In my last post about the Bear River Sportsman 900, I fixed a intake leak, reduced headspace, and ended up with a rifle that shot on par with a stock Daisy Powerline 880. Kind of disappointing, since I really like the handling characteristics and accuracy of the Sportsman 900. I’m not one to give up, so the story continues here.
I tore down the Sportsman 900 once more, determined to squeeze out the power potential that I know is there. As I mentioned previously, the mods I had done opened up some valve volume. To take up some volume, I took a 3/8″ length of some 3/16″ round stock and placed it inside the spring. This gives enough room for the valve to open and reduces volume allowing pressure to build quicker:
I reassembled and got no more velocity than before. There’s foolery at play and I’m going to get to the heart of it. As mentioned in my previous post, I hadn’t done anything with the two dimples in the pump head. This time, the pump head was removed from the piston, chucked in a power drill, and ground down against a belt sander. Once the dimples were gone, I polished the face with a piece of fine sandpaper against some glass.
This further reduces headspace, but not enough to account for the lack of power. I then turned my attention to the rubber bumper between the piston and pump head. It is a very soft material, and I suspect it is giving me grief. In its place, I inserted a nut that was ground down just enough to provide tension against the pump head pin:
I went ahead and replaced all o rings before I put it together once more. Ten pumps were put in and a 7.4 grain wadcutter loaded. This time, I got what I was after!
I gained nearly 85 fps and 2 FPE over my previous mods using the same pellet. The shot to shot velocity is very consistent. I haven’t tested heavier pellets yet, but I suspect they’ll produce even more energy than these light ones do. We are now looking at reliable squirrel and rabbit hunting energy.
There are many other things I’d like to do with these rifles. I just might have to pick up another refurb or two!
I’ve finally gotten in the parts I was needing to continue working on my 1322 ACP (air conserving pumper). One of those parts was a flat top valve and piston set from Airgunsmith. I highly recommend this setup, as the parts are well machined and thought out. The primary reason I chose this setup was for the felt oiler. Multistroke pneumatic airguns need to maintain a film of oil for consistent powerful results.
I also added a Crosman steel breech. I had to rethread the bolt handle, but aside from that, they make a killer breech for the money. It adds a nice heft to the carbine and gives a rock solid scope mount as well. There was a good deal of bolt flip with each shot, so for now, I’ve added a disc magnet below the bolt handle to correct that. This helped to tighten the extreme spread.
Once all the new pieces were installed, performance went up a good deal. With 11 pumps for the initial fill and 8 pumps between shots, it was averaging 505 fps with CPHPs. Accuracy is great when the LDC is properly adjusted and the right pellet for the barrel is selected:
H&N Sniper Lights and RWS Superpoints are nearly neck and neck in performance, easily capable of shooting dime sized groups at 20 yards. Since I am building this for hunting at sub 25 yard ranges, I just placed an order for 1750 of the Superpoints to keep the carbine well fed.
I wasn’t satisfied with the performance, as I’d like to be able to hunt squirrels with this rig. To improve performance, I turned my attention to tuning my free flight hammer. The spring guide and everything attached to it is accelerated with the hammer. The more massive this setup is, the more energy it robs from the hammer. I installed a nylock wingnut for the external stop, cut off the wings, and ground it as close to the nylon as I dared. All excess parts of the spring guide were ground down. Here’s the end result:
Performance has gone up dramatically. It is now tuned for an initial fill of 15 pumps, with 9 recharge pumps between shots. Average muzzle velocity with H&N Sniper Lights is now 553 fps and muzzle energy is 9.5 FPE. This is good enough for my intended purposes. Combining a quick sip of high pressure air with the LDC makes this carbine super quiet.
An even lighter spring guide combined with a 18″ barrel will probably get me over the 600 fps mark. I’m hoping to achieve that with no more than 10 recharge pumps. I’ll continue to document my progress as time allows.
If you never disassemble your Daisy 880, you’ll probably never need to do this modification. People like me who can’t make it a week without opening their rifle will quickly discover that the screws that hold the upper portion of the receiver halves together will strip out their holes leading to poor accuracy and problematic scope mounting.
More drastic measures may need to be taken later, but I’ve got a simple solution that so far has worked quite well. I carefully drilled out the existing holes with a 1/8″ drill bit, chasing the bottom hole a little deeper to give more thread engagement. The next thing I did was to thread them carefully using a 6-32 machine screw.
Now that the holes are threaded, I cut a couple #6 screws and dressed the ends so they would fit my receiver perfectly. I reassembled my 880, tightening these top screws first, then working my way down. The heads protrude just slightly and could use some paint, but the important thing is that my scope can now hold zero because the halves no longer flex along the top.
Should this arrangement wear out, I’ll simply drill all the way through and hold the two halves together with a machine screw and nut. In the meantime, I’ve got my accuracy and spent next to nothing on the modification! A similar process can be used for the two small stock screws, as these tend to wear out as well.