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Here Tackleberry gives his views, in full, on SGT’s 416 kit; a hotly anticipated product, which promises to set new standard in PTW receiver kits. Equally anticipated, I know a lot of people have been waiting for Tackleberry’s verdict on the kit before purchasing. Well, here it is. It’s comprehensive, it’s honest and it’s a damned good read.

The best 416 kit on the market? Read on.

“I don’t think I really need to say much regarding the quality and finish of this kit other than it is truely superb and surpasses anything else available on the market.

However as with all these things a certain amount of “smithing”, to coin a phrase, is required to make it all fit together and function properly. This is not to be taken as a bad thing, but more an indication that it’s sometimes difficult to replicate certain dimensions from the original RS products and combine them with the Systema PTW platform.

SGT has gone to great lengths to keep the dimensions of their 416 kit as close as is possible to the real thing…to the point of obsession. The company has to be commended on the fit and finish of all the components used here. The upper, in particular, is a masterpiece. This has also been carried over to the lower, where areas like the trigger guard are exact in dimensions to the the real thing.

Now, we all know the Systema PTW is as close as possible in its dimensions to the real AR15; so much so that fitting RS rails etc is default practise, because they bolt on pretty much perfectly. However, when it comes to this set up, it is a slightly different kettle of fish. The design of the HK416 needs to be slightly compromised to allow the fitment of working parts from the PTW. This has been achieved very successfully. Nevertheless, the build is not 100% straight forward and requires not only a good knowledge of general gun smithing, but also a good knowledge of the PTW platform.”

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The Upper

“The upper receiver assembly is actually pretty much 100% spot on. It only really requires good basic assembly skills. Everything fits together pretty much perfectly and the gundrilled outer barrel is simply a thing of beauty! Once assembled the inner barrel/hop assembly and the cylinder unit just slide perfectly into position.

As ever, with any PTW upper, it is very important to ensure the barrel nut is tightened sufficiently. That means not just doing it up “hand tight” like a regular AEG, but TIGHT! Properly torqued-up tight.

There are some that will tell you this is not necessary, but this is simply very bad advice coming from those that do not fully understand what they are dealing with.
Granted, the PTW obviously does not have to deal with the huge pressures involved with a live round being fired. What is often overlooked, however, is the fact that the PTW platform is made to very high tolerances. If the outer barrel is even slightly loose it puts the hop, cylinder and magazine out of alignment and thus affects feeding and firing.

So that Barrel Nut needs to go tight!

The only fiddly bit with the SGT 416 upper is the gas block area. Here a seperate threaded sleeve part is wound in and then the flash hider attached to that – rather than to the outer barrel direct. This is so different threaded sleeves can be used to mount different threaded flash hiders. I would advise bonding the threaded part into the gas block first, allowing the thread or stud lock to cure, then attaching your chosen flash hider.

The dust cover supplied is made of polymer, like those used in the manufacture of the real 416, from 2007 onwards (the slim profile outer barrel is another post-07 feature). The dust cover, like the real thing, is set to be sprung open. It has to stay in the open position as it cannot fully close and lock in place due to the PTW’s cylinder. You can if you like, and as Rich (of The Reptile House Blog) has done, choose to have the cover closed. This means cutting off the detent parts from the inside of the cover (easy, as it’s plastic) to allow the cover to close properly. If you are doing this, you will require a Systema Dust Cover Spring as it is wound in reverse to keep the cover closed (RS and the spring supplied with the 416 kit is wound to keep the cover open).”

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The Lower

“This is where things can get a little tricky.

As with the upper the quality of the lower receiver is first class. From the way it mates and matches to the upper, to the quality of the finish. It is however the finish, or the Cerakoting, that causes the first of the problems.

The Pivot & Take Down Pins are far roo tight in their respective holes. In fact, they are tight to the point of being jammed in place! This is simply due to a build up of anodising and Cerakote. It’s easily overcome by running the correct size straight flute reamer through the holes. It require nothing more than doing this gently by hand. All you should remove is the excess of paint etc without going through to the bare metal.

I will say at this point, while I am on the subject, that the Rear Take Down Pin Hole will need to be reamed again, once the lower and upper are assembled, as the holes need to be aligned. This is actually something that should be done with any new upper and lower, regardless of whether it is this kit, Prime, or OEM SCK.

Basically you assemble the the lower without the rear pin, set the postion of the Buffer Tube Cap, close the two assemblies (as you would to use the weapon as normal), then try to push the rear pin through. It should slide through, with no resistance. If it shows resistance or simply will not go through, then you will need to run the reamer through the hole. This may well take away a shave of metal, but this is essential for perfect fit.

In the case on this particular kit, there was no need to carry out additional reaming.

