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Old November 19, 2002, 07:29 PM   #1
Zak Smith
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Seeking "heavy" 223/5.56 data

I have a "new" AR-15 with a 16" 1-in-8" barrel, and I'm interested in what velocities other people have achieved with the "heavy" bullets in .223, specifically, the Hornady 75gr BTHP, or any other > 70gr bullet that can be seated to feed through a magazine.

What muzzle velocities are attainable with these bullets?

Over on AR15.com, there are reports of quite "HOT" loadings of these being used in 5.56-chambered M4's.

Last weekend I loaded up some with the Hornady 75gr BTHP and RL15. in new Winchester commercial brass.

24.0gr -> 2511fps (sd = 15.5)
24.5gr -> 2546fps (sd = 15.9)

thanks
Zak
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Old November 20, 2002, 09:56 PM   #2
5pins
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With my Colt with a 1 in 7 twist 20in barrel and Hornady 75 BTHP match.
25.0gr of Varget. 2707fps
24.1gr of Tac. 2716fps
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Old November 21, 2002, 10:09 AM   #3
Steve Smith
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Hmm, your numbers are a little low. I wonder what kind of primers you're using or if you got some slow powder. I push 77 SMK's at right at 2700 with 24.3gr of RL15, LC brass, Rem 7 1/2 primer, Wylde chamber and 1:8" twist. 80's go about 2650 with same load.

No personal experience with Hornady bullets.


Remember, speed is not as critical as accuracy. Achieving top speed at the cost of safety is not an option. Granted, speed decreases time in flight to the 600 yard berm, but safety is the main consideration. 24.5 behind a 75 grainer is close to what I ran with 77's, and it is at the top of what you want to do with that powder. Try changing primers and back off the powder at first. Short of that, try VV powders.

BTW, try to get your SD below 12.
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Old November 21, 2002, 11:23 AM   #4
Zak Smith
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Steve, from what I've read, the 77 SMKs have more bearing surface than the 75gr Hornady BTHPs, which could help to account for the difference. Also, my rifle has a short 16" barrel, but it also has the Wylde chamber.

Thanks for the advice.

-z
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Old November 21, 2002, 11:57 AM   #5
Steve Smith
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Bearing surface is much more on the 77.

16" barrel SAYS IT ALL. WHY DIDN'T YOU SAY SO EARLIER???!!!!


Nevermind, you did! Sorry.
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Old November 24, 2002, 02:24 PM   #6
antsi
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I am using the 75gr BTHP Hornadys over 24.7 gr AA 2520 and Win small rifle primers.

I don't have a chrono, but I did get a chance to chrono one round, once, and it was 2807 fps. My match rifle is a 20" barrel.

The Accurate data book says 2573 fps for minimum load and 2924 fps for maximum load. They tested from a 24" barrel.
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Old November 24, 2002, 06:58 PM   #7
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What is a "Wylde" chamber? Is it a little tighter than Mil-spec, or what? Thanx
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Old November 25, 2002, 10:07 AM   #8
Steve Smith
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Fatelvis, a Wylde chamber was built by Bill Wylde for Highpower shooters. Knowing we needed a long throat for our really long bullets, he built a reamer that had an almost GI speck throat (GI throats are so long you can often not touch them with an 80 or 90 grainer seated al the way out). His throat was obviously shorter than GI so that you could touch the rifling if you wanted and so that the freebore was limited, but it is much longer than that of the .223 SAAMI standard. In addition, he made the chamber slightly larger than a "match" chamber because semi-autos shouldn't have tight chambers when reliability is required. If you need exact numbers (throat angle, throat length, and such) I can get them for you.
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Old November 25, 2002, 05:40 PM   #9
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Not nessisary, but thanks for the info Steve!
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Old November 25, 2002, 10:47 PM   #10
Zak Smith
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Can NATO surplus 5.56 be fired in a Wylde chamber?

-z
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Old November 26, 2002, 08:07 AM   #11
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I've used Hogdon H335 (I think about 25.0 grains but check the book) with the Hornady 75gr BTHP bullet and gotten close to 2900fps. H335 is faster burning and for your shorter barrel, you'll get more out of it with less flash.

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Old November 26, 2002, 08:17 PM   #12
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Smithz, Im sure you could, given that the chamber isnt tighter than normal, its looser, and a generous leade is actually safer than a small one. I believe the chamber that Steve is refering to, is designed for reliability/accuracy, with heavy bullets. If you fire regular 55grn/62 grn bullets in it, they wont come close to jamming the rifling.
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Old November 27, 2002, 11:02 AM   #13
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I don't think there's anything that can't be fired in a Wylde. That said, for pure junk ammo I'd go with the 5.56 chamber...bigger. Remember, my chamber is cleaned about every 300 rounds.
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