6mm Mongoose

[Recondo 101]

Designed by a fellow shooter from Marianna, FL for the AR-15 platform to use LC brass without major alteration.
It is a 223 variant that is trim shortened by .050, then die formed to 6mm, fire formed to produce a 40 degree shoulder and a minimum taper body, to allow for a 32 grain water capacity and allow heavier bullets like the 95-105s to be used in the AR-15 magazine length. Mad Dog Weapons Systems offers the bbLs and dies.
This is the 6mm Mongoose round with an 80 grain Remington SP flat base at near 3,000 fps. The 80s shoot 3/8 inch groups with H-335 or Bulk 844 and do not fully penetrate a coyote, they blow up inside at 100.

 

[cjackson31]

What barrel length got near 3000 fps?

 

[Recondo 101]

Barrel is an 18 inch 1-8 twist with 844 surplus powder and an 80 grain flat base spire points.
This is a test target for the initial build, barrel break in, fire-form brass, at a calculated start load for 844 surplus. The holes in the black are click adjustments. The sight setting is to impact 1" high at 100. This yote was shot at 75 out the screen door off hand, from the back porch in the pouring rain. Bullet did not exit, like a typical 243 , 80 grain. It is effective for an after surgery rifle with very low recoil. That is why I built it, before my open heart surgery, so I would have an effective rifle for the recovery period.