Max Load Gone Wrong - Blown Out Primer

[azsixshooter]

I believe it is the Speer Manual that has two distinct sections separating the loads that are safe for the older guns from the loads that are set up for the modern actions.

I am certainly taking notes on all of this and can't thank you all enough for your help and advice. So far I have this:

-Use a chrony to safety-check actual velocity against published velocity. Don't use the data to ever exceed published loads, only to check that real velocity is matching published velocity as it should assuming the same length test barrels;

-Use the chrony to follow charge-to-velocity ratio...once the velocity stops increasing consistently with each grain or so of powder added then you've hit the wall and further increases in powder will increase pressure without appreciably increasing velocity;

-Increase powder .5 grains at a time until any sign of excess pressure is seen. At that point, stop shooting and consider the max load to be 6% less;

-Measure the case head before and after firing a questionable round. If the pressure is acceptable it shouldn't expand more than .0050";

The one I'm a little confused with though is the formula for reducing the load. What if it takes you below the published minimum? Isn't that dangerous too? Even in the sticky on this forum for posting extra heavy loads the moderator warns about under published power loads:

'As a forum moderator, I feel very strongly about this, and will not hesitate to completely delete, or heavily edit any post which I believe violates the spirit of this procedure.
There are also some real hazards to going BELOW certain minimums. Some loads with certain powders may give badly erratic pressures at very low load density. The above cautions should be observed when writing up loads UNDER manufacturers' posted MINIMUMS."

So if I followed the post above:

"The old rule of thumb, used by Speer before bullet companies could afford pressure guns, was that at the FIRST sign of excess pressure, stop and reduce the load by 6%. Don't use the load that gave ONE sign of excess pressure, definitely don't increase it, REDUCE it. Your individual gun-component system's maximum load under that technique would be 44.2 grains."

that would put me pretty far below the most current minimum load published by the manufacturer of the bullet that I'm loading behind, which is 46.5 grains of this powder.

Believe me, I'm not trying to be cocky or anything, I just want to sort out anything that I'm not tracking and make sure I understand it properly before I proceed. How do I know which book has the safest minimum to go by? They seem to vary pretty widely in this case.

I'm really curious how it worked out:

(starting load) 46.5 grains - No visible problems
47 grains - faint ejector slot imprint
47.5 grains - no visible problems
48 grains - no visible problems
48.5 grains - no visible problems
49 grains - no visible problems
49.5 grains - no visible problems
50 grains - visible problem with primer (that I should have seen and stopped)
50.5 grains - big problem

Maybe the abnormality at 47 grains was due to the recalled powder, if indeed I did get a can of the recalled lot. The store told me to follow the instructions on the website too and call Accurate if I have the affected lot. I'll be interested in hearing what they have to say if it is the case.

Also, I'm not planning to reload any of this batch of cases again, but I'm saving them for now to see if I can have someone more experienced take a look at them and maybe point out something I might have missed other than the signs I caught. Not that I'm planning on pushing maximums anytime soon, I'm just interested in learning the best way possible to work up loads so that I can do it safely.

[Wildalaska]

Go get some VN 560 and Norma or Lapua cases. Start with 46, your sweet spot will be with 48-50, OAL 3.100

Wildoal3.10Alaska TM

[azsixshooter]

Yes, I'm going to order some Norma or Lapua cases for sure. I meant to do that anyway as soon as I could afford some.

I'm going bowhunting this week up above the Grand Canyon so I won't be doing any loading until I get back. I will probably just use the other Federal cases I have saved up with the 46.5 minimum loads if I can still use this powder. I shot 20 of those with no trouble and had some okay groups that I can probably improve upon by shooting from a real bench rather than my tailgate.

[azsixshooter]

I checked the powder can when I got home and it's actually not the recalled lot number. There's a sticker on the bottom with a number like 010107. I guess that is the lot number, didn't see anything else that could be it anywhere else.

It's good to know that the first can of powder I ever bought wasn't a bunk, recalled lot!

I'm going to use the rest of it with some other once-fired Federal cases and 120 grain NBT's behind the mild and proven 46.5 grain loads. I think next I'll get some Nosler 130 grain Accubonds, Lapua or Norma cases, and VN or maybe Varget powder and see how my rifle likes that combination.

Thanks again everybody for all the help!

[Slamfire]

So basically, I'm just wondering where I stand now? Is something like this common enough and not anything to really worry about? Or should I have my rifle looked at by a gunsmith, maybe have the headspace checked or something?

Maybe I missed a post addressing this.

Blown primers happen. Leaking primers happen. We are all fortunate that rifle actions are made from steel, and cases are made from brass.

American practice was to use quarter hard cartridge brass. This typically has a yield strength of 40,000 psia. The maximum tensile strength is will be in the range of 49 to 59 Kpsia. http://www.meadmetals.com/brass.htm#

4140 steel is at least double or triple in yield and ultimate.

So, unless your action is made from really poor materials, has a poor heat treatment, the steels in your action have not stretched due to your blown primer.

However, if you ever burst a case head, the total load on your steel parts goes way up, because that 50,000 or 60,000 lbs of operating pressure gets spread across a larger surface area.

That's when someone should gage the rifle for headspace. Which may or may have changed. After that, maybe a magna flux inspection. I am not an expert on non destructive tests, maybe someone can suggest a test or two.

The most common damage due to blown or leaking primers is dishing of the firing pin tip, etching of the bolt face. Neither is good. But it will take more than one before the firing pin tip needs to be refaced. I really don't know if the bolt face ever needs to be resurfaced due to primer etch. I have some pretty bad etching on one bolt, I guess if it is bad enough that it totally eats through the firing pin channel, then I will have to do something.

If you ever blow a barrel, crack a lug, you need to be very cautious about reuse.

[HiBC]

First of all,I want to confess I have danced on the edge with pressures before.
When I built my .257 Ackley,I was chronographing 3355 with a 100 gr bullet.After I used up that 8 lbs of powder,I changed to a 115 gr bullet,and,somehow decided I wanted the barrel to last a bit longer,and I thought about margin of error and I have backed off.
Lets imagine you have a load 1/2 grain under extruded primers.You are down to twenty rounds,and you buy a new can of powder.Murphy's Law decides you just bought some bad high pressure recall powder.You don't have any margin.You go to a prairie dog town,dogs are up,and you get the barrel hot with the old ammo.Grab a new box of ammo with bad powder and hand it to THE KID.(Murphy's Law)The round is sitting in a 150 degree chamber while he looks for a dog.

We need some safety margin in our loads.

Something about my beard turning white tells me that early 1900's battle rifle rounds already found the sweet spot.We think this arbitrary units 3000 fps is something magic.
Really,2700 fps or so makes a lot of sense.Bullets are still jacketed lead.They are more dependable at 2700.We ruin less meat.The barrels last lifetimes.
Trajectory is perfect for sensible hunting ranges.That quickntwist 6.5 bbl was made for long bullets.A 140 Nos partition has about the same BC as the .308 match /sniper rounds.(.490) So all the scope reticles like a TDS or B+C ,etc will work well.But,that is just how In see it.It is your rifle,enjoy it your way.