LRRPF52 Wrote:Im not a fan of the mislabel expert. The moment someone stops learning and proclaims expert status, the more I am suspicious of their statements.
General shooters have been shooting Lapua brass since the introduction of 6.5 Grendel, because thats the only brass that existed at the time.
We cant and shouldnt rule out the likelihood of chambers that are not cut correctly, especially in the post-2020 era of mass retirement of competent engineers, the cultural acceptance of laziness and excuse tolerance, compacted with supply chain issues.
Sourcing reamers has been very difficult across the industry in many cartridges, which promotes allowances in drops in Toal Quality Management.
There are also many companies who make assumptions about how to cut a chamber and the feeding cone, without having conducted fleet rifle pyramid testing.
They know they can throw barrels out the door due to demand.
There simply isnt enough pressure being generated to cause this type of failure in a SAAMI spec chamber with proper cartridge support, assuming the cartridge was in battery.
Since Lapua brass is very prominent in the market, it is very presumptive to look there as the failure node.
In every one of the instances youre referencing over the past year, what barrels were involved? What type of feed cone did they have?
We are saying close to the same thing. It's a tolerance stacking issue with improper barrels. A tolerance stacking issue that shows up with Lapua's thinner web brass design, and nobody else'. 3 kabooms in 12 months- only Lapua. What does it take to realize something is wrong? There is an aggressive defense of Lapua that appears to compromise balanced assessment on this one.
As to expert - I study everything you say, as one of considerable experience and knowledge so that I can achieve best results from your experience.
DeNinny Wrote:BluntForceTrauma forgive my ignorance, but how does one know the type of feed cone they have for their barrel? How does one know if their barrel has a cone that goes deeper into the chamber than another barrel's cone?
To me, this area, while the round is in battery, is clearly where the case is unsupported. And theory says that the bigger this exposed area, the higher the chance of it promoting a failure under high pressure. All other things equal.
Reference the photo of the cutaway 5.56 chamber in Page 3, Post #51. A 5.56 chamber first has a 120° cone, or ramp, cut into the breech leading into the chamber, and then the edges are radiused .0625. So, when visually examining the breech, you'll see the flat surface of the breech and then a relatively wide "circle" that represents the angled cone and the radius around the chamber mouth. The smaller that "circle" around the chamber mouth representing a smaller angle and radius the more supported the case web area.
Attached is a completely random and unrelated photo I don't know what cartridges these barrels are chambering; I got the photo by Googling "AR15 feed ramps" but the photo gives a rough side-by-side comparison of the visual differences of different "cone" sizes. The cone on the right, for example, is smaller than the left.
:: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets
LRRPF52 Wrote:The stated load in the OP is not hot, given a normal chamber and the dimensions he has since posted that his chamber will allow.
I'm just saying it was relatively hot for OPs particular situation and barrel. And he exceeded what the manufacturer recommended. If he had stayed more safely below this he would have lowered his chances of a kaboom, in this scenario.
And I'm absolutely on board there are other factors besides this. For example it was a relatively hot load on a barrel that might have a slight chamber issue. Or it was a hot load relative to a piece of brass with a slight defect at the failure point.
"Hot" is relative and a spectrum, not all of a sudden absolute to me. When you push the pressure limits, you are going increase your probability of a kaboom. It might be fine for some cases, but it could stack on top of other factors.
LRRPF52 Wrote:...
Im suspecting the feeding cone not supporting the case. Brass is inherently soft, so it will push around even with low pressures. When unsupported, it will yield like this.
This is exactly where my head is at with it too. And it was possibly exacerbated by a relatively "hot" load. And possibly exacerbated by brass with a relatively thin wall at the failure point. And it was possibly exacerbated by heat.
And all of this is anecdotal. The only way to know for sure is to repeat the experiment with changing conditions, one at a time. For example same load, same barrel, but different case. Or same case, same barrel, but different load.
DN, I accidentally deleted your post, but, no Alexander did NOT give out his feed cone dimensions; that's sort of a trade secret. There is no SAAMI industry-standard for those dimensions so they're up to the whim of the individual barrel manufacturer.
:: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets
LOL BluntForceTrauma you went admin god-mode on me for a minute there.
And based on there being no spec, now I want to see a picture of OP's feed cone "circles" for his 12" and 18" barrels. He said the load was fine on the 18"... perhaps it has a smaller feed cone circle than his 12"...
Good advice, guys - thanks for all the inputs! I'm looking back over my load data, and my original testing with this load was in my PSA 20" upper getting about 2446 ave velocity. I noted perfect 4pm eject pattern with this load as well, so gassing seems good. Odin and PSA FWIW, as well as my 18" Faxon upper.
I did a COL test with this powder charge with a 123 gr Hornady BTHP in the 12" Odin I had the failure in. Interesting that in that bullet and test, I did have a few issues with Federal cases that were hard to extract. My notes:
"Note: all these (2.246 - 2.26) may be too long for throat length. In the 123 Hornady BTHP, I had bullets possibly stick in the lands and had click-no-bang, and then trouble extracting the unfired cartridge"
At the time, I theorized that it was a jam into lands issue, but this didn't exactly line up after I got the Hornady COL gauge which found jam length of 2.3050 for the HPBT and 2.310 for the ELD-M.
