.35 cal Wheels for MRod Mags

[rsterne]

I made a prototype of a .35 cal MRod magazine a couple of years ago, but with my new 3D printer I thought I would revisit this.... It took pretty much an entire day and 5 versions before I got exactly what I wanted....



On the left, the insert is sitting in a stock .25 cal housing.... On the right, it is sitting in the housing I modifed to fit the handmade wheel.... Next is a photo showing a couple of .35 cal wheels (bottom row), printed in PLA @ 100% infill, and above them a stock .25 cal wheel and spring....



You can clearly see that the MRod spring is too large in diameter to fit into the .35 cal wheels.... That is my problem at the moment, no proper torsion spring, I need one 7/16" OD with 360 deg. travel....  The .25 cal Mag housing and cover both need modifications.... A stock .25 cal housing and cover are on the right in the photo, with the modified ones on the left....



On the cover, the pin that fits into the circular groove in the wheel needs moving in closer to the center, because that groove is smaller in diameter.... At the moment the groove in the wheels is a complete circle, I plan to just use a drop of glue for the stop, once I determine the correct location, but it would be programmed in, once the pin location is determined.... The kidney shaped hole in the cover must be enlarged (but not as big as in this one) to allow the larger pellet to be fitted....

The most difficult modification is to reposition and enlarge the hole in the housing that the pellet passes through on loading into the breech.... In order for the larger pellets to fit inside the ID of the housing, the hole must be further to the left when viewed from the front of the magazine, and the slot around it, which slides over the barrel, must also move to the left, while remaining the same height above the bottom of the magazine.... The end of the barrel that the mag indexes on, remains at 1/2", with a mill required to make the slot in the housing longer.... Not only does the hole move over, but the web on the inside of the mag housing needs to be moved over and enlarged to clear the pellet as well.... It should be possible to do both operations from the front (side visible in the photo) without recentering the part in the mill.... Holding it rigidly will be critical, however, possibly a jig will be necessary....

I have a 7mm steel shaft for the mandrel on order, and 10 meters of 0.5mm stainless spring wire, to try and make my own torsion springs.... I found a handy online calculator for mandrel diameters that determined the required mandrel diameter....  https://www.daycounter.com/Calculators/Springs/ .... The spring wire, unfortunately, is coming from China and is 4-6 weeks away.... 

Bob

[PikeP]

Nifty spring calculator, I like that they share the equation, Dm= kD - d

Time to add that to my arsenal. Good work on the revision, if I were to build a 35 cal mrod I'd be looking here that much is certain.

[rsterne]

Yes, very cool calculator....

Bob

[bear air]

Awesome work Bob. This is my current airgun unicorn lol.