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Posted: 3/22/2014 4:03:19 PM EDT
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So I thought I found the perfect rail for my current build and more important one that works with my Mega billet side charging upper. Finding a rail (to my liking) without ant-rotation tabs that will work with the billet upper proved to be somewhat of a challenge.
So I ordered the 13” Parallax FFSSR rail and first hand impressions were positive with regard to ergonomics, finish and rail placement. So I get out the Mega upper, the barrel and slide the barrel nut down and hand tighten. At this point I’m just trying to get a feel for how this set-up is going to look. I slide the rail down over the barrel nut and immediately noticed quite a bit of slop between the nut and the ID of the rail. I measured the deflection at the front of the rail and recorded a full 3/16” of play (moving the rail back and forth between the 3 and 9, & 6 and 12 o’clock positions). The amount of deflection was an immediate concern. It just felt way too loose. Removed rail and nut and get out the mic and caliper. Barrel nut measured 1.3445” and the rail ID measured 1.360 (min) to 1.365 (max) yielding 0.0155” of clearance between the barrel nut and the smallest portion of the rail ID. The rail uses 6 screws at the 3, 6 and 9 o’clock position to fasten the rail to the barrel nut (2 screws at each clock position). IMO: With this amount of compliance, tightening down the 6 fasteners is just going to stretch the rail, the fasteners, or both. Furthermore, the screw holes in the rail are elongated (front to back) to accommodate installed variation. With sufficient force those elongated screw slots will also allow the rail to “pull”. Now place a bipod on the front end of that rail, 12” away from the attaching point, mechanical advantage/leverage will continue to pull and stretch on those 6 points. These are my thoughts anyway but maybe I’m being too critical. So I called Parallax and explained my findings and concern and I was sure the barrel nut OD or the rail ID were out of spec and this may have been a simple stack-up issue. The person who answered the phone didn't have any specs available to him. He said to give him a minute and he’ll go measure some parts. A few minutes go by and he comes back with a barrel nut OD of 1.34”. I stopped him right there, I asked him , “1.34” what? Do you mean 1.340” exactly?” He said yes. He goes on to say the rail ID measures 1.36” and also goes on to say that they sell thousands like this with no issue. So I asked him if he thought 0.020” of an inch of clearance was acceptable to which he answered yes. I disagreed and explained, with that much compliance, something is going to give. My instinct and experience told me this was too much clearance. So as a benchmark I pulled out a brand new Wilson TRIM rail and a brand new Diamondhead rail. Wilson: Barrel nut 1.350”, rail ID 1.354” yields a clearance of 0.004” Diamondhead: Barrel nut 1.3605”, raid ID 1.365 yielding a clearance of 0.0045” A far cry from the 0.0155” of free play in the Parallax FFSSR components. So, am I being too critical or would you move forward and take a chance with this rail? It's already loose and there is one thing for sure, it will not get any tighter. http://i601.photobucket.com/albums/tt91/n_parker_2009/DSC_0033_zps2b84c31f.jpg http://i601.photobucket.com/albums/tt91/n_parker_2009/DSC_0034_zps18a03c44.jpg http://i601.photobucket.com/albums/tt91/n_parker_2009/DSC_0039_zpsc0c057e3.jpg http://i601.photobucket.com/albums/tt91/n_parker_2009/DSC_0025_zps96d063f0.jpg http://i601.photobucket.com/albums/tt91/n_parker_2009/DSC_0041_zps973df577.jpg http://i601.photobucket.com/albums/tt91/n_parker_2009/DSC_0042_zpsa4780320.jpg |
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Dont remember this being an issue with mine. Just tedious to index rail perfectly.
Contact Andy Chen, [email protected] Andy was quick to answer my question. Barrel nut threads seemed stiff compared to spec nut. Turned out to not be a problem. |
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Have you tried tightening it down yet beyond hand tight? It may flex enough to get on there tight.
Let me tell you, stuff like this makes me appreciate spending the extra $$$ on a geissele mk5 with it's .001" tolerance between handguard and barrel nut, although that doesn't help you much with that thick walled upper. I even had to ditch my old side charging upper for one that would fit with the anti rotation tabs. That's fine I'll reuse it on a different build. Consider that you could dremmel your upper to fit a different handguard with anti-rotation tabs, or use a different handguard and remove the (probably overkill) anti-rotation tabs. A little modification to parts is worth the effort sometimes. |
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Quoted:
Let me tell you, stuff like this makes me appreciate spending the extra $$$ on a geissele mk5 with it's .001" tolerance between handguard and barrel nut, although that doesn't help you much with that thick walled upper. I even had to ditch my old side charging upper for one that would fit with the anti rotation tabs. That's fine I'll reuse it on a different build. Consider that you could dremmel your upper to fit a different handguard with anti-rotation tabs, or use a different handguard and remove the (probably overkill) anti-rotation tabs. A little modification to parts is worth the effort sometimes. Thank You, at least somebody gets it. Geissele was my first choice but as noted will not work with the Mega billet upper. Yes, I have considered modding my upper to accept ant-rotation tabs and I have a milling machine with a 9"x40" bed in my garage so I don't need for a Dremel for that operation. At this point I'm considering 2 options. 1) Use some shim stock to take up the clearance. 2) Return the POS and use the Wilson TRIM rail. |
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Quoted:
Negative. It's already in your mind now.. If you are like me it will always bug you. Send it back . None of the geiselles will fit? You're right about that. There will always be a question of it loosening up. No, none of the Geissele will fit that upper receiver. Parralax Tactical Super Slim Rail FFSSR adds a whole new meaning to the term FREE FLOAT! |
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