MDT LSS XL Chassis


The MDT LSS XL is a longer version of the LSS chassis, and is designed to take fixed buttstocks without the need of an adapter.

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MDT LSS XL Chassis

The LSS-XL chassis system is a variant of our highly popular LSS chassis. The LSS chassis was designed for compact use, short barreled rifles. A large amount of customers really liked the LSS chassis, but wanted to use a fixed buttstock, and use it with longer barrel systems.

This prompted us to design the LSS-XL chassis system which has a fore-end extended by 3″ and is designed to accept fixed rifle stocks without the need of using any adapters. In addition the Lengt of Pull (LOP) is 1″ shorter than the standard LSS, as fixed rifle stocks generally are longer than collapsible.

Using MDT’s Skeleton Rifle Stock: We do not recommend using the Skeleton Rifle Stock on the LSS-XL. It will work on the LSS using the fixed stock adapter. But on the LSS-XL with a shorter Length of Pull the cheek riser will be in the way of the bolt. (it does work on some actions if the cheek riser is raised)

Please note important action specific information at the bottom.

The LSS chassis is designed to accept any AR-15 butt-stock and pistol grip (purchased seperately), offering the option to customize from the wide variety of  Accessories available on the market.

The LSS chassis uses external box style magazines in .223 and .308 caliber for Short Action and .300WM or .338LM magazines for Long Action rifles, and supports installation of bolt on MIL-STN-1913 accessory mounting rails. Mounting holes are spaced for Magpul style L5 (11 slots) and L3 (7 slots) rails (1.600” / 3.200”) to be used on the bottom of the fore end up to 6.5″ in length.

Note: Long action magazines come in 3 different lengths: 3.715″, 3.775″ an 8.050″. This chassis uses 3.715″ length magazines.


  • Increases accuracy by up to 21%
  • Construction aluminum hard anodized to mil spec type III
  • Cerakote Finish in Black or Flat Dark Earth
  • Hole spacing for Magpul L5(11slot) and L3(7slot)Rails
  • Designed for Collapsible AR-15 buttstocks
  • Accepts most AR-15 Pistol Grips
  • Lightweight, free-floating modular fore-end
  • Will accommodate barrels up to 1″ diameter.
  • Compatible with AICS style magazines in .223 or .308 (SA) and 300WM, 30.06, 338LM (LA). (Long Action Magazine length 3.715)
  • Weight: 1.7lb – 1.9lb

The LSS-XL chassis system comes as a 1-piece chassis, with all required mounting hardware included. This includes new action screws, and a screw for the pistol grip.

To complete this chassis on your rifle, the additional items you need to purchase are:

  • Any AR-15 buttstock. (Fixed stocks are best suited. For Collapsible stocks consider any of the LSS Chassis)
  • A buffer tube for your buttstock. (Both milspec and commercial work on our chassis)
  • An AR-15 Pistol Grip. Ideally without a beavertail, or use a soft (bendable) beavertail.
  • At least one magazine
  • Please also see the HS3 Chassis System.


Howa 1500 / Weatherby Vanguard actions

  • This is the only action that we manufacture a chassis for, that has a flat bottom action. For this reason only the MDT Polymer magazines will work. It will be a tight fit, and the magazine may need to be modified slightly for a good fit and proper feeding.
  • For .223 models the bolt stop may be too long. This can easily be modified.

Savage models 10/110 11/111 12/112 16/116

  • For rifles with the bolt release at the bottom, the bolt release can be engaged through the side of the chassis, using a pin or tool. (Not included)

Tikka T3 – Long Calibers

  • Only the MDT Metal 3.56 magazine will fit with the chassis for this action and needs to be purchased separately.

Savage Axis

  • The original recoil lug that comes with the rifle is required for installation into the chassis.

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