HK G3 and MP5 Straightening Mandrel Designs and Specifications

Download the STEP files for these mandrels: G3-and-MP5-Straightening-Mandrels.zip

Several years ago, I produced a run of billet HK receiver mandrels. I still get the occasional query for them; unfortunately, I sold my shop when I went active duty and can only produce these on a very limited basis. At the time, I posted a half-assed low-res STL of the models I built which admittedly wasn’t very helpful. With the rise of overseas/domestic CNC machining resources that are now available to the consumer, I figured it was time to publish proper drawings. Also, it seems that someone has appropriated my original work for commercial use without bothering to inform me. I’m sure you can find these online. How annoying. I discuss this further at the bottom of the article.

Anyhow, these resources can be used to order your own mandrels direct-from-manufacturer for $800ish. The tolerances are my best assessment from a half dozen samples, 3D scanning, and a whole lot of trial and error. I welcome any input from those more experienced folks out there! I would also like to again extend thanks to holescreek, who provided the basis of information for me to get started in building HKs/their tooling and a few of the fundamental dimensions on the G3 mandrel.

As a footnote, the site currently run under the name weapons-builder, selling a wide array of HK roller delayed tooling, appears to have appropriated my work for commercial use. I was not consulted when they took my designs–they would have had, by the way, my blessing–the only thing I ever asked for was attribution. I am aware of this because non-critical dimensions were taken identically from my models, and they even included my picture from my shop of my mandrel in my press on the original–since revised–listing on their site.

You don’t need to pay their exorbitant rates to purchase or rent a tool–have a Chinese or domestic CNC shop spit you one out; the product will be the same and the prices lower.