bullittmcqueen
10-19-12, 15:25
I recently began gathering parts to build a mid-length upper using a modular free-float rail and retaining the standard A2 front sight post inside a cutout. I was primarily interested in an extended rail with the possibility of mounting a handstop underneath the FSP and a light at 10' next to the FSP with the gas block covered. After several weeks of searching repeatedly, the answer I kept coming back to was that there were very few options for this particular build type, and not many documented cases out there to look at for comparison. Numerous traditional quad rails fit this description, Daniel Defense, Centurion and the like. But I've had those and done that and was ready to try something lighter. Further, I have never found the necessity for all that rail space. It's useless weight for my rifle's operation.
I settled on the Samson Evolution EX 9" for this mid-length upper build. The other available rail I found was the JP modular rail using the extension, but that is a 2 piece system and the extension protrudes out in front the FSP, again, something I do not need and added weight. The Samson Evolution fit my needs exactly so I chose the EX 9. FWIW, Samson offers an extension for the Evolution as well.
This not a new rail by any means. There is another thread here documenting an installation back in 2010:
https://www.m4carbine.net/showthread.php?t=68825&highlight=samson+evolution
which is very in-depth and covers most of the specs of the rail. I was unable to find another user who had installed an Evolution EX on an upper and retained the FSP. I contacted Samson through email to ask if this was possible, and received no reply. I was able to find a post from Scott Samson on TOS stating that it was possible to achieve what I was proposing. So I went ahead and ordered the rail from Samson.
The upper used was a BCM BFH 16” standard profile mid-length gas system. This upper comes with a triangular end-cap that would obviously not fit the circular tube and would have to be removed. As well, the FSP would have to be removed and the bayonet lug ground off in order to achieve clearance inside the rail and preserve the free-floating characteristics of the rail. After removal of the flash hider, FSP, gas tube, and end-cap, I ground down the bayonet lug and retaining ears that housed the front sling loop. I used an electric grinding wheel very slowly and meticulously. After I was happy with the profile, I then refinished the exposed metal with Brownell’s AlumaHyde-II. Although the recommended set-up time for AlumaHyde is 1 week, I let it set overnight and then commenced installation, as I would not be touching or rubbing the painted areas and they would have plenty of time to dry underneath the rail when I was done.
http://dl.dropbox.com/u/5209291/Photo%20Oct%2008%2C%2012%2019%2034%20PM.jpg
http://dl.dropbox.com/u/5209291/Photo%20Oct%2008%2C%2012%2020%2000%20PM.jpg
I then removed the Delta ring in the standard fashion. The stock barrel nut is retained so I re-installed it onto the barrel/receiver after removing the Delta ring. Then the Evolution Rail was installed using the supplied 2-piece thermal bushing and hex screws to tighten the rail onto the thermal bushing. Samson sends easy-to-read installation instructions with the rail, but honestly after watching their installation video on YouTube, installation was straight forward. After placing the 2 pieces of the thermal bushing onto the barrel nut, the Evolution rail slides over the barrel and locks into position using grooves inside the rail that interlock with the bushing. I did have to re-torque my barrel nut to ensure proper alignment of the receiver rail and the top rail of the Samson, as initially they were slightly off-center. When I was happy with the alignment, I used a long riser over the junction of the top rails to ensure continuous alignment before tightening the 2 hex screws in the bottom of the rail to secure it into position.
http://dl.dropbox.com/u/5209291/IMG_2443.JPG
After the rail was in position, I only needed to re-install my FSP and gas tube. The Evo rail has two cutouts on the bottom of the rail which are located adjacent to the positions of the gas block taper pins. These cutouts would allow manipulation of taper pins for gas blocks or gas piston assemblies, etc. After pinning the gas tube back into the FSP assembly, I realized my dilemma. With the rail torqued onto the upper receiver, I had little to no chance of lining up the gas tube into the upper receiver while re-installing the FSP. I really did not want to take the rail back off, so I improvised using a wire coat-hanger that was straightened out and followed the path I wanted the gas tube to take. The tip of the coat hanger was advanced from the upper receiver, through the gas tube hole/barrel nut, and down toward the muzzle. I then slipped the gas tube over the coat hanger and commenced re-installing the FSP on the barrel. It worked perfectly, as I advanced the gas tube, it pushed the hanger out the receiver and went straight into the correct position, while causing no damage to the receiver or gas tube. I then positioned the FSP in its original location and re-installed the taper pins. After replacing the flash hider, I was done.
