Tell me when I should have realized, since this was a first in 40 years of loading my own ammo. 5.56mm, new Starline brass, CCI-41 primers, Hornady 75gr BTHP Match, Vihtavouri N-135 22.7gr. Coal 2.505, no crimp. Per Vihtavouri manual, max load is 23.3gr.
Started at 21gr and loaded 50 each progressing 0.5gr for each additional 50 rounds, ending at 23gr. Took the Chrono to my range and commenced recording velocity out of my 20” Compass Lake AR-15 1x7 twist Krieger barrel. 5 round mags.
21gr had no issues, accurate and primers looked good. Using a brass catcher, so have no idea about ejection pattern. Velocity averaged 2550fps.
21.5gr also no issues. Velocity averaged 2565fps.
22.0gr the second round wouldn’t fire. Trigger was inoperable. Ejected round, no primer indent. Separated upper/lower and found a smashed spent primer stuck below the trigger. Removed it and dumped empty from catcher. Primer was missing, and ejection marks engraved lightly in rim. My chrono records and charts SD and ES, and they were close to the same as the 21.5gr loads recorded previously. Cleared trigger and fired remaining rounds without issue. First time I had ever had a primer blow out, so I assumed the new case was bad. Primers were getting flat, but not exceptional from past experiences. Velocity 2604fps.
22.5gr the 10th round tied up the trigger again. Another blown primer. Switched to my Sig SBR 7” barrel, first round tied up the action to the point that I had to tap the charging handle with a brass hammer to open the bolt. Removed the upper, and pulled the bolt. A blown primer was flattened up above the bolt, flat against the carrier. It wasn’t looking good for the home team. Took the remaining rounds home and pulled the bullets/measured the powder. I measure each load, and verify my Hornady auto measure with an old RCBS digital, so I did not expect to find any overloads. All was good. The velocity of these rounds was averaging 2817fps. A 1/2 grain increase in powder gained 200+FPS in velocity on the CLE 20” barrel.
I haven’t checked my chrono ES and SD charts yet, but I hope I will see a noticeable trend indicating an issue. Primer flattening is no different between the initial 21gr loads and the 22.5gr loads. I never felt any gas. If the weapon had not tied up with the frozen trigger, I would have not known that I was having pressure issues. The large velocity increase at 22.5gr should have woke me up, but I was sitting at the gun, sending my chrono results home to print off later. I only noticed the delta in velocity after reviewing the printouts.
Advice is needed regarding what to be more aware of in the future, to avoid getting to the point of blowing a primer. Also, should I discard my brass from the over-pressured loads? I small base resize, but if the brass needs to go, I have others. The two weapons fired a couple mags of factory loads after the blown primers stopped my testing, and they appear in normal operating condition.
All thoughts for a safer path forward are appreciated. Thanks to all.
Started at 21gr and loaded 50 each progressing 0.5gr for each additional 50 rounds, ending at 23gr. Took the Chrono to my range and commenced recording velocity out of my 20” Compass Lake AR-15 1x7 twist Krieger barrel. 5 round mags.
21gr had no issues, accurate and primers looked good. Using a brass catcher, so have no idea about ejection pattern. Velocity averaged 2550fps.
21.5gr also no issues. Velocity averaged 2565fps.
22.0gr the second round wouldn’t fire. Trigger was inoperable. Ejected round, no primer indent. Separated upper/lower and found a smashed spent primer stuck below the trigger. Removed it and dumped empty from catcher. Primer was missing, and ejection marks engraved lightly in rim. My chrono records and charts SD and ES, and they were close to the same as the 21.5gr loads recorded previously. Cleared trigger and fired remaining rounds without issue. First time I had ever had a primer blow out, so I assumed the new case was bad. Primers were getting flat, but not exceptional from past experiences. Velocity 2604fps.
22.5gr the 10th round tied up the trigger again. Another blown primer. Switched to my Sig SBR 7” barrel, first round tied up the action to the point that I had to tap the charging handle with a brass hammer to open the bolt. Removed the upper, and pulled the bolt. A blown primer was flattened up above the bolt, flat against the carrier. It wasn’t looking good for the home team. Took the remaining rounds home and pulled the bullets/measured the powder. I measure each load, and verify my Hornady auto measure with an old RCBS digital, so I did not expect to find any overloads. All was good. The velocity of these rounds was averaging 2817fps. A 1/2 grain increase in powder gained 200+FPS in velocity on the CLE 20” barrel.
I haven’t checked my chrono ES and SD charts yet, but I hope I will see a noticeable trend indicating an issue. Primer flattening is no different between the initial 21gr loads and the 22.5gr loads. I never felt any gas. If the weapon had not tied up with the frozen trigger, I would have not known that I was having pressure issues. The large velocity increase at 22.5gr should have woke me up, but I was sitting at the gun, sending my chrono results home to print off later. I only noticed the delta in velocity after reviewing the printouts.
Advice is needed regarding what to be more aware of in the future, to avoid getting to the point of blowing a primer. Also, should I discard my brass from the over-pressured loads? I small base resize, but if the brass needs to go, I have others. The two weapons fired a couple mags of factory loads after the blown primers stopped my testing, and they appear in normal operating condition.
All thoughts for a safer path forward are appreciated. Thanks to all.
