Tuning FX Impact Mk2/M3 - slower first shot - no reg creep - quasi-scientific analysis

The FX plenum end part has a 1,5 mm hole.
I don't think enlarging that hole will help much in refresh rate since the regulator flow is the bottleneck.

Apollo said:

The FX plenum end part has a 1,5 mm hole.
I don't think enlarging that hole will help much in refresh rate since the regulator flow is the bottleneck.

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1mm hole and yes enlarging to 2mm does quicken the refresh rate bunch of us have already done it..

No, the original FX plenum neck part has a 1.5 mm hole, which is larger than the passage in the original AMP regulator piston.
So how exactly can enlarging the plenum hole quicken the refresh rate?

The O-ring design from Accu-Shot doesn’t really make sense. If it sits in a conical seat, it will eventually clamp down on the rod over time. You can use almost any material you like.

The only logical solution is to use an O-ring that sits flat and is secured in place either by a locknut, or with something like FX’s approach using a Delrin insert. Hency why they drilled the surface flat in the new plenum necks.

Why worry about refresh rate? I dont get it. I run a Huma regulator in my Impact, and mine refreshes under one second. I mostly shoot Benchrest with a single-shot tray, so it’s never been an issue.

PcpMachinist said:

re inventing the wheel, the new plenum is fine once installed in the gun strength wise its clamped in, it also takes the same o ring as the DRS Leopard and Panthera
the guys over at accu shot orings had these made roughly 4-6 weeks ago .

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I fixed my DRS Slow shot. Polish the valvepin and install a NBR 90 oring instead of PUR. Solved.

Ries said:

The O-ring design from Accu-Shot doesn’t really make sense. If it sits in a conical seat, it will eventually clamp down on the rod over time. You can use almost any material you like.

The only logical solution is to use an O-ring that sits flat and is secured in place either by a locknut, or with something like FX’s approach using a Delrin insert. Hency why they drilled the surface flat in the new plenum necks.

Why worry about refresh rate? I dont get it. I run a Huma regulator in my Impact, and mine refreshes under one second. I mostly shoot Benchrest with a single-shot tray, so it’s never been an issue.

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yes it does and they work ,you can get as technical as you would like, I've been to there shop , i have seen the 1000s of o rings Etc. have you seen or tested there plenum o ring ? or how its designed or shape or are you just assuming? all 4 of my impacts have them and im very happy with the purchase es and sd of all 4. anyhow this issue has been cured imo. watch this video there is plenty of them with the same results

PcpMachinist said:

yes it does and they work ,you can get as technical as you would like, I've been to there shop , i have seen the 1000s of o rings Etc. have you seen or tested there plenum o ring ? or how its designed or shape or are you just assuming? all 4 of my impacts have them and im very happy with the purchase es and sd of all 4. anyhow this issue has been cured imo. watch this video there is plenty of them with the same results

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I have tested alot before I purchased a plenum neck, I know what im talking about.

Why did FX change the part design now and milled the surface flat instead of conical? Because any oring under pressure will clamp overtime on the rod. The conical shape and pressure is the is main issue. The older impacts pre powerplenum all had the locknut to hold the oring.

I have Mubhaur his part and even informed FX sereval times about the problem. People who got the new plenumneck from FX or Mubhaur dont have the slow shot anymore, all without a “special compound” oring.



Watch at 5:26 , he shows the first slow shot there even with the “special” orings in it. Hmm sure its working..

As Ries already pointed out, there is no type of o-ring that can solve this issue in the plenum part with a conical seat.
FX has been aware of this problem from the very beginning, but they don’t want it to cost them.
That’s why they once changed the type of o-ring in the M4, but since the problem still persists, they are now forced to modify the part.
Which they continue to do in the cheapest way possible by modifying an existing part.

In reality, an o-ring is never the right type of seal for axial movement. This was mentioned earlier in the topic as well.
Still, in this application it worked well enough: in the first Impacts, in Mubhaur’s modified part, and now again in FX’s revised part.

A new o-ring will always provide some improvement at first, because there is fresh lubrication and the ring has not yet taken the shape of the conical seat. However, I would strongly advise against disassembling your Impact just to replace the o-ring, only to find out later that the problem still hasn’t been solved.