98Z5V Posted August 8, 2018 Report Share Posted August 8, 2018 47 minutes ago, Albroswift said: Where can I get actual tube lengths, example a Armalite 308 mid length = x, a carbine length = Y, Rifle length = z? I've given Armalite AR-10 Carbine tube length vs. AR15 midlength, right here in this thread. It's also in those links I just posted, above, man... It's all over the web... Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 8, 2018 Report Share Posted August 8, 2018 31 minutes ago, jtallen83 said: Armalite lengths, ... Rifle ( 223 ) ------------------- 15 3/16" National Match--------------- ? I have an Armalite AR15 National Match gas tube right here - it's identical in length to an AR15 Rifle gas tube, it just has different bends... Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 8, 2018 Report Share Posted August 8, 2018 (edited) Albro, I'm betting money that if you yank that gas tube out of your Anderson right now, it's gonna be an AR15 Midlength gastube, at 11 3/4" long. You can just do the easy thing, and make sure you're getting all the gas that you're supposed to have, and pick up that LBE Unlimited tube you showed, at 12 1/16" long (12.0625" - 12 1/16", they just didn't include the extra digits - or really it's an extra 25/10-thou short, so they're not copying Armalite?...). Either way is gonna fix your problem, and not short you on gas timing. It's not gonna increase your gas timing in some crazy manner, either, when it comes up "just a tick" past the center of the cam pin cutout. - That's better than being short... That's the easy, cheaper way... If you really do want it perfect, and centered up - on that Anderson barrel - you will need to make your detailed measurements (just like you said, end of tube to center of cam pin cutout), before you break it all down, then measure the OAL of that tube, and add that much. Add that shortage to the center of the cam pin cutout to the tube OAL. I'll tell you right now - from the center of a gas PORT in a gas tube, to the very end of the gas tube, is 0.600". You can measure from center of cam pin cutout, all the way to the gas port location in your barrel, and ADD 0.600", and that'll be your perfect gas tube length, that you'll need White Oak to make for you. I'll still bet that your gas port in the barrel is too small. You need to measure that. Indexed, numbered drill bits are the best way, unless you have a snap-gauge that measures under 0.100". Edited August 8, 2018 by 98Z5V Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 8, 2018 Author Report Share Posted August 8, 2018 Thanks, jtallen, for posting that. Trying to get all this clear in my head. Looks like for the Armalite sizes I would be correct in referring to my 308 gas system as Carbine or Mid, but not if I was talking DPMS or AR 15's Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 8, 2018 Author Report Share Posted August 8, 2018 Thanks, 98, plan on tearing it down soon and taking measurements you describe, I think I have a pin set around somewhere and know I have an index drill set. What hole size am I looking for? Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 8, 2018 Report Share Posted August 8, 2018 3 hours ago, Albroswift said: Thanks, 98, plan on tearing it down soon and taking measurements you describe, I think I have a pin set around somewhere and know I have an index drill set. What hole size am I looking for? I just went back through the thread here, brother, and I can't find your barrel length. I can't imagine it's a 20", with that gas system. Gotta be an 18"or 16"?... Need that barrel length info first, because gas port location and barrel length are the two biggest factors in gas port size... Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 8, 2018 Author Report Share Posted August 8, 2018 (edited) 18" barrel, M4-72 brake. Not the severe duty one. Edited August 8, 2018 by Albroswift Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 9, 2018 Report Share Posted August 9, 2018 Gas port should be somewhere around 0.081" on the low side, 0.086" on the high side... That will work. Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 9, 2018 Author Report Share Posted August 9, 2018 Thanks. I'll get the BAR off the bench and ready for hunting this weekend and then back to the Anderson. Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 Ok, .082 drill fit, .086 didn't fit. Close enough. Tube AR15 length as you predicted, 98Z No divots in bottom of barrel for gas block. Before I pulled it apart, put a 6.8 oz buffer in it and loaded some rounds with a powder that has a little more chamber pressure but also a little faster burning. Started low worked up. Got higher velocities gun cycled flawlessly. Very nice groups. SD for 10 round strings approaching single digits when i got to the sweet spot. Tried some more of my hunting loads, back to the same problem. So long story short, longer tube, maybe an adjustable block, and Alliant AR-Comp powder and I think I should be there... Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 My BAR 338 Win Mag Kevin Knight did his signature "slim-line brake" comp and played around with a couple other things for me must have been 15+ years ago. Working up some new loads, powder and bullets have come a long way, cut my groups in half yesterday. Delivers a lot of hurt down range on an unsuspecting critter. The VX-II 3x9 was a good scope at the time but after using my Viper HST on the 308 its got to go. Maybe after this season. