Two of the most common types of rail systems found on handguards pre-installed on assembled uppers are Picatinny rails and M-LOK rail systems, but they are considerably different.
The Picatinny rail is the staple and the standard which has been in use for basically thirty years. M-LOK rail systems are newer, but they also offer several advantages over Pic rails. Here’s what you should know before you buy your next assembled upper.
Picatinny Rail Systems
Picatinny rail systems consist of a series of roughly T-shaped ridges and slots. To attach a Picatinny rail accessory, it must be compatible with the rail. Typically, Pic rail accessories have two claws that tighten via fasteners to grip onto the tops of the ridges.
If you loosen the hardware partially, you can typically slide a Pic rail attachment backwards and forwards without removing it from the rail. This can be useful for, among other things, adjusting the eye relief of an optic.
So, what makes Picatinny rail handguards so popular?
Why Pic Rails Are Great
Here are some of the best reasons that Pic rails remain so popular:
- Since they have been a standard for about thirty years, there is a massive assortment of Pic rail compatible shooting attachments.
- Picatinny rails have raised ridges, which offer excellent purchase and traction, whether wearing gloves or not.
- Picatinny rails are heavy and very durable.
At the same time, despite the fact that Picatinny rails have performed admirably since they were introduced, there are some shortcomings associated with them.
Where They Fall Short
While there are many who love Picatinny rail systems, there are some drawbacks, such as the following:
- Some consider Picatinny rails relatively uncomfortable to grip since they have raised ridges.
- Picatinny rails are considerably heavier than M-LOK rail systems, which adds weight to the rifle, often unnecessarily.
- The raised ridges can snag on gear.
That being the case, whether or not an assembled upper with a Picatinny rail system is for you will ultimately come down to personal preference.
M-LOK Rail Systems
Unlike a Picatinny rail, M-LOK rail systems consist of an aluminum frame that has slots machined into it. These slots are roughly oval in shape, and to attach a compatible accessory, you insert the T-nut and tighten it via a screw. Like a Pic rail, there is some flexibility regarding how you can adjust the attachment in the slot.
The cool thing about M-LOK attachments is that, even though the T-nut gets inserted into the rail, you don’t need access to the inside to attach, adjust, tighten, or remove attachments.
So let’s take a closer look at what M-LOK rail systems offer over Pic rail handguards.
Where They Win
Here are some of the biggest relative advantages of assembled uppers with M-LOK rail systems:
- Even though they are newer, there are still a lot of shooting attachments and accessories that are M-LOK compatible, with more coming out by the year.
- M-LOK rail systems lack raised ridges, so most shooters find them comfortable to grip, even without gloves.
- Since they are smooth on the surface, there is little to no risk that an M-LOK rail system will snag on gear.
- M-LOK rail systems are considerably lighter than Pic rail systems, so they can be used to build a lighter rifle, carbine or ARP, in concert with other parts like skeletonized AR15 parts.
While there are some considerable advantages associated with M-LOK rail systems as indicated here, there are some drawbacks as well.
Where They’re Not So Hot
Some of the reasons you might want to choose an assembled upper with a Pic rail system rather than an M-LOK rail system are as follows.
- While there are many compatible accessories, there are still more compatible accessories for Pic rail systems.
- To use a Picatinny accessory with an M-LOK rail system you will need a special adapter (which will add weight).
- Some accessories might require thread-locker to prevent them from coming loose under the influence of recoil.
- Some operators claim that M-LOK rail systems are not as rigid as Pic rail systems, which makes it harder to hold a zero with a laser or an optic.
Again, which type of rail system is best for you ultimately comes down to what you prefer based on the relative advantages of each. Some shooters will prefer Pic rails whereas others will be better served by assembled uppers with M-LOK rail systems.
Shop AR-15 Assembled Uppers and Handguards Here
Not sure whether your next build should start with an assembled upper that has a Pic rail or an M-LOK rail system? No worries, we carry complete assembled uppers with both, as well as assembled uppers that have KeyMod rail systems instead, which are another relatively popular alternative.
Check out our full collection of complete AR-15 assembled uppers here and if you have any questions about these rail systems, about other upper parts, or about how to complete the build, get in touch with us and we will be more than happy to help.