Internal gas-block clearance and MLOK functionality over/under the gas-block with MEGA ARMS and Hodge Defense Systems Wedge Lock rails:
Mega 9.31", Hodge 10.75", Hodge 11.5"
9.3" MEGA rail over 10.5" barrel w/ carbine gas:
10.75" Hodge rail over carbine length gas barrel.
MEGA's wedge lock rails have been out for a while. Hodge Defense Systems recently let out a batch of their version of the rails. At this point in time, both versions are made of 7075 T6 aluminum billet and share the wedge lock mounting system with titanium barrel nut. The MEGA rails have rectangular lightning cuts on the 45* faces and two MLOK slots on the end of the 1:30 and 10:30 sides. The Hodge rails have circular lightning cuts and, inexplicably, only one MLOK slot on the end at the 1:30 and 10:30 face (I wish they had two). The versions are offered in different lengths, MEGA's are seemingly oriented around gas system lengths on their shorter rails for possible placement behind a front sight base. Warning: MEGA does not list the actual OAL on their site! The 9" is 9.312" OAL, the 12" is 12.625" OAL, the 14" is 14.625" OAL. Hodge rails are oriented around common barrel lengths. Hodge lists the actual OALs at 10.75", 11.5", 13.625" for use with common minimum barrel lengths of 11.5", 12.5" and 14.5" respectively. Both versions have the same internal dimensions, 1.225" diameter, which will be the focus of this thread relating to gas-block compatibility. When the Hodge version came out the listing included a note recommending use of the Hodge gas-block made by SLR Rifleworks for sake of compatibility with the slim rail design, which resulted in some questions about using other common gas-blocks.
For the sake of clarity and to avoid putting out misinformation I will show what this means using the SLR/Hodge GB7 gas-block as a baseline for compatibility in comparison.Note - Designed to be used in conjunction with the SLR Rifleworks GB-7 Pin Micro Gas Block (sold separately). Standard low-profile gas blocks are too tall.
Gas-block measurements:
SLR Rifleworks GB7 .750": pin on; base thickness- .136"; hump height- .425"; hump width at gastube pin hole- .337"; overall height- 1.31"; side wall width- .075"
Noveske Rifleworks .750": factory pin on; base thickness- .186"; hump height- .400"; hump width at gastube pin hole- .290"; overall height- 1.336"; side wall width- .075"
V Seven Weapon Systems .750" titanium: set screw, base thickness- .183"; hump height- .401"; hump width at gastube pin hole- .290"; overall height- 1.334"; side wall width- .075"
Syrac Ordinance gen 2 adjustable .750": set screw, base thickness- .197"; hump height- .437"; hump width at gastube pin hole- .297"; overall height- 1.383"; side wall width- .077"
SLR Rifleworks Sentry 7 titanium adjustable .750" (cerakoted): set screw, base thickness- .177"; hump height- .480"; hump width at gastube pin hole- .293"; width from hump side to leaf spring screw face- .510"; overall height- .1.407" ; side wall width- .076"
Internal Gas-block clearance:
All the gas-blocks above clear inside the Wedge Lock rails EXCEPT the SLR Rifleworks Sentry 7 adjustable. The SLR Sentry 7 adjustable gas-block will not clear inside the wedge lock rails. The screw holding the leaf spring in place contacts the side of the rail as the gas-block is .510" wide between the leaf spring screw face and the adjacent side of the hump. Now the screw face is barely short of making contact with the rail when the 9.31" MEGA rail is over the gas-block at the carbine gas location because the internal dimensions of the rail open up a little around the last MLOK slot, but with the longer Wedge Lock rails, the gas-block at carbine length gas position will sit deeper inside the rail where there is not as much clearance on the underside of the top rail for the gas-block hump. Even with the 9.31" Mega rail on a carbine length gas 10.3/5" barrel, where the gas-block has a hair’s width more room under the top rail, the SLR Sentry 7 is too close to the rail. The last thing you want is the screw of your leaf spring detent vibrating against the rail.
The other gas-blocks all clear inside the rail, even deeper inside the rail where the underside of the top rail is narrower. The gas-block compatibility issues warned about seem to focus more on MLOK compatibility since these typical sized lo-pro gas-blocks clear inside the rail well enough.
In a nut shell:
-The SLR Rifleworks Sentry 7 adjustable gas-block WILL NOT clear inside the Wedge Lock rails.
-All other .750” gas-blocks tested WILL clear inside the Wedge Lock rails well enough for use.
