Tell me what happened - Ladder Test

[Lemonaid]

Completely agree Klem.

[SCJim]

when I am load testing and I see the velocity curve beginning to flatten or even decrease with increased powder it is a big flashing red light that the pressure is beginning to expand the case rather than pushing the bullet faster. It is simply not a good idea to be doing .5 increments at the upper end of a load test with a powder that is notorious for sudden pressure spikes at the top end of the load.

[keystone183]

Key,

I don't think you can gloss over the headspace measurements in your Post #17. The difference between fired and unfired exceeds SAAMI spec for two of those cases. It only takes one and a hot load to pop like a balloon in the chamber.

28/8208 is a hot load but what happened in your situation is catastrophic; the case split and the bolt broke, on the first firing of a new case. Yes, it's a hot load but if the case is supported by the breech (with proper headspace) then a hot load will not always split the case, it will just break the bolt. And hot loads don't always break the bolt on the first firing. Like hitting it with a hammer it might take 100 or even 1,000 shots to eventually break that bolt.

Are you sure this friend of yours did not run those new cases through a sizing die before loading? I say this because it is normal to size cases for the first firing to guarantee the correct neck tension - I do this so I wouldn't be surprised if your experienced friend did. If the sizing die was screwed in too far those new cases will be even shorter and that means more headspace, so more chance of splitting. Hot loads make that even more likely.

Regardless, I think we've established that you shouldn't be loading 28/8208 behind a 123ELD, even if your cases are a tight fit in the breech. As for being able to predict this with how the velocities are nice and evenly spaced as they get faster, you are fighting the point. Why didn't my chono warn me? Your Chrono is not going to warn you every time that something bad is about to happen. The pressure can just build up nice and evenly until something breaks.

As for loads on this forum - I find them on average, hot. That means others are loading on the raggedy edge and breaking guns. No doubt there are guys who post their loads but then break something down the track and don't report it on the Forum. Maybe because they are embarrassed or don't care to warn others. It's not good news and they don't want to be associated with it. For every report of a broken bolt there are probably three more that go unreported. So, I would be careful taking loads on the forum at face value.

I don't use 8208 for bullets 120 or over and in your shoes with the ELD would not load over 27gns/8208. The extra 50fps is not worth it. If you are loading cases with more than .017" of headspace then even a mild load will split them, and then hammer that bolt with unconstrained pressure.

Consider also that pressure on that bolt was not even. I have seen partial case separations where the case did not neatly separate into twp halves. The split occurs at one spot first and does not go all the way around. I imagine full separations happen like that. One spot ruptures first and the pressure leaks out and back to focus on one side of the bolt. This means one bolt lug takes most of the unconstrained pressure. It won't take much of the 57K lbs to break a bolt if it is focussed. If the case doesn't rupture then more lugs share it evenly which is what it is designed to do.

I would throw away any fired case that is not a smooth feel on the inside wall with a paperclip. Again, it is not worth the risk. You will also have a circular trench in your breech where the case split. The plasma was focussed at the split and will have eaten into the wall of the breech. It won't affect anything however.

Your new cases will be the strongest they will ever be straight out of the box but if you exceed the ductility of the brass it won't matter, they will split even with mild loads. Obviously there's more chance of this happening with hot loads. New brass is also typically short, like factory ammo, designed to fit in every chamber. If your chamber is on the long side, and/or you bump the new case even shorter, and load hot, this will happen. Your chrono will not warn you.

Klem,

Thanks for all the feedback and input. I asked, he said he didn't size them at all. I'm going to try and tighten up my measuring skills and get a good feel for what the fired dimension actually is.

Besides the fact i think i'll not use 8208 for this barrel going forward, i am mostly concerned about the once fired cases. I have high hundreds of spent factory cases, of which some portion of them are from this chamber. Finding them and checking them would be no small task....

[grayfox]

Key,
Klem's graphs and QL bear out what I had suspected, and what I said... at 27/2540 you are at max for THAT Barrel, that bullet, load, powder/lot, etc.
(And by the way IMO that's pretty close onto an accuracy node for the 20" barrels I've known).
You need to believe the data and indications that really talk to you, that you're really getting, and "pressure" per se in the Grendel is not one of those. It comes too late to be of value to you. MV, powder load, QL stuff when you can get it..... those are the tea-leaves to pay attention to.
Yeah some guys may get up to 28, with their lot and their barrel. But yours gets to 27 and stop there.

