6.5CM flat primers

[JCSC]

I’m shooting a new ruger american predator in 6.5 CM. I have shot factory hornady 129 american hunter and 140 bthp american whitetail. Both showed flat primers across the board. No cratering or ejector marks, but no rounded edges left and the spent primer consumes the majority of the primer pocket. Obviously a bit of flowing.

I ran 4 ea hornady 129gr IB handloads from 40.5-42.5 @ .5 grain increments. This was H4350 with CCI 200. I pulled the 42.5’s and found similar flat primers across the lot, as I progressed.

Is this just a common theme with this round? I neglected to take photos, but these are pancakes.

 

[forty_caliber]

This isn't something I would call normal for 6.5CM. I'm running a Ruger Hawkeye and have never had this issue. Does the Predator use the same M77 action?

.40

 

[Ruger 15151]

I have noticed even in my reloads that primers are more flattened when the cases are bumped back to factory spec. I think this is because the extra space in the chamber causes the case to slam back against the bolt face more than with a fire formed case that has only had the shoulder bumped back .001-.002.

Partially flat primers aren't necessarily a huge concern. Again, without pictures, its hard to say.

However, when I am developing a load and looking for pressure signs, I'm more concerned with heavy bolt lift or a shinny round ejector mark on the case head.

If you didn't notice either of these you should be fine, especially given the fact that its factory loaded ammo which is generally not at the top load range anyway.

 

[Demi-human]

A little bit on the large side chamber and a little on the short side sized cases can show flat primers at normal pressures.

The firing pin forces the case forward, the primer detonation pushes the primer back to the bolt face, then the case expands and takes up head space.
If there is a bit more space than usual it may flatten the primers more as they are mashed back flat with the case head.

Are your handloads at the minimum sizing capable by your dies?
You may be able to size them less.

 

[Ruger 15151]

OP said he is shooting Hornady factory Ammo.​

 

[jmr40]

Using primers to determine over pressure is highly unreliable.

 

[JCSC]

This isn't something I would call normal for 6.5CM. I'm running a Ruger Hawkeye and have never had this issue. Does the Predator use the same M77 action?

.40

Not sure as I am not familiar. It is a 3 lug bolt.

 

[JCSC]

A little bit on the large side chamber and a little on the short side sized cases can show flat primers at normal pressures.

The firing pin forces the case forward, the primer detonation pushes the primer back to the bolt face, then the case expands and takes up head space.
If there is a bit more space than usual it may flatten the primers more as they are mashed back flat with the case head.

Are your handloads at the minimum sizing capable by your dies?
You may be able to size them less.

My handloads were bumped back .003. When I did a measure on the fired cases against factory new, I did not see any excessive growth.

I also agree reading primers is a slippery slope, but I load 7 different calibers and have never had any this flat, so it was alarming.

 

[Blue68f100]

I run small rifle brass since it will take the pressure easier. Most factory ammo is overly sized so it will fit all guns. So it's possible the brass is getting slammed to the bolt face. But I don't see that as a big contributor to flattened and flowed primers. Does the factory ammo fall in and out of the chamber freely? With a bolt gun try to limit the shoulder reset to 0.001" to prolong brass life.

 

[Demi-human]

My handloads were bumped back .003. When I did a measure on the fired cases against factory new, I did not see any excessive growth.

I also agree reading primers is a slippery slope, but I load 7 different calibers and have never had any this flat, so it was alarming.

I would be too.

Are you sure the bullets aren’t into the lands?

Does the factory ammo fall in and out of the chamber freely?

This. A short throat could raise pressure.


Strange for sure. Hard to say, and a picture is worth a thousand words...

 

[NMachine]

I remember reading somewhere a couple of years back about problems with RAP rifles chambered in 6.5CM. There were many complaints about oversized chambers. People were even having problems with factory ammo and near split case heads.

 

[JCSC]

Interesting about the oversized chambers. I didn’t really see any significant growth on once fired brass. I checked the shoulder and it had pushed forward a couple thou. The diameters hadn’t changed much, aside from the neck.

I am running .030 off the lands.

I will have to see what I get with the next few rounds of reloads. I wanted to see if I could tighten up groups vs the factory 129 interlock (1-1/4 MOA) and I achieved that at the 41 gr load.

 

[JFrank]

I’m shooting a new ruger american predator in 6.5 CM. I have shot factory hornady 129 american hunter and 140 bthp american whitetail. Both showed flat primers across the board. No cratering or ejector marks, but no rounded edges left and the spent primer consumes the majority of the primer pocket. Obviously a bit of flowing.

I ran 4 ea hornady 129gr IB handloads from 40.5-42.5 @ .5 grain increments. This was H4350 with CCI 200. I pulled the 42.5’s and found similar flat primers across the lot, as I progressed.

Is this just a common theme with this round? I neglected to take photos, but these are pancakes.

I’ve seen this before with excessive headspace, factory Ammo is what it is..

Moving forward ensure you’re not grossly over sizing the brass, perhaps back the die out a quarter turn, I use a comparator to measure before and after.
After the course increments are close
Use smaller increments when fine testing powder.
Maybe try a different primer also

 

[JCSC]

I use the same comparator. Anyone on here that knows the reading they get on a fired 6.5 CM with the .400 insert?

 

[JCSC]

I get 1.535 on new hornady and I am right there with sized brass as well. I had my fired stuff about .003/.004 longer.

 

[JFrank]

I get 1.535 on new hornady and I am right there with sized brass as well. I had my fired stuff about .003/.004 longer.

Ahh
I try not to set a shoulder back until the case is hard to chamber, at that point it should be fully fire formed and ready to bump about 2-3 thousand

 

[JCSC]

Thank you for the tip. I did not know it took multiple firings to fully form the brass.