weight of bullet VS twist rate

[gengra]

I'm working on a new load (.223). I have a DPMS lower with a Lothar Walther 24" 1:9 twist barrel. This weapon is going to be a long distance shooter. I would like to get as much weight at longer distances as possible. I went to the range and tested 55 win fmj, 60 horndey, 64 VLD berger, 70 VLD berger. They all shot well, I have been using H335, Benchmark and Reloader 7. I like shooting Berger's ("bergers are better"). The Benchmark powder seems to be metering the best with croney reading within signal digets. I would like to use the 64gr or 70gr. I need to know if 70gr. is way too much for the 1:9 or what?
Any input would be a great help!
Thanks
Gene

[waxthis]

Are you sure your twist rate is 1:9? Armalite uses Lothar Walther barrels and the twist is 1:8 in 5.56/.223. I can confirm that mine is anyhow, and a few other I know....

[gengra]

I just confirmed the twist rate, it is 1:9. I'm just wondering what weight of bullet would be best or at least a good start.
Thanks
Gene

[Sixgun]

62 or 55 will be best. I would not even waste your time with 70grs. 75's will most likely keyhole, It does with mine.[Flower]
1 in 7s like 62 to 75s.
good luck.

[RRD3]

You will find that the 70's will have issues at greater distances. .223 wasn't really made to push that heavy of a round. 50's and low 60's for me.

[waxthis]

62-69gr for me....69 seems to be the ticket with a 1:8, for me anyhow.....Good luck!!!
[Beer]

[SA Friday]

I have a Colt 1:9 barrel that will shoot 68 and 69gr bullets with great accuracy. I haven't tried the 70gr bullets in it. I won't even bother trying heavier, although I have talked to a few who have pushed 77gr bullets out of a 1:9 and had successful accuracy.

1:9 can be a pain in the butt with the heavier bullets, but the only way to tell if it will stabilize is to do the work. Reload and test... Best bet is to not push over the 68/69gr mark.

I have a 1:7 that stabilizes the heavier bullets extremely well, but the 50/55gr bullets are iffy out of it. Some do fine like Nosler BT 50gr bullets, others have been a complete bust.

1:8 barrels seem to be the best middle of the road doing well with 50/55gr bullets all the way up to 77gr bullets. Some even stabilize some of the super heavy 80gr bullets pretty well, but it's pushing the limit.

Ultimately, you are going to have to load up stuff and test it to determine if it's a feasible load for that barrel and rifle set-up. I have seen the occasional 1:8 barrel that didn't like 77gr bullets either. It's all about the testing.

[68Charger]

the factor I don't see being considered here is muzzle velocity...

Bullet RPM = MV X 720/Twist Rate (in inches)

so if a bullet is stable at 2450 fps from a 1 in 8", then you may need to push it to 2750 fps to stabilize it in a 1 in 9"

part of the equation is that different bullet shapes & lengths need higher RPM to stabilize, so perhaps you should be asking Berger.. they list a 73 grain match boattail for a 1 in 9" twist.. part# 22420

with a 24" barrel, and slow-burning powder (to keep pressure up with the longer barrel length), you can get the MV up enough to push the envelope.. and you don't have a "typical" setup that can use a "rule of thumb".. you'll have to experiment..

I've looked into longer barrels for .223, and have learned that any length beyond 20" requires slow powder to get significant velocity increase... no off-the-shelf ammo will be higher MV with 24" than with 20"

[gengra]

THANKS to ALL!!
Great info on my direction (test): I'm going to continue my testing around 64 to 70 gr. The 55 @ 60 Shot well. (I do want to try the 73,just for grins, I also have 16" colt with 1:7). Watching for the keyhole. I do need to fine tune the powder charge (burn rate, MV). I always liked H335, but Benchmark seems to be more consistent (handling, velocity, were I'm at in starting grains) Just need to check and see were it is on the burn rate. I have the length in the barrel and might as well use it. :)
Thanks again!
Gene

[DocMedic]

I've shot 75 Grain Match kings through my .223 1in9 twist Bolt rifle. Didn't have any issues, but part of that could had been that its a 26 inch bull barrel.

[Hannu]

Twist rate depends not straight on weight, but bullet lenght. For example, one of my match rifles with 9" twist shoots Berger 73gr lenght tolerant bullet just fine to 300 meters, but longer 70gr very low drag is doing some flyers at 300 meters.
First problem with stabilization is usually not keyholing, it is strange flyers. If there is keyholing, bullet is way too long or bullet velocity is way too low for stabilization.
One thing is if your rifle really has, for example, 8.7" or 9.2" twist instead if 9.0" It is is not very rare thing in cheap factory barrels.

You should also note, Lothar Walther stainless match barrels, hand finished at the German factory, are much better quality compared to, for example, Armalite original barrels.

Below is couple of groups shot with Nosler 69gr CC and BL-C(2), 5 shots from 100 meters. Sorry about bad picture quality, scanned cardboard targets... Barrel is 18" LW50 with 9" twist (bull profile, muzzle diameter .875"), round count 8800.

Hannu, Lothar Walther LW50 fan :)


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