HELP; pierced primers 6.5 CM

[Timetoshoot]

Ive been struggling to find a load that shoots under .5 MOA in a custom built 6.5 CM. After much load development and never finding a repeatable accuracy node with 140 VLD I switched to 140 Hybrid and settled on Horanday brass, Win primers, 41.7 H4350 at 2.848 COAL this is a jump of .050. This load will shoot best groups around .45 but averages .65. I used up the Win primers I had and decided to try Fed gm210m in an effort to tighten up the groups a bit. 41.7 is not a hot load and my previous pressure tests did not show pressure signs until 43.2. so I loaded up the exact some load with the new primers, I also loaded some VLDs to see if they would shoot any better.

In this pic of my brass, columns represent strings fired in sequence from left to right, with the first shot in string at the top.

far right; first three shots 140 hybrid with Fed primers, .27 one hole group at 100
2nd from right;140 vld 1st shot fine, second shot pierced primer, .9 group at 100
3rd from right; 5rounds 140 vld failure to fire
4th from right; 2 rounds 140 hybrid pierced primer, expanded the first group from .27 to .32
far left; 5 rounds original load 140 hybrid shot to .65 moa primers normal .63 group at 100

I pulled down the rounds that would not ignite and they all weighed 41.65 to 41.75.
Im at a bit of a loss and not sure what to do next…..

 

[KYpatriot]

An oversize firing pin hole can cause this, you can have it bushed, but before we get to that tell us more about the failures to fire.

 

[BC 6.8]

I haven't shot very many of the Berger VLDs, but I shoot the 140 AMAX and 142 SMK out of my Creedmoor. Your charge weight seems very reasonable, and I also use Fed 210 primers without any issues. The one thing I notice is the heavy cratering on the Federal primers. I would recommend doing another OCW or load work up with the Federal primers. My question would be what kind of action are you using? The firing pin hole may need to be bushed to prevent the primer issues. Also, I don't know how many pierced primers you have had, but the firing pin may be damaged. I would send the bolt off to GreTan Rifles since he is one of the best at installing bushings in bolts and will also turn the firing pin.

Gre'-Tan Rifles

The rounds that did not fire are concerning to me. Do you know how much you are setting back the shoulder of the case when you resize? If the cases are sized down too much you can have failures to fire and a host of other issues. I would measure the fired cases and the cases that did not fire with a comparator to measure the amount of shoulder set back. I try to set back the shoulders only 0.001-0.002" to maximize case life and prevent other issues.

If you have a local gunsmith that you trust, I would take the measurements mentioned above and get him to inspect the bolt and firing pin.

 

[Timetoshoot]

More info
The only pierced primers I've experienced are shown in picture.
Gun is remington 700 rechambered, new barrel, and blueprinted by well respected gunsmith from the hide. 900 rounds prior to rebuild, 650 rounds after rebuild. Using whidden dies, full length resize bump shoulder .001.
Not much to say about failures to fire except that they did not go boom.

 

[former naval person]

Two thoughts on the FTF...check inside the bolt. I've see debris cushion the firing pin blow. You do have a good bit of cratering around the firing pin identation. Typical of Remington bolts. Feds can be a bit softer in my experience. That may allow your slightly large firing pin hole to blank. If you have some debris in the bolt, such as firing debris from the pieced primer, that could cushion the blow enough to cause a temporary FTF, then wear away allowing firing to recommence.

 

[Timetoshoot]

Turns out Greg's shop is 50miles away, and he answered email on a Sunday.

Hoping bolt work cures it.