Some interesting reading for new reloaders

[Gaznazdiak]

Those who have been reloading for some time are probably aware of the issues covered in the article below, but for others like myself who are still learning, I hope it is as informative as I found it to be.

http://www.primalrights.com/library/art ... g-pressure

[No1Mk3]

Nice find Gaznazdiak, always good to read articles like this even after 45 years of reloading, it helps to reinforce the message. For new shooters, not just reloaders, it should be compulsory reading. We had an incident at Little River where a young fellow wore the bolt from a Blazer R8 in his face due to not knowing how to read pressure signs and using "some one else's reloads". Articles like this can save a life, and it is good to post them for all to read, Cheers.

[Daddybang]

Thanks for takin the time to post.
The "rifle" in the case was a big eye opener for someone who's never seen a truly catastrophic failure before

[Gwion]

Half way through it and starting to nod off!

Good article, though. Think i'll share it with club members.

[Gaznazdiak]

@no1MK3
My reading of it was rather timely. I had been wondering why a batch of 68gn match I'd just loaded were flying high and was thinking of all sorts of reasons, none of them being pressure.
After reading the article I inspected the empties and they all had cratered the primers. On inspecting some others I'd not got around to prepping, I discovered 24 more with the same issue.
It obviously was borderline because there was no flattening and the rims of the craters weren't sharp, but it was a disturbing wake-up to my complacent ignorance of how subtly something be over-stressing components.
Going to have to get a puller now, but better that than a glass eye.

[sungazer]

A really good article thanks for posting. The cleaning was also an interesting read.

[Gaznazdiak]

@sungazer
Yes it was, I would never have considered putting something like CLR anywhere on my guns, let alone down the bore.

[burek]

I'm at a reloading curious stage and appreciate the link mate. Very good read.

[straightshooter]

A few comments on the article before I finish breakfast.
The blown up M1A is obviously as a result of a barrel obstruction as evidenced by the longitudinal split in the barrel. No amount of care in handloads would save you from that one.
The bolt with the lugs sheared off was unlikely due to an actual rifle blow up. It looks like a M93 or M96 bolt and the receiver would have exploded into orbit long before the lugs failed. There would also be evidence of brass welded to the bolt face. More likely this bolt was a test piece where the lugs were stressed to tensile failure in a suitable press.
The writer gives a poor even verging on incorrect explanation of the mechanism of case head separation.
The writer confuses 'primer piercing' and 'primer blanking' and does not give an accurate description of the mechanism for either event thus obscuring the true cause of cratering.
There is more but it is nearly time to go to work.
The upshot of the article is correct, that we should at all costs avoid excessive pressures or for that matter repeated mild over pressures and I don't think that a few technical inaccuracies should detract from that message.

[Gaznazdiak]

"The writer confuses 'primer piercing' and 'primer blanking' and does not give an accurate description of the mechanism for either event thus obscuring the true cause of cratering."

Please enlighten us then.

[straightshooter]

Piercing a primer is exactly as the term suggests. The firing pin passes through the primer cup making a hole by displacing metal without detaching any of it from the primer cup.
Generally a primer might be pierced when the firing pin tip is poorly shaped, ie; it isn't a smooth hemisphere. True primer piercing is in fact quite rare.

Blanking is a metal working term referring to processes where a "coin" or cup is punched out of suitable material.
The first indication that the blanking process is "trying" to happen is primer cratering. This is usually blamed on firing pin clearance in the bolthead but as we soon shall see it has little to do with it.
Cratering can happen at quite mild pressures and can proceed to blanking at higher but still acceptable pressures.
In other circumstances (ie; in another action or with changes in the same action) there might be no evidence of cratering at even insane pressures.
Why is this the case?
First consider all the firing events where there is no evidence of cratering.
The trigger releases the striker assembly which moves forward and the firing pin indents the primer with sufficient force and to a sufficient depth to ignite the primer. Most importantly the striker assembly has not expended all it's energy thus far in the process, it must still retain more than enough energy to fully resist the force of the firing process without being pushed back into the bolt.
If the firing pin is pushed back whatsoever into the bolt it will then vacate space for the primer cup to extrude into the firing pin hole in the bolt. This raised extrusion of the primer cup with the nice hemispherical indentation of the firing pin is what you see as cratering
Depending on the degree the firing pin is pushed back you will see effects ranging from slight cratering to heavy cratering to blanking. All is dependant on the ductility of the primer cup.
What are some of the reasons for this effect?
Marginal or inadequate striker assembly design.
Loss of mainspring tension.
Internal friction of the striker assembly in the bolt.
Firing pin rubbing inside the bolt head (quite common).
Insufficient firing pin protrusion.
Generally it's a combination of some or all of the above.