Anyway, taking a few steps back…

The next area that requires attention is the mag catch. The supplied catch is slightly smaller (supposedly RS size) than the Systema item. Even with that in mind, it is a little tight in its slot. Probably more to do with the Cerakoting than anything else. However a gentle massage with some fine wet n’ dry around the slot and on the catch itself relieves it enough so it doesn’t jam.

Personally I would prefer to have the lower made to accomodate the Systema catch is it far nicer and better made than the one that comes with the SGT 416 kit.

Moving back to the Pivot & Take Down Pins we come to the Stopper Pins & Springs. Or, to be more precise, the holes in the lower which accept them. Again these are far too undersized. You cannot get the supplied Stopper Pins in, let alone the Systema ones which are slightly smaller in diameter. This means both holes need to be drilled out using a 2.5mm drill. In fact, the front one is nowhere near deep enough, so you need to push in a little further.

Once done the Stopper Pins and springs slide in nicely. It is important to apply a little grease to all the parts, particularly where the Stopper Pins interact with the Pivot & Take Down Pins.

Dummy Pins and Selector Cap: Unfortunately the Dummy Pins need a tiny application of Super Glue to retain them. This is a little disappointing, as they are similar in concept to the method used by Prime. Prime’s pins have a far tighter dimension which means they only need to be tapped in with a hammer and suitable drift. With Prime, pins are tight enough in the holes so that once they are in, they are in, and they stay put. However with the SGT that is not the case and you have to break out the Super Glue.

The hole for the Dummy Selector Cap needs a little relieveing for the cap to fit. This is good, as it means you can remove just enough so the cap can be tapped into place and stays tight; although a little Super Glue is ideal here as well.

You can of course use the Ambi set up, but this requires a lot more working to the hole to allow freedom of movement of either the Slave Lever or the Indicator Cap. In this case the build required the use of the Supplied Dummy Cap.

And now to the big one, the fitting of the Gearbox. As many will already know, the lower has been machined so that the Gearbox sits too low inside the recess. The height seems to be okay at the front, but it drops away towards the rear.
This has the effect of compromising the contact patch of the Sector Gear Teeth against the Piston Rack Teeth. It’s not much, but enough to cause the Sector Gear to jump teeth, or simply not engage. As a solution, SGT has supplied nothing more than a washer to sit under the Gearbox’s rear mounting lug.

This is quite simply a very bad patch for a machining error!

Just propping up the Gearbox at its weakest point is an extremely bad idea and the washer is a poorly thought out solution. Using the washer alone would mean all the loadings created by firing the PTW would be transferred to this one point; resulting in the lug simply cracking off and the Gearbox dropping.

The correct way to do this is to apply thin packing shims to the underside of the Gearbox itself, so that it makes contact with the bottom of the receiver. The Gearbox is then supported at its strongest point. This has been implemented in Rich’s build and will be done in all subsequent SGT 416s built by me.

As well as this, it’s still important to use the supplied washer in its intended place, so that the mounting screw can be sufficiently tightened to secure the whole assembly properly. This now sets the Gearbox in the right place and ensures all loadings are spread evenly across the Gearbox and the lower…and consequently ensures the correct contact between Sector Gear and Piston Rack.

I will point out here that this is not an issue specific to SGT. In fact, it has to be done to some Prime lowers; even OEM Systema lowers can require the same treatment.

This now brings us neatly to the final area to take on. The Buffer Tube Cap.

This needs to be spaced correctly to give the right amount of tension to the detent in the back of the cylinder. Too loose and it all moves around. Too tight and undue stress and tension is applied to the weakest point of the lower receiver. Normally the cap sits around 0.20 ~ 0.50mm proud to produce the right amount of tension. However, SGT has built such a perfect mating interface between upper and lower that spacing the cap too far out (and we are talking fractions here) means the upper will not close down properly. This is because the cap now comes into contact with the inside of the upper.

You can play around with shims to get it perfect. In this case you will have to to get sufficient tension on the detent, but not so far out that it fouls the upper. However, it could do with a little more space to allow the cap to come out a little further to get that tension just right. The correct solution to this would be to have an internal chamfer machined during the CNC process. It’s not much, but it is necessary.

So that just about sums it up!

The SGT 416 kit is beautifully made. It’s not 100% perfect, but then nothing is.

Some tweaking at the manufacturing end would iron out most the little issues, but with all these things there will always be a certain amount of fitting required to get the job done just right.”

Thanks very much to Tackleberry 🙂

A final note: I didn’t provide all of the parts which come with SGT’s kit to Tackleberry for my build. Some items, like the BUIS, buffer and stock I won’t be using, in favour of RS items which I already own.


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