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Cross Machine Tool UHP15A


I’ve been shooting a left handed Stag AR-15 for a few years now, and wanted to build a new true left-handed rifle from the lower up.  The Stag is great, but it still rides on a standard right handed, non-ambidextrous lower.  Thanks to the fine folks at CMT-TAC, the’ve come to the rescue with a great full ambi lower.

The UHP15A lower has everything you’d expect for a great billet lower:

  • Full Ambi controls: Bolt catch and mag release:
  • Threaded bolt catch pin (no roll pin installation needed)
  • Integrated oversize trigger guard
  • Compatible markings for 45° safety selector
  • And generally great manufacturing

The Lower Controls

First we’ll start out with the ambi mag release.  It’s gated to help prevent unwanted mag drops, and is easily accessed and manipulated with your left index finger when holding left handed. The back side is conjured to the trigger guard, and has a bit of a point, so It may snag, but that hasn’t happened to me yet, as I’ve only bench shot this rifle. It’s also set up so you can use a standard LPK mag release.  No special parts are needed to build up this rifle.

The ambi bolt release on the side works just as well.  While operating left handed, I like to close the bolt with my right thumb, it just feels natural that way.  It’s also situated behind the dust cover if you have a standard wrong sided upper on the the rifle.  If you’re holding the rifle right handed, and have an extraordinarily strong index finger, you could close the bolt.  If not, two fingers will work.

These controls are the main reason to pick up this lower. The rest of the lower is a well made billet lower. The maxwell is flared, the integrated trigger guard will let you wear gloves, and it fits like a glove with my upper.

The only improvement I would add, is a threaded rear take down detent hole.  My Aero Precision forged lower has this, and it’s great for the build. Even better when you decide to take off your buffer tube and forget the dentent and spring are still behind the end plate.

Now that you’ve got this lower in hand, you can only make it better better by putting a UPUR-1LH atop this.