Adjustable Gas Block vs Tube?

[Hoot]

I know a lot of you have worked with adjustable gas devices to tune you Grendels, so I thought I'd ask here.

I have an over-gassed .308 and the common corrective action is an adjustable gas block or tube.

My question is which is preferable? The only factor to me would be a block fits a given barrel diameter and if you get rid of the rifle, you have a block that may not fit any other barrel you own. A tube, while obviously you have to decide the length you need, can move to another setup with the same length gas system.

Also, what about reliability and maintainance. Is there a strong opinion WRT that between the block and the tube variety?

Thanks,

Hoot

[warped]

I would go with a block, you may not need a new one, they can be drilled and tapped for a stainless set screw and therefore adapted.

[Drifter]

I like the blocks better than the tubes.

The adjustable blocks are not much more costly versus non-adjustable, so I wouldn't worry about removing the block if you eventually sell the upper.

Also, I suggest using Rocksett on the adjustment screw to prevent unwanted movement (at least until the carbon builds up and holds it in place).

[Hoot]

Warped, thanks for the suggestion, but I already pondered that approach. The free-space between the barrel and the tube's port on the block that came with the rifle is only like 3/16 inch, so I wouldn't have much wiggle room to drill and tap without getting into trouble. I could however, find a non-adjustable block that does have more room and mod it. Hmmm....

If anyone is wondering, it's an RRA LAR-8 Predator HP. After a 30-shot shoot-n-clean break-in, the first loads were using the Amax 168 over 41.7gr AR-Comp in LC 1-fire, prepped brass, using four different primers (yeah kind of a lame first date) and all I can say is Wow! Four 5-shot strings at 100 yds, using OCW round robin technique, yielded groups of .96, .66, .59 and .29 inches. The .29 is just a ragged hole. Talk about getting lucky on your first date. Won't go into more detail as this is the Grendel specific sub-forum.

Hoot

[ofreen]

I've used both and both function as well as the other regulating gas as far as I can tell. There may be an access issue to the screw with some adjustable tubes and some handguards.

[LRRPF52]

You can also use a Tubbs flat wire extra power recoil spring. I have had nothing but good results with adjustable gas blocks on AR10's...Namely the JP Steel blocks. Don't go with aluminum...they gall and expand faster, causing gas leakage when the gun heats and cools.

I've heard of other people having leak issues with the MGI adjustable tubes, but haven't played with them myself.

[ss355]

I had an AK that was horribly over-gassed from the US factory that assembled the kit on their receiver. It was so over-gassed that it was painful to shoot. When I finally determined what the problem was, I ran across some cat with the same problem who drilled his gas AK block and threaded it to accept different sizes of carburetor jets to vent excess gas. It apparently worked like a champ for him, so I decided to go the same route. Those darned gas blocks are pretty hard, and I had a devil of a time drilling it. That should have been my clue to go extra slow and lube the tap well, but I rushed the job and broke the tap in the hole. I decided to shoot it as it was, and I'll be danged if the flutes on the tap didn't offer just about the right amount of venting. It's now a much more pleasant gun to shoot!

You could drill a really small hole in the gas block to intersect the bore between the barrel gas port and the gas tube. It would be trial and error, though, to find the correct size, but it is an inexpensive alternative. However, if you drilled too big, you might have to break a tap in the hole to partially plug it. [/sarcasm]

[LRRPF52]

You can also drill higher in the gas block, and intersect the gas tube slightly if you're worried about the barrel, as long as you don't drill straight into the gas tube and severe it. Reputable gunsmiths who have done this on AR's is where I would turn to.

[Hoot]

Thanks for all the good ideas everyone. I'll ruminate on it and come up with a game plan. I have a well equipped man cave and bits as as small as .5mm and taps down to 0-80. One of my drill presses is set up with a B&L stereo scope for fine work. I just thought the obstructing screw would have to be at least a #6 to do the job right and that's probably not thinking outside the 9 dots. I'll figure something out, or simply buy a block. All kinds of options...

Hoot

[warped]

If you buy one get the JP

[Clod Stomper]

Thanks for all the good ideas everyone. I'll ruminate on it and come up with a game plan. I have a well equipped man cave and bits as as small as .5mm and taps down to 0-80. One of my drill presses is set up with a B&L stereo scope for fine work. I just thought the obstructing screw would have to be at least a #6 to do the job right and that's probably not thinking outside the 9 dots. I'll figure something out, or simply buy a block. All kinds of options...

Hoot

I have done it. And it sounds like you're set up better than I. I believe I used a #6 screw. It won't completely cut off gas, but I didn't want to do that anyway. To shut off the gas completely, you'd need a #8 and enough "meat" in the gas block to drill a hole that large.

It's a straightforward operation. Just make sure to drill between the bore of the gas block and the gas tube hole. You can get closer to the gas block, like LRRPF52 said, but beware. If you get it too high, where the screw will contact the gas tube, you'll have to cut a bit off the tube, and the skin on those gas tubes is super hard.

Will

[smoke13]

I'm running this adjust gasblock and tube combo from PRI $80 http://www.midwayusa.com/viewProduct...tNumber=992168