TFB Review: The Daniel Defense M4A1 FSB Upper

Matt E
by Matt E

When it comes to AR15s, the market is absolutely flooded with options and variations that are so overwhelming, it can sometimes make your head spin. One of the models that has always been of interest to me is the MRE style handguard from Knights Armament as well as the Daniel Defense DDM4V1 with a quad rail that goes around the fixed front sight post. By today’s standard, it may be an older way of doing things but it still has a place in the market. Let’s take a closer look at the Daniel Defense M4A1 FSB Upper.


I decided to pick up one of the Daniel Defense M4A1 FSB uppers from Brownells a few weeks ago based on the fact I recently reviewed and enjoyed the Socom 14.5″ upper receiver I bought previously. The M4A1 FSB upper has a 14.5″ M4 Socom heavy profile barrel with no muzzle device attached. The upper receiver didn’t come with a charging handle or bolt carrier group. The lack of a muzzle device, charging handle, or bolt carrier group allows people to get whatever muzzle device they want to get pinned and welded. My M4A1 FSB upper also came with Daniel’s A1.5 fixed rear sight as well as the A2 fixed front sight block.

The RIS II rail is a full quad rail that encloses the FSB and allows for mounting accessories in front of your front sight. The 12.25″ RIS II rail is known to be sturdy and this variant also is anodized FDE to give the rifle a different look. Just like other Daniel Defense models, this M4A1 FSB upper comes standard with Daniel’s cold hammer forged Chrome Moly Vanadium steel barrel that has a 1/7 twist rate. MSRP on this upper is $899.99 and it is available now.

Specs List

MSRP$899.99ManufacturerDaniel Defense
Manufacturer Part #-M4A1 FSPModelM4A1
Caliber223 RemingtonBarrel LengthN/A
ColorFlat Dark EarthAccessoriesFlash Hider
Type of Barrel1:7DescriptionCarbine
SubcategoryUpper ReceiverFinishAnodized
Range Time

To finish building this rifle out, I snagged one of the Aero Precision military marked lower receivers and built it out with B5 Systems furniture. In terms of optics, I threw an EOTech XPS red dot on it along with a Ground Combat Modular Verticle Grip and a SureFire M300 Mini Scout. My M4A1 upper receiver came with a sling mount on the quad rail which made it really simple to throw on a 2-point sling and head out to the range. So far in my testing, I have roughly 550 rounds through the M4A1 FSB upper with good luck so far. The quad rail going past the front sight post allows you to mount a flashlight much further forward than other options with a front sight block but can lead to having a front-heavy firearm if you end up putting too much upfront.

With just the SureFire M300 attached with a simple pressure pad, the M4A1 is very well-balanced and can move quickly between targets when working various drills at the range. The A1.5 fixed rear sight in conjunction with the EOTech and front sight made for a fast accurate sight picture that didn’t seem too busy for me. Shooting the M4A1 both suppressed and unsuppressed proved it wasn’t so overgassed that it was uncomfortable to shoot like some uppers tend to be, but it was nice to see the M4A1 upper can be shot both ways without changing springs or major parts.

In terms of accuracy, the M4A1 did fairly well with the heavier 77gr ammo through the 1/7 twist barrel. With SIG Elite Match 77gr ammunition, the M4A1 FSB upper grouped an average of 1.91″ at 100 yards out of 3 different groups of 5 rounds each. The best group with the 77 gr ammo was 1.68″ and with regular 55gr PMC ammo, it opened up to an average group of 2.32″ with 3 different groups each consisting of 5 shots each. Having a chrome-lined barrel and being able to do this kind of grouping is fairly standard and completely acceptable in my eyes. This isn’t a match-grade barrel and I’m not expecting sub-MOA groups out of it when it’s built for durability over time.

Place In The Market

When it comes to AR15 upper receivers, there are countless options with plenty of variations but the M4A1 FSB upper is truly a throwback to earlier times when there wasn’t a wide variety of low-profile gas blocks and full-length rails. It’s an interesting piece of military history and was the cutting edge for a few years back in the early and mid-2000s. The overall size and configuration are still extremely usable and give that classic look without being heavy or cumbersome. Throwing a classic-looking EOTech and vertical grip on it allows people to have that classic look while having a very capable and accurate rifle. With the Restomod rifle movement where people build out classic-looking rifles with modern machined components, I think this is a perfect way of building one of those rifles.

Overall Thoughts

So given my time with the Daniel Defense M4A1 FSB upper receiver, I think it is a great option to give people a chance to use something from the early days of the GWOT era when firearms were evolving rapidly, and it’s an interesting mix of old and new. In terms of functionality, the M4A1 FSB upper did well in every situation. It’s certainly one I will keep for the foreseeable future and between this and my 14.5″ Socom rifle I built, I always seem to grab this M4A1 FSB option just for its charm and just because it’s drastically different from other modern options.

Check Prices on Daniel Defense M4A1 FSB Uppers

What do you guys think about the restomod/retro rifle movement that’s been going on? Do you guys think it’s good to have different options or do you think they should be left in the past? Let me know your thoughts in the comments below. If you have questions about this rifle or firearms in general, feel free to shoot me a message on Instagram @fridgeoperator. Stay safe out there and we will see you in the next review!

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Matt E
Matt E

I'm an avid shooter and love educating whether it's at my job or in the shooting community. I'm an average joe that really loves talking with other people about firearms and other passions.I'm active on Instagram on @fridgeoperator.

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2 of 22 comments
  • Social_Artifice Social_Artifice on Apr 26, 2024

    running that hanguard with a SOCOM barrel from Colt, surefire war comp.

    Sighting system currently is XPS from Eotech with the G45 magnifier.

    Running a KAC Vertical grip at the 1/3 of the way foward on the hand guar and their RAS forend hand stop with the QD under the sight block. I have it setup to do arm extended and arm tucked, and to control the light with both, works well for lots of different shooting positions.

    I took 10 days of tactical 2 gun instruction last year with that rifle. At first the intructors called it a relic, but then it faired very well, we did lots of dynamic shooting positions, I'd say I entered as one of the less experienced shooters and finished in the top 20% by the completion.

    If I could I'd like to find a more weight optimized barrel and go to an EXPS sighting setup, contemplating the unity system, I don't like the flip to side magnifier... I'd almost prefer a basic QD clip on over that feature.

    I contemplated a ARMS folding A2, but not seeing a potential benefit with the eotech holographic, its not a problem.

    Took a minute but got a light setup I like I can control from both support hand positions very easily.

  • Predrag Djuric Predrag Djuric on Apr 26, 2024

    An interesting rifle.