Steve from NC’s Wicked-Cool Air-Conserving Pumper — Springer Quiet, First-Class Sporter Trigger, and Full Power from 3 Pumps

Monday, January 5, 2009

Here's a prototype of the ACP that I tested with a forward mounted -- scout-rifle style -- red dot.

Elsewhere, I have already expressed my admiration for Benjamin/Sheridan multi-stroke pneumatic (MSP) air rifles. Well-crafted of durable materials, they are an excellent value, delivering a whole lot of air rifle for a fairly modest expenditure.

Despite their attractions, there are three areas in which Benji/Dan pumpers could be improved. First is “all that pumping.” Even if you routinely shoot a just six pumps per shot (the factory maximum is eight pumps), shooting a five-shot group means 30 pumps. If you’re testing five different pellets, you’re up to 150 pumps, and it suddenly starts to become a workout. Second is noise; at 6-8 pumps a factory-fresh Benji (or Sheridan) can be somewhat raucous. Third, the factory trigger, while not awful, certainly could stand improvement.

Enter Steve Woodward, AKA “Steve from NC” on the forums. Steve is an engineer, and he has created an “Air Conserving Pumper” (ACP) based on the Benji/Sheridan chassis that requires fewer strokes, is quieter, and has a much nicer trigger. Further, he created his ACP using mostly off-the-shelf parts from either Crosman Corporation or the local hardware store and just two custom parts.

Here’s how he did it. Through experimentation he found that the hammer on the Benji MSP “bounces.” When you trigger the shot, the hammer opens the valve that releases air that causes your pellet to go down the barrel. So far, so good – that’s what the hammer is supposed to do. But then the hammer “bounces,” releasing more air from the valve – with NO benefit. All the extra air does is release more of the pressure from your precious pump strokes and make the report louder.

So Steve devised a “Butterfly hammer debounce device” (HDD) which prevents the hammer from bouncing and releasing more air. With some air still retained in the gun this means (A) the report is quieter and (B) you can use that retained air to reduce the number of pumping strokes needed for your next shot. To make everything work better, Steve also changes out some of the factory valve parts with some valve parts from the Benjamin AS392, reduces the pump headspace, and takes some coils off the hammerspring. (There is a lot more to it than this brief description allows – a total of about 20 modifications and new parts are needed to convert 392 to ACP392), but as we’ll see in a moment, the modifications produce the intended results.) Steve also installs one of his trigger Supersears to make the trigger smoother, lighter, and much less creepy.

Here’s how the finished ACP works. From dead empty, you give the rifle a basic charge of 5 pumps, and then 3 more pumps. Load it and shoot it, and it launches a pellet at around 13 fp. To recharge the ACP, you need only three pumps. They required roughly the same effort as the last three pumps in an eight-pump charge on a factory Benji. (Sometimes you need only 2 pumps, and sometimes 4, but there is a clever gizmo – The Pump Arm Pressure Sensor – that Steve installs in the forestock that lets you know how much pumping is enough. Paying close attention to the Sensor and pumping only according to the clues it provides is important, as overpumping will actually reduce power and, in the extreme, can result in valve lock).

This is how the Pump Arm Pressure Indicator works.

Because the ACP conserves air – and doesn’t blow a lot of excess out the muzzle – the report is significantly reduced compared to a stock Benji at 8 pumps or a Steroid Benji 392 at 6 pumps. In fact, it sounds about as noisy as a springer of comparable power, but without the twang or springer recoil.

Further, because it conserves air, if you need a quick second shot, you can have one. Just cock and load the ACP again, pull the trigger, and you’ll get a second shot of 8-9 fp.

Thanks to one of Steve’s Supersears, the trigger is about a nice as you’ll find in a Benji/Dan pumper.

Is there anything you give up for all this wonderfulness? Yes: variable power. An ACP must be shot at the power level it’s tuned for: an initial charge of 8 pumps, and 3 (average) recharge pumps.

In a nutshell: Steve from NC’s wicked-cool ACP delivers fewer pumps, less noise, better trigger. And now you can have one for your very own – just click here.

Til next time, aim true and shoot straight.

– Jock Elliott


  1. albert timinski says:

    want to buy a depinger for my benjamin maurader where do I buy one

    1. Jock Elliott says:


      Sorry, I don’t know.

  2. Mr. Allen Coutinho says:

    Hi, I have seen the full Demo on Utube and found it to be something great, Just today i have purchesed one HDD and im going to fix it myself. its a real great piece of instrumunt and i hope my shooting goes well. I’m really longing to go hunting now. Thanks to all the staff as well.
    A big big thank you HDD

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