UTG Pro RBU6BM Mil-Spec Stock Assembly Black Synthetic 6 Position for AR-15, M16

The UTG Pro RBU6BM is a mil-spec 6-position collapsible stock assembly built for AR-15 and M16 platform rifles. Whether you're setting up a new build or upgrading an existing rifle, this modular stock kit gives you the adjustability to dial in your fit—a feature that shooters of every body type and shooting style appreciate. The precision-machined aluminum receiver extension and polymer stock work together with minimal wobble, so you get a consistent, solid cheek weld every time you shoulder the rifle. That stability matters when you're chasing accuracy at the range or hunting where every shot counts.

This isn't a stripped stock; UTG Pro included the complete assembly in the box. You get the black synthetic stock, aluminum buffer tube, castle nut, locking plate, action spring, and carbine buffer. The six adjustable positions let you fine-tune length of pull to match your frame and shooting gear—longer for open-country hunting in heavy layers, shorter for precision work at the bench or quick transitions in dynamic scenarios. Mil-spec diameter means it'll drop into any standard AR-15 lower receiver without fuss.

UTG Pro holds these parts to tight tolerances, so fitment is clean and repeatable. The tear-drop ring and castle nut secure everything solid. If you've got an armorer's wrench on hand, installation is straightforward; if not, it's a tool worth owning anyway if you work on AR-15s at all. This is the kind of no-frills, dependable upgrade that works whether you're building your first rifle or your fifth.

Key Features

• Six adjustable positions allow custom length-of-pull adjustment for different body types and shooting applications
• Precision-machined aluminum receiver extension engineered to mil-spec tolerances
• Minimal wobble and tight fitment ensure consistent cheek weld and weapon control
• Complete assembly kit includes stock, buffer tube, castle nut, locking plate, action spring, and carbine buffer
• Mil-spec diameter compatible with standard AR-15 lower receivers
• Black synthetic construction is durable and weather-resistant
• Tear-drop ring and castle nut provide secure lockdown

Specifications

Frequently Asked Questions

What AR-15 rifles is this stock assembly compatible with?

The UTG Pro RBU6BM is mil-spec diameter and fits standard AR-15 and M16 pattern rifles with mil-spec lower receivers.

Does this kit include everything I need to install it?

Yes. The assembly comes complete with the stock, aluminum receiver extension, castle nut, locking plate, action spring, and carbine buffer. You'll need an armorer's wrench to install it, but that's a separate tool.

How much adjustment does the 6-position collapsible design offer?

The six positions allow you to adjust the length of pull to match your body type, shooting gear, and application—from extended length for hunting in heavy clothing to compressed length for bench shooting or close-quarters work. The exact adjustment range isn't specified in our data, so confirm the positions with the manufacturer if you need precise measurements.

Will this stock wobble or move on my rifle?

The UTG Pro design is engineered with tight tolerances and minimal play between the stock and receiver extension, so you'll get a solid, stable cheek weld and consistent weapon control shot to shot.