Originally Posted by texaswoodworker
I hadn't heard about the bullet causing the pressure. I had always heard it was the thicker brass and slightly longer neck.
Thanks for the info Jon.
when bullets are pressed into the lands thats what causes a pressure spike. when benchresters are doing that or getting close to doing that they arent using anywhere near max loads so they retain a safe pressure level.
with military rounds they are usually at or over max saami spec to begin with as the only spec that matters to the military is what they want the average round to be.
so given the cheapness of government for awarding contracts there isnt a whoooooole lot of QC going on and you end up with bullets that weigh more than they should arent seated quite as deep as they should have an ogive a scootch longer than they should and a charge weight higher than is normal.
when you get all those factors combined in the one in a thousand round in the uber cheap surplus you got from south africa and your running em through your 223 chambered bushmaster thats taken you the better part of a year or more to wander through in many range trips with nothing going wrong all of a suddon on round 853 the magic forces of chance combined to make a really hot over long over weight out of spec round that jams into the lands and your bushmaster turns into a shrapnel device.
now on a 556 gun nothing woulda happened but the gun going bang and you get a slightly larger bit of recoil you prolly wouldnt have noticed. on a 223 chamber your going to the emergency room to have aluminum and steel removed from your hide surgically.
its not just one factor thats the difference in 556 vs 223 altho most folks oversimplify and blame just the brass. all the factors in and of themselves arent the sole cause of kabooms with 223 firing 556 its the combination in JUST the wrong way that turns it into a bomb. lots of folks who shoot 556 out of 223 and claim to do just fine is simply because they havent come across that magic round yet...
as a reloader you CANNOT use surplus pulled military bullets in your 223 chamber for handloading WITHOUT knowing your OAL to the lands and what the longest ogive is on the surplus pulled bullets your using. whis is true of using any heavy hunting bullet in a 223 chamber. you REALLY need to have a chamber gage that measures the distance to the lands and then a gage that measures from the base of the cartrridge to the front of the ogive so you dont hit the lands.
the SAME problem and factors are true for 7.62x51 and 308 winchester except reversed with the notable exception of the FN scar17. it is safe to fire and use 308 winchester loads and all bullets and saami spec charge weights and load lengths in the FN scar17 even though the barrel is stamped 7.62x51 their chambers are actually cut to 308winchester spec in order to utilize the heavy 175+ grain smk
personally i wish manufacturers would drop the 7.62x51 and 223 chambers and stick with 556/wylde and 308 chambers. would make us all safer with no loss in available accurate barrels.