Tuesday, March 24, 2009

Magnetic Derrick's Crosman Bolt Hold Open

Crosman 22XX and 13XX's are easiest to load when the muzzle is simply pointed downward. The pellet is dropped into the loading port and the bolt closed behind it. Loading the gun horizontally is harder because the pellet often catches in the recess for the breech bolt. Vertical loading also helps negate shaving the edge of the pellet on the breech bolt recess, but can be annoying if the bolt doesn't stay rearward--especially if there's a scope spanning the opening. Adding a small magnet to the rear of the bolt allows it to stick rearward to the hammer cocking pin until you intentionally close the handle.

I picked this particular gun from the pile because the bolt was an especially loose fit. Removed the 2 bolts holding the breech...

Unscrewed the bolt handle, and here we are.

I want to add a magnet to this end--the end that cocks the hammer. The hammer itself actually sits below and parallel to the bolt handle. A steel pin connected to the hammer sticks upward allowing the bolt to move the hammer rearward. Once rearward, the sear engages, holding the hammer in place. Got it? By adding the magnet to the rear of the bolt, it will stick to the hammer pin when cocked, thus holding the bolt in the rearward, open position.

I was buying some supplies from Enco last week and I knew immediately what I was going to do when I saw these rare earth magnets.

I chose to use the smaller of the 2 sizes I purchased. Enco's part number: 327-6459 A whopping 30 cents each. I was feeling so spendy I ordered all of six. Check the Enco part number if you want all the specific measurements. The magnets are made by Eclipse Magnetics.

Magnet stuck to the end of the bolt.

View #2.

I chucked the bolt in the 3 jaw. No real super-high NASA precision needed. Spotted with a center drill held in the tailstock.

Center drills are short, stubby things made to be rigid as all get out. Keeps the tip from flexing and wandering across the workpiece. They basically put a starting hole right where you want it.

Spotted.

Switched to a 1/8" end mill. This will bore a flat bottom to the hole for the magnet to rest in. Flat bottomed holes are "counterbored".

Yeah, I know. You looked at the magnet specs and did the math, didn't you? I made the bore diameter 0.005" too big. It'll be OK.

Test fit the magnet. I bored to make it flush with the end of the bolt.

Another view of the end of the bolt. Magnet is magnetically held.

Gorilla Glue time. Epoxy would also be a fine choice. Just want to make sure the magnet stays stuck inside the bolt.

Last look before she gets reassembled. Note: I let the glue dry for half an hour. I decided it probably wasn't a good idea to reassemble the gun with wet superglue on the bolt.

Cocked the hammer and pointed the unloaded gun downward. Gave it some moderate shaking. Bolt stayed put. Testing complete.

You can just see the magnet in the bolt. I'm glad to have a visual to ensure that it stays put. Could've used a larger and more powerful magnet, but consider that the magnet only needs to hold the weight of the bolt and the bolt handle. If your gun has a larger and/or heavier custom bolt handle, a slightly larger magnet--Enco part number: 327-6460 would be a better choice.
Beware: those little babies will set you back 45 cents each.

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