.223 twist needed for 75-80 gr projectiles

[acts238]

what twist is needed for 75-80 gr projectiles in a .223 ?
will a 9 twist stabilize 75-80 gr bullets ?
or will I need to find a 7 or 8 twist ?
advise from any of you with .223 reloading exsperience greatly appreciated

 

[gcoulsey]

Re: .223 twist needed for 75-80 gr projectiles

My 1/9 shoots 77grn scenars, and 77SMK just fine,
I have no experience with 80's though because of mag length restrictions!

 

[ksthomas]

Re: .223 twist needed for 75-80 gr projectiles

Willoghby,

No, you'll need a 1x7" or 1x8" twist if you plan on shooting the 75s-80s. You may find some 1x9" barrels that will occasionally stabilize the 75s, under some conditions. But you'll be so close to the edge of stability that you'll eventually run into flat out instability. Always go with a faster twist when making such choices; you need to make the decision based on the longest/heaviest bullet you ever plan on shooting. It'll shoot shorter, lighter bullets just fine, but the other way around will give you problems every time.

Hope that helps.

 

[BoilerUP]

Re: .223 twist needed for 75-80 gr projectiles

1:9 stabilizes 75gr HPBT/77gr SMK just fine; my 26" 1:9 Savage barrel puts a 75gr HPBT out at 2860fps and has a stability factor of 1.41.

The same barrel stabilizes the 75gr A-Max @ 2950fps good enough for 0.7MOA groups at 200yd, though at 500' ASL/80°F (the environmentals for all calculations in this post) its stability factor is a razor-thin 1.01.

The 75gr Berger VLD @ 2950fps has a stability factor of 1.15.

I just had a 22" 223AI barrel arrive last week, and I ordered it with a 1:7 twist so I could have the option of 90grs if I wanted to try them, and to provide better stabilization in cold temperatures. With a 1:7 twist, the 80gr A-Max @ 2900fps has a stability factor of 1.56, 75gr A-Max @ 3000 is 1.69, and 75gr HPBT @ 2900 is 2.35.

 

[Grumpy61]

Re: .223 twist needed for 75-80 gr projectiles

my 700 XCR comapct 1:9 will not stabilize the Hornady 75 bthp

 

[Niles Coyote]

Re: .223 twist needed for 75-80 gr projectiles

Willoughby, what altitude are you at? I am going with a 7.5 twist so I can shoot 80 a-max in cold winter temps at ~600asl. At my altitude an 8 looked like it may work most of the time but I decided not to chance it. You likely have a few thousand feet advantage and can get away with a slower twist.

 

[Belisarius]

Re: .223 twist needed for 75-80 gr projectiles

1-8" will be perfect for the 80-82 gr bullets. My ar shoots 80gr. a-max superbly. <object width="425" height="350"> <param name="movie" value="http://www.youtube.com/v/0J_5PbLR-q4&feature=g-upl"></param> <param name="wmode" value="transparent"></param> <embed src="http://www.youtube.com/v/0J_5PbLR-q4&feature=g-upl" type="application/x-shockwave-flash" wmode="transparent" width="425" height="350"> </embed></object>

 

[kraigWY]

Re: .223 twist needed for 75-80 gr projectiles

1:7, you MIGHT get by with 1:8s, you WILL get by with 1:7.

Also if later in life you decide to go with the 90s the 1:7 will work.

 

[Deadshot2]

Re: .223 twist needed for 75-80 gr projectiles

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Willoughby</div><div class="ubbcode-body">what twist is needed for 75-80 gr projectiles in a .223 ?
</div></div>

Stability is dependent on Bullet Weight, LENGTH, and SPEED.

Take a look at this calculator and plug in the variables. Use a variety of barrel twists to see which will give you "stability reading" in the green.

JBM Stability Calculator

It's fine to follow the various suggestions that are centered around "my rifle shoots XX great with a YY twist but this calculator will give you an idea of what will happen with your circumstance.

 

[Ultraman550]

Re: .223 twist needed for 75-80 gr projectiles

Check out .223 Wylde 1:8 or 1:7 twist.

 

[FALex]

Re: .223 twist needed for 75-80 gr projectiles

24" Savage Model 10 1:9 shoots the 75gr Hornady BTHP perfectly.

 

[Smithcollector]

Re: .223 twist needed for 75-80 gr projectiles

It depends. Some rifles will stabilize with a 1/9, others need faster.

Elevation and temperature make a difference.

Litz' book includes an excellent description of the factors as well as some of the math behind it all.

 

[redbullitt]

Re: .223 twist needed for 75-80 gr projectiles

My 1/9 does not seem to like anything heavier than 70g... I am at around 1000ft elevation, so that does not help.

I can't wait to rebarrel it to run the heavies. Never had a rifle that I wanted to wear the barrel out on lol.

It does shoot GREAT with the 69s though.