Parallax Tactical FFSSR Rail Brings New Meaning to the Term "Free Float"
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 slid the barrel nut down to the receiver 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/slop, 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 (barrel nut), 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. He said just tighten down the screws, it will be fine.
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” (keeping in mind the Diamondhead rails is slit allowing it to compress around the barrel nut when tightened down)
A far cry from the 0.0155” of free play in the Parallax FFSSR components.
There are other issues as well. The flats across the barrel nut measure 1.232", which is 0.018" short of 1-1/4", yes the wrench was quite sloppy. Oh not to mention the wrench flats on the barrel nut measure 0.483" wide so the crows foot would not slide onto the nut without modification.
So, am I being too critical? I welcome your thoughts on their specs.
One thing is for sure, it will not get any tighter.
BTW: My first post on this forum.
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