This tube rail comes in a very nice box and is well packaged. In terms of packaging, I’d put it below Daniel Defense but above Samson and Wilson Combat – who seem happy with a bit of bubble wrap (Samson) and maybe some newspaper (Wilson) before finding a box of the approximate length.
Out of the box, the rail is no less impressive. Finishing is top notch in terms of both the mil spec hard anodize and the way the ribs and cooling holes have been machined. No sharp edges and it feels grippy and positive. I like it that VTAC’s version lacks the sharp edges of the standard Troy Alpha (the one with the circular vents), so hats off to VTAC for working with Troy on that refinement.
Markings are beautiful. The indexing on the top rail is crisp, as is the Troy logo and on the side, the VTAC one.
Outer diameter is 1.74″ – so its a smidge narrower than something like the Samson Evolution (1.80″), but not as narrow as the Midwest Industries SS Gen 2 (1.5″). I’d put the approximate weight as somewhere between the two – so, for me, this rail is somewhat intermediate between the tubes I’ve owned.
Although The Alpha rail retains many features – including the anti-rotation tab – it differs from the earlier TRX in that the proprietary barrel nut and pinch bolt system have been replaced.
The Alpha rail no longer requires a proprietary barrel nut, so there’s no need for a specialist tool and the existing barrel nut can be used. If your existing barrel nut is already installed and torqued to the correct spec, this alone makes life much easier – though you need to dispense with the delta ring and spring if these are still part of your barrel nut assembly. Many people choose to simply cut these off, rather than removing and dismantling the barrel nut assembly, but it’s up to you.
For the purposes of fitting this rail, I bought an RS DPMS barrel nut from Midway UK. A friend fitted an RS Alpha rail to his PTW and found his OEM Systema barrel nut was not to spec, which caused him install problems – so I took no prisoners. Removing the existing barrel nut also means I’ll have a chance to make sure the barrel nut is properly torqued and timed.
Similar to and as a consequence of Troy’s decision to utilise the standard barrel nut, the rail’s mounting system has been redesigned, with three internal locking devices which secure the rail to the barrel nut, activated by hex nuts. Given that this rail is RS, these are to imperial standards and Troy includes the appropriate size allen key.
OK…so the parts I bought ready for the install: an RS PRI barrel nut torque wrench head and an RS DPMS barrel nut. I’m not that impressed with the quality of either – both items are a bit rough around the edges – but I’m hoping they’ll do the job. Note to self: as with so many things in life, you get what you pay for with RS kit.
At least the tolerances will be spot on, right? Oh, wait…
Bizarrely, the wrench head doesn’t fit the RS barrel nut without a fight (top), but it does fit the Systema barrel nut (bottom)…
If you recall, I bought the RS barrel nut as I was concerned the Systema barrel nut was off spec!
At this stage of test fitting, both barrel nuts were inserted into the rail, both timed correctly and both allowed the rail retention devices to tighten correctly upon them. A very simple test and not conclusive evidence that both barrel nuts will work when in situ. Here’s one of the DPMS nut, sort of timed:
What I did find, however, is that aside from differences in the two nuts’ tooth profiles, the barrel nuts are different lengths, as illustrated below:
The Systema barrel nut is quite clearly longer than the DPMS one. I think this can mean one of two things: either the DPMS nut is too short for the rail to be locked into it, when the rail buts against the receiver, or, the Systema barrel nut will cause the rail to exhibit a gap between it and the receiver. Either way, the Systema barrel nut appears to be better quality than the DPMS one.
I’m going to try the DPMS barrel nut first.
Here’s the lineup for the rail install:
1. Clamshell upper receiver block
2. Barrel nut wrench head
3. Torque wrench
4. Cheat’s vice – a cheap and cheerful Black & Decker Workmate
The three items are absolutely essential to get the barrel nut torqued to RS spec. A decent vice is also essential, but I can just about make do with the Workmate.
Here are the consumables I’ll need for the rail install:
1. Grease – a smear of which will be used on the receiver’s barrel nut threads
2. Threadlock – recommended by Troy to secure the three rail retaining bolts
3. Duck tape – to hold the cylinder and barrel/hop in the upper while the torquing and timing goes on
4. Flat white coffee – optional (although I recommend Coffee #1)
5. Microfiber cloth…just in case
Here are the parts I’ll need:
Pretty obvious what they are, but just to note that the cylinder and barrel/hop are required to reinforce the upper when it’s tightened down in the clamshell receiver block
First thing to do, is smear the receiver’s barrel nut threads with grease, then insert the barrel into the receiver and get the barrel nut hand tight. I always read on RS forums to tighten and untighten the barrel nut three times, so that’s what I’ll do – though there is no resistance and the nut fits fine. Any excess grease is wiped off with the microfiber cloth.
Next, insert the cylinder and barrel/hop into the receiver and use a swatch of Duck tape to make sure it all remains in situ. I can’t use the charging handle to retain the internals, because it will interfere with the jaws of the Workmate. You shouldn’t have this problem with a proper vice:
The upper then goes into the clamshell receiver block and into the ‘vice’…this is the easiest way to arrange it with what I have at my disposal. I then slip the wrench head over the barrel and onto the barrel nut:
At this point I realise that because the wrench head has no cutout, I won’t be able to see the gas tube hole as I time the barrel nut. Still, so far I just need to crank the torque wrench to 30 ft lbs and tighten the barrel nut until I hear the click.
Next, I whack the torque wrench up to 60 ft lbs and time the barrel nut’s teeth to the gas tube hole. This is trial and error, because I can’t see what I’m doing, but eventually I get there – testing the timing with the gas tube and gas block assembly. I then tighten this on:
I now test fit the rail on the torqued and timed barrel nut. The rail goes on, timed to about 1 O’clock and is then twisted anticlockwise, so the rail’s antirotation tab butts up against the receiver. The barrel nut is thus held in a groove inside the rail, which holds it on.
Fit is good, so I prep the rail retention bolts with threadlock and tighten them equally. The bolts draw the rail into the receiver and make it plumb. Care needs to be taken that the top rails of the receiver and rail line up. I normally use a carry handle for this, but this install was easy enough to do without one.
The upper mocked up, looking dirty with a pair of Diamond Head sights:
It’s not over yet, however. As is common with this kind of rail, there’s not quite enough clearance between the rail and the front receiver takedown pin tab on the lower, in order to shotgun the upper. This means a tiny bit of material needs to be removed from the lower bottom edge of the rail.
You can see how little clearance there is, here:
A mate took the rail away, sorted the clearance and claimed to have ‘enjoyed’ doing it. For someone like me, who believes DIY means Don’t Involve Yourself, I find this difficult to believe – but I’m extremely greatful for the mod.
You can see that not only does the upper and lower now fit together, but there is plenty of clearance to shotgun the receiver:
Here’s the detail of the mod. The secret ingredient isn’t marker pen, it’s black nail varnish…