Primer craters and piercing

Reloading info for the 5.7x28mm

Moderator: Grantness

Post Reply
trevorstuart24
Junior Member
Posts: 21
Joined: 31 Mar 2022, 13:48

Primer craters and piercing

Post by trevorstuart24 » 31 Mar 2022, 14:11

I’m having an issue with my reloads which are resized on Redding dies, trimmed to 1.132, seated with 40gr v-max to OAL 1.582, Cci 400, and charged with 5.8gr of true blue.

The primer strikes are cratering and occasionally piercing the primer. When they pierce, a small bit of primer remains in the firing pin hole and causes a light primer strike on the next round until it is cleared. This does not happen with factory ammo(SS197), although even factory ammo shows a small amount of cratering. I initially shot about 200 rounds of reloads before getting this primer blanking issue. Now it happens about 1/30 rounds. The primer cratering has been there the entire time.

I’ve been as meticulous as possible with the reloading process and I’m pretty certain they are all 5.8gr charges. I’ve tried using the heavier EA recoil spring as well as the stock and the results are the same. Firing pin seems undamaged and protrudes .06in from bolt face. Bolt face seems to have some slight markings the size of a primer circle.

Is this a sign the shoulder is bumped too much causing a gap between the case head and bolt face? My stock ammo has a slightly longer headspace although the resized cases still meet the case gauge minimum specs… just barely. Any method to determine the perfect sized shell for a given guns headspace other than the case gauge?

Or is this a sign I should be crimping? I haven’t noticed any movement of bullet seating but I do see a fine mist of what may be unburned gunpowder when shooting the reloads.

I’m including pics to better understand. From left to right: SS197, reload with crater, reload with piercing.

Image Image Image Image Image Image Image Image

trevorstuart24
Junior Member
Posts: 21
Joined: 31 Mar 2022, 13:48

Re: Primer craters and piercing

Post by trevorstuart24 » 01 Apr 2022, 10:08

So I measured a stock case unfired sitting in the chamber from the start of the chamber to the head of the case. Distance .145 in. My reloaded case distance .125. Measuring the distance from chamber of barrel unloaded to bolt face .165. So my stock bullets are floating in the chamber by .02in and reloads are floating by .04in. I’m thinking this could explain the cratering and blanking.

How close do you think I should headspace my cartridges? Just imagining how things are working I would think if I erred on the side of the cartridge shoulder to head distance being longer than the gun headspace I would still be ok since the chamber would have to extend out to accommodate the longer cartridge(shoulder to head). Or should I aim to be slightly under that gap from head to bolt face?

User avatar
panzermk2
Forum Supporter
Posts: 12380
Joined: 19 Aug 2008, 15:51
Location: Pr. CEO Elite Ammunition
Contact:

Re: Primer craters and piercing

Post by panzermk2 » 01 Apr 2022, 11:00

Nope, has nothing to do with head spacing. Fun fact the chamber doe not match up perfectly like a 45ACP or 9mm.

Your OAL target should be min 1.585. MIN since there are variances with bullet AOL do too the V Max poly tip.

Now as long as you have NOT removed the coating on the brass. Also for a fact you are using CCI SR 400 Primers

The bullets being seated a little to deep and the batch of TB you have is hot. Powder varies from lot to lot.

That's it. Initial pressure spike is pushing the primer onto the still extend firing pin. This can also happen if you have swaged your primer pockets to much allowing your primers to move to much. Normally if you are using any 5.7 brass you just want to kiss the rim of the pocket, if it's crimped brass just enough to remove the old crimp.

DO NOT full swage the primer pocket.
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
Image

trevorstuart24
Junior Member
Posts: 21
Joined: 31 Mar 2022, 13:48

Re: Primer craters and piercing

Post by trevorstuart24 » 01 Apr 2022, 12:14

Thanks for the response Jay. Why do you think my stock rounds are also showing cratering as well? Seems odd for an underpowered round to show pressure signs. Wouldn’t increasing my cartridge headspace to more closely match the gun both reduce cratering, deny too much primer movement, and improve accuracy? Say aiming for just below the case gauge max instead of sitting just above the case gauge min?

I’m attaching a photo of what initially led me to believe I’ve got a headspace or firing pin spring issue:
Image

Thanks for your expertise.

User avatar
panzermk2
Forum Supporter
Posts: 12380
Joined: 19 Aug 2008, 15:51
Location: Pr. CEO Elite Ammunition
Contact:

Re: Primer craters and piercing

Post by panzermk2 » 04 Apr 2022, 07:58

That is for normal cartridges, and even then not always true.

The 5.7 operates completely different from any standard cartridge. You have to keep in mind even the low power SS197 is over 40k psi chamber pressure.
Much higher than standard hand gun cartridges. The initial pressure spike for even SS197 is about 70k psi it lasts about 2 milliseconds. Increasing the head space will actually give you 2 initial pressure spikes. The last thing you want to do with the 5.7 is increase the bullet jump.