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 12, 2018 Report Share Posted August 12, 2018 At least you got to see what it was made of, man - Good digging into it like that. Gasport diameter should be okay at 0.082". Think you'll have to redesign that hunting load? It wasn't cycling the gun, but the warmer loads were? Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 Actually, the opposite, I believe: The hunting loads are optimized to accelerate the bullet linearly along the entire barrel, minimizing chamber pressure but maintaining a high pressure the whole length of the barrel. Easier extracting cases, less damage to the rim from the extractor. The AR Loads seem to like a faster burn rate, getting the bullet up to speed faster but less pressure during the dwell. IMAO, all my malfunctions are/ were due to the bcg cycling too fast and slamming into the back of the tube, (actually the upper's ears at first!) as we have slowed it down, first the 150 gr bullets started to perform, (More acceleration earlier in the barrel) Now everything with the AR optimized powder is performing. The hunting loads simply over-gas the system, even with the 6.8 buffer and all the other corrections we have made. I didn't have any factory loads left, but I would bet I would have mixed results depending on what the manufacturer intended for their use. While I have it apart, adding an adjustable gas block, The Superlative Arms looks like a nice unit, (and a 12-1/6" tube of course). I went really low with starting loads and still locked back so I bet I could lower the pressure in the gas system even a little more and work up a little more velocity, I was at 2725 with the 150's and was no where near max case volume or load data, should be able to get it over 2800. Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 Maybe mount the VX-II on my labradar... Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 12, 2018 Report Share Posted August 12, 2018 11 minutes ago, Albroswift said: IMAO, all my malfunctions are/ were due to the bcg cycling too fast and slamming into the back of the tube, (actually the upper's ears at first!) That was 100% due to a poorly designed/shipped recoil system, right there. Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 Lucky they didn't use an AR15 barrel, everything else was... Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 (edited) I have a timing question, Advanced Reloading Class: where do you think the bullet is when the gas key clears the end of the gas tube?? Edited August 12, 2018 by Albroswift Quote Link to comment Share on other sites More sharing options...
jtallen83 Posted August 12, 2018 Report Share Posted August 12, 2018 1 minute ago, Albroswift said: I have a timing question, advanced Reloading Class: where do you think the bullet is when the gas key clears the end of the gas tube?? Down range. That doesn’t negate the effect on the action though, short tube still equals less gas acting on the BCG. Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 12, 2018 Author Report Share Posted August 12, 2018 Correct, bullet is out about 100 yards when bolt travels 1 inch, so say bullet is at 50 yards when tube clears. How much pressure is still in the barrel? Quote Link to comment Share on other sites More sharing options...
jtallen83 Posted August 12, 2018 Report Share Posted August 12, 2018 17 minutes ago, Albroswift said: Correct, bullet is out about 100 yards when bolt travels 1 inch, so say bullet is at 50 yards when tube clears. How much pressure is still in the barrel? I suppose the pressure could be extrapolated with math but then why? Math can lie, pulling the trigger always tells the truth, works or it doesn’t. Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 13, 2018 Author Report Share Posted August 13, 2018 (edited) The bullet always tells the truth... Edited August 13, 2018 by Albroswift Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 13, 2018 Author Report Share Posted August 13, 2018 I like the science behind it, being a lifelong member of the society of torque and recoil Quote Link to comment Share on other sites More sharing options...
Albroswift Posted August 13, 2018 Author Report Share Posted August 13, 2018 2 hours ago, jtallen83 said: I suppose the pressure could be extrapolated with math but then why? Math can lie, pulling the trigger always tells the truth, works or it doesn’t. Just wondering how much hot gas (if any) comes out of the tube after it disengages from the key. Kind of relating to the 12.06 tube vs the 11.75. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 13, 2018 Report Share Posted August 13, 2018 Research dwell time. There is only pressurized gas entering that gas tube from one bullet point to another. From the time that bullet crosses the gas port in the barrel, all that pressurized gas behind it (it's propellant), enters the gas port, and it continues until that bullet leaves the barrel. Point A being the gas port and Point B being the muzzle. As soon as that bullet leaves the barrel, you cannot increase any pressure, and it drops off fast. This event is over in microseconds. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 13, 2018 Report Share Posted August 13, 2018 30 minutes ago, Albroswift said: Just wondering how much hot gas (if any) comes out of the tube after it disengages from the key. Kind of relating to the 12.06 tube vs the 11.75. This is more gas timing than available pressure. With a tube that's too short, you're cutting of the needed gas supply for the recoil, extraction and ejection, and reloading operations, early. Doesn't seem like much, but it can make the world of difference. Quote Link to comment Share on other sites More sharing options...
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