Bear River Sportsman 900 Project

I picked up a refurbished Bear River Sportsman 900 back in July. Right out of the box, it had a intake check leak. I bought it primarily to develop a LDC for it, but went ahead and attempted to contact Bear River regarding the leak. They finally emailed me back a couple days ago. This got me to tear down the rifle and see if I couldn’t fix it myself since I’ve gotten pretty much nowhere with them.

Ready to slay some Special ops squirrels!
Ready to slay some Special ops squirrels!

Luckily, the leak was caused by a bit of fuzz sticking to the intake check seal. I reassembled the rifle and chronographed it. It averaged a measly 583 fps with 7.4 grain pellets at 10 pumps. Time to tear it down again and fix everything they did to keep kids from overpumping the rifle to valve lock.

The ugly face of headspace
The ugly face of headspace

The piston features 2 dimples, the valve inlet is a whopping 7/64″ hole 1/4″ deep, and the inlet check has a deep phillips screw pattern leading to terrible pump efficiency. The first thing I did was remove the check seal, chuck the check guide into my drill and grind down the face until it was smooth. I also removed some of the excess material, increasing valve volume and decreasing spring tension.

Making the inlet check better
Making the inlet check better

I then polished the face smooth. The next thing I addressed was that massive inlet hole in the valve. To do so, I drilled a 7/64″ hole into the inlet check and superglued a piece of hex wrench in it. This still allows air into the valve, but takes up almost all the dead space, leading to much higher pressures.

The finished inlet check optimized for maximum pressure
The finished inlet check optimized for maximum pressure

At this point in my project, I haven’t addressed the dimples in the piston head. Instead, I noticed that the metal head of the piston was able to move forward and backward. To eliminate this, I wrapped copper wire around the rubber bumper, forcing it deeper, locking the metal piston head in the foremost position.

Overview of the rifle's guts
Overview of the rifle’s guts

I did some tweaks to the trigger and striker that I’ll address in a future post. All the pump and valve o-rings were changed before reassembly. So where are we now that we’ve made these mods? The same 7.4 grain pellets now hit an average of 645 fps, a gain of 62 fps and 1.25 fpe. Basically, stock Daisy 880 territory. I’m going to continue modding this rifle, the rifle fits me perfectly, looks great, and shoots very accurately. There is still potential waiting to be unlocked. If you’d like to get a LDC like the one in the top picture, use the contact page to let me know, and I’ll help you get a hold of one.

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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