Blown primers on 6.5 CM-Problem Solved on page 6!

[bomberodevil]

I'm doing some load development on a 6.5 CM Christensen Arms Mesa, with a 22" barrel. This rifle has approximately 300 rounds, and has been easy to develop loads for. I have developed loads for Nosler 140 AccuBond at 2734 fps with 41.2 grains of H4350, with 3-round groups at sub .400 moa, and SD of 6. I also have a load with Nosler 140 grain BT, 41.0 of H4350, .360 moa, an IMR 4350 load below .400 moa. All of these loads had zero pressure signs, and MV in the low to mid 2700 fps.

Today I try some load development with Hornady 143 ELD-X, H4350, Nosler brass, Federal 210 primers. I begin at 41.1 grains of powder, with intent of going to 41.8 in 0.10 increments, shooting for accuracy. Hodgdon site has 41.8 of H4350 as their max load.

At my first load at 41.1, I blow the primer. Thinking that was an fluke, I fire two more, both with blown primers. This is below my 140 grain AccuBond and BT loads that have zero pressure signs, and 0.7 grains below the Hodgdon site max loads. I pulled the rest of the loads and reloaded, starting at 40.3 grains of H4350. I can't believe that 41.1 grains of H4350 is over pressure. Any thoughts?

 

[Rosebud]

Is the 143ELD jammed into the lands. Longer bullet will do that and cause pressure spike. Hornadys max load is 41.5 for that bullet. Maybe start at 39 something and see . I usually don't start at near max . Never know what you're gun will do.

 

[bomberodevil]

Is the 143ELD jammed into the lands. Longer bullet will do that and cause pressure spike.

Good point. I forgot to mention, I take 8-10 measurements with the Hornady gauge and a fire-formed case from my rifle to measure the CBTO with every different bullet I use, and then start at .030" off the lands for hunting loads. I'll re-measure it this weekend, but my CBTO was 2.218", COAL at the lands was 2.876", and the COAL after backing out .030" was 2.846". I also trim every case to SAAMI prior to loading.

 

[Barrelnut]

Another issue might be that Nosler brass is thicker and therefore had less internal volume vs Hornady brass. This can raise pressures. Hodgdon site states that they use Hornady brass for their 6.5 CM loads, so you have to take that into account.

 

[BoomFlop]

You didn't start low and work up. Less than .5 grain from max from the bullet manufacturers published data is not a good place to start. Your AC load is over Nosler's max charge and probably enough information to back way off before using the same information for a different bullet.

Any change in component requires you to start low and work up, even if it is for a simple 10 shot pressure ladder.

Also, 1 blown primer is enough for me to call it quits much less 3.

Good luck,
Steve

 

[bomberodevil]

Another issue might be that Nosler brass is thicker and therefore had less internal volume vs Hornady brass. This can raise pressures. Hodgdon site states that they use Hornady brass for their 6.5 CM loads, so you have to take that into account.

Another great point. The majority of my loads have been with Hornady brass, but I have 50 pieces of Lapua brass for my AccuBond hunting loads, and some Nosler brass for the ELDX. That could account for some differences. I should just switch it all over to Lapua, and that's my plan as the Hornady and Nosler wear out.

 

[bomberodevil]

You didn't start low and work up. Less than .5 grain from max from the bullet manufacturers published data is not a good place to start. Your AC load is over Nosler's max charge and probably enough information to back way off before using the same information for a different bullet.

Any change in component requires you to start low and work up, even if it is for a simple 10 shot pressure ladder.

Also, 1 blown primer is enough for me to call it quits much less 3.

Good luck,
Steve

I didn't look up the Nosler load data since they don't have a 143 grain bullet. I looked up the Hodgdon data, since they use the exact bullet I was using, and the exact powder and primer I was using. I thought three out of four identical components was better than zero identical components. I started 0.7 grains below their max load, with plans to work up by small 0.1 grain increments.

It's possible that this is simply an overpressure situation and a lesson learn for me, but my staring load was below max and below what I've loaded in this rifle before with zero pressure signs. I'm thinking the brass might be the difference.

 

[gillettehunter]

Any chance you have a carbon ring? That can cause pressure to spike.
Bruce

 

[BoomFlop]

I didn't suggest that you looked at the Nosler data. I stated you used previous data with a Nosler bullet, which you are over max charge and just backed of a few tenths with a new bullet.

Once again, you haven't loaded this bullet with that set of components, so you need to start at minimum and work back up.

I'm not busting your chops, I want you to Be Safe!

Steve

 

[The Oregonian]

Always start low and work up if using a new component.

 

[DHBWA]

Nosler brass….Hint….

 

[436]

Did anyone say head space yet? and double check your scales

 

[Tidus56]

Another issue might be that Nosler brass is thicker and therefore had less internal volume vs Hornady brass. This can raise pressures. Hodgdon site states that they use Hornady brass for their 6.5 CM loads, so you have to take that into account.

This is my thoughts as well. Hornady has more internal volume than Nosler brass.

 

[Muddyboots]

By chance, have you checked your bolt face after 3 blown primers?