A5 markers with a RVA or regulator can improve the consistency and accuracy by doing a FVA (Front Velocity Modification) and using the regulator pressure or RVA tension to adjust velocity and eliminate the front velocity screw (FVS) from the equation.

The front velocity screw works by creating turbulence in the power tube thus reducing velocity by reducing air efficiency. Theoretically accuracy and marker consistency can be improved by making the power tubes air efficiency better.

As you can see the screw is protruding out into the power tube and even if we screw it out some it will still have a square profile in a round tube.



This is the FVS before modification.



First I mark the powertube and FVS so I know which way the tube curve is in relation to the FVS.



Here is the final alignment mark.

Next you'll want to choose a dremel wheel to match the inside curvature of the powertube.



Next carefully grind the FVS down to the desired size.



Don't try and grind it down all at once. Clean the part and insert it until you get the right depth.



The completed FVA mod. Notice how nice and smooth the FVA is in the powertube.

So let me get this straight. If you have a regulator, such as a Palmer Stabilizer, there is no loss in performance if you eliminate the velocity adjustment screw from the equation altogether?

I've heard of people doing this if they have an RVA, but not with a regulator.

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I've read a very good tutorial on FVA mod / regulator /RVA velocity adjustment (Anyone want to post it?). Basically using a combination reg pressure and RVA adjustment velocity could be managed very easily. Some of the benefits of reducing the pressure of the marker were more shots per tank, better consistency, and quieter operation.

In fact JCS manufactured the gold power tube as a result of A5OG member input. The gold power tube had no velocity screw.

With my setup I use just the reg to set my velocity with great results. The input pressure to my marker is around 650psi @ 280fps.

Well in that case, I'll have to consider trying this out.

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knight, some people will disagree with this, saying that you should have a RVA and not just a Regulator.

but i a a firm believer that it is prefectly fine with only a regulator. the function of a regulator is not usually to set and contol velosity, but you certiantally can do it.

i have both a palmer and a RVA on mine. i have set my palmer to my desired PSI and then adjust the velosity with the RVA. this is how i believe a regulator should be used on a A-5, but i am not going to say its the only way. if you don't care about a certian PSI level, use it to adjust velority, and you can do the FVA mod.

This is an intreasting way to do this mod. My self, I just screwed in a shorter screw. I have found that on occations I prefer a little back pressure from the FAV. It seems to help the cyclone - espically on cold days.

i'll give you that. that's the only reason i kept mine. playing in pa, if it's not june through august, you can expect rain/sleet/frogs/feces at anytime.

Glenn Palmer actually suggests that the front velocity screw be backed out as far as possible without it being removed (in otherwords until its flush inside the power tube). Then adjust the regulator until you chrono a FPS of around 300. From there, then use the front velocity screw to "fine" tune your FPS to 285 or less. I'm sure this same procedure would work if you have the rear velocity adjust instead.

The FVA mod is typically for people who already have their screw sitting flush in the tube, or who have a RVA and either can't afford the Gold Power Tube (or just wants a cheaper alternative). If you do this mod or buy the Gold Power Tube, and don't have a RVA, then a Regulator is a must have to ensure the FPS is kept to acceptable safe levels.

One of the main purposes of the FVA mod is to allow the screw to sit flush, and to still allow the Power tube to be removed when field stripping your A-5.

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wait, let me get this straight. If i have the gold power tube I dont need to do that mod? I have it along with the JCS RVA and i am also planning to get a palmer stabilizer, possibly an LPK.