300 Fireball casting

[pug]

Got a chance to cast the chamber in my Oly 300 Fireball this evening. Thought I would pass on some of the dimensions for those who might be interested. The neck is 0.338" diameter so plenty of room for the thicker .223 brass. Loaded ammo rounds run 0.333" for me. Because of the size I don't see me ever running the thinner brass. Neck length is .325" long being conservative. I would not have any trouble running 1.4" long brass but that is something you might double check yourself with a case OAL button from someone like Sinclair.

On a side note about the diameter of the necks I had quite a bit of blow by with subsonic loads due to the size of the neck and the thicker stiff brass. Previously I had turned some necks to see if the thinner brass would cure the problem but with the low charges just didn't get a good seal. I finally got some more vv N110 powder in and I have to say to me it is a way better powder for subsonic use. Gives a much better case fill and expands the neck to get a better case seal. Think its a little cleaner and since it is a single base extruded powder it appears to give a little more positive action cycling with the lighter loads. It cannot compare however to the supersonic loads of H110 and 1680 since you can't get enough powder in there for max velocity. 8.0 gr of N110 still puts me around 1000 fps with 150 grainers. Haven't clocked supersonic 150s yet but if you are interested just let me know or I will get to it later.

[320pf]

Pug,

I have an Olympic Arms barrel as well. Thanks for the information. I am assuming that the chamber dimensions for my barrel are similar.

I have wanted to try V110 but I have not been able to find any at the local stores.

Have you tried AA#9. I have found it to be a great powder for the 300 fireball. Of all of the powders I have tried, it always gives me the best groups in my upper for both subsonic and full power loads.

Here are the chrono results that I have:

180 gr Sierra SPBT GameKing 7.5 gr AA#9 1034 fps
180 gr Sierra SPBT GameKing 12.5 gr AA#9 1680±11 fps extrem spread 30 fps
180 gr Sierra SPBT GameKing 13.5 gr AA#9 1775 ±7 fps extrem spread 5 fps
180 gr Sierra SPBT GameKing 14.0 gr AA#9 1786 ±8 fps extrem spread 6 fps

165 gr Sierra HPBT GameKing 8.5 gr AA#9 1087 ± 6 fps extrem spread 12 fps
165 gr Nosler Ballistic Tip 8.5 gr AA#9 1007

The 8.5 gr subsonic loads work very well in my AR-15 upper. The action cycles very reliably.

Check out the Accurate Arms website. They list several subsonic loads

http://www.accuratepowder.com/data/PerCaliber2Guide/Handgun/Standarddata/30Cal(7.62mm)/300%20Whisper%20page%2076.pdf

320pf

[pug]

I couldn't find it local either but I needed enough bullets primers and other powders so I got it all from Grafs. I have #9 and I'm still working it all out. Haven't really did any accuracy testing yet as I still have the Tacpoint and iron sites mounted. I have mostly been tuning the rifle to cycle the light stuff and trying a pistol length AGT. Next is accuracy, expansion and penetration testing after I mount a scope on it but I really don't want to pull off my Burris or Weaver competition to try but I have my eyes open for a good deal. Actually the Weaver T6s are on sale at a good price but with the trajectory of the 300 I was looking for a BDC built in.