Good info dpete. I didn’t think to check the port size when I had it apart. Gonna be hot enough all week I might as well check that out while I’m waiting for it to drop below 100 degrees here. I’ll have a read of the links.
Follow-up…
After reading links provided here I checked port size. Instead of .096 I found .077 (drill bit) was the largest that would fit - and it was snug. Gas block port is north of .130 so that .025 spacing from the shoulder would not have mattered.
Thanks for the heads up!
The hole in the gas block should be .125 or a tad bigger. The inside of the gas tube is .125 so anything over that is extra large and not necessary as long as you get the block as centered over the gas port hole as possible. Drilling the gas port hole is easy. Numbered drill bits from any hardware store are all that is needed. A hand drill works, a drill press works better. Support the barrel and run either one slow, oil the bit and the hole, and use light pressure on the drill. You want the drill bit to eat slowly. If you are concerned about punching through too fast you can put a wooden dowel into the barrel.
dpete, Hadn’t thought about the dowel. Confess the thought of drilling it myself makes me feel like an instant girlie-man. Michael at Criterion encouraged me to send it to him but what a hassle and then there is the risk in shipping. I’d think the bore axis being perpendicular would be critical - if I could stabilize it firmly on a small drill press maybe that would be smart. I don’t have a good feel for how well a bit would follow the original hole but if it would do a good job there perhaps I’d be safer than I think. Was a decent trim carpenter and welder in past life but a machinist would run me out of his shop.
Just a question. Would you still change out the Superlative gas block now that the problem looks to be the port size? And would you make the port .0960? Seemed like places call for a minimum and max, and some called .0960 the max. I was thinking if it was the max and I did drill it at that size than an adjustable gas block my be smart to keep.
I prefer the idea of not having to use an adjustable gas block if not necessary. So I would drill the port to the correct size and go from there.
As to drilling the gas block, I would use the 0.077 drill bit to align the port to the press, as we know that fits snugly. Then change out the bit to the correct one(pick one size smaller than the minimum recommended port size and go up as necessary).
Thnx George.
When drilling the gas port you cannot get it wrong! The hole that is already there is the perfect guide hole and the turning bit will naturally want to follow it down. Just take it slow and all will be well. While you are working on the gas system and have the rifle in pieces, take the entire BCG out and soak it for about a week in Mobile 1. When you are ready to shoot, pull it out of the oil, let it drip off then clean off the bolt face. Slap it back in the rifle and go shoot. Bring extra oil along with you and use it. During break in with these large frames you want oil oozing out of every orifice while shooting to make sure all the metal on metal surfaces mate together smoothly. These big girls need a lot more lube to get going properly, compared to their little cousins.
Just to be clear, he isn’t drilling the gas block, he is drilling the gas port…big difference.
@SgtDog You already have the adjustable gas block. You might as well drill once at .0960 and be done with it, get the rifle functioning with a decent round count through it, then you can start fine tuning the gas with the block if you have to. You can dial down the gas with the block, but you can’t dial it up if you drill an in between hole size first and the rifle doesn’t function properly. You’ll end up pulling it all off again and redrilling to the proper .0960".
Oops, yes. Meant gas port.
Adding the complexity of an adjustable gas block to a system seems suboptimal compared to a properly sized gas port. Not sure why anyone would want to oversize a gas port just so they’d then have to choke it down with a failure prone device.
You are correct. You don’t want to oversize it. .0960" is the proper size determined by folks with years of experience troubleshooting large frame ARs that people have purchased from manufacturers that think they know better than the creator of the design.
The OP read the links, he has the info to get his rifle running, all he needs to do now is put that knowledge into practice.
I did read the links. I am concerned about finding sharp bits without ordering and waiting. Home Depot or Ace doesn’t inspire confidence with Chinese products…
Btw, while ‘Survivalshop’ gives these number from Tactical Machining:
DPMS LR-308 Style Rifle
18" rifle 0.308. 0.096
I did find in the links where some posters referred to ranges with minimum and maximum.
Ref: “supposed to be 0.0890" mimimum to 0.0960" max, actually drilled at 0.0760". Drilled it out to the minimum 0.0890" and it “kinda-sorta” worked most of the time, went back and drilled to 0.0960" and now it works like a champ”.
And another anecdotal case given, the poster, 1911popo, got good performance at .0930.
If I find bits tomorrow I plan on giving it a try. I’m gonna get as close to .0960 as I can without going over. I’ll bring calipers when I go shopping.
When you go to the hardware store (not Loew’s, Home Depot, etc.) a real hardware store, ask for numbered drill bits for drilling steel. They are measured in decimals of inches (.0890", .0960" etc.) #41 = .0960". #42 = .0935". #43 = .0890". There are metric and fractional (3/32") sizes in between those but you have the idea of what needs to be done. A good titanium or cobalt coated bit will last you many years of drilling through steel in the future.
if it’s a Faxon barrel, you need an Armalite AR-10 gas tube. If it’s an Aero or BA barrel, then it’s the AR-15 gas tube. They are different. wasn’t sure what brand of barrel.
Gas tube length:
Per 98Z5V - gas tube should END in the middle of the cam pin cutout, in the upper receiver. Short of using caliper to measure I’m as close to center as my eye can discern. If I knew how to post a picture I would. Hope to get to the port today. I’ll post how drilling goes.
Eyeballing to the center of the campin cutout is good enough. 1/2 way is perfect, short is not good (the gas key recieves gas from the tube for less time), a tad long is ok. No need to pull out a caliper.
Gas tube length in 308 ARs is just one thing that builders have to be aware of and make sure to get right. No Milspec bites azz otherwise. AR15 builders don’t even have to think about it. Milspec measurements are pretty much set in stone.
Well crap, Milwaukee 3/32” (.0938) is the closet I can find in Titanium. They have the wire #’d bits in Irwin but they are neither Cobalt or Titanium.
I’m gonna buy a #43 (.0890) for a step-up from the existing hole and a #41 (.0960) for final pass, just in case you fellas think they are good for a one-use application.
Stop me if that’s a bad idea due to hardness mismatch. Or if stepping up from existing .0770 (best I can measure) to the .0960 should just be made in one step.
The Irwins will do just fine. Just keep the port hole and the bit oiled as you drill and go slow using light pressure. The bigger hole cannot be drilled crooked, the bits will want to follow down the original hole.
Thank you! Last question. In steps be best or all at once? Think I just found cobalt so got the option once their truck comes in this afternoon.
(Btw, I realize the “last question” are just famous last words{
Your talking about less than .02" in drilling up. All at once should work just fine. Oil it up, go slow, and if your concerned about plunging too deep put a dowel inside the barrel.
Was this barrel purchased new? What does the manufacturer have to say about the port size?