Bill wylde designed the chambering to shoot 80-90 gr loads single loaded in an AR for 1000 yard matches.
here is a copy paste from John Hollingers chamber reamer list
Chamber Freebore Lead Angle 80SMK OAL Comments
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5.56
Target .0566 1 deg,
13 min 2.465 This was designed by a C. Hildebrandt at Savage. I believe it is used in the savage .223 rifles. I do not have this reamer, but it should work well for HP.
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.223
JGS#514 .025 3 deg,
10 min 2.435 I believe this is used by Krieger and Mike Bykowski. I use it for slow twist varmint uppers but I think it is a little short, and too steep of a lead for HP.
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.223
Wylde .0619 1 deg,
15 min 2.475 Designed by Bill Wylde. Shoots everything good, and has slightly generous body dimensions for reliability. Eats anything you put in it.
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.223
Holliger .106 1 deg,
15 min 2.530 Designed for the 90 JLK. The longer throat allows a little more velocity.
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5.56
CLE .025 1 deg,
30 min 2.450 Of course we all know Frank's rifles shoot just fine!
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5.56
Bushmaster .0250 1 deg,
30 min 2.450-
2.475 Info from Bushmaster (thanks!). These are one of the best out-of-the box barrels, and handle up to 80 gr bullets no problemo.
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with .0619" of freebore, its much longer than a 5.56
RR