KP9 Stock Adapter: The 5.5 Mount That Opens the Rear

The best KP9 stock adapter in our lineup is the JMac SM-5.5. It is one 1.4 oz mount that replaces the factory rear at the 5.5mm folding interface and takes every JMac stock, where the 1913 route needs two parts. On the KP9 it fits with conditions, so confirm your rear uses the 5.5mm hinge pin before you order.

What does the SM-5.5 change on a KP9?

The SM-5.5 is machined from 7075-T6 aluminum with a Type 3 hardcoat and weighs 1.4 oz. It is a direct factory stock replacement with two height options for cheek weld. It folds, but it does not lock in the folded position. Once it is on, you can run the ST-7R skeleton tube, the SS-8RP SS® skeleton stock, the TS-9RP triangle with built-in rise or the AB-9R arm bar setup.

The SM-5.5 fits the Arsenal SGL 31-94, 31-95, 31-84 and 31-85. The KP9 is not on that list, which is why it is a fit with conditions rather than a straight fit.

Which KP9 triangle stock should I run?

The TS-9RP-T on the SM-5.5. It is our tan triangle with a 0.275" built-in rise and a rubber buttpad, and it pairs with the tan 7.72" handguard.

Can I run a 1913 stock on a KP9 instead?

Yes, through an adapter. The RSA-5.5 bolts on with factory hardware and gives you a 1913 rear. Put the SM-1913 on that rail and you can run JMac stocks, or most other 1913-style stocks and braces. Choose this route if you already own a 1913-style rear you like.

Which KP9 M-LOK handguard should I choose?

Our best KP9 handguard is the 7.72-inch HG-AKM-7.72L, because our product page lists 7.72" as the KP9's optimal length and it installs with no host modification. It has M-LOK slots at 3, 6 and 9 o'clock, a 1.3" inside and 1.5" outside diameter, and it clamps to the barrel at the rear instead of the receiver. You keep your rear sight. On the KP9 it uses the HG-AKM-LM-SJ lower mount. It comes in black, green and tan. Green and tan are limited runs.

Above it, the GT-KPR9 gas tube adds 1913 rail. It weighs 3 oz, partly sleeves over the gas block, and per the product page does not touch the gas block or rear sight block.

Do I need anything else for the KP9 front end?

Two things are worth knowing. The KP9 handguard has a sling-loop cut, so we recommend the RC-QD to bridge it and add a front QD point. And do not add the OM-AKM optic mount to a host with a factory hinged dust cover.

KP9 and 5.5mm rear fit table

Fit and availability are separate. Check the product page for current stock. This guide covers fit, not legal status. Check current federal, state and local law for your configuration.

Which cheek riser do I need on a KP9 stock?

Match the riser to your optic height. CRIM risers come in 1/4", 1/2" and 3/4". The CRSU adjusts to three heights, so one riser covers an optic change.

FAQ

What stock mount do I need for a KUSA KP9?

The SM-5.5. It replaces the factory rear at the 5.5mm folding interface and accepts every JMac stock. On the KP9 it fits with conditions: confirm your rear uses the 5.5mm hinge pin.

What is the KP9 stock pin size?

We have not confirmed the KP9's rear pin size. The SM-5.5 is made for 5.5mm-pin AK100-series folding rears, so confirm your KP9 uses a 5.5mm pin before you order, or contact us and we will check.

Can I put a 1913 stock or brace on a KP9?

Yes. Add the RSA-5.5 adapter, then the SM-1913 mount. That route runs most 1913-style stocks and braces, including JMac's.

Does the MMS handguard need modification on the KP9?

No. The 7.72" HG-AKM-7.72L installs on the KP9 with no host modification, using the HG-AKM-LM-SJ lower mount.

Does the KP9 gas tube touch the gas block?

No. Per the product page, the GT-KPR9 partly sleeves over the gas block without touching it or the rear sight block.