View Full Version : Two Years with TWS Gen2 Dogleg Rail.
Over two years of use, I've found that the TWS Gen 2 Dogleg rail suffers from the same issue that all previous AK top cover optic mounts have: shifting zero.
Zero shifts if the top cover is struck, when the top cover is opened and closed, and it also shifts to a lesser extent during firing. It still functions well enough to make good COM hits out to 200 yards, but it degrades the typical 2-3 MOA accuracy of my SLR-106 to as bad as 6 MOA within its 2-4 MOA horizontal, 1-3 MOA vertical, 'diagonal arc of error.'
I found that the front hinge section, which replaces the rear sight, does not fit tightly in between the "ears" on the rear sight block, at least on my example. I believe this is because my rifle is Bulgarian, which I understand have rear sight blocks with wider gaps. This contributed to horizontal shift in zero. I was able to solve this issue after Mr. Fesas suggested adding a shim here. I achieved this by making a "U" shaped shim out of a bent and drilled section of feeler gauge, fitting it around the front hinge section which fits into the rear sight block, using the hinge pin to hold it in position. This reduced my horizontal zero shift, but did not effect the vertical.
Bending the side spring tab further inward to increase its tension seemed to offer another slight reduction in windage shift, but not enough to eliminate it. It had no effect on vertical shift.
After shimming other areas in vain, I finally found the primary culprit: The rear of the cover can twist longitudinally! The camming latch, which replaces the stock rear section of the recoil assembly, cams against the top cover, forcing the rear of it against the top of the rear trunnion. Since it is comparatively narrow and is in the center of the topcover rear, I believe it is not supplying sufficient lateral stability and may not apply enough downward force to prevent the rear of the topcover from being able to twist very slightly. It does apply enough force for friction to prevent the top cover from settling back into it's precise original position each time the weapon is jolted sufficiently, resulting in the TWS Gen 2 Dogleg Rail's inability to reliably hold zero.
I have communicated my findings to the designer, along with an idea for a solution that I hope will at least serve to help illustrate the problem.
This experience has proven educational and has made me wonder about the real abilities of top cover mounted optics in military use, like the Valmet and Galil's rear iron sights, to retain zero and if they do how those designs might be looked to for a solution.
I sincerely hope Mr. Fesas is able to finish the refinement of his TWS rail, as it seems so close to succeeding where everyone else has failed. His is still the lightest and among the most position-flexible optic mounting solutions to date for the Kalashnikov rifle.
This experience has proven educational and has made me wonder about the real abilities of top cover mounted optics in military use, like the Valmet and Galil's rear iron sights, to retain zero and if they do how those designs might be looked to for a solution.
They do, but only because the rear sight is light, and movement of the rear sight all in all has much less impact than movement of the whole optic. Valmet Hunter models (essentially RK made in .308 and .30-06) had rail mounted on the cover but it was not very succesful design decision in the end.
robert60446
10-06-13, 16:59
That's awesome update man - thanks!
Good review indeed. I stir think the RS mounts are the best option for optics on ak's.
pointblank4445
10-06-13, 19:36
Thank you very much for this write-up; you touched on some things I've wondered about regarding this system.
They do, but only because the rear sight is light, and movement of the rear sight all in all has much less impact than movement of the whole optic. Valmet Hunter models (essentially RK made in .308 and .30-06) had rail mounted on the cover but it was not very succesful design decision in the end.
That makes sense. I think I found the amount of movement needed to vary point of aim off of zero 4 MOA. Try looking through a red dot optic with a piece of paper marked in 1mm increments directly in front of the objective lens. Now make click adjustments for 4 MOA in any direction. The movement of the optic's reticle is something like 500 micrometers (a little under 0.02")- half a millimeter's movement at the optic translates to a roughly 4 MOA shift. To get the error down to something more acceptable, say 0.25 MOA, the optic platform could not shift more than about 31 micrometers, or about 0.001".
Good review indeed. I stir think the RS mounts are the best option for optics on ak's.
I think you may be correct, but there are some disadvantages to his rail: You can't fold the stock on an AK-74m/AKS-74 type stock, and as wonderfully light as he was able to make his rail, the lightest one still results in an overall weight gain, with an Aimpoint T-1/H-1 optic, of about 7oz. Overall weight gain with the same optic mounted on the TWS is less than HALF that, at 3.25 oz total weight gained.
The Ultimak comes out lighter than RS' mounts, but with a G2 Surefire and Vltor mount, puts about 3/4 lbs in front of the weapon's point of balance, making it even more nose-heavy.
In my opinion, the TWS cover needs a wider latch for more lateral stability and a lever camming system, instead of reliance on spring tension, to increase the camming force which would reduce the amount of shift and increase repeatability. Actually, it would benefit from camming in both axes and eliminating the spring tension idea altogether. It was an elegant idea, but one which I believe has shown that it has failed the test of real world use.
I think you may be correct, but there are some disadvantages to his rail: You can't fold the stock on an AK-74m/AKS-74 type stock, and as wonderfully light as he was able to make his rail, the lightest one still results in an overall weight gain, with an Aimpoint T-1/H-1 optic, of about 7oz. Overall weight gain with the same optic mounted on the TWS is less than HALF that, at 3.25 oz total weight gained.
