Pressure signs...How flat is too flat

kingudaroad · May 2, 2006, 04:36 PM

I assume some flattening of primers is to be expected as you get close to a max charge but there must be a point where you need to back off. I guess I'm not sure how flat is too flat.

Leftoverdj · May 2, 2006, 05:21 PM

It ain't an exact science and primers can differ, but it the primer is still radiused at the edge, you're probably OK. If the edge is square and semi sharp, you're at max. If the edge has developed a little rim from spreading out into the chamfer of the primer pocket, you're too hot.

cdoc42 · May 3, 2006, 10:44 AM

I've not found that flat primers are a good pressure indicator. Some are softer than others. Cratering of the primer from the firing pin is a clue but that also depends on primer softness. If you work a load up from 10% under max to max, at some point in your reloading career you'll find the bolt difficult to open. That's a pretty confident sign that pressure was too high. Knock the rest of that load apart and drop to the lower charge. If not accurate, change powders and start all over. Sometimes, however, the bolt is seemingly tough to open but I can blame it on the resized case. This is in loads where I have already established accuracy and safety and I notice the problem. But I don't completely full-length resize - I set the shoulder back 0.002" and sometimes for whatever reason the case doesn't resize like it should (maybe used too often?). Lots of varibales to consider. Just use your head and any time something doesn't seem right, stop where you are and evaluate. If you are not comfortable with a situation, discard the load. Start over.

918v · May 3, 2006, 11:21 AM

Primer appearance alone is not a good indicator of pressure. It should be taken into account with other variables. For example, when reloading 45 ACP, waiting for a CCI primer to flatten out is extremely dangerous, while a Federal primer will flatten out before max pressures are reached.

May 2, 2006, 04:36 PM	#1
kingudaroad Senior Member Join Date: March 11, 2005 Location: austin Posts: 735	Pressure signs...How flat is too flat I assume some flattening of primers is to be expected as you get close to a max charge but there must be a point where you need to back off. I guess I'm not sure how flat is too flat.

May 2, 2006, 05:21 PM	#2
Leftoverdj Senior Member Join Date: October 15, 2004 Posts: 934	It ain't an exact science and primers can differ, but it the primer is still radiused at the edge, you're probably OK. If the edge is square and semi sharp, you're at max. If the edge has developed a little rim from spreading out into the chamfer of the primer pocket, you're too hot.

May 3, 2006, 10:44 AM	#3
cdoc42 Senior Member Join Date: March 13, 2005 Location: Pennsylvania Posts: 1,687	I've not found that flat primers are a good pressure indicator. Some are softer than others. Cratering of the primer from the firing pin is a clue but that also depends on primer softness. If you work a load up from 10% under max to max, at some point in your reloading career you'll find the bolt difficult to open. That's a pretty confident sign that pressure was too high. Knock the rest of that load apart and drop to the lower charge. If not accurate, change powders and start all over. Sometimes, however, the bolt is seemingly tough to open but I can blame it on the resized case. This is in loads where I have already established accuracy and safety and I notice the problem. But I don't completely full-length resize - I set the shoulder back 0.002" and sometimes for whatever reason the case doesn't resize like it should (maybe used too often?). Lots of varibales to consider. Just use your head and any time something doesn't seem right, stop where you are and evaluate. If you are not comfortable with a situation, discard the load. Start over.

May 3, 2006, 11:21 AM	#4
918v Junior member Join Date: September 25, 2005 Posts: 1,372	Primer appearance alone is not a good indicator of pressure. It should be taken into account with other variables. For example, when reloading 45 ACP, waiting for a CCI primer to flatten out is extremely dangerous, while a Federal primer will flatten out before max pressures are reached.