MLOK functionality at the slots over/under the gas-blocks must then be considered. Since the SLR sentry 7 will not clear inside the rail, it was not tested for MLOK functionality.
MLOK functionality over/under the gas-blocks:
The Wedge Lock rails are quite thin and ergonomic with an exceptionally robust profile for strength. This does create some issues with MLOK compatibility at the gas-block. The short of the story is that with exceptionally thin rails like the Wedge Lock and MLOK’s larger internal profile (as compared to keymod using BCM’s patented inverse keymod screws) the back of the screws and/or the t-nut themselves ends up contacting or interfering with the gas-block inside the rail at the slots over and under the gas-block, even when the recommended SLR/ Hodge GB7 gas-block is used.
To test function I used an Arisaka Defense inline ring mount (some of the nicest attachments out there). A Magpul aluminum cantilever rail with two different screw lengths available from Magpul’s replacement MLOK hardware package (the cantilever rail ships with the longer of the two screws from that kit), and I also used a Magpul MLOK handstop kit and a MLOK type 2 rail panel.
-At the 01:30 and 10:30 o’clock slots, with all gas-blocks tested, the MLOK screws WILL clear the gas-block.
-At the 3 and 9 o’clock slots, with all gas-blocks tested, the MLOK screws WILL NOT completely clear the sides of the gas-block and the screws need to be shorter/shortened. Type 2 Rail panels WILL clear the gas-block sides.
All the gas-blocks have a side wall width of about .075”. The Magpul cantilever rail with the included long screws are so long that they contact the gas-block and can not be tightened, but the shorter screws from the replacement MLOK hardware kit will clear the gas-block sides. The Arisaka Defense MLOK attachment screws do not quite clear the gas-block either. Magpul’s MLOK specification calls for a minimum of .25” of thread sticking behind the attachment into the rail. The spec seems generous to account for variations in thickness of different MLOK attachments and rail designs from manufactures using the free licensee. The Arisaka Defense mount used has .27” of thread behind the attachment, which IS within the MLOK spec range. Upon request Arisaka offers screws compatible with their mounts that have .20” of thread behind the attachment, but they can not be shipped with the attachments due to the MLOK licensing. The shorter Arisaka Screws should clear the gas-block just fine. The DIY option is to take a file to the back of your screws and make them fit. The shorter-than-spec screws or shortened screws will work just fine with the Wedge Lock rails since after you get the t-nut tension dialed in, the difference between tightened and loose-enough-to-remove-the-attachment is only about a half turn.
-At the 6 o’clock slot, with all of the gas-blocks tested, even with the recommended GB7, MLOK functionality WILL NOT be 100%.
Due to the thinness of the Wedge Lock rails none of the lo-pro gas-blocks tested will clear a t-nut placed directly underneath the gas-block. This affects the 6 o’clock MLOK slots. Placement of a MLOK handstop kit or MLOK vertical grip may require the user to move the attachment forward or backward one-half slot or one full-slot to work around it. Not a big issue just a possible inconvenience.
The main dimensional difference between the recommended Hodge/SLR GB7 and the other lo-pro gas-blocks is the thickness of the base. The GB7 is about .05” shorter than the others because the GB7 relies on cross pinning to the barrel for securement and the set-screw is only for holding the gas-block while drilling the pin hole. The thickness of the base of the other gas-blocks supports the full thread length of the 10-32 3/16” long set-screws for set-screw style securement, which must be torqued to about 25in/lbs and include thread locker. Even though the Novekse factory gas-block only has one set-screw and is pinned to the barrel like the GB7, it has a thicker base with set-screw length threads like the other set-screw secured style gas-blocks (probably for streamlined manufacturing). The thinner base of the GB7 does give it an advantage over the other gas-blocks in that ONLY IT can accept a Magpul Type 2 MLOK rail panel directly underneath the gas-block, BUT only if the included set-screw is removed after pinning since it sticks out as far as the base of the other gas-blocks. One could just leave it out after pinning or replace it with a 10-32 1/8” long set-screw to keep gunk out of the threaded hole.