51760 psi... pretty much 100% for the Saami out of that barrel.

I don't have QL so I use MV quite a bit as a primary indicator, that's my MO of looking at the real world data that my gun is giving me.
Book loads, someone else's gun, the inter-web... all of these are mere approximation to your barrel, bullets, brass, your powder lot, etc.

As a $0.02 contribution, I don't think it is so much "too much headspace" as it is simply what that rifle, rifle barrel, will do.
That low-mid 2500's is great for shooting that 20"-er, you don't need (or want!!!) 2600 from that gun/load/etc!!!

[keystone183]

Key,
Klem's graphs and QL bear out what I had suspected, and what I said... at 27/2540 you are at max for THAT Barrel, that bullet, load, powder/lot, etc.
(And by the way IMO that's pretty close onto an accuracy node for the 20" barrels I've known).
You need to believe the data and indications that really talk to you, that you're really getting, and "pressure" per se in the Grendel is not one of those. It comes too late to be of value to you. MV, powder load, QL stuff when you can get it..... those are the tea-leaves to pay attention to.
Yeah some guys may get up to 28, with their lot and their barrel. But yours gets to 27 and stop there.

51760 psi... pretty much 100% for the Saami out of that barrel.

I don't have QL so I use MV quite a bit as a primary indicator, that's my MO of looking at the real world data that my gun is giving me.
Book loads, someone else's gun, the inter-web... all of these are mere approximation to your barrel, bullets, brass, your powder lot, etc.

As a $0.02 contribution, I don't think it is so much "too much headspace" as it is simply what that rifle, rifle barrel, will do.
That low-mid 2500's is great for shooting that 20"-er, you don't need (or want!!!) 2600 from that gun/load/etc!!!

So where do you find what muzzle velocity is acceptable for each powder you are using with a particular bullet, so that i can reference it

[Lemonaid]

8208 XBR web data for 24 inch bbl. Hodgdon 123 sierra max vel 2497, Barnes 120 max vel 2498, Nosler 123/125 max vel 2440, Sierra max vel 2450

[keystone183]

XBR web data for 24 inch bbl. Hodgdon 123 sierra max vel 2497, Barnes 120 max vel 2498, Nosler 123/125 max vel 2440, Sierra max vel 2450

That data would have told me that my 27gr load was already well above max for a 20" bbl.

[Lemonaid]

That data would have told me that my 27gr load was already well above max for a 20" bbl.

Speed=Pressure, some barrels are "fast" and get more velocity for given powder than average and some are "slow" Your mileage/speed may vary.

[keystone183]

Speed=Pressure, some barrels are "fast" and get more velocity for given powder than average and some are "slow" Your mileage/speed may vary.

All due respect, that doesn't help at all.

[Lemonaid]

If your loads are going over the book max speed, you are over pressure is a good rule of thumb.

[keystone183]

If your loads are going over the book max speed, you are over pressure is a good rule of thumb.

And if the particular combo isn't in the book?

[SCJim]

And if the particular combo isn't in the book?

two options
1. find a combo that is
2. pay your money, take your chances. Might blow your rifle up and end up in the emergency room, might not

[Klem]

And if the particular combo isn't in the book?

Then find another source you trust. For me it is the internal ballistics calculator, QL., especially when there is limited book data on what is a relatively new bullet.

The bullet is not even in the V3.9 QL database yet, however you can measure the dimensions and enter this youself. This makes you a pioneer in the shooting community. In that situation I would be conservative.

Then there is headspace, which you have yet to resolve with the ability to measure. Once you can consistently measure headspace then you can eliminate it (or not) as a compounding variable that caused the accident. It may have been the root cause, or a lesser compounding factor, or it may not be an issue at all. But, until you can get consistent readings off that gauge none of us will know for sure whether headspace was a factor.

[keystone183]

Hope to get the measurements sorted out this wknd... Someone suggested depriming first. Do you agree? Also, any others tips or trucks?

I like being pioneering....

[Klem]

Key,

Depriming eliminates the possibility the primer is proud of the base which will confound the measurement. This requires you remove it without changing the headspace. I have a universal deprimer die but you can do the same thing with a fine punch and a hole in a piece of wood. Obviously you cannot run it through a sizer just to get the primer out.

You can also run the flat side of your calipers along the base to feel for anything proud; either the whole primer or cratering from the firing pin. If you feel no interference you don't need to remove the primer. This is what I do and rarely do I have to remove the primer.