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Posted: 8/22/2026 6:49:11 PM EDT
[Last Edit: Chromekilla][Edited]
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Happened across this thread. https://www.theoutdoorstrader.com/threads/gauging-ar-bcgs.3618622/ Seems to match pretty well the rumors of what to buy. ETA: I'm suspecting his gauges are as follows Bolt Shoulder .529 gr, .530 green 2, .531 yel 1, .532 yel 2, .533 red. Gas Ring Run .498 g 1, .499 g 2, .500 y1, .501 r 1, .502 r 2 Bolt Tail .250 g 1, .251 g 2, .252 y, .253 r. Gas Key .180 g, .182 r It would be interesting to see him also gauge the bolt tails themselves, as well as the bolt faces and cam pin holes. |
Callsign-ChuckYeager
That man is a homo and a liar-TrojanMan
Hell, a Ford just breaks down on you. It doesn't fall apart AND try to kill you at the same time-Bloodsport2885
That man is a homo and a liar-TrojanMan
Hell, a Ford just breaks down on you. It doesn't fall apart AND try to kill you at the same time-Bloodsport2885
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There are certainly quality differences in BCG between some manufacturers. But I also wonder if some of the specs for go-nogo on these parts might not actually reflect what is really needed or not. I also wonder if many if the nitiride ones are machined with the expectation of the added thickness of chrome, which nitride wouldn't provide. |
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| Interesting that essentially no one had a perfect score for all bolts tested…except Daniel Defense’s 3 samples. |
I wanted a mission, and for my sins, they gave me one.
No rules today, sport…just orders.
It’s not about how many people you kill, it’s about how many you save.
No rules today, sport…just orders.
It’s not about how many people you kill, it’s about how many you save.
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This information brings some questions to mind. What effect would these BCGs have on a gun? How differently would the same rifle shoot using the same ammo with each bcg? Would a less efficient bcg work better in an overgassed rifle? At what point would a rifle not work due to an out of spec bcg? |
"Do what you do, just do it less shittily." Ben "The Realest" Stoeger
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Originally Posted By mike4eva: Aren't DD using Microbest? I wonder if they test them inhouse before considering them GTG? |
Isaiah 1:18 - "Come now, let us reason together," says the LORD: "though your sins are like scarlet, they shall be as white as snow"
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Originally Posted By Brawnydog: This information brings some questions to mind. What effect would these BCGs have on a gun? How differently would the same rifle shoot using the same ammo with each bcg? Would a less efficient bcg work better in an overgassed rifle? At what point would a rifle not work due to an out of spec bcg? I am curious about this too. I'm sure out of spec bores would not seal gas very well, and will cause more gas leakage and a dirtier action. Possibly if bad enough, it may leak enough to cause cycling problems? |
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Originally Posted By Brawnydog: This information brings some questions to mind. What effect would these BCGs have on a gun? How differently would the same rifle shoot using the same ammo with each bcg? Would a less efficient bcg work better in an overgassed rifle? At what point would a rifle not work due to an out of spec bcg? Tolerance stacking is a thing. A slightly out of spec bcg may work fine in one rifle, but may not in another depending on the spec of the barrel for example. May also work fine for a while, but not after some wear. |
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Originally Posted By Postal0311: There are certainly quality differences in BCG between some manufacturers. But I also wonder if some of the specs for go-nogo on these parts might not actually reflect what is really needed or not. I also wonder if many if the nitiride ones are machined with the expectation of the added thickness of chrome, which nitride wouldn't provide. I think this is probably the most interesting angle perhaps. I'm not personally the biggest fan of nitride, especially when you stack 9310 and the heat treating. Nitride is probably a fine coating, but I think most mfgs run to thick chrome specs and then coat with nitride which likely isn't as thick. |
Callsign-ChuckYeager
That man is a homo and a liar-TrojanMan
Hell, a Ford just breaks down on you. It doesn't fall apart AND try to kill you at the same time-Bloodsport2885
That man is a homo and a liar-TrojanMan
Hell, a Ford just breaks down on you. It doesn't fall apart AND try to kill you at the same time-Bloodsport2885
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Originally Posted By Brawnydog: This information brings some questions to mind. What effect would these BCGs have on a gun? How differently would the same rifle shoot using the same ammo with each bcg? Would a less efficient bcg work better in an overgassed rifle? At what point would a rifle not work due to an out of spec bcg? |
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Keep in mind that the primary issue most BCGs test d had was “inefficient gas”…which AFAIK is the tester’s subjective evaluation based on the dimensions he saw. The actual effect: UNK. |
I wanted a mission, and for my sins, they gave me one.
