Fixed or Carbine: which stock for your MDT chassis system?

What is the difference between a conventional AR Fixed stock and a conventional AR Collapsible stock (also known as Carbine Stock)? Which one should you get and which type of buttstock will fit on your MDT chassis system? These are a couple questions that we’ll address in this post in an attempt to bring clarity on this topic and make it easier for you to select which buttstock and chassis system are best suited for you.


There are a few notable differences between an AR Fixed stock and an AR Collapsible (or Carbine) stock. To start with the obvious; a Fixed stock has a set overall length: the length of pull (LOP) can only be adjusted by 1”-1.5”, usually through an adjustment mechanism on the buttpad. The Fixed stocks are usually designed from a solid piece which offers a level of rigidity and durability that will ensure repeatable performance.

Fixed Stock Fixed Interface Buttstock
Carbine Stock Collapsible Buttstock w/ Carbine Interface

On the other hand, a Carbine (or Collapsible) stock usually has a shorter overall length but it can be adjusted to suit your personal length of pull (LOP) preference. The body of the buttstock slides along a buffer tube which in some cases incorporates a preset number of positions.

Fixed vs Carbine interface view

MDT Chassis Systems and Buttstocks

MDT has been using the terms “Fixed” and “Carbine” to describe the interface between the chassis system and the buttstock. Our “Fixed” chassis systems are recognizable by their “tear drop” shaped stock interface while our “Carbine” chassis systems are characterized by their “circular” shaped stock interface.

Carbine and Fixed interface difference

So when it comes to choosing the right buttstock for your chassis system, the choice will primarily be dictated by the shape of your chassis interface. Most of our chassis systems are designed using one type of interface only but there are exceptions. However a variety of combinations are possible with the use of our Fixed Stock Adapter or Lock Plate. Ultimately, you can adapt any buttstock on MDT’s chassis systems.

Fixed stock adapter and Carbine to fixed lock plate MDT Chassis Buttstock Interface Chart

In Conclusion

In the end it really comes down to three things:

  • 1. Which chassis are you going to put your rifle in?
  • 2. What length of pull (LOP) do you need personally?
  • 3. And finally, what ergonomics and features are you expecting to have on your buttstock?

Hopefully this post helps you navigate through your options and decide which chassis/buttstock combination is best suited for you.

Our support team remains available to clarify any points that are still making you feel uncertain about where to go from here. Getting you to Shoot Better™ is what drives us.