[Gaznazdiak]

@straightshooter
Perhaps you can help me diagnose a cratering issue over which I am currently scratching my head.
I have loaded some Hornady 68gn Match BTHP with 25.5gn of 2206H with a 5/1000in jump. On working up the load this gave the smallest groups at 100m.
I hadn't checked for pressure signs until after reading Greg Dykstra's article so I hadn't seen any sign on the other loads in the work up. After the reading article I started checking, something I now know I should have been doing from the start, and noticed that the Hornady 68gn Match were cratering.
I lowered the load by .5gn, cratering.
I lowered it again by .5gn, still cratering.
As the minimum load of 24gn was not accurate enough for my needs I haven't bothered testing that.
As I also load Nosler 70gn BTHP RDF and Berger BTHP VLD target projectiles @25gn, and Nosler 50gn Ballistic Tip @27gn with no pressure signs whatsoever, I am at a loss as to what could be causing this.
If you, or anyone else reading this, can offer any constructive suggestions I would by grateful.
Perhaps my rifle just doesn't like the Hornady 68's, even though their 35gn V-Max are giving great accuracy with no problems.

[sungazer]

Please dont take this the wrong way I am only saying this because of my own experiences. I would have a good look at your measurements and techniques in making the measurements when it comes to seating depth. Both establishing the 0 on the lands point and then backing up from there. I found it very hard to measure to the lands and it has taken me a year of trying different methods and improving my skill in some of those methods. I found it very easy to make mistakes.
When you are so close to the lands there is little room for error both on your measurements side and in the bullets dimensions. What I mean by that is when so close to the lands I found that there was a big difference in POI from a bullet that touches the lands and one that doesn't. This some touching and one not can translate to what is ultimately what looks like flyers but is really caused by the seating depth. Better to know you have them jammed or well off not in the zone of uncertainty in measurement. That uncertainty in measurement has multiple sources like I am trying badly to explain. Bullet dimension variances, Measurement of the 0 point of lands, Measurement of distance from the lands, and measurement variance in the seating die. Do you measure every on after seating? it is a good exercise to measure 20 and see what the tolerance is.
Anyway I hope you get my drift through all that.
PS the Nosler are on the grapevine need to be measured and batched bullets.

[Gaznazdiak]

@sungazer
When still as low on the learning curve as I am, there will never be offence taken at advice given constructively.
As I am still building my "kit" I had someone with a shed load of instruments, and decades as a military weapons instructor and target shooter, take the measurements for me for each projectile I use and calculate best OCL for each given ogive.
As I am using a Lee die set that does not have a calibrated seating die I have been measuring every fifth round to check OCL and they have been consistent.
One thing I forgot to mention in my above question, when I had tried lowering the load by 1gn, I tried seating one more round, 1mm deeper with the same load and the cratering was less pronounced but still visible with a loupe, where previously it was obvious by touch and unaided sight.
I must admit, even though I batch both my brass and my projectiles by weight it has never occurred to me, embarrassingly, that the extra weight of the pills would be as a result of extra length.
I am currently having one of those DUHH moments.
This could also explain why my self inflation at being able to give Tony Rabbit the good news at 400m turns to embarrassed frustration at large groups when shooting at the rifle range from 500 to 900m.
Seems I'm going to have to do a lot more reading a some more spending.
Thanks for the advice.