No rules today, sport…just orders.
It’s not about how many people you kill, it’s about how many you save.
No rules today, sport…just orders.
It’s not about how many people you kill, it’s about how many you save.
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A few things: 1) A test done on the M16 a while back showed a 260% increase in leakage area around the bolt tail and gas tube results in a 300 psi drop in piston cavity pressure, 2,800 psi to 2,500 psi. Not enough to effect operation in a normally set-up weapon. In fact, ammunition variation causes more variation in cavity pressure, and we are talking about round-to-round variation within a lot. 2) This only list the color of the gauges and not the dimensions of the gauges. Upon what criteria is his "going to be inefficient" based on? Within the maximum material condition (MMC, smallest hole, biggest shaft) and the least material condition (LMC, largest hole, smallest shaft), the leakage growth is only 100%, so a 260% increase in leakage area would mean about a 1.5 times increase is gap or 1.5 times the tolerance. Conclusion: A lot of smoke, a lot of mirrors, not much substance. Click bait. |
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Originally Posted By spyderboy03: I had a rifle I reduced the gas port on significantly. It wouldn't run with a Spike's phosphate BCG, but it would run with Geissele REBCG's. SOTAR gauged an REBCG a while back and it gauged as very efficient. The Spike's worked fine when suppressed or in other builds, so I always assumed it was just less efficient. The fact the you "reduced the gas port . . . significantly" is telling. You cannot tell if the change in results was due to the difference between an LMC and MMC bolt/carrier combination (with both being in tolerance), or even some other issue. |
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Originally Posted By KILLERB6: Keep in mind that the primary issue most BCGs test d had was “inefficient gas”…which AFAIK is the tester’s subjective evaluation based on the dimensions he saw. The actual effect: UNK. I don't think it's necessarily a matter of this one's good or this is junk. To me it's basically just a view that attempts to provide numbers into something that is basically just a wild guess what to run/buy. |
Callsign-ChuckYeager
That man is a homo and a liar-TrojanMan
Hell, a Ford just breaks down on you. It doesn't fall apart AND try to kill you at the same time-Bloodsport2885
That man is a homo and a liar-TrojanMan
Hell, a Ford just breaks down on you. It doesn't fall apart AND try to kill you at the same time-Bloodsport2885
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Oh, and one more thing about chromium plated bolts/carriers, first I hope they are actually "thin dense chrome" not "hard chrome plated". Hard chrome seriously reduces fatigue life, thin dense chrome does not. The original AR-15 bolts were thin dense chrome plated. Two, if they are Hard chrome plated, the normal way to account for the extra thickness added during the plating process is not to machine the part under-size. You machine the part normally and and use a chemical etch to reduce the parts dimensions. This is because you can control the amount of material removed (about 0.0005") much more accurately, and because it preserves the relative dimensions, which in precision parts in important. The last reason is it simplifies supply. Thin dense chrome is normally 0.00005" to 0.0005" thick so might even be applied without dimensional adjustment and still be in tolerance. (Don't let the thickness make you think it doesn't wear as well and hard chrome, it is actually better in many ways.) |
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Originally Posted By lysanderxiii: A few things: 1) A test done on the M16 a while back showed a 260% increase in leakage area around the bolt tail and gas tube results in a 300 psi drop in piston cavity pressure, 2,800 psi to 2,500 psi. Not enough to effect operation in a normally set-up weapon. In fact, ammunition variation causes more variation in cavity pressure, and we are talking about round-to-round variation within a lot. 2) This only list the color of the gauges and not the dimensions of the gauges. Upon what criteria is his "going to be inefficient" based on? Within the maximum material condition (MMC, smallest hole, biggest shaft) and the least material condition (LMC, largest hole, smallest shaft), the leakage growth is only 100%, so a 260% increase in leakage area would mean about a 1.5 times increase is gap or 1.5 times the tolerance. Conclusion: A lot of smoke, a lot of mirrors, not much substance. Click bait. I agree. The whole concept strikes me as nothing more than SOTAR concocting a justification to sell people a $330 set of unnecessary gauges. That opinion might offend some, but all I see is an excuse to sell expensive gauges. Buy BCGs from proven, quality brands, verify their function, and go about your business. |
