A Substrate Build: Enhancing The Sig Sauer M400 SRP Tactical Carbine

A little over a year ago I bought and tested the Sig Sauer M400 SRP Carbine.



The M400 SRP is exactly as shown in the image. I decided that it was time to make a few enhancements on an already awesome weapon. I did not, however follow the list of goodies I have linked in that thread. I decided to go a different route instead.

I decided to work from the inside out on this one. I started with the stock bolt. My original idea was to replace it with a Low Mass bolt and carrier assembly which would have cost me 250 bucks. However I quickly realized that I didn't need such an upgrade as low mass bolts are for saving ounces on a weapon that is already light. And the upgrades I was going to make down the line were going to lighten this weapon up by a lot anyway. I left the bolt and carrier assembly alone save for 2 springs: The extractor spring and the ejector spring.

Those of you who shoot AR 15s know that they can heat up. You also know that when you heat up steel(music wire springs) after a while they will deform, they will lose their tension, and can even work-harden until they break. I decided to look for some more heat resistant, shape retaining springs in the form of Chrome Silicon alloy springs by Tubb Precision. I also decided to purchase their flat wire version of the buffer spring, also a CS alloy spring. While heat resistance in the buffer spring isn't really that paramount, shape retention and longer shooting cycle life is.

My next enhancement was the trigger. I was going to shell the 350 bucks for a 1.5 lbs Jard trigger assembly. However, I not only would have had to buy a low mass bolt and a superlight titanium firing pin, I would have to spend the money every weekend I went shooting on ammunition with very soft primers...I want a weapon that can shoot any kind of ammo. So I went with a 3.5 lbs. CMC Single Stage Tactical Trigger with a flat trigger blade. It is a remarkably smooth trigger and at 3.5 pounds there is NO travel time as you can see from the linked YouTube video(Not made by me). That means very little movement and more accurate shots. I spend 174 bucks on it and it was well worth it.

I then moved outward and focused on the furniture. While I am a long time user and lover of Magpul products I did not use Magpul MOE for the entire build. Instead I used the BMS Battlelink Minimalist Stock from Mission First Tactical. It is a solid stock for its shape and extremely light. Made for both Commercial and Mil-Spec buffer tubes..Be sure you know which one you have!

I did use a lot of Magpul products in this build, however. Let me start with the handguards.

The Magpul MOE handguards are built to take advantage of the modularity and "Barbiedoll" aesthetics of the AR platform. Which means you can easily add control accessories, lights, optics, and lasers. They are also lighter than stock handguards and they do not use over molded plastic materials. They are injection molded and extremely heat tolerant.

For added weapon control(the only gun control you need) I purchased the Magpul AFG Angled Foregrip. Having used vertical foregrips on many weapons I just don't get proper ergonomic control of my weapon. I had previously been exposed to the AFG on a friends AR and I loved it so on my weapon it went.

Then it was time to take advantage of the quick disconnect points built in to the lower receiver. For that I bought the Magpul MS3 Multi-Mission sling. Fully adjustable, it does not come with a built in QD swivel but there are places that sell them with the QD swivel adapter attached. The position of the QD socket and the design of the sling make it easy to rest the weapon by your side, or have it at the ready immediately. This is important, I believe, in a defensive weapon - which is the intent of the weapon as originally bought, and it is the state of mind being kept in making these enhancements.

It was then time to move on to sights. Here again I went with Magpul products for my flip up back up sights. Since the M400 SRP is a flat top railed weapon it does not have a rear or front sight. So I decided that I would purchase the Magpul MBUS front and rear back up sight system. Like most Magpul products they are made of high strength injection molded polymer material. They are fully adjustable and can be used to a high degree of accuracy by those of us who are used to using iron sights...But this brings me to my next enhancement...

The EOTech 512. This holographic battle sight has been field proven. With over 1000 hours of continuous use on 2 lithium-ion aa batteries, proven rugged construction, and accuracy, it was an obvious choice for my defensive weapon. It features a 65 MOA circle around a 1 MOA dot. This means that it can be calibrated easily for both close quarters and ranged(1-300 meters) combat. With the exception of the far more expensive(and frankly better) Trijicon ACOG reflex sight...No other sight system can come close to what EOTech has created in its line of products.

I then needed something for low light, or simply dark room use. I was looking for something lightweight and energy efficient and I found just that when I came across the Torch low profile backup light from Mission First Tactical and manufactured by Princeton Tec. This is possibly the lightest weapon light on the market and it is run by a single watch battery. I mounted it next to the AFG, I can easily activate it with my thumb, and it gives me a 12 hour burn time at 20 lumens. More than enough for home defense.

There was one last thing...If you look at the flash hider on the stock SRP it just doesn't look like it would belong on a weapon that was so personalized. I don't like compensators because of the localized noise they produce. Compensators are for target shooting anyway and this is a defensive weapon. I needed to find something that fit the mold of a defensive weapon AND looked good on the end of my rifle. I decided to purchase the Yankee Hill Machine Annihilator Flash Hider. This flash hider not only looks good, but it send a message and functions as advertized. You also do not have to time it for installation. You simply removed the old flash hider and crush washer, install the new washer, and grab a wrench and torque the Annihilator down until it won't turn anymore and you're good to go.