The other advantage of the shorter base GB7 is that it will accept the placement of a t-nut in the half-slot directly in front of the gas-block because it is short enough to allow the long side of the t-nut room to pivot and tighten. This advantage is shared by the Noveske factory pinned on gas-block and the V Seven Weapons Systems gas-blocks because despite having the thicker base supporting the set-screw thread length, they also have radiused edges and corners. This material removed allows the t-nut room to pivot and tighten in front of the gas-block like the shorter GB7 does. Gas-blocks like the Syrac Gen 2 adjustable with set-screw thread length bases that do not have radiused corners and edges will not allow a t-nut enough room to pivot and tighten in the half-slot directly in front of the gas-block on the Wedge Lock rails. It is worth noting that the base thickness was the tallest on the Syrac Gen 2 of all gas-blocks tested. A different low-pro gas-block with thread-length base that is slightly shorter than the Syrac but still has squared edges and corners may accept a t-nut in the half-slot in front of it with some forcing and finagling. One could finagle a t-nut inside the rail at the desired half-slot it in front of the gas-block already in the tightened position and thread the screw into it like backing plates of older designs.
With the MEGA 9.31” rail and a 10.3/5” carbine gas length barrel, the most used MLOK slots on the end of the rail sit directly over/under the gas-block. With the longer Wedge Lock rails the gas-block will be positioned a little deeper inside the rail, only affecting the lesser used 3 and 9 o’clock slots toward the middle of the rail and maybe the placement of forward grips on the 6 o’clock slots. The 6 o’clock slots are likely the only potential MLOK functionality issue to arise with the longer rails and barrel combos since it is only over the gas-block that the MLOK compatibility becomes an issue.
MLOK functionality at the 6 o'clock slot under the gas-block in Summary:
1. SLR Rifleworks/ Hodge GB7 .750” pin-on gas block with shortened non-thread-length base and squared edges/corners: WILL NOT clear a MLOK t-nut directly underneath the gas-block; WILL clear a MLOK t-nut placed directly in front of the gas-block; WILL clear a Magpul type 2 MLOK rail panel directly underneath the gas-block.
2. Noveske factory pin-on and V7WS set-screw .750” gas-block with thread-length bases and radiused edges/corners: WILL NOT clear a MLOK t-nut directly underneath the gas-block; WILL clear a MLOK t-nut placed directly in front of the gas-block; WILL NOT clear a Magpul type 2 MLOK rail panel directly underneath the gas-block.
3. Syrac Ordiance Gen 2 and other common lo-pro set-screw and pin-on .750” gas-blocks with thread-length bases and squared edges/corners: WILL NOT clear a MLOK t-nut directly underneath the gas-block; WILL NOT clear a MLOK t-nut placed directly in front of the gas-block; WILL NOT clear a Magpul type 2 MLOK rail panel directly underneath the gas-block.
I only tested the .750” seat gas-blocks measured but other common lo-pro gas-blocks with similar dimensions like Vltor, Daniel Defense, BCM, SLR Rifleworks non-adjustable, 2A Armament, Battle Arms Development, Black River Tactical MicroPin/Tune, MicroMOA Baby Govnah all *should* clear inside the rail and will likely fall into the third category of MLOK functionality at the 6 o’clock slot. I am not sure about Geissele’s Super gas-blocks since they have a different profile than the ones tested. BCM’s gas-blocks look thicker on the sides in photos than some others which could affect 3 and 9 o’clock slots. Maybe someone can take measurements and provide a comparison. I would think MicroMOA’s adjustable Govah gas block will probably not clear inside the rail or will have worse MLOK functionality than demonstrated here if it does. Also the Next Intent Tactical adjustable gas-block seems to fit inside the rail as seen in this Wedge Lock install video but I would bet the MLOK slot on the 3 or 9 o’clock side is unusable based on the lope-sided shape of the gas-block.
https://www.youtube.com/watch?v=hPIDoQ1ELHw
I did not test .625” gas-blocks. I wound guess that a .625” gas-block that is scaled down and not just a .750” sized gas-block with a .625” bore (BCM) might provide more clearance at the MLOK slots at the 3, 6, and 9 o’clock positions, potentially not requiring shorter/shortened MLOK screws for the 3, and 9 o’clock slots and more functionality at the 6 o’clock slots.
For users wanting an adjustable gas-block your options seem limited to the Syrac Ordnace Gen 2 and maybe the Superlative Arms gas-block maybe also Next Intent Tactical. I highly recommend at least using an adjustable gas block that has a detent mechanism.
One could also utilize the more robust option of gas-port restricting gas-block inserts like those available from Black River Tactical to dial in your gas. Soon I will post a tutorial thread on how to install a gas-block port insert and some of the compatibility issues involved.
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Originally Posted by jerrysimons
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