Surprise cratered primers !! (long post)

[Tsonka]

I have a concern with surprise cratered and split primers!!

Round info:
6mm Creedmoore
2nd gen RPR with a 26in LRI Barrel
Berger 105gr Hybrid bullet
H4350 powder — not a new container, probably shot 50 rounds worth with no concerns.
Lapua brass on second firing
296 rounds through this set up with no previous concerns

2 changes which were just made in my round:

1. I recently ran out of the Federal Match primers, could not find any small rifle primers and came up with a box of Federal Bench Rest primers of unknown age
2. I purchased an expander mandrel and went from full length sizing to neck size only then using the mandrel for an expected .001 neck tension.

When seating the primers using my Frankford Armory hand primer tool. They felt normal when seating. I typically shoot Federal Match AR primers which is what my preferred store stock’s. In the Lapua brass I have found they like to extend just a touch so my muscle memory is to run my finger over the primer to verify its flush. I noted these primers were recessed just a touch. Not an alarming amount, you would have had to directly looked at it to see it, but there was negative flushness.

I ran a powder charge chrono ladder to check for any change in my velocity node.
My chrono results were as expected, no change in node. However I had cratered and split primers!

Chrono results (MagnetoSpeed V3)

39.2 = 2990
39.4 = 3017
39.6 = 3026
39.8 = 3053
40.0 = 3062
40.2 = 3075
40.4 = 3091
40.6 = 3095
40.8 = 3125
41.0 = 3142
41.2 = 3161
41.4 = 3180
— Stoped due to primer concern

I am confident on my powder charge. I have both a ChargeMaster and Hornady scale. When I shoot a ladder I check the charge on both. The Hornady likes to read a bit lighter than the RCBS and do the +/- .1 flip flopping when the RCBS is stable. If I get them both reading the same I call it good.

Bullet seating depth is the same as it has been .023 off the lands.

Bolt feel was normal

Bolt face was clean after shooting

No abnormal bullet impact’s on paper

All else was normal.

Now for picture’s


The primers

This is 40.2 - 40.8gr H4350

Same but looking down

This is 39.8 and 40.0gr H4350 looking down (my standard load is 39.8)

I am expecting that the primers have soft metal cups?
Providing my pressure are not high, are they safe to my rifle to shoot?

 

[Average guy]

I would bet that the cratering is from a softer or thinner cup on the bench rest primers. The ar primer is a tougher cup by design for auto loading rifles. What’s your location

 

[Tsonka]

Wichita Kansas

 

[Average guy]

Wichita Kansas

Going to say if you were close to Wyoming I could maybe help your primer situation.

 

[TRG65]

I've shot several thousand small rifle primers in my RPR without an issue shooting 6.5x47. However, I've heard I'm one of the lucky ones and that many RPRs need to have the firing pin turned and the bolt bushed like the Rem 700. Your primers look exactly like my SRPs when I use a Rem 700 before it gets sent to GreTan. I also generally try to use the CCI 41s because they help as well. But it looks like you were able to get away with it using the AR primers, but the softer cups are showing the need for firing pin bushing.

 

[Tsonka]

Thanks

I am confident I am not over pressure, Ill take responsibility for that statement. Im even ok with cratered primers as long as I know why and are expecting them.

My concern is damage to my firearm

 

[Tsonka]

TRG making note of your suggestion

Im almost 1800 rounds into this rifle, total original and a rebarrel. Up until now I have only reloaded with AR primers

However. With the factory barrel, I often shot Hornady Match factory loads and had normal primer impact. This is my first ever cratered primers

 

[TRG65]

Tsonka, If memory serves the factory Hornady match 6mm Creedmoor (I'm thinking about getting a barrel in this but haven't yet) are like the 6.5mm Creedmoor and use LR primers. It's not an issue with the LR, it is an issue that shows up when you use a SRP in a rifle that has a firing pin and firing pin hole that is set up for "normal" 308/LRP dimensions. For instance, my son's Bergara, which is a Rem 700 clone worked just fine with Hornady 6.5 mm Creedmoor factory, and Federal and several other all LRPs. The LRP reloads were fine as well. I got some Lapua SRP and in my first tests got all craters and even one pierced primer. Sent the bolt away to GreTan, and the problem went away. Now that rifle gets a steady diet of SRP with no issue. The firing pin size/bushing issue is one reason I've not run anything but LRP brass in my 6.5 Creedmoor AR10.

 

[Tsonka]

TRG after researching, I think you are correct, that’s what my issue is. Thanks for the reply

 

[MCHOG]

I purchased an expander mandrel and went from full length sizing to neck size only then using the mandrel for an expected .001 neck tension.

This is unrelated to your question, but you shouldn't trade full length sizing for mandrel neck sizing. Although dies come packaged to neck and full-length size at the same time, they serve different purposes. Just take the stem out of the full length sizing die, run your cases through it, and then use the mandrel. You'll need to get a universal depriming die also, but they are inexpensive.