slow velocities on .223 reloads


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shoots45s
March 8, 2013, 12:44 PM
I tested some reloads for my .223 using a 55 gr soft point and CFE223 powder for their velocity.

I got an average speed of 2704 fps and std dev of 16.6 so the speed is consistent.

The load data for this powder says the speed for min and max charge (26.0 and 27.8 gr) is 3133 and 3329 using a 24" barrel.
Extrapolating, I should expect a speed around 3200 fps if using a 24" barrel. So I'm about 500 fps slow.

My barrel is 16" so I expect slower bullets, but at this site http://www.loadammo.com/Topics/October05.htm, indicates that for 223 to expect about 48 fps speed reduction for each 2" shorter barrel. That would account for about 300 fps.

Would the gas charging system account for the other 200 fps? If not. what other possibilities for the lower speeds?

Thanks

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sixstrings101
March 8, 2013, 12:52 PM
I was always told its 50fps per inch

rcmodel
March 8, 2013, 01:02 PM
Many factors make it nearly impossible to match ballistics lab velocity data.

First, they use SAAMI spec pressure test barrels which are better then yours!

Second, all testing is done at perfect atmospheric conditions such as 70 degrees, perfect humidity, etc.
Was it cold when you were shooting?

Third, are you using a Speer bullet like they were, or some other brand?

Forth, are you using Winchester case, and Winchester primers like they were?

Fifth, does your AR-15 have a 1/12 rifling twist like their test barrel??

At any rate, if you are getting 2,704 out of a 16" AR-15, thats about par for the course for a lot of factory .223 in a lot of barrels.

And no, the gas system is not accountable for your lower velocity.
The bullet is out of the barrel and well down range before the gas port in the barrel even realizes it went by on the way out..

rc

kingmt
March 8, 2013, 04:38 PM
Why do people harp on this so much. I normally try to slow mine down so I get a bit more penatration with think jackets.

dagger dog
March 8, 2013, 05:01 PM
Speer has a chapter in their #13 Reloading manual titled "WHY BALLISTICIANS GO GREY"
makes for some interesting reading especially if your chronograph results don't make sense.

rcmodel
March 8, 2013, 10:09 PM
See, thats why I have never owned a chronograph.

I simply don't worry about velocity.

I worry about accuracy & excess pressure.

And I still went gray & bald worrying about that all these years.

rc

TheCracker
March 8, 2013, 10:21 PM
I get 2914 out if my 16" 223 barrel with h335 if that helps any.

ArchAngelCD
March 8, 2013, 11:40 PM
Like said above, you will probably never generate the same higher velocities posted in the load data. There are just too many variables.

Hodgdon load data:
55gr SPR SP bullet
Varget 25.5gr = 3174 fps
H335 25.3gr = 3203 fps

My loads shot from a 1:12 22" bolt action rifle:
25.0gr Varget 2797 fps AV
26.0gr Varget 2965 fps AV

25.0gr H335 3057 fps AV

As you can see even from a 22" barrel my actual velocities are nowhere near those posted by Hodgdon on their site. The results you are getting look perfectly normal to me, you should not worry about it...

GeneCC
March 8, 2013, 11:49 PM
The load data for this powder says the speed for min and max charge (26.0 and 27.8 gr) is 3133 and 3329 using a 24" barrel. Extrapolating, I should expect a speed around 3200 fps if using a 24" barrel. So I'm about 500 fps slow.


There are so many variables.... manufacturing tolerances on your barrel versus the "lab's" barrel. Variations in the primer. Variations in the powder. Neck adhesion to the bullet. Overcoming crimping force.

As rcmodel points out you can see variations due to "cold bore", atmospheric pressure and so on.

The big difference is barrel length. I'd say that you're "just about right" for the difference of 500 ft/sec. You're talking eight inches of difference between your rig and the 24" test barrel.

rcmodel is also correct about port pressure. There will be some gas flow through the port but as I recall the port on an AR-15 series about is about 2mm across versus 5.56mm (or so) for the bore. You're talking a much smaller area for the gas port.

I think 5.56 is 24.3 mm squared versus 3.14 mm squared for a 2mm diameter gas port. One is 13 percent of the other and the rate of gas flow would be proportional except...

Progressivity of the powder comes into play. A lot of the combustion is completed by the time that the bullet passes under the gas port. You get some residual of course but it's not a lot. I don't recall the percentages but by the time the bullet has crossed that point that bullet has a lot of its energy already onboard for the trip. Plus you have that difference in area between the gas port and the bore working for the bullet.

It's an interesting thought, to consider how much energy is taken by the port but figure that it's just enough to handle the operation. The energy budget for that rifle isn't as high as the energy dumped into the projectile.


I'd say that you're just about right. What you're seeing is part of the reason why the US Military modified its ammunition to function more effectively in the M4 carbines that many of our soldiers use today. As I recall the M855 round was intended for the larger M16A2 and its NATO equivalents. The M4 has a shorter barrel and thus required more energy at the muzzle to engage people at reasonable distances.

ljnowell
March 9, 2013, 12:12 AM
Shoot45s, we typically use the manuacturers numbers as a guideline. An approximation if you will as what the velocity could be, if we used identical components. Its rarely right.

In fact, I only use a chronograph when developing over pressue loads. A good example, a few years ago I was looking to get everything I could out of a 185gr GDHP in my Glock21. I used power pistol, winchester cases, and winchester primers. At the time the max load published by Alliant was 9.3gr. My velocity gave steady gains all the way to 9.6gr, with no pressure signs(I know thats not reliable in a low pressure pistol cartridge) and it all seemed ok. When I tried to push it a little higher things got interesting. At 9.7gr velocity out of 10 rounds either stayed the same, or went down just a hair, none of them gained velocity. Ay 9.8gr they consistently lost velocity over the previous load. I came to the conclusion that I had hit the wall of diminishing returns.

Does this help you? Maybe, maybe not, but it is a good story.

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