View Full Version : Troy 13.8"MRF Stability and Gas Block Compatibility on an SPR

01-17-12, 01:08

First and foremost as a longtime lurker of this forum who has recently decided to become active I'd like to say hello to everyone here at M4C!! I look forward to a productive stay and meeting everyone here on the boards. Now onto business.

Recently I have begun a long range build on the 5.56 AR platform which I intend to shoot out to 600 yards using a BCM 20" 1/8 SS410 barrel with a Troy MRF-RX 13.8" rail system and VLTOR stainless .750 clamp on gas block. I would like to use a clamp on gas block to keep the gas block as stabile as possible without pinning it however I am aware that clamp on GB's compatibility with free float rails running over top of them can be iffy at times. Therefore I am curious if anyone has had experience with this setup or knows if I will run into any problems mounting the rail with the clamp on GB. I used the search function prior to typing this up however I was unable to find anything useful.

Secondly, although I intend on using the Troy rail system for the purpose of it's low weight and cost I am curious about the stability of the rail and it's practicality on an SPR. While lurking, I ran across a few instances of individuals having issues with Troy rails mounting/staying mounted properly on the upper receiver. With that being said Can I expect any issues with this rail system on an SPR? Has anyone in this community had experience with this rail system on an SPR? Furthermore for my purposes where weight is a consideration would the Larue 13.2" rail be a more viable option? While understanding both Troy and Larue are top tier manufactures I looked at the Larue rail originally for it's reputation within the precision shooting community but shot it down for the troy rails due to the aforementioned reasons but I much rather have a more stabile/reliable rail as opposed to a lighter and cheaper rail that may not be ideal for my intended uses. I appreciate your input in advance.


01-17-12, 06:54
When you're looking at reports of shifting, is it the MRF or the TRX? They have different mounting systems so you need to make sure you're seeing the same model you're looking at. Also, flex is one thing and shift is another. Flex isn't so bad, and at that length is almost unavoidable, shift is very bad, especially if you have front sight or other aiming system attached to the handguard. My TRX will flex, but I cannot perceive any shift.
flex = the barrel will move within the rail, or the rail around the barrel, when opposite pressure is applied to each, but the system returns to center when pressure is released.
shift = flex but the parts do not return to center.

I'm also not sure the MRF is as light as you think it is? Check here

while I don't have the 13.8 listed for many (because not many make that length) it is heavier than the Larue, and if you compare the MRF at other lengths it's on the heavy side compared to other makes. It may still be worth it for you given the low cost, but just something to be aware of.

01-17-12, 09:56
Like Rob said the mounting of the MRF and TRX are different. The MRF use the standard barrel nut and the TRX use a proprietary one. If you are buying a barrled upper and you either donít want or donít have the tools change the nut then the MRF is the way to go. If on the other hand you are doing the build then consider the TRX.

I recently replaced my MOE handguard with the Troy MRF 13.8. This was on a BCM 16Ē 1/8 410 with the mid-length gas system. I cut down the FSB and it fit fine. You should have no problems with the Vltor gas block but I would recommend the one with the set screws not the clamp on. IIRC the BCM barrel comes dimpled for a set screw gas block.

01-17-12, 11:54
Thank you Rob and 5pins for your response. To answer your question yes, the MRF rail is in fact the rail I found problems with on the boards and it is a shift, not flex. I did a quick search and found the two threads that raised my concern linked below. Granted the threads I found were a couple years old and business QC can certainly improve in that time I figured it's better to ask then suffer the possible consequences. The problem was more or less with the rail mounting to the barrel nut and the barrel nut becoming loose and thus not torqued to spec. Up until Rob's post I was still under the impression the TRX Standard and MRF both mounted to the factory barrel nut. However I now know this is false.

Links to the threads for reference:


As far as the weight of the rail system is concerned Rob you are correct. I was under the impression the Troy MRF/TRX quad rails were MUCH lighter than they really were. I saw "only adds 4oz to the weight of the rifle" on Troy's website under the 13.8" product description and therefore thought of it to be a lighter rail than the Larue system however I now know this is false as well.

In the end I'd like to save money where possible as money is a concern being a student but I much rather pay a little bit extra up front and avoid any misfortune down the road. It looks as of now I'll be considering the Larue option with the set screw gas block more heavily unless I find something concerning.

01-17-12, 22:14
If it's a range-only rifle, the MRF-RX is a great handguard, because it allows you to mount stuff, and that big heavy handguard helps soak up what recoil a 5.56 platform makes.

For your use, I'd be heavily considering (based on cost and you mentioning that simplicity of modifications matters) just turning your existing rifle into a modified SDM-R silhoette.

Install the Centurion C4 12.0 handguard (can do that with metal snips and a dremel if you dislike removing parts, but simpler if you do). Keep the FSP, and you'll have an affordable, solid rail installed that also has 4 sling QD points, is on the lighter end of things, and importantly doesn't require a barrel wrench to install.

If you don't have the upper already, I'd say bump yourself to an 18" upper (HighCaliber, Centurion, Noveske, BCM, ADCO) and pick a rail that works - all of those offer rifle length and extended rails on complete uppers, and I suspect you'd be happiest with the 18" configuration anyway.

01-18-12, 12:33
I have a MRF 13.8 on my 16" BFH mid-length upper and am running the VLTOR set screw gas block, but I also sent it to Rainier Arms to have it pinned on. The rail clears the gas block just fine. As far as lock-up, it is just fine. Mine clamps down to the factory barrel nut tight and has not shifted in 2 years time. Those who have trouble with the rail shifting probably don't have their barrel nuts torqued to spec or don't have their mounting screws loc-tited. The rail also has tabs on either side that extend next to your upper to keep the rail from rotating in the event your barrel nut did come loose.

Like I said, this rail is on my carbine. In that role, I feel that it is a bit too heavy. If I could go back I would have gone with a DD Lite 12 or the Centurion C4 12. Now, having this particular rail on an SPR would be fine in my opinion. With long and heavy barrels, bipods out on the end and larger optics, not to mention the position you will be shooting from, weight becomes much less of an issue.

If you are interested in picking up an MRF 13.8 used, I have mine for sale in the equipment exchange.

01-18-12, 23:49
Llama, thank you for the link to the C4 rail. It looks very interesting, I like only 14.2oz and using the factory barrel nut. As for using the rifle it will for the most part probably end up being a range gun. However looking into the near future (next 6 months or so roughly) I will be moving to Arizona for college where I could easily see myself moving the rifle around in the mountains out there wether it be hunting, recreational shooting, or what have you. That is why weight is of a concern to me and I apologize for not being more clear from the get go.

I currently have an upper awaiting a barrel, rail, and other necessary components and while lurking around have looked into 18" barrels in the past as information found here showed me 18" barrels perform similar to 20" barrels in terms of muzzle velocity and stabilizing heavier rounds. My only concern with an 18" barrel is that I currently have a 16" middy rifle set up with a 12" DD lite rail that can more or less fill the role of a "recce" rifle so to speak if need be. Granted the barrel isn't stainless or 1/8 twist, just a standard BCM 1/7 gov't profile nor do I have any aftermarket trigger but I would imagine a 16" barrel would perform similar to an 18" as an 18" would to a 20". However with that being said I am certainly open to new and different ideas as that is a primary reason I am here :). For a long time the only information I had access to was by lurking and thus did not ask questions of my own. I'm still kicking myself for not becoming active sooner lol.