Alliants 223 load data off?

[lte82]

So I have been shooting Alliant 2000-MR quite a bit, and I realized today that something odd is going on.

With my 308 loads, I'm actually getting nearly identical results with what Alliant says I should get, and hit pressure signs right near the max listed load. With the 223 however, my velocities are nearly 10% slower than what's listed, and I can run quite a bit more powder than the max listed load with no issues.

If I were to just go off of my 223 data, I'd say I had a "slow batch", but judging by my 308 data I'd say I had a "fast batch".

Could the 223 load data just be off on alliants website? I know all guns are different, but I've never actually seen load data off this much on one cartridge, and almost dead nuts perfect on the next.

 

[Bear24]

what bullet and brass are you using? also, is this a bolt gun or AR?

 

[lte82]

what bullet and brass are you using? also, is this a bolt gun or AR?

Both 308 and 223 are AR's. LC brass in 308 and 223, and had similar results with Winchester commercial brass in the 223 as well, though that was even slower than in the LC brass. 77gr in the 223, 168 & 175 in the 308.

 

[Bear24]

Both 308 and 223 are AR's. LC brass in 308 and 223, and had similar results with Winchester commercial brass in the 223 as well, though that was even slower than in the LC brass. 77gr in the 223, 168 & 175 in the 308.

Ok, well I can't speak for AR loads because my load for my bolt rifle 223 are loaded .110" longer than AR mags will allow with the same 77g bullet. However I can load quite a bit over the stated max load. I do believe that the pressure is very gradual to a point and then spikes fairly rapidly from 26g to 27g my load picks up 350fps and I am running them 3100fps out of a 24" barrel which is smoking fast!

 

[lte82]

Ok, well I can't speak for AR loads because my load for my bolt rifle 223 are loaded .110" longer than AR mags will allow with the same 77g bullet. However I can load quite a bit over the stated max load. I do believe that the pressure is very gradual to a point and then spikes fairly rapidly from 26g to 27g my load picks up 350fps and I am running them 3100fps out of a 24" barrel which is smoking fast!

3100 fps sounds almost unreal! I never noticed that jump when I went up to 26.8gr, but I was only shooting through a 20" barrel. Maybe the extra 4" make a big difference?

 

[BoilerUP]

3100 from a 24" 5.56 with 77s sounds...warm.

 

[Bear24]

3100 fps sounds almost unreal! I never noticed that jump when I went up to 26.8gr, but I was only shooting through a 20" barrel. Maybe the extra 4" make a big difference?

3100 from a 24" 5.56 with 77s sounds...warm.

Yes it is, but no major pressure signs just slight primer cratering, no ejector swipe or stiff bolt. I have only shot that load in <50* weather and I'm going to cool it off a little anyway, there is no need for me to push the 223 that hard all the time.

 

[smschulz]

Some variation can come from the reference barrel differences.
Make sure the length and twist are the same to compare effectively.

 

[BobinNC]

So I have been shooting Alliant 2000-MR quite a bit, and I realized today that something odd is going on.

With my 308 loads, I'm actually getting nearly identical results with what Alliant says I should get, and hit pressure signs right near the max listed load. With the 223 however, my velocities are nearly 10% slower than what's listed, and I can run quite a bit more powder than the max listed load with no issues.

If I were to just go off of my 223 data, I'd say I had a "slow batch", but judging by my 308 data I'd say I had a "fast batch".

Could the 223 load data just be off on alliants website? I know all guns are different, but I've never actually seen load data off this much on one cartridge, and almost dead nuts perfect on the next.

If your AR has a 5.56mm chamber, rather than a .223 chamber, right there could be your difference of 10%...... 5.56mm chambers have longer throats than .223 chambers and usually produce less velocity in those chambers than loads intended for .223 Rem chambers.

Most (but not all) reloading data lists only .223 rem loads, not 5.56mm loads. .223 rem loads will exhibit low pressures and velocities when fired in 5.56mm chambers. Conversely, 5.56mm loads will produce excess pressures when fired in .223 Rem chambers.