Have you seen this review: http://www.theakforum.net/forums/22-optics-accessories/155356-side-rails-suck-rs-regulate-300-series-side-mount-review.html
I had a TWS rail, and it held zero just fine when simply opening and closing the cover. But I am pretty sure that if I stood on the dang thing, or did push-ups on top of an optic mounted on it, or threw the rifle 6 times onto frozen rock hard field, until it lands squarely on the TWS mounted optic, it very likely would have been a different story. A 3 ounce gain for the kind of strength, durability, and ability to hold and return to zero that is demonstrated in the review is I think worth it. It would be for me in any case.
Have you seen this review: http://www.theakforum.net/forums/22-optics-accessories/155356-side-rails-suck-rs-regulate-300-series-side-mount-review.html
I had a TWS rail, and it held zero just fine when simply opening and closing the cover. But I am pretty sure that if I stood on the dang thing, or did push-ups on top of an optic mounted on it, or threw the rifle 6 times onto frozen rock hard field, until it lands squarely on the TWS mounted optic, it very likely would have been a different story. A 3 ounce gain for the kind of strength, durability, and ability to hold and return to zero that is demonstrated in the review is I think worth it. It would be for me in any case.
Have you seen this review: http://www.theakforum.net/forums/22-optics-accessories/155356-side-rails-suck-rs-regulate-300-series-side-mount-review.html
I had a TWS rail, and it held zero just fine when simply opening and closing the cover. But I am pretty sure that if I stood on the dang thing, or did push-ups on top of an optic mounted on it, or threw the rifle 6 times onto frozen rock hard field, until it lands squarely on the TWS mounted optic, it very likely would have been a different story. A 3 ounce gain for the kind of strength, durability, and ability to hold and return to zero that is demonstrated in the review is I think worth it. It would be for me in any case.
I have read a few of Voron's reviews. He's quite a character and writes good reviews. He's certainly got a thing for defending Russian optics. ;)
With the AR15 as my yardstick for performance, 9 lbs is about the maximum I'm willing deal with in a 5.56 weapon, and I expect that to include a white light, red dot optic, sling and all other accessories. Having experienced a few occasions running around for several hours with a rifle, weight and balance and how they affect arm fatigue are important to me. 4 oz is a quarter pound and I have found this amount of weight, and particularly where it is on the weapon, makes a far greater difference in handling characteristics than it would seem on paper.
How extensively did you test your TWS' ability to hold zero? Before I made a point of testing it, I passed off the shifting in groups and "thrown" shots as anomalies. I was willing to live with some zero shift when opening and closing the cover, but I eventually found just being bumped on either side would cause the zero to shift in a manner that was not repeatable (you couldn't just 'bump' it the other way to bring it back to zero, etc), and I found that it was shifting slightly even with just the disturbance of recoil.
I think many users have not noticed the shifts because "It's an AK" and the variance seems to be along the lines of a Gaussian curve with most shots falling into what could be considered "normal" accuracy that is still generally good enough to get hits out to 300 yards. It's very easy to simply pass off misses at that distance as the fault of the rifle or the shooter or some other anomaly. It also might be more apparent to me since I mounted my R-1 as far to the rear as possible. The effect would be lessened somewhat if the optic were mounted farther forward.
I theorized that using spring tension was not sufficient to prevent the top cover from shifting, that any force which exceeded the spring's force would cause the cover to move. This wouldn't have been a problem if the top cover had just returned to it's original position after an impact- which is what the cover is intended to do.
I'm sure this could vary with different rifle and rail samples, but the design can't soundly cope with being twisted longitudinally; it is frequently twisted longitudinally and lacks a mechanism to deal with this twist and return to a point of origin with accuracy greater than +\- half a millimeter. Half a millimeter at the optic translates into angular variences of about 4 MOA. When considering this as a twisting motion, it accounts for the greater windage variance and lesser elevation variance of holes in the target I witnessed, which would probably look, if examined in greater detail, like an arc instead of a diagonal line.
It needs greater rotational stability, which could probably be provided by wider cam surfaces and greater camming force.
Thanks for the 2 year update.
I've been using TWS rails since they came out, and I've not seen any issues with zero on any of the 3 rifles. That being said, each rifle has only seen a few thousand rounds. 2 things are critical, I think, to having good results. First, I know of folks who give up on installing the rear sight leaf spring because it is difficult. That's a very bad idea. The other is taking too much material off the base of the cam button to fit it into the trunnion. Not saying anyone that has a bad experience has done one of these, just that I've seen or heard of issues resulting from these items.
With that said, I think the krebs rail, although a bit high, or the RS mounts are more rugged. I just don't have side rails on any of the guns with the TWS installed, which is why they dont have RS mounts. However, although I can't say I've abused the TWS guns terribly, they are still holding strong. Of the two with magnified optics, I get just over 1 MOA with the 74 and SST, and around 2 MOA with a polish kit 7.62 and SST for 5 shot groups.
The front hinge area is delicate feeling enough that I am rather careful with them when I have the top covers open, but so far so good. The next AKs in the stable will probably have side rails, and thus RS mounts, on, though.
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