.25 cal Umarex 1894 Conversion

Building or modifying BB, Airsoft, and Pellet type of guns. Show off your custom designs, find tips and other discussion. Target practice only!
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Xamllew
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Wed Mar 18, 2020 12:20 pm

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I picked up this fun .177 rifle last year. A handy little lever action and a decent plinker, but I actually primarily wanted it for the mechanism which imitates the real gun with shells that chamber and eject with a wonderful metallic ratcheting. I spend a lot of time loading empty shells, working the lever, and watching them eject and fly all over the place, quite cathartic. It wasn't long, however, that I realized that the unique shell-loading allows for a huge range of ammunition to feed, darts, pellets, bbs, 4.5mm metal rods, anything of the correct diameter and not longer than the shell will work.

To convert this rifle I started by increasing the tension in the hammer spring to give the valve a little harder kick which increases co2 usage and power. This thing runs off of 2 12g co2 bulbs, you get around 90 shots from those 2 bulbs, so even if you double the output you should still get a good number of shots per fill. Then I needed to swap out the barrel. This was a fairly straightforward process as the barrel is just a simple smoothbore and resembles an airsoft barrel. The rifle disassembles beautifully, it takes little more than a minute to bring the gun down to the point where I can pull the barrel, breach, and magazine tube out, the valve, co2 chamber, and lever action linkage can be dropped out in less than 5 minutes once you get familiar with it. You could literally replace valve o-rings in the field so long as you had a screwdriver and pliers.

Anyway, a few dremel mods are required to change the barrel, first, the rubber gasket/breach needs to be drilled or melted out to the appropriate diameter, my method was to simply heat up a .25 cal bearing, then push it through the breach, melting it out to the correct size, this is a simple and brutal method but it did work. Next the muzzle cap, this holds the muzzle end of the barrel in place in the outer barrel, the cap is fitted to the 4.5mm barrel and must be drilled out to accept the new barrel. Now the barrel is ready to insert into the outer barrel shell, fitting the breach gasket, and fitting into the muzzle. A few wraps of teflon tape around the barrel will give a snug fit and ensure the barrel doesnt jettison itself upon firing.

My next step is to order some 3d printed 6mm Umarex shells, which someone over on Thingiverse has done and tested, and they feed reliably according to them. I will then drill those shells out to 6.35mm. After that I will update and give you guys a performance report.
Last edited by Xamllew on Fri Mar 20, 2020 10:17 pm, edited 1 time in total.
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jackssmirkingrevenge
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Thu Mar 19, 2020 9:02 am

Very cool project!

We have these at the shop and were just discussing how it would be the basis for something a bit more hardcore :D

I guess the valve looks a bit like the one on airsoft revolvers?

Image

If so you might want to look into the possibility of opening up the flow a little, it might provide more benefits than a stronger hammer.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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Xamllew
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Thu Mar 19, 2020 3:31 pm

jackssmirkingrevenge wrote:
Thu Mar 19, 2020 9:02 am
Very cool project!

We have these at the shop and were just discussing how it would be the basis for something a bit more hardcore :D

I guess the valve looks a bit like the one on airsoft revolvers?

Image

If so you might want to look into the possibility of opening up the flow a little, it might provide more benefits than a stronger hammer.
Thanks.

The valve stem is similar but only has two holes at the sealing face. I don't have proper tools to widen them right because they're drilled very close to the edge so drilling isnt an option.

I actually just got back from some quick performance testing of a valve mod. I pulled the valve apart and bored about 0.5 mm off the inner wall of the valve body to increase volume. I also smoothed down a very rough machined 180 degree turn that the air had to take to reach the valve body. I have gotten a noticable velocity boost from this, in fact, some shot trajectories are slightly curving like an airsoft bb, probably caused by the rubber seal in the breach interfering with the shot. The tests may have been flawed though as my pre-valve mod tests were done in the morning instead of the afternoon which was about 10 degrees cooler and thus lower pressure, so stay tuned while I further confirm the performance.
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