Hornady Amax factory ammo = cratered primers

[GarandThumb]

Took my rifle out for the first time. Main goal for today was just breaking in the barrel and testing functionality.

Fired wolf 107gr steel case, wolf 120 gold, ppu 120 and hornady 123 amax.

The hornady shot the tightest groups (all 1 moa or better) but the primers on the hornady ammo has noticeably raised craters on the primers. The wolf steel primers looked normal, the wolf 120s had an ever so slightly raised crater. No other pressure signs (ejector marking, flattened primers).

The eject pattern of everything was in the 3:00 to 4:30 zone.

Could this just be a soft primer cups on that factory ammo?

[JASmith]

Have you chambered and extracted a live cartridge to inspect for engraving marks on the nose?

Check the Wolf ammunition too.

Peak pressures get bumped up a few thousand PSI when the bullet is in contact with the land before discharge.

[GarandThumb]

Have you chambered and extracted a live cartridge to inspect for engraving marks on the nose?

Check the Wolf ammunition too.

Peak pressures get bumped up a few thousand PSI when the bullet is in contact with the land before discharge.

I'll have to check when I get more ammo but I don't think they are hitting the lands. I have the Hornady OAL gauge and tested with a number of bullets including nosler 123s and 140 A-Max and they could all be seated beyond mag length.

I took a closer look at the bolt and it looks like the firing pin hole is a good bit larger than a typical 556 bolt. How does your Grendel bolt compare to a 556/223 bolt?

[JASmith]

...I took a closer look at the bolt and it looks like the firing pin hole is a good bit larger than a typical 556 bolt. How does your Grendel bolt compare to a 556/223 bolt?

Can you post a picture of your bolt face so that some the more knowledgeable folks can look at it?

Thanks!

[Wheelhorse]

I'm thinking the cup on the Hornady primer is softer than the others and is flowing into a recess around your firing pin. As JASmith said, a good close up of the bolt face would help.

[LRRPF52]

I'll have to check when I get more ammo but I don't think they are hitting the lands. I have the Hornady OAL gauge and tested with a number of bullets including nosler 123s and 140 A-Max and they could all be seated beyond mag length.

I took a closer look at the bolt and it looks like the firing pin hole is a good bit larger than a typical 556 bolt. How does your Grendel bolt compare to a 556/223 bolt?

That's the likely issue right there. I just measured several Grendel bolts, and they are all at or under .060" firing pin hole diameter. A large firing pin hole will not support the primer, and you will see primer cup flow into the space. This is true on bolt guns as well.

[Savage Shooter]

I get the same "primer cup flow" on my Alex Arms Grendel and my Savage LRP in 6.5 Creedmoor. It happens with Hornady factory ammo with both guns and even at the lowest pressure loads when I am doing load work up, i.e., on 100% of all rounds fired. I have had to ignore this "traditional (although not absolutely reliable) pressure sign indicator in my load development. I have to look for other signs, such as the primer flattening and sticky bolt on my bolt gun - plus I always use a chrono to show me velocity spikes when doing load development. It still un-nerves me a bit to see it, but I have had to get used to it on those guns.

[Klem]

Primer pocket flow as in your photo is a symptom of too much gap between the diameter of the firing pin and firing pin hole. So, there is too much space and that circular peak is allowed to form.

You can fix this two ways - source a bolt with a smaller hole or source a larger diameter firing pin (if there is such a thing in an AR).

F Class bolt guns shooting 1000yd competition often need more pressure than SAAMI to get there with still plenty of stability. Putting more powder in than the SAAMI recommended peak pressure it safe enough with a quality barrel. To stop primer pocket flow/bleed that comes with higher pressures shooters can swap out the factory bolt for an after-market with narrower pin and finer gap between the pin and the firing pin hole. This is designed to give more support to the primer.

An example is PTG's choice between a standard 0.78" pin hole or a narrower 0.62" version for the Rem700. While there is more chance of piercing a primer with a narrower pin it is offset by the extra support to the base and the lesser gap for bleed. Shooters often use thicker cupped primers to help with this also.

If unchecked that sort of primer flow can lead to donut shaped disks breaking off every now and then and accumulating in your bolt to the point is causes soft strikes and no-strikes. Not a catastrophe but requires a decent clean-out of the bolt.

If it is a factory round then it should not be doing that. I reckon your firing pin hole diameter is too large.

[Wheelhorse]

Want to see some funky primers?
Look at some out of a 938 Sig.
I have two of them and both are the same. Sig says it's the way the area around the firing pin is made, and it's normal.

[GarandThumb]

Here are a couple of good photos. It wasn't until after I took these that could tell what was going on.

This first one:

556 bolt on left, Grendel in the middle, and new 556 bolt on the right. The hole definitely looks bigger on the grendel bolt:




Here is a close up of the grendel bolt. Looks like the hole is beveled:



Since it's beveled I dont think I have to worry about bits getting down into the bolt. It is interesting that the crater is far more pronounced with the hornady ammo vs the others so it could just be softer primer cups.

I'll know more once I start reloading but for now I dont think this is anything to worry about.

Thanks for the replies