Building a precision AR-15: Questions about barrel, bolt, twist, etc...

[REM_11]

I'm admittedly not a long distance shooter. I am looking to build a new varmint upper, however. I may need or see moa at 1k, but the information in this thread is priceless. Thank you, guys, for explaining the theories, as well as first hand knowledge.

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[rljatl]

Check out Centurion Arms. Monty may have a Douglas/CLE barrel already in stock.
https://www.centurionarms.net/

FWIW, I have a Centurion MK12 upper that will shoot 3/8" five shot groups all day long at 100 yards.

[Agnostic]

Very cool thread, thanks to all for contributing! I have learned quite a bit from it.

As a laboratory employee, I know that theory often does not allow for perfect predictions of real world performance.

[opsoff1]

Very cool thread, thanks to all for contributing! I have learned quite a bit from it.

As a laboratory employee, I know that theory often does not allow for perfect predictions of real world performance.

Amen to that - a classic (and disasterous) "oops" was the US nuke test at Bikini Atoll in 1954. The Castle Bravo detonation was supposed to be a 5 or 6 mega ton yield. The <ahem> experts miscalculated and the actual blast was almost 3 times what they expected - 15 mega tons. It resulted in the the worst accidental radiological contamination ever by the US. It was the first fusion (hydrogen) bomb ever detonated. When it went off, it formed a fireball over 4 miles wide and was seen 250 miles away. The blast left a crater 1-1/4 miles wide and 250 ft deep. Ten minutes after the blast, the mushroom cloud was 25 miles high and 62 miles wide. It contaminated over 7000 square miles of the Pacific.....that was a serious "Oh shit" moment for the engineers...
My bet is they went right back to work crunching numbers, after they cleaned their shorts.

[SWThomas]

Excellent choice. I've been incredibly impressed with the accuracy I'm getting from my CLE recon. What length did you decide on?

20". Heavy contour with CLE's match chamber. I got a matched bolt and gas block with it too.

[SWThomas]

Check out Centurion Arms. Monty may have a Douglas/CLE barrel already in stock.
https://www.centurionarms.net/

FWIW, I have a Centurion MK12 upper that will shoot 3/8" five shot groups all day long at 100 yards.

Already ordered the CLE. I should have it in two weeks.

[Tzed250]

Amen to that - a classic (and disasterous) "oops" was the US nuke test at Bikini Atoll in 1954. The Castle Bravo detonation was supposed to be a 5 or 6 mega ton yield. The <ahem> experts miscalculated and the actual blast was almost 3 times what they expected - 15 mega tons. It resulted in the the worst accidental radiological contamination ever by the US. It was the first fusion (hydrogen) bomb ever detonated. When it went off, it formed a fireball over 4 miles wide and was seen 250 miles away. The blast left a crater 1-1/4 miles wide and 250 ft deep. Ten minutes after the blast, the mushroom cloud was 25 miles high and 62 miles wide. It contaminated over 7000 square miles of the Pacific.....that was a serious "Oh shit" moment for the engineers...
My bet is they went right back to work crunching numbers, after they cleaned their shorts.

Castle Bravo was actually the second ever thermonuclear shot, but the first "dry" one.

From Wikipedia:

Ivy Mike was the codename given to the first test of a full-scale thermonuclear device, in which part of the explosive yield comes from nuclear fusion. It was detonated on November 1, 1952 by the United States on Enewetak, an atoll in the Pacific Ocean, as part of Operation Ivy. The device was the first full test of the Teller-Ulam design, a staged fusion bomb, and was the first successful test of a hydrogen bomb.

Due to its physical size and fusion fuel type (cryogenic liquid deuterium), the Mike device was not suitable for use as a weapon; it was intended as an extremely conservative experiment to validate the concepts used for multi-megaton detonations. A simplified and lightened bomb version (the EC-16) was prepared, and scheduled to be tested in operation Castle Yankee, as a backup in case the non-cryogenic "Shrimp" fusion device (tested in Castle Bravo) failed to work; that test was cancelled when the Bravo device was tested successfully, making the cryogenic designs obsolete.

The reason the the engineers/physicists said "WTF!!!" at the Bravo shot:

It was expected that lithium-6 isotope would absorb a neutron from the fissioning plutonium and emit an alpha particle and tritium in the process, of which the latter would then fuse with the deuterium and increase the yield in a predicted manner. Lithium-6 obeyed this assumption.

When the lithium-7 isotope is bombarded with energetic neutrons, it captures a neutron then decays yielding an alpha particle, a tritium nucleus, and the captured neutron. This means more tritium was produced than expected, and the extra tritium is fused with deuterium. In addition to tritium formation the extra neutron released from lithium-7 decay produced a larger neutron flux. This caused more fissioning of the uranium tamper and increased yield.

This resultant extra fuel (both lithium-6 and lithium-7) contributed greatly to the fusion reactions and neutron production and in this manner greatly increased the device's explosive output. The test used lithium with a high percentage of lithium-7 only because lithium-6 was then scarce and expensive; the later Castle Union test used almost pure lithium-6. Had more lithium-6 been available, the usability of the common lithium-7 might not have been discovered.

And now, back to our regularly scheduled program...


I can see that this thread is going to compel me to spend money.

[opsoff1]

I work with a guy who was a USAF technician during a bunch of the Bikini and Eniwetok tests - Retired now in his 80's, and man o' man does he have stories about that stuff. He said they lost virtually every piece of test instrumentation /sensors - most of which was literally vaporized when it went off. He is out on sick leave a lot - skin issues...go figure.

[Tzed250]

I have a vested interest in these "fireworks" as my dad, also USAF, helped develop the "bottle rockets" that went along with them. One of his launches:

http://m.youtube.com/watch?v=mrnfRfawtI0

[opsoff1]

[QUOTE=Tzed250;1829738]I have a vested interest in these "fireworks" as my dad, also USAF, helped develop the "bottle rockets" that went along with them. One of his launches:

Chilling stuff - I remember doing the "Drills" when I was a kid in Florida in the early 60's...under the desk and cover your head...