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Old November 7, 2012, 12:32 PM   #1
Reef
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.223/5.56 reloading question

I recently picked up a Sig M400 that has a 1 in 7 twist. Does anyone have any experience with 55 gr ammo with that twist rate?
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Old November 7, 2012, 12:47 PM   #2
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You need to shoot between a 70 to 75 grain bullet for best results in a fast twist barrel like 1-7. 55 gr. will be to light and fast in that barrel. JMO
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Old November 7, 2012, 12:49 PM   #3
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That is what I was afraid of, thank you for the reply.

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Old November 7, 2012, 12:50 PM   #4
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I've got a colt 6920 and ran some factory .223 through- Federal 100 round value pack from Walmart- for sighting and plinking. It ran just fine. Though I was limited to a 25 yard lane, and used a bipod instead of a full rest I was getting some geat groups, and it sighted in like a dream. I'd also point out the M193 is a 55 grain ball cartridge, though 5.56 rather than .223.
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Old November 7, 2012, 12:57 PM   #5
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Quote:
I recently picked up a Sig M400 that has a 1 in 7 twist. Does anyone have any experience with 55 gr ammo with that twist rate?
Pardon my ignorance, but what's the barrel length? If it's a short barrel, you should give a box of 55's a try before you dismiss them.

And what about 62 grain?
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Old November 7, 2012, 12:59 PM   #6
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16" barrel.
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Old November 7, 2012, 01:03 PM   #7
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62 grain would be the M855 and M855A1 the military chose over the M193, according to Wikipedia for humane reasons.
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Old November 7, 2012, 01:08 PM   #8
g.willikers
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Doesn't it depend on the bullet?
There's different length bullets for any given weight, depending on the design.
That can make a difference in how a given bullet behaves in any barrel.
A longer 55 grain bullet style might do quite well.
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Old November 7, 2012, 01:18 PM   #9
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62 grain would be the M855 and M855A1 the military chose over the M193, according to Wikipedia for humane reasons.
Yes, but (since this is a reloading forum) it is also a popular weight for FMJ bullets without a steel billet in the tip. Homogeneous lead core will in theory anyway give better accuracy.
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Old November 7, 2012, 01:53 PM   #10
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There are lots of 55gr loads out there. Flat base soft nose spitzer, m193 clones, hollowpoint flat base...

The 1:7 twist will stabilize them just fine. You won't know about accuracy until you try.

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Old November 7, 2012, 08:03 PM   #11
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55gr in a 1:7 is not "optimum" but it will shoot just fine. Probably better than the average shooter to tell much.
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Old November 8, 2012, 01:52 AM   #12
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I have a 1:9 twist 16" barrel, and my best shooters are 65gr SGK's
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Old November 13, 2012, 02:46 PM   #13
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I shoot both factory and handloaded 55gr. projectiles out of my 1/7 barrel with great accuracy.
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Old November 13, 2012, 04:10 PM   #14
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Thanks. I've shot around 200 factory rounds and a handful of reloads, all 55gr. with no issues. I had read somewhere about that twist rate causing the smaller bullets to come apart in-flight due to the rotation rate. Hasn't happened.

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Old November 14, 2012, 12:46 AM   #15
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1:7 twist and 55 FMJs ~100 yards...No sweat. Have fun.
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