Shawn asked me to do a data dump on the Colt 901 for Part 2 of the series.

Initial Modular Rifle Patents
Paul Hochstrate, Laurance Robbins, and Arthur F. Daigle

Colt engineers first filed a patent application for their Modular Rifle design in June 2004.

“…(M)agazine well 46 may be replaceable and removable such that magazine well 46 may be replaced with a different magazine well to change caliber.”

The magazine well and the trigger group mated to the upper receiver using an interrupted tongue and groove interface. They were then pinned in place by the standard push pins. Note that the trigger group and the magazine well are only held in place relative to each other by the upper receiver and the trigger guard detent pin. I suspect this was done this way to prevent infringing upon Mack Gwinn’s patent for the “MGI Hydra” modular lower receiver. All of this meant that proprietary upper receivers would be required

Besides the retention tabs at 68 and 84, note what appears to be an M14 magazine (48).

If you look at the awarded patents other than the first, they appear more focused upon changes to the operating system related to the use of a traditional gas piston. However, all are related to the first patent awarded.

https://patents.google.com/patent/US7131228B2
https://patents.google.com/patent/US8051595B2
https://patents.google.com/patent/US8640372B2
https://patents.google.com/patent/US9279632B2
https://patents.google.com/patent/US9612072B2

CM901 Patents
Laurance Robbins, Kevin Langevin, and Kevin Audibert

Colt engineers filed their first patent application in October 2009.

“Accordingly, while existing firearms are suitable for their intended purpose, it is desired to provide a firearm that has the advantages of a single firearm while being adaptable for firing multiple types of ammunition rounds.”

As will be described below, with the use of an adapter, for example adapter 190 in FIG. 1C, lower receiver 44 may be compatible with any suitable caliber upper receiver, for example, 5.56x45mm NATO upper receiver 170, 230 or
250, 6.5 Grendel R. Rem. SPC, 7.62×39 mm, Rem. or otherwise. In the embodiment shown, each non 7.62x51mm caliber may have a corresponding magazine well adapter, though in some alternate embodiments, a common magazine well adapter may be provided configured to mate more than one caliber magazine to the magazine well of the common lower receiver.

Clearly, the desire to use legacy M4/M16 upper receivers overrode any interest there was in the modularity of the earlier prototype design. Thus, Colt’s engineers went back to the drawing board to design what became the CM901.

https://patents.google.com/patent/USD674859S1
https://patents.google.com/patent/US9459060B2
https://patents.google.com/patent/US9823031B2
https://patents.google.com/patent/US10101101B2

CK901 Patents
Paul M. Hochstrate and Kevin Langevin

Colt engineers filed their first patent application in August 2013.

“Accordingly, it is desirable to provide a rifle or firearm other than an AK 47 that is capable of firing a 7.62×39 mm round.”

It is interesting to note that while the bolt diameter and barrel extension are the diameter of the 7.62x51mm variant, the bolt lugs’ length and corresponding depth of the barrel extension’s lug recesses are that of the 5.56x45mm.

https://patents.google.com/patent/USD719234S1
https://patents.google.com/patent/US9404694B2
https://patents.google.com/patent/US10520269B2

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