AR 1/9 twist 24" bullets and velocities

[BobbyJ]

Wanting to try a 223 varmint gun I decided to order a barrel for one of my ARs to see how well it shoots.
Ordered a match grade 24" 1/9 twist (All they had in stock)

Will a 1/9 work with 40 grain Vmax? I see some people are getting like 3700-3800 fps out of the 40s but I am assuming they are using 1/12 twists.

I ordered some 53gr Vmaxes to load. Using CFE 223 for now but will need more powder soon. Was thinking TAC might be decent.

Curious on people with 1/9 24" barrels are getting and what varmint bullets work best. Is 40gr too light?

 

[jelenko]

I think a consideration is the resulting spin rate of the bullet vs the manufacturer's recommendation.
Spin rate = 720XMV/Twist rate

For example, a bullet with a MV of 3700 fps in a 1:9 twist barrel is spinning at 720x3700/9 = 396K rpm.
From Hornady and Sierra, for their match grade bullets, they recommend 260k [Sierra] and 280k [Hornady]. The reason for the recommendations is to avoid the bullet coming apart - especially as the lead core heats up close to melting.

If you used a 69gr bullet going 3000 fps, the rpm's are 240K.

 

[SSchnd]

You could always call White Oak Armament in Carlock IL, John does varmit and Match rifle barrels also as well as Service Rifle tubes. We all know barrel blanks are hit or miss stock there days, but a phone call is simple.
I prefer 1/8 or faster. Just a thought 309-376-2288, Jane at the office is a great gal.

 

[BobbyJ]

I think a consideration is the resulting spin rate of the bullet vs the manufacturer's recommendation.
Spin rate = 720XMV/Twist rate

For example, a bullet with a MV of 3700 fps in a 1:9 twist barrel is spinning at 720x3700/9 = 396K rpm.

I used 9-Twist RPM = 3700 x (12/9) x 60 = 296,000 RPM not 396k

In another thread a fellow said for explosive effect he found pushing the bullets to higher spin was better than say the same bullet shot out of a slow twist at the same velocity. I think he said the Vmax was around 300k for best explosive result yet not come apart.

I would probably shoot the 40s at 3600 fps = 288k which I think is below Vmax top.

 

[jelenko]

296,000 RPM not 396k

Yeah. My typo!
396K would be something else.

 

[ben lurkin]

Yes. My 1:9 barrels shoot both the 40 gr vmax and Noslers just fine. Pretty accurate too. One is a NM RRA barrel and the other is a Wilson. They do well with anything in the 40-69 gr range; which is why I chose that twist.

 

[BobbyJ]

Yes. My 1:9 barrels shoot both the 40 gr vmax and Noslers just fine. Pretty accurate too. One is a NM RRA barrel and the other is a Wilson. They do well with anything in the 40-69 gr range; which is why I chose that twist.

Good to know, I have a 1/9 24" match grade on order. They had no 1/12 in stock it was 1/9 or wait 3 months. I started to think about it and though 1/9 or 1/10 is probably best for 223 anyway. Wonder why they don't offer it in 1/10, 1/11 etc. Its always 1/8 or 1/12 nothing in between. My .204 is 1/10 which I like because the 1/12 can't do the 40gr well.

 

[BobbyJ]

How are you guys finding out the max RPMs of bullets? I don't see it listed in my manuals nor in the specs. Is it like a company secret they only tell you if you call them and ask?

 

[BobbyJ]

You could always call White Oak Armament in Carlock IL, John does varmit and Match rifle barrels also as well as Service Rifle tubes. We all know barrel blanks are hit or miss stock there days, but a phone call is simple.
I prefer 1/8 or faster. Just a thought 309-376-2288, Jane at the office is a great gal.

Thanks, I did leave White Oak a message there was a 3 day lag in the reply, I had already ordered by the time they replied. They only had 20" 1/8 or 1/12 twist I was looking for 24" which are on backorder.

They don't seem to carry 1/9 or 1/10 twist in 223. I went with 1/9 which seems to cover more weights than 1/12 and I will probably shoot the 53gr Vmax.

I will probably order another barrel if this one works out and I will try to get a White Oak next time, they are priced pretty good come with a gas block.

 

[jelenko]

How are you guys finding out the max RPMs of bullets? I don't see it listed in my manuals nor in the specs. Is it like a company secret they only tell you if you call them and ask?

I first found out in talking with a Hornady tech about the accuracy I was seeing in the H75's. One of his first questions was what the twist rate and muzzle velocity were. He then mentioned the 280K max.

After hearing that, the next time I was talking with a Sierra rep, I asked him what their recommendation was for the SMK77's. They recommend 240K - 260K, so, I guess, 260K max. He was very quick to add that going over their recommended rpm didn't affect accuracy [unless, of course, the bullet doesn't make it to the target].

It does beg the question on why they don't just publish their recommendations/max's.

 

[BobbyJ]

I first found out in talking with a Hornady tech about the accuracy I was seeing in the H75's. One of his first questions was what the twist rate and muzzle velocity were. He then mentioned the 280K max.

After hearing that, the next time I was talking with a Sierra rep, I asked him what their recommendation was for the SMK77's. They recommend 240K - 260K, so, I guess, 260K max. He was very quick to add that going over their recommended rpm didn't affect accuracy [unless, of course, the bullet doesn't make it to the target].

It does beg the question on why they don't just publish their recommendations/max's.

Yes you would think that would be a standard spec. Twist does matter so depending on the bullet velocity and twist it might help people choose a bullet more in line with their rifle.

 

[SSchnd]

Thanks, I did leave White Oak a message there was a 3 day lag in the reply, I had already ordered by the time they replied. They only had 20" 1/8 or 1/12 twist I was looking for 24" which are on backorder.

They don't seem to carry 1/9 or 1/10 twist in 223. I went with 1/9 which seems to cover more weights than 1/12 and I will probably shoot the 53gr Vmax.

I will probably order another barrel if this one works out and I will try to get a White Oak next time, they are priced pretty good come with a gas block.

They were out in Camp Perry with us knuckle dragging service rifle shooters for National Matches, Glad you got a reply.