How not to test subsonic loads....

Okay, this my story of a gun ruined...

I went to the range over lunch to test some loads for my 300/221. The previous day I had started playing with the 250 grain bullets from Hawk Bullet in New Jersey; I tried a starter load of 8.9gr H110. They shot fine, even cycled the action. I previously experimented with 200gr and 220gr Sierras and I was excited about trying the big 250gr pill. I loaded three rounds each of 9.0gr, 9.2gr & 9.4gr of H110 and put my shooting stuff in the truck for a range visit today.

Well, I got out to the range, set-up the chrono and loaded my mag. I had all nine rounds in the mag, stacked in ascending powder charge. I usually shoot one at a time and manually record the f.p.s. with each shot. I fired the first three rounds, the action cycling each time, but no readout on the chrono... maybe I wasn’t crossing the “sensor eyes” correctly?? So, I realigned myself and took the fourth shot... [thud]... that sound that you don’t know what it is, but you know it’s not good...

I pulled down the gun and looked at my barrel.... It was split – none of the previous rounds had exited the barrel... you can see for yourselves, but it looks like the add-on bayonet lug helped keep the barrel from splitting completely.... I have no idea why things didn't work like they did the day before... temperature maybe? it was 20 degrees colder... wrong powder charge or omitted charge? can't be, I intenionally inspected all the cases with a flashlight before I seated the bullets. Each charge was individually weighed and inspected...

d'oh... now I have to build another one...

Sight tower band "blown open"

View of split barrel - It split from the
handguard cap to the muzzle...

More views of the barrel...

Can you see a peek of copper in the crack??

Bayonett lug removed....

You can see the split goes all the
way to the handguard cap...