Recrowning the Benjamin Nitro Piston air rifle
by B.B. Pelletier
Blog regular Fred PRoNJ is back with another great guest blog that’s actually a follow-on to his previous one, where he tested several of his guns for accuracy.
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by Fred Nemiroff, aka Fred PRoNJ
I really enjoy shooting the Benjamin Trail Nitro Piston Hardwood air rifle. The cocking effort is relatively light for the power it produces (18 ft-lbs of energy), recoil is mild and it’s light. I can shoot this until I get bored, but I really wanted it to be as accurate as my spring-piston rifles. I know beans about accurizing a rifle, so my first cry for help was to this blog. I’ve never heard about crowning or recrowning a barrel until our blogger participant from Russia, duskwight, mentioned the “recrowning kit.”
Brian in Idaho, a fellow Three Stooges fanatic, told me about the trick of lapping the chamfer of the crown with a brass screw and polishing compound. It was either BG Farmer or Chuck who told me not to be concerned about ruining my barrel, that anything I did could always be salvaged.
Doing searches on the internet resulted in recrowning kits for sale — but for $360 and up. The kit consists of a reamer, a handle and a pilot that fits in the barrel so you keep the chamber and crown concentric and at a perfect right angle, respectively, to the barrel. No thanks. Then, I stumbled upon a YouTube video made by Larry Potterfield of Midway USA firearms supply, and I was off.
The first step was to remove the shroud from the barrel. Here, you can see that the muzzlebrake has a hex fitting:
Now that I had the shroud off, duskwight had suggested I try shooting the rifle, as I might be pleasantly surprised. Nope. This is the target without the shroud:
Here’s a close-up of the barrel crown and chamfer. Look closely, and you can see all the tool marks, especially on the chamfer in the barrel. Would fixing this really change anything?
What you can’t see is that the crown is not perfectly flat and perpendicular to the barrel. Three passes with a mill file removed bluing on about two-thirds of the surface of the crown but didn’t touch the bluing on the rest of the crown. To me, this meant part of the crown was lower than the rest. Seven more passes, and I was now filing the entire surface.
After 30 careful passes with the file, the crown was flat with no machine tool marks. I then took a piece of fine grit sandpaper and wrapped it around the file and polished the crown a bit to get rid of the file markings. Next came the chamfer.
Using a variable speed drill and a large, brass wood screw whose head was just slightly larger than the barrel diameter, I dipped it into some ancient valve polishing compound I had in the garage and applied the slow-running drill to the barrel.
Here’s a photo using my DSLR, which gave me a better macro focus. The barrel has been cleaned up and the photo enlarged. To the naked eye (mine, at least) those markings at 12:00 are not visible. I suspect it may just be a reflection from the fill light I was using.
I took a rag, sprayed some
The first shot, the one right in the X-ring, is my “fouling” shot. The next 5 produced that group which is .46 inches end-to-end. The center-to-center measurement is .24 inches. It’s right in the area of the expensive German rifles.
Later on, I shot another group that was .415 inches, which would translate to .195 inches center-to-center. Hmmm, I wonder if I could improve my other rifles? That Discovery wasn’t too impressive.