Beeman P17 Modifications

I’ve had my Beeman P17 for a couple of years now and have made some very extreme modifications to it that I thought would be interesting to share. If you haven’t seen the video of it on my homepage, I’ll include it here:

In the video, you can see it is no longer a pistol, but has been turned into a carbine. I accomplished this by using a drill and 1″ belt sander to turn down a Crosman .177 barrel to mimic the stock pistol barrel. The front end of the plastic “slide” has to be drilled out to 7/16″ to allow the barrel to slide through. The trigger guard had to be reshaped, as did the grip to provide the clearance for a full cocking stroke.

A longer barrel adds an amazing power increase. Stock, it would shoot 7.4 grain pellets in the 410 fps range. With the long barrel, the velocity is up to 484 fps. 10 grain pellets shoot an average of 433 fps, meaning we’ve effectively taken a 2.8 FPE airgun and boosted its output to 4.2 FPE, most of that power coming from a longer barrel. I believe there are still gains to be had with even longer barrels, but that’s hopefully a subject of a future post.

P17 Carbine - Gained over 1 ft-lb with all the modifications!
P17 Carbine – Gained over 1 ft-lb with all the modifications!

I’ve done some other tweaks, replacing the piston o ring with a slightly larger #117, upgrading to higher quality o rings, slightly drilling out the transfer port, reshaping the end of the valve stem, and working over the trigger mechanism.

The longer barrel quiets the pop of the P17 fairly well, but could still really benefit from a LDC. To shoot at full power, the LDC would have to be removed between shots, quite inconvenient. A strange twist of fate allows me to shoot mine at stock speeds with an LDC attached.

As much as I love shooting, it didn’t take me long to wear my P17 out to the point where it wouldn’t cock the hammer. I tore it down and figured out what was going on – the steel fingers on the back of the valve had worn and stretched to the point that they no longer engaged the hammer, leaving the valve constantly open.

I remedied this by applying a blob of solder between the fingers and shaping it to match the profile of the fingers. To hold the valve open allowing the piston to backdraft air through the transfer port, I left space between the fingers and filed the solder to alter the timing:

Groove for delayed hammer pickup
Groove for delayed hammer pickup

Yes, there’s a little too much moly grease in there. I’ll clean her up a bit when I reassemble after the photo shoot. Essentially what this does is allow the piston to suck air in for about the first 1″ of its stroke. Here’s a shot showing the pickup, note that it is inside the boundary formed by the steel fingers:

Delayed pickup in action
Delayed pickup in action

The P17 carbine looks sexy with its carbon fiber LDC and is unbelievably quiet. Accuracy remains stellar, with the only air rifle in my collection that can beat it being my Walther LGR, a purpose built 10m match rifle.

P17 carbine sporting a LDC
P17 carbine sporting a LDC

Here’s what it looks like at full cocking length with LDC in place:

Cocking with LDC in place
Cocking with LDC in place

I think there is still timing optimization waiting to be unlocked. The piston only backdrafts for about 1″ of stroke, at full cock, there is an additional .5″ of stroke available. Further filing of the solder might improve velocity further by allowing a longer backdraft. At any rate, it is a almost silent setup with enough power and accuracy in its current form to take out mice, house sparrows, and the like.

Author: admin

I've enjoyed shooting and hunting with airguns since my early teen years. For over ten years, I have shared my passion for airguns on this website.

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