Using a 16" pencil barrel (.625) with 11" TRX Extreme handguards. I’m sort of partial to clamp-on gas blocks but will defer to a set-screw one if I have to (and learn the pleasures of dimpling barrels I guess - LOL)
Anyone know the inner diameter of the TRX Extreme handguards, and what are the most cost effective but still good performing gas blocks out there that will fit under the handguard?
Thanks!
Pretty much any low pro will work under there.
Excellent.
So, here’s a question - what’s to keep me from buying one of these:
http://www.midwayusa.com/viewproduct/?productnumber=410205
And shaving down the FSB (top and bottom, since I have no need for the bayonet lug or front sling attachment point).
Is this a do-it-yourself with a Dremel job, and I assume that pinning it will be a preferrable way of mounting vs. clamps or set screws? And it is pretty lightweight with all that extra metal off, eh?
Please use better quality parts than Doublestar. You can get a Troy low pro gas block for $35.
OK, follow up. My .750 M4 barrel had a JP adjustable gas block on it - I had to manhandle (read - heavily mark/scratch) it to get it off today while removing my DD Lite handguards which I sold. I’m putting on TRX Extreme HGs and know that there is no way it will fit underneath them. So I need to get a new gas block for it. The barrel already has the two slots for the tapered pins for a FSB - is there a manufacturer of GOOD quality FSBs that I can buy and then cut down and pin in instead of using set screws or clamps?
Excellent.
So, here’s a question - what’s to keep me from buying one of these:
http://www.midwayusa.com/viewproduct...tnumber=410205
And shaving down the FSB (top and bottom, since I have no need for the bayonet lug or front sling attachment point).
Is this a do-it-yourself with a Dremel job, and I assume that pinning it will be a preferrable way of mounting vs. clamps or set screws? And it is pretty lightweight with all that extra metal off, eh?
If your barrel is stripped, youre better off installing a low profile gas block like the one 500grains suggested or the Vltor low pro. With gas blocks, set screwed or pinned or both are the way to go IMHO. Set screws on a dimpled barrel should do just fine if it’s completely covered by the rail.
My .750 M4 barrel had a JP adjustable gas block on it - I had to manhandle (read - heavily mark/scratch) it to get it off today while removing my DD Lite handguards which I sold. I’m putting on TRX Extreme HGs and know that there is no way it will fit underneath them. So I need to get a new gas block for it. The barrel already has the two slots for the tapered pins for a FSB - is there a manufacturer of GOOD quality FSBs that I can buy and then cut down and pin in instead of using set screws or clamps?
Use the FSB and taper pins that originally came with it. Otherwise, just use a low pro gas block.
While shaved FSBs are ideal, it is only practical when your barrel comes pre-pinned with the FSB to begin with.
On the subject of re-using FSBs, it’s not impossible but it’s definitely not recommended.
http://brdengineering.com/Home_Page.php
Check out the site above, it’s very helpful. All 3 options are thoroughly discussed and should help you decide which route to take.
I have his dimple and GB pinning jigs and am really happy I got them. The dimple jig especially as it doubles as a gas port location reference tool.
I bought a .625" FSB and cut it down, and then in half to only require one pin, and sent the whole thing off to ADCO to get pinned in place on a DD .625" barrel.
I bought a .625" FSB and cut it down, and then in half to only require one pin, and sent the whole thing off to ADCO to get pinned in place on a DD .625" barrel.
I meant impractical from a DIY standpoint. A bit too tedious compared to just getting a low profile gas block IMHO.
To the OP, just to clarify, didnt your barrel come pre-dimpled from the factory?
Rob, did you weigh your cut FSB and compare it to one of the usual low pro GB’s?
Ive been curious about this ever since I saw it on a 14.5midlenght cut down GotM4 did for another member.
I’ve always ordered my barrels with front site bases and then dremeled them down myself. The cost of a barrel with the FSB is comparable to the cost of a stripped barrel and additional gas block and I don’t have to send it off to have it pinned. To date I’ve done 3 this way with the lightweight Troys.
Rob,
Is there any disadvantage to using the sawed in half gas block? I’ve considered doing mine that way but haven’t yet. A 9" Troy with a carbine gas system barely covers the block and just like the idea of the gas block being fully under the rail.
I think two pins are better than one. I’ve seen pins walk, and especially when you remove and re-pin yourself taper pins never seem to go back in quite as tight. In my case it’s being drilled & pinned all at once so I think that will be less of a concern.
I like La Rue’s .625 lo profile
If it’s available. Most people advertise 0.625" black block, including Vltor. At the time of my purchase, most were not in stock. Only Midwest Industries had one. Unlike others, they use three hex screws. I have no complaint, it fits under the Troy TRX Extreme handguard really well.
Not that I recall - will have to look at it again.
I don’t have the original FSB.
Why is using another FSB not recommended? Am I missing something here - it appears that putting on an FSB and putting the taper pins through in the two places they go is pretty straightforward.
It doesn’t work that way. The FSB is drilled while on the barrel such that every one is different. There is no guarantee that the pins from one to another will line up.
Hmm - so is it possible that after installing the new fsb that the gas hole in the barrel will not be lined up with the gas hole in the fsb?
I just find it very odd that if FSBs are pretty standard, that they don’t swap out with one another like so many other AR parts - I don’t really know of any other part on an AR that isn’t interchangeable from one to another rifle.
Other parts swap out easily because they are machined with the mounting system in place while FSBs and barrels are not. They are mounted, aligned, secured, drilled and reamed then pinned as one… Each pin hole is essentially unique to the barrel and FSB set.
Yes, even with low pro gas blocks, hence the need for jigs, reference marks etc… to ensure proper port to port alignment.
http://brdengineering.com/FSB_Installation_Jig.php
This is what you need to help you install an FSB. The 3rd photo shows the new FSB without the holes. Note that after the FSB is secured perpendicular to the spindle, he states that “the #31 bit is centered by eye on the FSB pin pads”. That alone is enough to risk misalignment due to slight location differences from barrel assembly to barrel assembly… not to mention the possiblity that the holes were drilled with the FSB not perfectly perpendicular on one, while perfectly perpendicular on another. In the end, it just has way too many variables for such a tight tolerance requirement.
Wow, learn something new every day - seems a sort of stupid way of doing things when everything else is swappable. One would have that they would have standardized this a long time ago.
Ah, well - looks like I’ll be going the Low-Pro gas block route instead - it also appears my JP adjustable gas block may just work with the TRX handguards, which solves the problem.