Increasing the head space will make it worse and in fact cause your firing pin to get trapped into the primer jamming your gun up and neck separations.

You can't apply standard handgun cartridge concepts to the 5.7.

The flattening, flowing and cratering for the 5.7 is normal and part of the operation of the cartridge. This is why for full power 5.7 you have to use small rifle primers
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
Image

trevorstuart24
Junior Member
Posts: 21
Joined: 31 Mar 2022, 13:48

Re: Primer craters and piercing

Post by trevorstuart24 » 04 Apr 2022, 08:54

So when I load to 1.585, chamber a round, and eject it without firing, I notice horizontal marking on the bullet ogive. I notice this up until an OAL of 1.57. Wouldn’t that indicate I’m chambering my bullet just past the lands, and risking increased pressures from that?

I notice this ogive marking on the ss197 as well. But not on ss195 which is actually longer, just under 1.59, but a more narrow bullet.

I can replicate this marking on the ogive by just placing a bullet in a disassembled barrel and putting some pressure while spinning the bullet so it’s not an extraction or feed ramp mark. And my barrel is sparkling clean so it’s not a carbon buildup scratching it.

Pics(the marking is just below where the brass meets the bullet. Not the higher up mark made from seating the bullet.):

Image
Image

User avatar
panzermk2
Forum Supporter
Posts: 12380
Joined: 19 Aug 2008, 15:51
Location: Pr. CEO Elite Ammunition
Contact:

Re: Primer craters and piercing

Post by panzermk2 » 05 Apr 2022, 13:18

1) Spec for the round is 1.590. With the advent of the new style re enforced magazines and the rib in the front you need to load to 1.585 MOAL. If you load to MOAL of 1.590 some bullet ogives will jam against the rib. I have loaded rounds up to 1.60 and had to manually feed them in and not had any issue.

2) The chamber does not match up perfectly with the round. Again not like normal cartridges.

3) You're not hitting rifling since the 5.7 uses progressive rifling and also non standard depths and heights of the lands and grooves.

4) Again, even IF it was hitting the rifling that is not a bad thing. With the 5.7 since bullet jump is bad.
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
Image

trevorstuart24
Junior Member
Posts: 21
Joined: 31 Mar 2022, 13:48

Re: Primer craters and piercing

Post by trevorstuart24 » 05 Apr 2022, 13:50

when you say fn uses progressive rifling do you mean that it's depth and/or angle is progressive or the twist rate? either way some rifling begins right after the throat right?

i understand how a large bullet jump would be bad but i'm under the impression that a very small bullet jump to no bullet jump is ideal. if loading a bullet past the lands, i am placing a large amount of pressure on the bullet(which i can see in the deformation of the copper) and this creates a likelihood of bullet set back. that can't be good. even with a solid crimp it seems like an unnecessary risk.

i know you don't believe i'm actually hitting the lands but humor this hypothetical: which would you prefer, going .01 past the lands or jumping .01?

User avatar
panzermk2
Forum Supporter
Posts: 12380
Joined: 19 Aug 2008, 15:51
Location: Pr. CEO Elite Ammunition
Contact:

Re: Primer craters and piercing

Post by panzermk2 » 06 Apr 2022, 10:59

Progressive twist

And I am not sure what you are seeing but 40gr Vmax bullets loaded to AOl of 1.595 won't hit the rifling.
Jay Wolf
Pr. Elite Ammunition

"Engineers, the oompa-loompas of science!"

Be'ein Tachbulot Yipol Am Veteshua Berov Yoetz
Image

trevorstuart24
Junior Member
Posts: 21
Joined: 31 Mar 2022, 13:48

Re: Primer craters and piercing

Post by trevorstuart24 » 08 Apr 2022, 06:06

You were correct in that my true blue is likely a bit hot. I got a chronograph and comparing others load data I could see a difference in velocities. Thanks for pointing that out.

I have measured and determined my OAL to hit the rifling at 1.5735. This is using a case shoulder sized to the chamber min length level(B) of the Sheridan case gauge and a 40gr v-max. I suspect my barrel chamber was reamed slightly longer than others but I’ve read that it isn’t unheard of to find FN chambers reamed slightly larger to ensure fit of ammunition.

If anyone is interested in determining their own seating depth I recommend using a fired case with a new bullet. Put some loctite on the inside neck, hand seat the bullet super long, push the cased bullet into the barrel as far as it will go, wait 20 minutes, pull it out, and measure your OAL. Subtract the difference in shoulder from your fired case and unfired sized case. Subtract this difference from your measured OAL.

I will be testing accuracy at an OAL of 1.573 +/- .01 to see what my gun/bullet likes.

Post Reply

Who is online

Users browsing this forum: No registered users and 8 guests