No such problem exists with the 308 win, hence published loads usually come closer to matching real velocities.

 

[bigedp51]

BobinNC hit the nail on the head and is 100% correct, below are the pressure differences between the shorter .223 throat and 5.56 throat. Just remember that the max pressure rating for "BOTH" cartridges is 55,000 psi.

Below the green bar on the far left is a factory loaded .223 cartridge in a .223 chamber, it is just below 50,000 psi and shows the factory round is not loaded to the max pressure of 55,000 psi. The second green bar shows a .223 fired in a AR15 chamber and the pressure is approximately 45,000 psi. The first blue bar on the left is a 5.56 NATO round fired in a .223 chamber at approximately 59,000 psi and 4,000 psi over the max rated pressure. The last blue bar on the right is a 5.56 NATO round fired in a AR15 chamber with a longer throat just a smidge below 55,000 psi and at its normal rated pressure.

5.56 vs .223 – What You Know May Be Wrong
http://www.luckygunner.com/labs/5-56-vs-223/

And now to muddy up the waters my Savage bolt action .223 with a 1 in 9 twist has a longer throat than either of my AR15 rifles. So remember that SAAMI chamber drawings are "guidelines" and are not written in stone, and the firearms manufacturers do not have to follow these "guidelines" on production rifles. (SEE LINK BELOW)

HOLLIGER ON .223/5.56 CHAMBERS
NJ HiPower - Cartridge Tech Specs

If you look at the first chamber specifications listed above for Savage rifles the throat is longer than AR15 rifles. And two other chamber are even longer than the AR15.

 

[lte82]

I never knew the throat could make such a huge difference on pressure and velocity. The chamber is 223 wylde, which is pretty loose to start with, and it has several thousand rounds through it so Im sure the throat has eroded some on top of that.

Thanks for all of the info!

 

[BoilerUP]

Even from a Wylde or 5.56 chamber, 3100fps with 77s from a 24" barrel is waaaaaaaaaay fast...especially when one considers Mk262 specs from a 20" barrel at "only" 2850.

Even with uber-powder, no way 4" of barrel picks up 250fps over Mk262.

 

[Bear24]

Even from a Wylde or 5.56 chamber, 3100fps with 77s from a 24" barrel is waaaaaaaaaay fast...especially when one considers Mk262 specs from a 20" barrel at "only" 2850.

Even with uber-powder, no way 4" of barrel picks up 250fps over Mk262.

Not trying to derail this thread but I am just going off what my magnetospeed said and it was confirmed out to 600y. I only shot 15 of those rounds and don't plan on using that load any more because it doesn't pass my sanity check as I have the same thoughts as you on it. However there was only slight cratering of the primer and it still had nice round edges to it. This is out of a surgeon action with at .223 chamber. load was 27g PP 2000MR loaded 2.36 COAL. I get 2800fps with 26g and loaded 2.26 COAL

 

[BoilerUP]

Not trying to derail this thread but I am just going off what my magnetospeed said and it was confirmed out to 600y. I only shot 15 of those rounds and don't plan on using that load any more because it doesn't pass my sanity check as I have the same thoughts as you on it. However there was only slight cratering of the primer and it still had nice round edges to it. This is out of a surgeon action with at .223 chamber. load was 27g PP 2000MR loaded 2.36 COAL. I get 2800fps with 26g and loaded 2.26 COAL

Okay my bad...for some reason I had "gas gun" in my head with that 3100fps from a 24" barrel.

A 24" bolt gun loaded long seems less impossible to achieve those speeds than an AR at mag length.

 

[CharlieNC]

223 LC brass has more water capacity than commercial brass , whereas 308 LC has less.

 

[bruddah]

Good info.

 

[USMC-FURY]

These MORON powder companies are so behind in the load data its pathetic! Most data for .223 is out of a 24 inch barrel with a 1:12 twist , and Accurate is the only one with .223 and 5.56 load data. If they would wake up and generate data from 7.5, 10.5, 14.2, 16 inch barrels with 1:6, 1:7, 1:8, 1:9 twists they would sell a lot more powder! LAZY F'ers