I have just recieved word that my LMT upper is in. I am getting ready to order my forearm and could use some help. Here is a list of what I would like to do.
I have an LMT Upper 16 in.
Would like to go with the JP Enterprises V-Tac forearm rifle length which is 12.5 in long. It is my understanding that in order to do this I must change the gas block.
It appears that there are several types of gas blocks available,
pinned
2)Clamp style
Set screw
Or I can grind down the existing gas block. JP also has a tube extension that allows a carbine length guard to be extended and go around the stock forward sight. Here are my thoughts
1)I do not like the standard front sight and would prefer it was removed. I also do not like the idea of the of extending the tube as I am afraid it will loosen up.
2) I would prefer to minimize the number of fasteners.
From what I have read it seems the DD and Vltor gas blocks are good. So far as far as looks I am leaning towards the Vltor right now.
Any suggestions or input would be great. Preferences towards one style or the other, pinned vs clamped vs set screw etc. Other suggestions are encouraged.
What I like to do is grind down the existing FSB. It’s what I’ve done on my 3gun rifle on a RRA midlength bbl using a JP VTAC 12" tube.
Here’s some old pics of it.
Here’s what is looks like before adding a rail or FF tube covering it. I can get small enough like the pics below that it’ll fit under a DD Lite Rail or LaRue rail.
Thanks for the pics. I had seen those when I searched the topic. As others have said before nice job. I like the idea of using the original sight ground down from the aspect there is no question if it will fit and work. However I do not know what the reaction the part will have to having most of its mass removed. Also I would prefer if possible to preserve the original gas block in case I had to sell the gun or in case I decided at a later date to change back to the original configuration for some reason. Although I have not ruled out the possibility of doing this I am trying to explore all my options prior to this outcome or if this is becomes the apparent best method I will use it.
Thanks for your ideas they are good ones.
To others please chime in and let me know what has worked for you. Not necessarily with the JP system but any long rail system on a shorter barrel as far as the gas block goes. I have already researched the rail systems and decided on the JP system but in theory this obstacle must be overcome whenever a long 1 piece free float rail is put on a carbine rife it seems.
It’s not a mechanical part. Gas just flows through it just as it would if it were a full size FSB. The gas doesn’t ‘know’ nor care that it was a FSB and is now a low-profile pinned gas block. The biggest thing you need to worry about is the material of the gas block, for reliability is should be steel or stainless steel like the barrel. And it this case it’s steel.
I have however ‘shaved’ a FSB down for use on a ARES G35 piston conversion and I threaded the gas tube roll pin hole for a 4-40 set screw and it’s holding up very well.
After some more research I found JP Enterprises makes an adjustable gas block. This will work with there forearm and allows the gas system to be “tuned” for different loads etc.
On a range/competition gun only…they’re great. They have no business on a ‘social’ gun.
I used to use a JP adjustable gas block on a 20" bbl on my 3gun rifle. It sucked for me. I now use a ‘shaved’ FSB.
If you’re planning on putting an adjustable JP gas block on a 16" CAR length barrel get a steel/stainless steel one. Also it won’t fit under a JP freefloat tube without ‘shaving’ as well. Then have it pinned. “Set screws are NOT the way!”
Thanks, for the input. I am looking to build a good shooting gun that works well. I do not tolerate failures well FTF, FTE, stuff like that will drive me crazy. If I want temperamental I will brake out the Automag III (which I love and bought knowing of its temperamental nature). But the AR I feel should be like my SIG, pull it out of the box, fire until hearts content with out a problem.
I will look into the JP gas block a little more but maybe that one I will stay a way from. They now make a shaved version of the gas block by the way that will fit under the tube which is stainless steel. I was a little apprehensive about the set screws any way. Also a little nervous about the screw to adjust the gas output.
Have you had any experience with the VLTOR gas block. JP service said it will fit under there rail system.
The VLTOR gas blocks are my favorite low profile gas blocks. I do recommend pinning them as well, if not in the very least dimple at least one of the set screws and red loc-tite it. They’re very small and will easily fit under a JP tube.
It uses cap screws to clamp the band around the barrel. I like this idea for 2 reasons. The first being I think it will give more clamping force and will be less likely to loosen as more torque can be applied to the fasteners. I also like the idea of the clamping torque being more evenly applied to the barrel. Again over thinking this but who knows . Secondly I like the fact that if a cap screw were to loosen up, get lost, or stripped it will be easy to replace.
While I understand how the idea of pinning works what steps do you use to locate the pins. How important is pin placement on the barrel. Are there detentes that the pins pass through. Or do they just gouge out a section of the barrel when they are driven in?
I have a ‘cheater’ gas block that I’ve cut the top portion off the make sure it’s gas port is TDC on the bbls gas port. Then I dimple the rear set screw with a drill. I would do the same if I were drilling then reaming for a taper pin, I don’t currently don’t have a drill press so I don’t pin.
Pinning requires a mill or good drill press and vise as well as some quality drill bits, correct reamer for your pins and some pins. I’d use a 0/2 taper pin, same as a stock FSB. I’m currently not pinning my blocks as they are all dimpled and Loctited. They are also completly covered by the FF handguard.
. Secondly I like the fact that if a cap screw were to loosen up, get lost, or stripped it will be easy to replace.