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Old July 19, 2021, 07:13 PM   #1
gaseousclay
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5.56 77gr ammo for self defense

Can any of you weigh in on the effectiveness of 5.56 77gr ammo over say 5.56 55gr ammo? Also, does twist rate matter between these two cartridges? My S&W M&P sport II has a 1:9 twist rate, but I read a couple of articles that suggested 5.56 77gr is best used in a barrel with a 1:7 or 1:8 twist rate. I’m assuming the barrel twist rate will effect accuracy the heavier the load of the cartridge? Or does it not matter?
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Old July 19, 2021, 07:44 PM   #2
Shadow9mm
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the 77g may or may not be stable in 1:9 twist gun. Only way to tell for sure is to grab a box and see how it shoots.

More than anything the type of bullet you choose will be important. A hunting or defensive type bullet is what I look for.

I generally stick with 55g as it seem to be more available in many bullet types.
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Old July 20, 2021, 07:14 AM   #3
Hawg
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I don't know about 77 grain but 72 grain shoots better than 55 grain in my Sport II
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Old July 20, 2021, 08:10 AM   #4
Django11
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You’ll probably have to do some trial and error on weather your rifle will shoot certain ammo particularly well. May just depend on what you consider to be acceptable. There’s lots of YouTube videos of people shooting gel blocks with various types of ammo that you can use as a reference on effectiveness.

I would assume that 77 gr would do the job, but there’s plenty of other good options with lighter bullets. Kind of up to you to decide which is going to work best for you.

To answer your question about twist rate . 1:9 twist barrels tend to prefer 50-62 gr projectiles while 1:7 will prefer 68-77 gr. That isn’t necessarily cut and dry but more of a reference.
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Old July 20, 2021, 08:56 AM   #5
ChasHam
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I think that the distance to target in a self-defense scenario-- which is what you asked about-- would be short enough so that the differences you mention wouldn't really matter.

Target shooting or hunting? Probably another issue.
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Old July 21, 2021, 03:56 PM   #6
HiBC
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I forget where,but I've seen gel tests of 75/77 gr HPBT loads. Gel is not flesh and bone,but it appeared yaw and slug breakage would indicate significant trauma.

I don't think they drill an icepick hole. The hollow "nosecone" portion of the jacket,IMO,plays some part

Its hard to absolutely draw a line, but I would not expect a 1 in 9 twist to stabilize most 77/75 gr bullets. I won't say it won't work,but I would not expect it to.

A 1 in 9 does great with 69 gr bullets.

Last edited by HiBC; July 21, 2021 at 04:02 PM.
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