Hello everyone. Long time lurker, first time poster.

Around 6 months ago I bought my first AR15, an M&P sport II. I have made no mods to it as I originally just wanted a relatively basic, carbine length rifle to familiarize myself with the AR platform. Now that I have owned it for a little while and put a few rounds through it, I'm looking at tailoring it more for what I want it to be: Home defense/civil unrest situation, but also just to take to the range for some fun at 25-100 yards.

What I want are: red dot optics (with no A2 front), vertical front grip, folding front sight, possibly a tac light.

So, opinions please. Im not really a fan of co-witnessed irons, hence the folding front sight for when the optic is running at the A2 front sight's expense. Also, I don't necessarily want the expense of going free-float - I still want this to be a learning rifle at this stage. I am thinking of a drop in carbine length quad rail, picatinny VFG, a railed gas block, and MBUS pro folding front sight.

Would I need a new end cap if I replace the handguard with a quad rail such as the UTG drop-in and Rock River railed gas block? Would this be the right height for the MBUS pro to mount on the gas block and line-up correctly with the standard MBUS rear I already have.

So many questions, I know. But I appreciate feedback from people more knowledgeable than myself.

Rock River Arms AR-15 Gas Block Sight Base .750 Diameter Aluminum Matte Black - AR0122ASY - 99981
Leapers UTG PRO AR-15 Carbine Length Drop-in Quad Rail - MTU001T - 4712274526013

My opinion, if I was going through the work of replacing the gas block and wanted a quad rail, I would go with a free float. I would also reconsider the quad rail and go with something in Keymod or M-Lok.

If I wasn't going to free float, then I would just go with a drop in hand guard that allowed me to attach stuff where I wanted it... probably something from Magpul. If you shoot with both eyes open and focused on the target downrange, you won't even notice the front sight.

For your stated use, "Home defense/civil unrest situation", a light would be more useful and desirable than a vertical grip.

What I would do is get your optic first, practice shooting either absolute or lower 1/3 co-witnessed with your red dot and front sight post. You may find that you don't mind the front sight post, it doesn't bother me at all. If not, then you can start looking into rails and another gas block. I prefer m-lock myself, but everyone's different. Like cypertext said, if you go through the work of replacing the gas block you might as well free float it, keep in mind though that a front post is more suitable on a duty gun, and free float rails tend to shift under extreme hard use which will through off the zero of your back up irons.

I'll echo what others have said above. Might as well go free float if you are gonna change the gas block. Plus, you'll be able to get at least a 12" rail as compared to the carbine drop in you're thinking about now. It's much more comfortable shooting with a longer rail. Check out aero precision, alg and utg if you want some budget friendly free float rail options.

To answer your question...You should be able reuse your end cap if you want to go the railed gas block route. It should be the right height also.

Your links aren't working for me, so not sure which gas block you are looking at, but if it is the AR0122ASY, it looks like there could be some issues...

Rock River Arms: Gas Blocks

I may be wrong, but that block looks like it is meant to be pinned in place... if so, it probably will not line up with the existing slots for the pins on your barrel, as the barrel and FSB are mated and drilled to fit together.

Agree with everyone. If you change gas blocks, free float is the way to go. So many options.

__________________
Still carrying my S&W 642

Thanks for all the input, I guess I'll do some re-evaluation.

My opinion:

Go to PSA. Buy a complete upper fitted just the way you want. Pop standard upper off, put PSA upper on. Quick, easy, done.

PSA 16" 5.56 1:7 Midlength Nitride Lightweight Keymod Freedom Upper w/BCG & CH - 7782479

Why in the world would I advise such a thing? Overall cost. For $350 shipped, you get that complete upper, BCG, charging handle. No muss no fuss. No pounding out the tapered A2 front sight pins that S&W installs in reverse of every other manufacturer of AR's. No buying a bench block, hardened punches, barrel wrench, torque wrench, anti-seize compound, a vise (if you don't have one), and headspace gauges. I've been there. I've done that. I've totaled up the amount of $$$ I spent on tools, kit, parts, etc for an AR. It can get stupid fast. Thought I'd spend $$$ on the tools because I'd be building AR's all the time.

You'll have two upper assemblies. One for your dream use of optics ready home defense. The other to practice the fundamentals of shooting with iron sights.

Also by not altering your factory complete OEM upper (and by your post your lower), the S&W 1 year warranty and lifetime service policy will remain inforce. That is a very nice safety blanket to have.

If you ever tire of switching uppers down the road, then you can buy a stripped lower and build it out for your PSA upper. Building out a lower requires fewer special tools than an upper.

__________________
-John

this is my sport, with Magpul vertical grip, handguard, pistol grip with a truglo sight, still have the front A2 and its dead on at 100!


Sent from my iPhone using Tapatalk

That red dot appears to be very low from the pic... is it co-witnessed with the sights?

^
Aint no way it's co-witnessed, it's sitting way too low.

That looks pretty similar to how I will have mine set up. Since starting this thread I ordered a Bushnell TRS25 that should be here monday or tuesday, I also got a got a riser so I'll have to see how that co-witnesses.

So, I'll throw my input into the pile, what you are going to spend on your mods you could almost buy another upper configured the way you want. Look at CBC Industries, they run sales on complete uppers. The advantage is you keep your base rifle and have the option of changing it with the pull of two pins to a different rifle .

I would like to offer a different perspective.

By the time you buy the new parts, remove the old ones and then install the new ones, you will have spent hundreds of dollar plus a fair amount of your own time (which has a value) and you will be left with a modified entry-level gun and a bucketful of parts.

If you were to just go buy a rifle that fulfilled these requirements then you would have two rifles rather than one rifle and some "leftovers". And you would always have the option of selling the S&W to help fund the new rifle.

Just so you know, this leads to buying a lower and customising it to what you really want

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Not quite. I just picked up a Sport II because they were $499 and I couldn't resist it. Optics planet w/coupon - BCM KMR 13" rail and a vice block. Cut and modified the sight post into a low pro gas block last night. Like $180 spent. I knew what I was planning to do up front, so that will make a little difference, but you're not buying another rifle for $180. At worst, the OP would need to spring for a new gas block, though a shorter rail would also be less expensive. Of course, my whole argument goes out the window if you take the do it yourself factor out. I will admit, knocking out sight post pins is a royal pain. If you aren't using the post again, not so much.


I say, if you have the ability, buy a 9 or 10" free float rail, a low profile gas block, and a folding front sight, hit youtube and do it yourself.

I'm doing exactly what you're asking on my rifle right now. I have all the parts on order for my free float handguard, gas block, and fold down front sight.

Current rifle is the MP15 MOE Mid.

Wish I would have gotten the gas block. Took me like an hour and a half to cut that front sight post and grind it down with a dremel Saturday night. I read somewhere about some guy doing it with 1 cutoff wheel. He must have had a good one. I think I used 5. I saved the money on a low pro gas block, and I guess what I have fits the barrel perfect, but man, would not have done it again in hindsight. Turned out really good though.