Rainier Arms Introduces UHP15PDW Compact Lower For SBRs

For those looking for a more compact option, Rainier Arms has introduced a “PDW” lower receiver for the AR-15, with a more compact buffer tube and collapsible dual-rod stock arrangement. An article at Guns.com elaborates:

Rainier Arms is taking orders for the UHP15PDW, a compact, integrally-stocked totally bad ass AR-15-based lower for short-barreled rifles and personal defense weapon-style builds. The lower — that has a lot of neat features going for it — is a joint effort by Cross Machine Tool and Battle Arms Development.

The lower was designed from the ground around an all-new buffer and stock assembly. The stock mounts directly to the receiver on a pair of telescoping arms and collapses down almost 2 inches shorter than a standard carbine lower and stock.

The stock consists of a machined aluminum buttplate and molded carbon fiber cheekpiece that while small, get the job done. Most other “bolt on” skeleton stocks don’t offer any real cheek support at all. It’s a four-position stock with a quick-detach sling swivel point at the center of the stock’s toe. The adjustment latch is on the rear of the receiver underneath thebuffer tube in an ambidextrous position.

The Battle Arms Development influence is pretty visible with the ambidextrous controls. The selector marks are compatible with short-throw safeties like Battle Arms’ own BAD-ASS modular safety selectors. The rest of the controls a fully-ambidextrous as well, including the bolt and magazine release levers.

All the small parts including the ambidextrous levers have a black nitride finish, which is harder and smoother than parkerization. It’s a small touch and a lot of people wouldn’t notice it but it’s there.

Like a lot of non-standard receivers the UHP15PDW is CNC machined from 7075-T6 alloy aluminum and sports a MIL-SPEC hard anodized finish. The holes are reamed for improved concentricity and the magazine well is wire-EDM cut for precision. The mag well is slightly flared for faster, more reliable reloads.

Another advantage of the UHP15PDW is that it’s lightweight. PDW stocks on ARs trade length for bulk and can add a lot of weight to the firearm. The complete UHP15PDW lower weighs 2.25 pounds which is in-line with a standard AR lower complete with A2-stylefurniture.

Here comes the hard part, the sticker. The UHP15PDW is on sale for $625, which makes it expensive even by premium component standards. Even still, with it’s features and fully-functioning PDW stock we’re sure Rainier Arms will have no problems moving them. It’s important to remember that these are near-complete lowers minus the pistol grip, right-side (standard) magazine release button and fire control group.

For now the UHP15PDW lower receiver stands out as one of the most promising new PDW options on the AR-15 market. It may cost a little more than the alternatives but it doesn’t cut any corners and offers more than most at the same time.

$625 is quite a tag for just a lower, but there are not many options on the market for compact lowers of that type, so the new UHP15PDW may be able to move at that price.

Nathaniel F

Nathaniel is a history enthusiast and firearms hobbyist whose primary interest lies in military small arms technological developments beginning with the smokeless powder era. In addition to contributing to The Firearm Blog, he runs 196,800 Revolutions Per Minute, a blog devoted to modern small arms design and theory. He is also the author of the original web serial Heartblood, which is being updated and edited regularly. He can be reached via email at nathaniel.f@staff.thefirearmblog.com.


  • Vitor Roma

    Man, I know DI is super smooth out of a long gas tube, but it seems far from ideal with such a short tube, all those very high pressure gases with plenty of unburnt powder.

    • Giolli Joker

      Olympic Arms for their Stubby adopted a pigtail shaped gas tube, indeed.

    • Xanderbach

      Just use .300 blk. Should do the trick- more effective out of a short barrel at pdw ranges.

      • Vitor Roma

        Ah, I agree, .300blk is the way to go in any barrel shorter than 10″ and more suitable for short gas tubes.

  • hikerguy

    If that’s just for the lower It makes me wonder what a conplete weapon would be. Prolly not cheap.

  • TheNotoriousIUD

    I like those stocks but do you have to use one of those weird BC’s with the buffer on the end?

    • Jeff Smith

      The buffer tube is shorter than mil-spec, so I’m guessing you do.

      • TheNotoriousIUD

        Wonder how that would affect full auto fire.

    • kalash

      just a shortened buffer, same bcg similar to the lwrc UCIW

  • That’s the first one of these “rod-stocks” I’ve seen that actually looks like something I’d put my face on. Bonus.

  • Steve Truffer

    “…near-complete lowers minus the pistol grip, right-side (standard) magazine release button and fire control group.”
    So… complete minus almost everything? Ouch.

    While browsing Arfcom, I noticed that someone came up with an AR buffer that sat partially in the rear of the bolt carrier, to allow use of a repro m231 tube and wire stock (cool as hell) With a standard lower, lacking rainier’s ambi features, it seems to go 2.6 inches shorter than a standard carbine buffer tube (~0.75 inches shorter than rainier’s design).

    If someone were to go with the M231 design, it would likely be less expensive, and one could still add padding to the buffer.

  • Tyler Browne

    Gotta chop that pistol grip down as well. No point in having it extend past the mag length

  • patrickiv

    I like it.

  • DAN V.

    That optic doesnt belong on that weapon. Iron sights and/or micro red dot gtg.

  • Cymond

    Are they selling the Liberator trigger alone, or do you still have to buy a complete gun from them?