Practice, the master of all things. - Augustus
IG: @cqbr.kurdt
Want To Buy: Savannah Mk18 RIS II in light blonde/bronze - LMT SOPMOD Gen 1 Tan - Geissele S3G
IG: @cqbr.kurdt
Want To Buy: Savannah Mk18 RIS II in light blonde/bronze - LMT SOPMOD Gen 1 Tan - Geissele S3G
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Originally Posted By lysanderxiii: A few things: 1) A test done on the M16 a while back showed a 260% increase in leakage area around the bolt tail and gas tube results in a 300 psi drop in piston cavity pressure, 2,800 psi to 2,500 psi. Not enough to effect operation in a normally set-up weapon. In fact, ammunition variation causes more variation in cavity pressure, and we are talking about round-to-round variation within a lot. 2) This only list the color of the gauges and not the dimensions of the gauges. Upon what criteria is his "going to be inefficient" based on? Within the maximum material condition (MMC, smallest hole, biggest shaft) and the least material condition (LMC, largest hole, smallest shaft), the leakage growth is only 100%, so a 260% increase in leakage area would mean about a 1.5 times increase is gap or 1.5 times the tolerance. Conclusion: A lot of smoke, a lot of mirrors, not much substance. Click bait. This site needs a "Like" button. |
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Just to share my 44 years on this platform employing personal, Army and Department rifles , a couple of things come to mind. I’ve also discussed this with the AMTU Gunsmith’s at Fort Benning back in the mid 2000s when I was part of the army reserves Small Arms, Readiness Group. The mating surface of the carrier key and carrier are super important. If they are not perfectly flat, you’re going to lose gas and the gun will choke. Small honing stones and fine grit on a true flat will fix this. Gas tube alignment as it receives the incoming carrier key during the loading and lock up. You can use your thumbs and push and pull on the center of the gas tube to get the Bell end of the gas tube more or less perfectly “aimed/aligned”. Reduces wear to the gas tube bell for a better seal/longer lasting tube and less friction. Remove the bolt from the carrier and slide it in the upper and you can feel the key as it first meets with the gas tube. The more you adjust it to get gas tube and gas key in near perfect alignment, the smoother the gun will run. Bolt Cam. Rare, but once pulled an unknown make BCG from a Franken Gun during the AWB days, and the channel cut in the BCG for the cam was wonky; it would eat a cam every few hundred rounds. |
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Originally Posted By GrizzlyAdams: You are confused. Originally Posted By GrizzlyAdams: Originally Posted By mike4eva: Aren't DD using Microbest? I wonder if they test them inhouse before considering them GTG? You are confused. I swear I had heard that here. But also on Reddit: https://www.reddit.com/r/ar15/comments/miwfpd/deleted_by_user/ There are people there saying they worked at DD and the 5.56 BCG are (or were) Microbest. And sionics starts with their parts and machines them. |
| When shooting suppressed, reduced efficiency might not matter as much since you have excess pressure to control anyway. That being said, slop in one area of manufacturing can mean that other specs and methods are questionable and can lead to early failure and even damage to other components. For that reason, I'd rather have higher quality components where I know the specifications I'm dealing with, vs lower quality with more unknowns. |
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Originally Posted By KorneoDahGreat: Some companies arent mil-spec so they will fail these tests. The carriers will run even if they are not to tight specifications, but may cause issues quicker. The video enlightened me about the tolerance areas that I was unaware of.  AR-15 Bolt Carrier and Rifle Cut Away Demonstration Not sure if I did the toob link right, so here it is https://www.youtube.com/watch?v=Uv6a1hs9U5o |
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Originally Posted By Piratepast40: When shooting suppressed, reduced efficiency might not matter as much since you have excess pressure to control anyway. That being said, slop in one area of manufacturing can mean that other specs and methods are questionable and can lead to early failure and even damage to other components. For that reason, I'd rather have higher quality components where I know the specifications I'm dealing with, vs lower quality with more unknowns. |
Preferred pronoun: MARINE
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