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Old 07-03-2013, 02:24 AM   #1 (permalink)
Active Member
Join Date: Jul 2013
Location: Calgary, Alberta

DIY Mag fed marker - TX1 (Warning: picture intensive)

Hey all, first post here so I thought I would try and make it a good one..

This is my first attempt at a mag fed marker, for simplicity sake I decided to use an existing platform and adapt it to suit. In retrospect I actually increased the complexity of the project by going this route, but live and learn.

Project TX1 was started September 2012.

Main goals of this project are as follows:
  • AR platform, compatible with most standard AR furniture (MAGPUL YAY)
  • Electro - but must not appear to be. Needs eyes, doesn't need blinking lights
  • Better mag fitment than available mag fed markers (sorry milsig/Rap4, I don't like wobbly mag wells)
  • Very few visible fasteners (MUCH harder than it sounds)

I chose the BT TM7/TM15 internals. I liked the simple engine design, low pressure operation, AC threaded body, and small electronics footprint.

Machining day 1, September 23rd, 2012: Lower receiver begins

Turned a blank on the manual lathe and loaded it into the 4 Axis vertical milling machine. Bonus points if someone out there recognizes the brand of machine...

Note: The machine had a bad Y-axis ball screw at the time, which caused some unwanted vibration

Then I bought a house... and didn't work on it again until late November / early December.

Below you can see the general layout of the marker, the BT TM portion is rotated upside down, and the solenoid protrudes from the bottom of the upper receiver into the lower receiver. The circuit board is at the top of the TM body. The original plan was to use a 13cui tank, but due to time constraints that plan was later dropped in favor of a remote line.

Now at this point the lower receiver is still only 80% finished..this is important later. I get bored easily so I move on to the upper receiver. Date on these photos ranges from December 8 - 18th, 2012.

Same sort of idea as the lower, turn a blank on the manual lathe, bore to fit the TM7 body, mill on the VMC until crispy brown. Enjoy.

Solenoid poking out

First picture of a semi assembled state. Mag inserts, and ejects paintballs into the TM7 breach. December 18th, 2012.

Project took a 4 month hiatus after my daughter was born, and once I had enough sleep to think again I got back at it.

Now my decision to use a existing part starts to bite me in the a$$. Some of the parts I have drawn in solidworks turn out to be better in theory than in practice... or rather hard to machine.

Example #1: The T handle, and top slide. Originally I designed the T-handle to both turn the marker on when pulled back, and turn the air off.. WAAAAAAY too complicated. Quick redesign, now it turns the marker on only.

The other piece pictured is the top slide which guides the T-handle,closes up the upper receiver and mounts the RIS rails. It was originally designed as 1 piece with a rectangular cutout for the T-handle. It is very thin, in spots less than .100". Another redesign, and it was split into 2 pieces.

Example #2: Built in LPR
Remember that 80% complete lower receiver? The reason it was 80% complete was because the original design called for the low pressure regulator to be built into it, along with the ASA for the tank-in-stock. Needless to say I opted out of the idea, designed a separate LPR to thread into the back of the lower receiver using the standard AR buffer tube thread (1 3/16"-16UN 3B Mil-STD).

Slapped a rail and scope on the top for reference, but pay attention to the back of the lower receiver.

BAM! Threadmilled.

Added an NPT port to the top slide end (the second portion of the top slide)

I have to point it out, as a machinist it bugs the hell out of me.. but there was a mistake I made on the lower receiver and a tool offset was .01" instead was a .001" which gives a nice little gap between the back of the upper receiver and the lower.:banghead:
General tolerance for the marker is +/- .005", slide fits are generally within .001"

My original design also called for a rifle length 1 piece shroud, also referred to as "11.5 inches of how the hell do I machine that..". I reconsidered, and went with 6.5" carbine length instead LOL

June 2nd, 2013

And that's where I'm at now. Any questions or comments are always appreciated, thanks for looking!
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