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Benelli M4 - Building a H2O


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Got a bunch done today. Broke down the collapsible stock for plating.



The button spring is in the bag. Those springs are coated in grease.


Tore down all the other accessories that have come in. Still waiting on a few small parts. A few small OEM parts are back ordered, so that will slow some of this down.


I also knocked out the loading port job tonight. It's my least favorite part of doing one of these builds. No matter how many you've done, putting a file to someone else's 1800 dollar shotgun is always scary. The first step of one of these port jobs is to use painters tape to give yourself some guidelines on what you want to do. Take into account the bolt release, the profile of the trigger pack and how aggressive you want to open up the area around the magazine. I used one of my complete trigger packs to plot my cuts. My Wilton vise has been getting a lot of love this year. Mounted to the top of my Milwaukee work benches has been a huge improvement. The top of the work benches (I have 4 of them) are covered in rubber mats. I put the mat beneath the vise so that I have a nice work surface that doesn't mar anything. I put painters tape on the sides of the receiver and used padded vise jaws.




Be sure to check your side profiles.





The point of no return. Once you've broke the anodizing, there is no turning back.


A few minutes in. The initial cut is to profile the shape. Using a large flat file, you can keep both sides uniform.



Deeper, and making a lot of chips now.



Continue checking your side profile to see how much material has been removed and if each side is uniform with the other. If that's the goal at least.



My favorite bits with the Dremel. Having the pen attachment makes things a lot easier.



This bit breaks the corners with ease and removes the tooling marks.




After I cut my profile, I removed material from the inside to enlarge the mouth.




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After the polishing out was done, I took the flat areas down to 1000 grit to be sure tooling marks were gone. I didn't go any further than that because NP3 won't have that mirror finish anyway. What I do I wrap the end of the sand paper around a flat file. Then I work over the flat areas to be sure all the hit spots are removed. Usually you'll see deep scratches or tooling marks that are deeper. It can take a bit of effort to sand those imperfections away.


Once done though, it's amazing how beveled those corners become. The factory receiver is full of 90 degree angles inside there that can cut your fingers when you're loading fast.

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Nice work...definitely not for the faint of heart. I was admiring the Vickers sling that is on the H20 in your pics and figured out that the pattern is Kryptek Typhon and thought one of those would compliment my H20.

Turns out that BFG is phasing out that pattern and the padded portion of the Vickers sling is no longer available in Kryptek Typhon. Too bad about that because I think it's a very cool pattern suited well to either a black or silver gun. 

But at least I was able to purchase an unpadded version complete with the silver triglides! 

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I ran into that same problem when ordering a sling for this M4, they only had black kryptek for the front portion of the sling. So for this one, I bought an all black one with gray plastic triglides. I might have put a gray pull tab on it, but I can't remember. The sling is still inbound.


Notice we can post more than two pictures to a post finally!



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BlueForceGear sling and the handguards returned from Tango Arms for the stippling. Nice work as always. 


I have a painter who has color matched the NP3 finish quite well. He is going to do the lamp head and the plastic ring that holds the rubber button of the flashlight’s tailcap in place. These parts can’t be plated in NP3 since the electronics cannot be removed and that ring is plastic. 

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  • 2 weeks later...
4 hours ago, StrangerDanger said:

Got some really bad news today. Robar is closing shop as of tomorrow. As it sits, there will be no more H2O’s with traditional NP3 finishes.


Never would have thought they’d go under.

:( Damn! That’s hard to believe considering they’ve been the standard of the industry. 

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Oh man!  Not doubting SD but that is hard to believe.  They have another side of the company that does some of these coatings/platings for the aerospace industry.

I wonder if the entire company is closing shop or just the Robar side.  They also have started manufacturing their own firearms as well.

What are the going to do with all the guns and parts that they have on hand for existing work orders?  This really bites.  Now what am I going to do?


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I couldn’t believe it either. I had to email them myself to verify. Sure enough, they’re out of the game. A lot of manufacturers relied on their plating services. 


Apparently they’ve been looking for investors or a buyer for awhile now. So if you have a bunch of money, you could pick it up for pennies on the dollar. 



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Yep, always love the lifetime warranty gimmick. I wonder if they sell the plating side of the business if they'll have to assume all those warranties.


