Pressure signs - craters on primers

[Heym SR20]

I notice on a couple of the loads approaching the book max, that the primer has a bit of a crater where it looks as if it has been forced into the firing pin hole. I take this as a sign of pressures getting high so should not use this level of loading. Saying that, some of the RWS factory ammo is also doing this.

 

[bewsher500]

Much more a sign of pin to bore tolerance on the bolt face than pressure signs
even mild loads do that on some rifles

I personally use primer flattening and margin profile between primer pocket and primer as a better indicator

 

[hammo]

Much more a sign of pin to bore tolerance on the bolt face than pressure signs
even mild loads do that on some rifles

I personally use primer flattening and margin profile between primer pocket and primer as a better indicator

What he said.
My CZ 527 shows mild cratering even with factory loads.

hammo

 

[Cyres]

Quite common in .223 with heavy bullets so need to move to harder primers eg Remington 7.5s.

D

 

[plumber01]

I have played about with 223's, and when absolutely taking the p*&ss, I can assure you a compressed load of 26gns of N135 will definitely blow the primer clean out of the case, ! sensibly what you should look for is the primer being flattened against the bolt, this is pushing it. but please bare in mind temp etc can make a difference. the manuals are there for a purpose and although you may hear of target shooters pushing boundaries they do it at their own risk, but tend to do it an rifles chambered for long heavy bullets in very strong varmint barrels . do you really need your bullets screaming out of the barrel, and will it really help you . Just get an accurate load and stick with it .you cant overkill something............although I did introduce a fox at about 40 yards to a 270,,, well the back leg looked like a fox . good luck and take care with loads, especially in smaller calibers, a little can be a lot over .

 

[Laurie]

What primers are you using? 223 Rem should have BR or SR magnums as they have thicker brass cups to withstand pressures. Standard models have 0.020" cup thickness and often a weaker brass alloy and were designed for .22 Hornet, 218 Bee and similar early lower pressure cartridges. .222 Rem and its 50,000 psi loads are about as high pressure as these primers will take.

SR BR / Magnums have 0.025" thick cups and take pressure / avoid cup extrusion back into the firing-pin hole much better.

Having said that, the symptoms you describe are also - as said by Bewsher, hammo, and Cyres - usually very much down to a loose firing pin to bolt-aperture fit and is a fact of life in many factory rifles. You certainly want to avoid getting to the position where the primer cup is 'blanked' - where a small plug extrudes so much it detaches and is blown back into the bolt. The escaping gas around it does the firing pin tip and the bolt-face no good at all eroding them and making the situation worse if it happens often enough and the plug is usually trapped inside the bolt body ahead of the striker body and can cause misfires if not removed.

 

[hybridfiat]

I agree with Plumber. Cratering is a sign of high pressure and I'd be wary of going ignoring it and loading higher.

 

[Cyres]

Laurie is quite correct esp as at times a tiny bit of the primer gets inside the bolt.Several years ago it happened to me on a fox squeezed trigger and nothing happened, not a nice experience. This was also combined with an over length case. Anyway stripped bolt and cleaned out metal primer fragments.

If you read Lauries excellent article on reloading heavy bullets in .223 he explains the issue.

Since then I have always used Remington 7.5 Bench rest primers and have not had any issues.

There are no pressure signs ie flattened primers and this is using Varget. Also please note that .223 case volumes can vary so what in one case is not compressed in others will be. This can even happen between batches of Lapua brass.

You thus need to be careful to check your brass and dont mix up different types/batches.

D

 

[Sauer90]

Flattened primers aint necessarily an indication of high pressure a heavy bolt lift on the other hand.
Cratering is normal for a cock-in-a-shirt-sleeve firing pin fit.
Remington have a warning on the std. primers not to use in high pressure ammunition.

 

[ChesterP]

Laurie is quite correct esp as at times a tiny bit of the primer gets inside the bolt.Several years ago it happened to me on a fox squeezed trigger and nothing happened, not a nice experience. This was also combined with an over length case. Anyway stripped bolt and cleaned out metal primer fragments.

If you read Lauries excellent article on reloading heavy bullets in .223 he explains the issue.

Since then I have always used Remington 7.5 Bench rest primers and have not had any issues.

There are no pressure signs ie flattened primers and this is using Varget. Also please note that .223 case volumes can vary so what in one case is not compressed in others will be. This can even happen between batches of Lapua brass.

You thus need to be careful to check your brass and dont mix up different types/batches.

D

+1

Cratering MAY be one indication of high pressure but it can also relate, as Laurie points out, to the tolerances on bolt aperture to firing pin and even to the firing pin profile. My CZ527 has a small hollow on the tip of the firing pin which leaves small craters in even moderate loads, so not necessarily an issue. As pressures increase, I look for the shoulder of the primers squaring off, until eventually, they pancake flat. I would never shoot loads up to the point at which a stiff bolt lift was noticed as this is usually an indication of being over safe pressures. It only needs a warm day, especially with Viht powders, and trouble looms on the horizon. I prefer to look for signs of primer flattening accompanied by cratering (ie no flattening and only cratering may NOT be a sign of pressure) and any ejector marks on the case head. Both are clear warning signs and usually always occur prior to any stiff bolt lift with standard primers.

 

[hybridfiat]

My rifles are all set up with less than 2 thou headspace and tight firing pins.
The Savage Lever Action 243 is the only exception.
If I get flat primers and cratering it means HIGH pressures.

 

[the prowler]

Had a primer blow on a sako 75 17remington. Heavy rain that day, gun fired very oddly. Case ejected and primer was gone and primer pocket was badly damaged. Ammunition was always safe. So may be a result of rain getting in breech!?

 

[takbok]

Had a primer blow on a sako 75 17remington. Heavy rain that day, gun fired very oddly. Case ejected and primer was gone and primer pocket was badly damaged. Ammunition was always safe. So may be a result of rain getting in breech!?

I had the same thing happen with my Sako 75 6x45 - it was raining heavily and I'm sure the ammo got soaked resulting in blown primers.