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Old January 10, 2019, 01:33 PM   #1
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Heaviest bullet for ar15 in 5.56 (single feed)?

I know magazines will take Hornady OTM and some 77 gr bullets. But what about single feed? What's the heaviest bullet most ar15s can chamber?
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Old January 10, 2019, 01:45 PM   #2
Jim Watson
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Mine is a 6.5 twist made for 90 grain SMK and VLD.
I had the throat lengthened to allow longer OAL for more powder space but it did not make much difference.
A regular A2 7 twist should handle 80-82 grain bullets.
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Old January 10, 2019, 02:00 PM   #3
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I've shot 80s and 90s out of my 1:7s, worked good.
Kraig Stuart
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Old January 10, 2019, 06:42 PM   #4
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Heaviest bullet for ar15 in 5.56 (single feed)?

Chambering by single feed is not the main issue but stability when fired, and good engagement in case mouth (cylindrical area of the bullet). Start with stability, bullet length, barrel twist, and then load longest bullet your specific barrel can handle stabilizing because why bother launching it otherwise.

I have 1:8 twist 75gr Hornady ELD bullets working in 20” barrel. It’s listed as not stable in 1:8 by Hornady but I think it is just marginal and seems ok in my shooting environment and barrel. They make up to 90 gr ELD with long ogives so it’s relatively easy to chamber a bullet without being lodged into the rifling lands but be something too long to stabilize.

I’ve measured these bullet lengths, it is not super easy to find them for all bullets.

Hornady 75 gr ELD-M 1.116”, G1 .43, G7 .220
Hornady 70 gr GMX 1.047”, G1 .350
Hornady 73 gr ELD-M 1.056”, G1 .398, G7 .200
Hornady 75 gr BTHP OTM 0.988” G1 .395

Andrew - Lancaster, CA
NRA Life Member, contributor, CGF / SAF / CRPA / FPC / NAGR / NRA-ILA contributor, USCCA member

Last edited by lordmorgul; January 10, 2019 at 06:50 PM.
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Old January 11, 2019, 05:30 PM   #5
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Thanks for all the information. My twist is 1:7 so I think I'm good there.
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Old January 13, 2019, 11:41 AM   #6
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Remember... there is a lot of difference throat / freebore between the various manufacturers.

What heavy weight .224 bullet works for one barrel may not work well in a shorter throated barrel.

And your OAL will be effected as well from the variety of chamber dimensions.
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