Sunday, September 23, 2012

SBR Build Completed! (and How to install the Troy Battlerail Bravo)

The upper parts have finally arrived and have now completed the build as of 9/18/2012; I have been waiting for this rifle completion for nine months and considering the coincidence in length of time, it can be said that my SBR is born. Least to say I'm thrilled and haven't been this excited since a midget discoverd the husky section.

The parts in the build have been covered in previous posts but to recap here for the final build;

Lower Receiver Parts

Colt AR-15 Lower (Pre-Ban)
Magpul MOE Trigger Guard, MIAD grip, & B.A.D. Lever
Geissele SSA Trigger
Vltor A5 Kit & IMOD stock
A.R.M.S. #71L Front and Rear Polymer BUIS

Upper Receiver Parts

Stag Arms Model SBR 11.5" BBL + Upper
Troy 11" BattleRail Bravo
Magpul ladder rail covers
BCM Gunfighter Mod 4
**soon to be added**
Griffin Armament M4SD II Compensator

I zeroed the rifle at 50 yards which also is know as the Combat Zero and if you use an A2 rear sight; it is possible to zero at 50 yards utilizing the Improved Battlesight Zero. The reason I chose the 50 yard zero has to do with how the 5.56mm projectile travels where at a 50 Yard zero the projectile hits Point Of Aim (POA)/Point Of Imapct (POI) and again at around the 200 yard mark and intermediate distances are a relatively flat trajectory that is +/- 1.6" out to the 250 yard range. This deviance is compensated with hold overs which means to hold my POA over the target a known amount above my expected POI at distances outside of the near and far zeroes and once trained with the hold overs, hitting 2" steel targets out at different distances are easy without having to fiddle with the elevation of my sights which makes for faster shots on target in a competition with multiple targtes at varying distances. The reason this zero works is the misconception of bullet travel path that when it exits the barrel, the projectile goes straight and drops down but in reality it is an arch which maintains terminal velocity over a longer distance. When the rifle is zeroed at 50 yards, the barrel is not level to ground pointing straight at 50 yards but at a slight angle upwards to produce an arch in the bullet path that is consistent with your aim where the upward angle is ever so slight to the shooter's perspective that it appears to be straight on. A very awesome explanation has been posted on the m4carbine forum by member Molon that is worth a read if you want to know more about the 50 yard zero and how it works (scroll down further on his post to check out the Revised Improved Battlesight Zero if you are using the A2 rear sight, very much worth the read).

The #71L sights which are the low profile polymer offering from A.R.M.S. Inc. is a pretty good sight, I like the rear sight better than Magpul's because it has the short range notch at the top of the sight already but the front sight needs a little work. The front sight simply has too much flat black with no definition and found it hard to quickly acquire the sight post center in the rear peep. I painted white alignment lines on the bottom and top surrounding the front post as well as the top ~1/4" of the post florescent green. The quick fix makes the sight pop out and is now a significantly easier, faster, and repeatable sight alignment.

White base coat

Florescent green applied to post

View from the peep

There are components on this rifle (aside from the short barrel) that I have been wanting to test out and the parts lived up to my expectation. The BCM Gunfighter charging handle (CH) with the Mod 4 paddle which is the medium size latch works exactly as advertised. I resisted buying the Gunfighter CH for the longest time as I was just being a cheap bastard.....until I recently managed to break my CH on my other AR exactly where the BCM literature mentions it. I manipulate the CH one handed with my support hand (that would be my left as I am right hand dominant) and with a standard CH, the one hand manipulation puts all of the stress against the roll pin that attaches the latch/paddle to the handle as well as adding a side way torsion that visibly warps the handle a bit. The BCM CH does not experience the warp as it is a much heavier duty CH compared to the GI and the added rigidity makes the CH manipulation easier. Looks like I will be ordering the second one to replace the replacement on my other AR now.

Comparison shot between the BCM (bottom) and GI (top) CH

Another part is the Troy BattleRail Bravo measureing in at 2.2" wide and 2.44" high which is the update that redesigned the existing TRX and BattleRail line where the new rail is lighter weighting in at 13.35 oz. and attaches to the rifle with less parts for a better, more solid fit and has a closer resemblance to the Alpha series of rails. I shot the SBR for an hour and a half straight while sighting it in and it never got hot, maybe a little warm but nothing uncomfortable at all and with the combination of the Magpul ladder rail covers, I was able to keep a solid thumb over grip on the rail the entire time without any heat issues that would necessitate gloves. At one point when I was adjusting the front sight post, my left hand came in contact with the A2 flash hider just to remind me how burning hot the rifle is (much cursing ensued), it was easy to forget the fact with the rail which did an amazing job at keeping the blistering heat at bay. The only gripe I have with the rail is the finish which I have already started to see wear spots on and it has seen exactly one indoor range trip.

There seems to be no good explanation of the Bravo rail's mounting method or for that matter how it works; so here it is finally, how to mount the Troy Battlerail Bravo. Troy did away with the proprietary nut and uses the existing castle nut on the AR platform which makes for better parts commonality and a simpler installation process. The rail has four screws and tabs and the tabs slide between the barrel and castle nut and the screw tension binds the castle nut between the clips and the rail.

All of the parts

Here the clips slid between barrel and castle nut to illustrate where they will go

You will need to hold the clips inside of the rail and thread the screw in and turn a few turns to keep them in place, the idea is to have enough slack that the tabs will slide in between the castle nut and barrel on their own during installation. Aside from the clips, the rail has keyed sections at the end of the rail that will need to be lined up with the castle nut ridges for installation which you can see highlighted in red. It becomes obvious when mounting that you will need to install the rail off center for the ridges to line up to the castle nut and will than need to be twisted to center for alignment before tightening the screws.

As for the sum of it's parts, the SBR overall functioned flawlessly. I did not experience a single malfunction but to be fair I haven't really put it through it's paces yet either. The Vltor A5 system gave the SBR the reliability of a rifle length buffer system that I was looking for. The FA BCG certainly performed well with a smooth feed, solid lock up, and a very positive ejection at around 4'clock which is where the case should be ejected towards. The dwell time couldn't have been timed better between bolt, buffer size, and tube length in conjunction with spring tension which also makes for a rifle that recoils very flat and straight back that allowed easy follow up shots once I got used to the shorter barrel getting influenced by the bullet spin as it exits the barrel more (the force exerted on the projectile from the rifling forces the barrel to move up and to the left) compared to my 16" AR. As i mentioned in the parts list above, I am waiting on the Griffin Armament compensator to try out in the very near future and will be writing about it here. Now to choose an optic for this rifle....

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