He has left it up to me to decide what to do. I'm considering a Teflon -S coating. But I hate experimenting with someone elses equipment. I've done nickel boron in the past and it was a nightmare due to tolerance stacking issues. Every moving piece had to be fitted by hand to make the shotgun functional.


There are other companies that offer nickel with teflon. I noted that some of the photos they use showing the substrate surface at a microscopic level were the same pictures Robar used to hype their process. So we might be able to go that route and end up with a generic brand of NP3.

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  • 5 months later...

Parts came back from Wright Armory on Wednesday. They’re the new go to for Np3 plating. Normally Robar would electro-pencil serial numbers on each part except small screws and such. At Wright, they laser engrave the control numbers in tiny font size 4 lettering. They place them on spots that aren’t likely to show when assembled. I had about 600 parts with this batch. The only negative was they mixed the parts from my sorted bags. So having a couple hundred screws and washers to figure out what goes where can be challenging. 

They no longer plate titanium parts either. So I’ll have to get the magazine tube and a few other parts painted to match. 

One off topic mistake I made was sending in the shell plates to my Dillon 650. Apparently there are five plastic plugs in each plate. I thought they were metal plugs. Well they melted I guess so now I’m buying more plugs from Dillon. 


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Sweet!  Did you have those done in NP3 or NP3+?

I sent my M4 and other parts in to them this week.  They seem very organized over there.  The day it arrived they sent me a quote and had the job logged in their system with in 5 1/2 hours of receiving.  Time to wait and squirrel away more cash to pay off the other half.  Based on SD's wait time I figure I have about 4/5 months.

Thanks again to SD for all of his help.  A lot of guys that have his level of knowledge aren't nearly as forthcoming with sharing.

He saved me from sending in my CC mag tube for no reason.


Edited by Milspec
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This one is done in NP3. I talked to their techs for a while about the benefits of NP3+. The only benefit of the plus is it has better corrosion resistance, but at a cost. The Np3+ surface hardness is lower than regular NP3. The NP3+ also costs a little more. So unless you’re living in a lighthouse, NP3 would serve most people best. 

Mine was done in about 14 weeks, so get your money together a little quicker!

Glad to help. I took a few pictures of the receiver last night. The loading port job came out nice. I’ll post them up in a bit. 

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1 hour ago, Milspec said:

It looks like NP3 has a hardness range of 48-51 rc which is a little tighter spec range than NP3+ which appears to be 35-50.

I guess it's a roll of the dice where your hardness ends up with the NP3+.  I wonder if I should call them and have it switched to NP3.

I would. It’ll be more abrasion resistant. I could tell the difference between the two types hardness wise. Should save you a few bucks too. 

The M4 isn’t known for rusting anyway and regular NP3 rates extremely high for corrosion resistance. 

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43 minutes ago, Milspec said:

It looks like you had the choke plated as well.  I’m assuming that doesn’t cause any issues with fit? 

Yep.  No issues at all or performance changes that I’ve noted. Just one less part that can rust and bind up. I recommend getting one of those Briley choke wrenches. I’ve never had a choke loosen up on me since I began using that tool. 

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The Benelli M4 H2O got assembled today. I haven't finalized the installation yet since I have to get the magazine tube and the weapon light head painted to match the NP3 finish.

I used the 10403 Limbsaver with this build which eliminates the need for the Noveske adapter plate. I just had to buy some M4 machine screws that are 2.5mm allen heads. The thread pitch is 0.7 and the length was 16mm. A hole must still be drilled in the bottom of the buttpad to allow the receiver extension to pass into the buttpad when the stock is fully collapsed. Since the 10403 has raised edges that index inside the aluminum portion of the buttpad, it makes it easier to center your drill. I stepped up from 1/4, 3/8, 1/2, 5/8 to the final 7/8 inch Forester bits on the drill press checking for proper alignment with the stock at each interval. Moving forward, this will be the setup I use. It has fewer parts and is cheaper.




















Even the old pistol grip stock was fully disassembled and all the internals were plated.



The OEM trigger pack was plated. It will act as a spare.



How bright is the Surefire M600DF at 1500 lumens? Pretty damn bright!



The new buttpad design. Note the raised edge on the inside of the buttpad that stabilizes the pad inside the pocket of the stock.

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