pressure signs ???

[adam]

I have tried to take some pics of the primers on a latest batch of loads i have used whilst testing new bullets. Im sorry they are not clearer but its the best my camera can do. The bolt is normal to lift and open and the cases are showing no signs of splitting or head separation, but I was wondering if the primers looked ok to you guys. They dont appear to be completely flattened the only thing that concerns me is that where the firing pin has struck the primer it looks as though a small round ring has risen from the primer face , almost as though it has tried to squeeze its self between the firing pin and bolt body. Its not huge maybe only 20thou or so. Sorry for the crappy explanation!!!

[acloco]

Check your firing pin protrusion on your bolt. Should be in the 0.040" range.

Shape of firing pin can provide this issue as well.

This is also why good gunsmiths bush the firing pin holes on boltheads as well.

[Glen]

What did you shoot them thru? Remington is known for cratered primers due to an overly large firing pin hole & undersized firing pin. There also appears to be minimal flattening from what I can see.

[adam]

Its been fired through my custom built rifle, running a Stiller predator action. I looked at some factory Hornady 40gr rounds that I had fired and there apears to be a very slight rise on the primers of those but not quite as pronounced as on my re loads. All I want to know is if this constitutes as over pressure? What does a flat primer from excess pressure actually look like?

[Fred_C_Dobbs]

Pressure gets higher as you move right.



Notice how the ring between the primer and the rim gets narrower and shallower as you move right, indicating the primer is getting flatter. Notice, too, there is no cratering in the leftmost round. Second leftmost, slight cratering. By the rightmost round, the cratering mysteriously has vanished because the primer made a mandrel of the bolt face and smushed the cratering back into the primer. Not good.

In severe cases, the top of the primer will smash against the bolt, then flow sideways out of the primer pocket. When you extract that primer, it still will be wider at the top than at the base. In profile, it will look like a top hat, and that's what it's called. #4 above probably has some top hatting. It also is a load to run screaming from.

Some primers are "softer" than others and a little flattening and/or cratering is to be expected. With my .204 and the primers I'm using, I'd consider #2 from the left acceptable. Numbers 3&4, no. YMMV.

Also, some rifles also are more prone to cratering. My Savage .204 craters even with every factory load I've ever shot. It could be because of an overly large firing pin hole but I'm told it also could be because of an underpowered hammer spring.

[Joe O]

Adam,I had excessive cratering in a new Savage LRPV,with all factory ammo,and moderate reloads.No pressure sign,so I knew the firing pin to hole dimention was bad(should never have left the factory).I sent pics to customer service and the send a UPS pick up order for my gun.They installed a new bolt head wich cleared up 95% of the cratering(livable).The pics that Dobbs posted ilistrates the difference between cratering and high pressure,very well.

[Rick in Oregon]

Pressure gets higher as you move right.

Fred, nice photo lineup for clarity. Excellent post showing the effects of primer flattening for the newer guys.

[adam]

Thanks alot guys I'm using CCI BR4 primers as they are giving me the best groups. I would have thaught also that being a custom action from the likes of Stiller that the firing pin and hole would be optimized!!!!!?

[TD-Max]

Check your firing pin protrusion on your bolt. Should be in the 0.040" range.

Shape of firing pin can provide this issue as well.

This is also why good gunsmiths bush the firing pin holes on boltheads as well.

My Sako gave the occasional misfire, but generally would strike the second time. Took the bolt to my 'smith when I picked up my Sako 22-250 and he checked it out. Firing pin protrusion was like .077" which is way too far. Supposedly this pushes right past where it is supposed to be striking. He took it out and stoned it down to in the .050's and it has not misfired since. He also echoed the comments on the shape.

[Fred_C_Dobbs]

Fred, nice photo lineup for clarity. Excellent post showing the effects of primer flattening for the newer guys.

Thanks, Rick. I only ever steal the good stuff.

Thanks alot guys I'm using CCI BR4 primers as they are giving me the best groups. I would have thaught also that being a custom action from the likes of Stiller that the firing pin and hole would be optimized!!!!!?

I try not to shoot anything except BR4s in my .204. And they are pretty "soft."

One pressure sign by itself usually isn't cause for concern, unless that one sign happens to be happens a blown casing. Until you start seeing a distinct squaring at the shoulder of the primer, I think you're golden.

A couple of weeks ago I spoke with a man who used to run small arms tests for DoD at the Aberdeen Proving Ground (which is my coy way of saying I think he knew his stuff) and he told me cratering also can be traced to a too weak hammer spring or striker spring. He said a strong spring helps resist the flowing of the primer back into the firing pin hole. When I told him what was going on with my Savage, and that there was one gun shop noted for bushing the hole and reducing the slop, he strongly suggested I try the next step up in a Wolff spring before sending it out.

If it hadn't been for his bona fides, I'da probably snickered and said, "Yuh, ...right." Instead, I'm looking for a Wolff spring for a Model 12.

[adam]

Fred, nice photo lineup for clarity. Excellent post showing the effects of primer flattening for the newer guys.

Thanks, Rick. I only ever steal the good stuff.

Thanks alot guys I'm using CCI BR4 primers as they are giving me the best groups. I would have thaught also that being a custom action from the likes of Stiller that the firing pin and hole would be optimized!!!!!?

I try not to shoot anything except BR4s in my .204. And they are pretty "soft."

One pressure sign by itself usually isn't cause for concern, unless that one sign happens to be happens a blown casing. Until you start seeing a distinct squaring at the shoulder of the primer, I think you're golden.

A couple of weeks ago I spoke with a man who used to run small arms tests for DoD at the Aberdeen Proving Ground (which is my coy way of saying I think he knew his stuff) and he told me cratering also can be traced to a too weak hammer spring or striker spring. He said a strong spring helps resist the flowing of the primer back into the firing pin hole. When I told him what was going on with my Savage, and that there was one gun shop noted for bushing the hole and reducing the slop, he strongly suggested I try the next step up in a Wolff spring before sending it out.

If it hadn't been for his bona fides, I'da probably snickered and said, "Yuh, ...right." Instead, I'm looking for a Wolff spring for a Model 12.

Thanks for the input. I will have a chat with my smith about bushing the firing pin.
So long as its safe to shoot though

[Wrangler John]

I posted this previously, it's a fired Federal Match primer that ignited 25.2 grains of Rl-10x with a 26 grain Barnes Varmint Grenade. This load is a published load and moderate in pressure. The primer shows a bit of cratering which is normal for this primer (and the CCI product). It was fired in a Savage Precision Target action which has a small diameter firing pin that doesn't require bushing. I set the pin protrusion to .055" which is within specification. Use of the Remington 7 1/2 BR primer with a heavier cup is recommended for those desiring to eliminate this artifact from softer, thinner cups. This is not a sign of abnormal pressure in the absence of flattening, pin holing or leakage of the primer, or shiny ejector mark on the case head, or hard bolt lift.