After taking an already reliable stock weapon and adding internal and external enhancements for accuracy, control, form, and function I feel confident that I have created one of the best AR platform weapons I will ever use.






Happy Shooting!

A picture would be nice.....
Sounds like you built a real Cadillac

reply to post by dashen


Sorry haven't taken one yet.

I will as soon as I can and I will add it to the OP.

PICS..Here ya go.

a reply to: projectvxn

Was just about to demand a picture of the final product, but alas I was smart enough to scroll down

Nice looking rifle, wish I could throw some lead out of it my self.

Awesome build! Very nice!!!

Oooooooooooo nice. Like the magpul furniture, the mbus, the eotech and the ............. Wait........ Hell I like the hole thang. Very good job.

The backup sights will be installed once I place the rail on top and move the EOTech forward.

originally posted by: projectvxn
The backup sights will be installed once I place the rail on top and move the EOTech forward.

I made the mistake of buying the 552 (iirc?) Absolute garbage. How are you liking the 512? Any battery contact issues?

And how do you like the flat blade trigger? I went with a timney but I'm looking for a another trigger for a different build.

a reply to: TiedDestructor

I love the CMC trigger. Timney makes very good drop in triggers but I opted for the cheap but functional.

I bought the 512 eotech nv compatible sight. Not what I would call garbage, but to be honest if I could have afforded the trijicon acog I would have bought that instead. I prefer not using batteries and my experience in the army made me love em. Not battery contact issues at all.

originally posted by: projectvxn

PICS..Here ya go.

Very nice!
SnF

originally posted by: projectvxn
a reply to: TiedDestructor

I love the CMC trigger. Timney makes very good drop in triggers but I opted for the cheap but functional.

I bought the 512 eotech nv compatible sight. Not what I would call garbage, but to be honest if I could have afforded the trijicon acog I would have bought that instead. I prefer not using batteries and my experience in the army made me love em. Not battery contact issues at all.

I didn't mean to infer the sights were garbage; just mine. I had the base AA model.

I do love a trijicon. But you nearly have to be rich or enlisted to justify one. I am neither. I mean you could buy a rifle for that $

a reply to: TiedDestructor

Mine also runs AA batteries. Depending on what batteries you use you could wind up with damage to the system. There are 2.5v AAsize batteries out there that would fry an eotech. 1.5v batteries are the only ones you can use.

Did you buy your eotech used?

As far as acogs are concerned even with my military discount it would still cost me just under 950 bucks. I paid 360 for the 512.

originally posted by: projectvxn
a reply to: TiedDestructor

Mine also runs AA batteries. Depending on what batteries you use you could wind up with damage to the system. There are 2.5v AAsize batteries out there that would fry an eotech. 1.5v batteries are the only ones you can use.

Did you buy your eotech used?

As far as acogs are concerned even with my military discount it would still cost me just under 950 bucks. I paid 360 for the 512.

It came from the factory on my RRA Government Model along with a surefire light ect. And $950 discounted? Sheesh.

Jam up deal you got on yours.

a reply to: TiedDestructor

Yeah alot of the time the discount is crap. Better than paying full price like the government does though.

a reply to: projectvxn

What is the over all length of the rifle with the stock collapsed?

a reply to: sputniksteve

26"

Fully extended its like 32-34" but I didnt measure it yet.

Looks amazing.

My AR definitely doesn't stand up to yours, but I have a Windham Weaponry carbon fiber and I have to say the AFG is one of the best additions to rifles ever. I have an AFG on the Windham and another also on my Saiga 5.56. The straight vertical grips just didn't do it for me either.

I also have the same MOE handguards (they just look beautiful!) and MBUS sights. I haven't been able to push the rifles accuracy yet, as Im limited to only 25 yards at my local range.

a reply to: buni11687

I agree the AFG is fantastic, I much prefer it to the vertical grip, not only does it save space and make your rifle much less cumbersome it just feels much better and is better for accuracy in my opinion. And yeah those MOE handguards sure are pretty, wish I had them myself.

So recently I went to the range with a few friends and we had a competition. We all recently returned from the 'Stan and the other guys bought rifles. All of them wanted to try them out.

So we had some fun with it.

10 rounds per person.

Each with individual targets and our own rifles.

After independent review I was declared the winner despite my momentary lapse in trigger control, evidence of which can be seen by the one stray hole off to the lower right of the target. I was also unsupported. If I had a tripod or a supported position my grouping would have been much tighter.



This competition grouping is NOT the best I got. When I had finally sighted in the EOTech and got a proper co-witness with my Mbus Pro sights the groupings were extremely tight.

None the less I took a weapon that consistently hit 4-8 MOA stock, to 1-1.5 MOA modified. The competition gave me roughly 1.5-3 MOA accuracy off-hand position. Enough to put a round in center mass consistently at 300 meters. I'm happy.