back when gas cap is almost removed. This piston seems to over gas more than old piston.

That is so wrong:brickwall:.
Try it without the piston rings, starting at B+15, with the suppressor on.
Let us know.

 

[MightyHunter]

TommyG. What is the diameter of both piston shafts? I just measured my stock piston shaft and it is 0.219 inches

 

[lateck]

Very interesting. ... That piston is extremely different then one's from the past or the one I have.
The check rings and tit on the flat of the piston are new.

Lateck,

 

[MightyHunter]

Lateck, since your suppressor piston doesn't have sealing rings it would seem that keltec is still evolving the suppressor piston design. Is your RFB a gen 2?

 

[CyberScoper]

That is the first gen 2 piston I have seen with piston rings installed. Neither of my gen 2 suppressor pistons, nor "standard" pistons have rings, and both "standard" pistons I have are slightly different configurations, but work.

I'm with Blake. Try it without the rings, or at least align the gaps in all three rings together. Your pictures have two of the three gaps lined up. It looks like KT is trying to make a piston that can be used for both suppressed and unsuppressed.

What is shaft diameter of the suppressor pistons, if you have calipers available? Mine are 0.248 inches. Yours is smaller, because it has a lip at the end. And, is it a solid round shaft, or does it have a flat? Same question for the shaft tip. Is it round, or does it have a flat?

And come on guys, I learned in anatomy that extra feature is a "nipple" , but I understand why they have it. Now I want one.

 

[TNC]

Oh the humanity!...is there no hope for a uniform solution to this issue?

 

[TommyG]

Shaft Dia. Old .217 Suppressor .217 Both shafts are round except on end, both have square ends Old Gen 2 piston has 4 lands that measure .498, Suppressor piston has 3 lands .496 1 has rings. I forgot that with suppressor piston without suppressor installed I had lockup with cap almost removed. With old piston lockup at around 15 to bottom

 

[MightyHunter]

Please correct me if I am wrong. I seems that the suppressor piston will lock back with the cap almost removed with or without the suppressor installed. If that is the case you can shoot it with the suppressor or without and not adjust the cap. That's great

 

[CyberScoper]

Well if it consistently locks back on an empty mag with the cap removed, no need to have the cap on. Installing the cap would over gas it. My interpretation of the OP's post is that his is borderline needing the cap. With use, it will probably need a few more clicks.

 

[TommyG]

The way I read the manual you open gas cap clockwise to under gas and close until bolt locks back on empty mag. then 2 additional clicks. If you can't under gas then you will not be able to set correct bolt lock back. I can tell the difference in recoil when my RFB is over gassed. I'm afraid that using my RFB in uncontrolled over gassed condition will damage the firearm. There's a reason it's adjustable. I was hoping that the suppressor piston would work suppressed or not without swapping pistons. I will try suppressor piston without seal rings in a couple days when range is open.

 

[MightyHunter]

I will be very interested in your findings from your range work

 

[CyberScoper]

It is interesting the new suppressor piston pictured on KT's website has a solid round shaft with no squarish end indicating it is most likely a 0.248" diameter shaft. Otherwise, it would flop around in the 0.250" cylinder bore the shaft slides inside. It matches the configuration of the suppressor pistons I have, but different than the one TommyG posted. His definitely has a smaller shaft, 0.217" as he has stated, and I can see the squarish shoulders on the tip. That squarish tip still has the corners machined to be tangent to a 0.248" diameter.

I suspect KT sent the wrong piston. I suggest a call back to KT and request to talk directly to the one of the tech's that is thoroughly familiar with suppressed RFB's, not the screener that answers the phone.

http://www.keltecweapons.com/rfb/rfb-accesories/rfb-suppressor-piston/

 

[MightyHunter]

That looks exactly like my standard (non-suppressor) piston except mine has a shaft diameter of 0.219 inches. Each ring is 0.500

 

[BlakeHanson]

I suspect KT sent the wrong piston. I suggest a call back to KT and request to talk directly to the one of the tech's that is thoroughly familiar with suppressed RFB's, not the screener that answers the phone.
http://www.keltecweapons.com/rfb/rfb-accesories/rfb-suppressor-piston/

KT may be trying to redesign the piston:headstratch: or it is an early prototype of the gen2 sent by mistake (witness the "nipple").
The piston he received is interesting. The gen2 system was all about eliminating the expensive piston ring from the gen1 setup.
The piston rings will make the piston more efficient/powerful (which is the last thing you need with the excessive back pressure of a suppressor).

He may be holding a "collector" piston of which only a few exist...
possibly worth thousands!

 

[MightyHunter]

BlakeHanson you are right it is a rare collector's piston. Could this be a gen 1 piston?

 

[BlakeHanson]

BlakeHanson you are right it is a rare collector's piston. Could this be a gen 1 piston?

No. The gen1 is much bigger diameter across the piston lands and shorter.
They look like this:

 

[MightyHunter]

Yep, completely different. As my Dad would say "That piston TommyG received is a puzzlement"