http://dl.dropbox.com/u/5209291/IMG_2446.JPG
http://dl.dropbox.com/u/5209291/gastubehanger.JPG
I settled on the Samson Evolution EX 9" for this mid-length upper build. The other available rail I found was the JP modular rail using the extension, but that is a 2 piece system and the extension protrudes out in front the FSP, again, something I do not need and added weight. The Samson Evolution fit my needs exactly so I chose the EX 9. FWIW, Samson offers an extension for the Evolution as well.
This not a new rail by any means. There is another thread here documenting an installation back in 2010:
https://www.m4carbine.net/showthread.php?t=68825&highlight=samson+evolution
which is very in-depth and covers most of the specs of the rail. I was unable to find another user who had installed an Evolution EX on an upper and retained the FSP. I contacted Samson through email to ask if this was possible, and received no reply. I was able to find a post from Scott Samson on TOS stating that it was possible to achieve what I was proposing. So I went ahead and ordered the rail from Samson.
The upper used was a BCM BFH 16” standard profile mid-length gas system. This upper comes with a triangular end-cap that would obviously not fit the circular tube and would have to be removed. As well, the FSP would have to be removed and the bayonet lug ground off in order to achieve clearance inside the rail and preserve the free-floating characteristics of the rail. After removal of the flash hider, FSP, gas tube, and end-cap, I ground down the bayonet lug and retaining ears that housed the front sling loop. I used an electric grinding wheel very slowly and meticulously. After I was happy with the profile, I then refinished the exposed metal with Brownell’s AlumaHyde-II. Although the recommended set-up time for AlumaHyde is 1 week, I let it set overnight and then commenced installation, as I would not be touching or rubbing the painted areas and they would have plenty of time to dry underneath the rail when I was done.
http://dl.dropbox.com/u/5209291/Photo%20Oct%2008%2C%2012%2019%2034%20PM.jpg
http://dl.dropbox.com/u/5209291/Photo%20Oct%2008%2C%2012%2020%2000%20PM.jpg
I then removed the Delta ring in the standard fashion. The stock barrel nut is retained so I re-installed it onto the barrel/receiver after removing the Delta ring. Then the Evolution Rail was installed using the supplied 2-piece thermal bushing and hex screws to tighten the rail onto the thermal bushing. Samson sends easy-to-read installation instructions with the rail, but honestly after watching their installation video on YouTube, installation was straight forward. After placing the 2 pieces of the thermal bushing onto the barrel nut, the Evolution rail slides over the barrel and locks into position using grooves inside the rail that interlock with the bushing. I did have to re-torque my barrel nut to ensure proper alignment of the receiver rail and the top rail of the Samson, as initially they were slightly off-center. When I was happy with the alignment, I used a long riser over the junction of the top rails to ensure continuous alignment before tightening the 2 hex screws in the bottom of the rail to secure it into position.
http://dl.dropbox.com/u/5209291/IMG_2443.JPG
After the rail was in position, I only needed to re-install my FSP and gas tube. The Evo rail has two cutouts on the bottom of the rail which are located adjacent to the positions of the gas block taper pins. These cutouts would allow manipulation of taper pins for gas blocks or gas piston assemblies, etc. After pinning the gas tube back into the FSP assembly, I realized my dilemma. With the rail torqued onto the upper receiver, I had little to no chance of lining up the gas tube into the upper receiver while re-installing the FSP. I really did not want to take the rail back off, so I improvised using a wire coat-hanger that was straightened out and followed the path I wanted the gas tube to take. The tip of the coat hanger was advanced from the upper receiver, through the gas tube hole/barrel nut, and down toward the muzzle. I then slipped the gas tube over the coat hanger and commenced re-installing the FSP on the barrel. It worked perfectly, as I advanced the gas tube, it pushed the hanger out the receiver and went straight into the correct position, while causing no damage to the receiver or gas tube. I then positioned the FSP in its original location and re-installed the taper pins. After replacing the flash hider, I was done.
http://dl.dropbox.com/u/5209291/IMG_2446.JPG
http://dl.dropbox.com/u/5209291/gastubehanger.JPG