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Old 01-30-2018, 07:11 PM   #1
Bluntforce
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Spinz AR vs. M4 upper

If you have an M4 upper but want to change barrels for a classic 20” chrome-lined 1:12” A1 profile do you have to find a “rifle” upper.

The difference is in the barrel extension only isn’t it?
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Old 01-30-2018, 11:01 PM   #2
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Why not just assemble another complete upper assembly and have both?
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Old 01-31-2018, 01:02 AM   #3
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Cool

That’s what I should do. Probably won’t wear a barrel out anyway.
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Old 01-31-2018, 11:50 AM   #4
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What Dink said. I believe if you go from a carbine to a rifle, you also need a different buffer tube. I know the tube on my 24" is way different than the one on my Oracle. But then the long gun has an A1 shoulder stock and the Oracle has a 6-position POS.
Also Blunt says his 20" has a 1:12 twist? All my 5.56/.223 stuff has either 1:7 or 1:8. Is there any advantage to such a slow twist?
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Old 01-31-2018, 01:52 PM   #5
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Holy shit! Lost a page of explanation. Fuck phone posting.
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Old 01-31-2018, 02:03 PM   #6
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Spinz

Slow twist means bullet keyholes in flesh easily.

Early AR were supposedly cut on worn out equipment and 1:12 = massive wound was purportedly happy accident.

Extremely fast bullets give meteor explosive effect. According to a physics teacher a raindrop or dense fog can cause a bullet to shatter if it is going fast enough.

The U.S. Army supposedly got bullets up to 9,000 fps in the 1930s and shot mules with them. Effect was said to be more like being electrocuted than hit with conventional bullet.

Will get book off shelf, give the quote and all that.

The twist rate and its humanity or lack thereof was something the Swiss and Swedes took seriously and had their 5.56s tweaked to kill you kinder. If it’s a matter of mere speed, twist rate would end up being an accuracy tweak

Will get coffee, book and start citing magic mule story.
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Old 01-31-2018, 02:06 PM   #7
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Quote:
Originally Posted by cerberus View Post
Also Blunt says his 20" has a 1:12 twist? All my 5.56/.223 stuff has either 1:7 or 1:8. Is there any advantage to such a slow twist?
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Military twist for SS109 ammo is 1:7. That twist is also desirable for 69 and 77 grain ammo.

1:12 was the original military twist back when they expected to use 55 gr lead core bullets. But you can shoot 55s in 1:7 just fine.
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Old 01-31-2018, 02:43 PM   #8
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The Rifle in America by Philip B. Sharpe. 1938.
Published for the NRA by Odysseus’ Editions. My copy is a special reprint in pig skin special edition for Firearms Classics Library and a big deal.

Getting on with it.
Page 570-571. Rifle in America, Philip B. Sharpe. Chapter 31. The Future American Rifle.

“This author recalls experimental research conducted with one of the early experimental.220 Swifts in a velocity in excess of 4,000 f.s. A report came to him from one of the experimental engineers and was duly witnessed.

It seemed that a mule condemned for service was about to be executed and experimenters desired to use this mule as a test object. The experiment was conducted with two prominent physicians in attendance to observe the effect of the very tiny high velocity bullet.

The mule was tied to a stake at a range of about 75 yards to await his demise. The rifleman stood by with a .30/06 Springfield with heavy expanding hunting ammunition, ready to put the mule out of misery. A single shot with the tiny 46-grain soft-point bullet was fired into the mule and the section selected for this shot was the paunch. Hunters of experience insist that this is the poorest possible shot on game and, since it eventually dies, it invariably escapes from the hunter and can travel many miles before exhaustion takes its toll.

When the experimental shot was fired the mule fell over as though struck in the forehead with a sledge-hammer. There was no reflex action to the muscles; he died instantly and without a quiver. The doctors immediately went to work. One of these noted surgeons examined the wound and failed to find it serious enough to cause death-from all general appearances. Yet the mule was dead! An autopsy was performed and one astounded surgeon remarked:

“This is the most amazing experiment I have ever witnessed. This mule has all the symptoms of death by electrocution rather than death by gunshot wound.”

Page 569

“The United States Army has been conducting secret research for a number of years and at Springfield Armory early in 1937 a tremendous velocity of 9000 f.s. was achieved. Believe it or not!”
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Old 01-31-2018, 03:11 PM   #9
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Hey Blunt, thanks for doing all that typing.
I shoot a .22-250 45gr loaded to 4110 and while it's dropped everything I've shot with it with one shot I've never had those 'mule' results. I've also never shot anything in the belly.
As an aside, why doesn't a bullet, when crossing the sound barrier, (either up or down) destabilize like a plane does?
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Old 01-31-2018, 03:15 PM   #10
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Spitzer nose, no control surfaces, consistent internal density and pressure.
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Old 01-31-2018, 08:32 PM   #11
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Bart

Phone ate another post. Have to just get a BRN-601 if I want good old timey meat axe performance. Opening post was a convoluted mess. Don’t have 20” barrel yet. Need to just get an old school rifle if I want an old school rifle.
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