It is interesting that I've only noticed the ring on one other case out of the 40+ I've shot in that batch so far. Next step is actually measure the powder from a few rounds when I get my puller...
LRRPF52 Wrote:Please place any Lapua brass you dont want on the EE.
Ive been loading Lapua brass in Grendel since 2009. Its the best brass there is for the cartridge in my experience.
For someone to get a case failure on first firing with a load well-within limits indicates a problem somewhere else.
Im suspecting the feeding cone not supporting the case. Brass is inherently soft, so it will push around even with low pressures. When unsupported, it will yield like this.
stonehog, was your extractor still intact?
Yes - the extractor was in good shape, but the bolt was out of spec after this firing per seating the no-go gauge.
Stone.thanks for posting.
None of this is worth getting hurt over.SAFETY FIRST.
I've noticed earlier in your post and the last one that the original bolt didn't pass headspace after kaboom.It couldn't have grown/shrunk,unless chunks are missing.
You said it's an Odin barrel.Is it an Odin bolt?Odin and some toolcraft/psa bolts were 2.80" long and used a shorter firing pin.Standard grr bolts are 2.81" and use a milspec pin.
You said some of your brass measured .001 less than fired brass.Semi autos need .003 bump min.
Sooo.Possible cause.
1.headspace
2.to long a case.
3.milspec pin in an Odin bolt
Any one, oob assplosion
Or,POS piece of brass.
I've been loading unsized unfired bass.Never again.
Thank you sir,You might have kept me from hurting me.or others.
The Lapua hate in this thread belies the lack of information of why it happened. It could be that the tolerances of the action parts are such that an OOB situation is possible in this rifle, regardless of the brass manufacturer.
The only thing we can say for certain is related to proof of the null hypothesis. If the hypothesis is that Lapua is flawed then the null hypothesis is that Lapua does not fail in all situations. What percentage of failures we are willing to accept is up to the shooter.
Any QL hate also belies how it is a extremely useful computer prediction for the average shooter. For example, how else would we know that the OP's load is 106% compressed at his stated OAL? Crunching powder changes burn characteristics and introduces the unknown, always more pressure, and in this case may be the reason deflagration turned into detonation. Regardless, it is a computer program which is only as good as inputs: GIGO. The 106% prediction is based on the default case volume, which could be more or less based on reality. If the OP weighed the water capacity it would be a better pressure prediction. QL default is 35.99gns of water. My unfired Lapua is 35.13gns (less capacity than default), so predicts 108.4% compressed and higher than default pressure of 67.5K lbs peak pressure. While I accept QL is not exact this is a hot load in any conservative discussion.
From Bill Alexander on Sniper's Hide which 52 was also part of the discussion (March 22, 2022);
[INDENT]The Grendel chamber geometry and bolt was designed in concert with the Lapua case. The chamber "if" correctly dimensioned and with the correct feed cone geometry will allow chamber pressures well in excess of 68k psi without the case deforming. Obviously this is for Proof loadings only and should NOT be used as the basis of any load development. It will damage the rifle! The absolute maximum is 51,800 psi and MAOP pressures are held around 50k psi. Pushing loads to 52kpsi allows zero envelope for pressure excursions, which will and do happen even with the most carefully assembled loads.
Stretching of the case above the web results from either an incorrectly machined barrel or excess residual bore pressure as the case is extracted. I do not have direct experience of the 6mm ARC but simple expansion ratio calculations indicate the timing will need attention. This is not just the size and position of the gas port in the barrel but also the reciprocating mass which includes the impulse from the fire control group.[/INDENT]
If anyone wants to get rid of their unsafe Lapua brass, I will safely dispose of them by gradual destruction over 20 firings.
stonehog Wrote:Good advice, guys - thanks for all the inputs! I'm looking back over my load data, and my original testing with this load was in my PSA 20" upper getting about 2446 ave velocity. I noted perfect 4pm eject pattern with this load as well, so gassing seems good. Odin and PSA FWIW, as well as my 18" Faxon upper.
I did a COL test with this powder charge with a 123 gr Hornady BTHP in the 12" Odin I had the failure in. Interesting that in that bullet and test, I did have a few issues with Federal cases that were hard to extract. My notes:
"Note: all these (2.246 - 2.26) may be too long for throat length. In the 123 Hornady BTHP, I had bullets possibly stick in the lands and had click-no-bang, and then trouble extracting the unfired cartridge"
At the time, I theorized that it was a jam into lands issue, but this didn't exactly line up after I got the Hornady COL gauge which found jam length of 2.3050 for the HPBT and 2.310 for the ELD-M.
It is interesting that I've only noticed the ring on one other case out of the 40+ I've shot in that batch so far. Next step is actually measure the powder from a few rounds when I get my puller...
stonehog for your remaining ELD-M rounds from this batch, are you absolutely certain that they jam into the lands? Forget the COL gauge and how it compares to the HPBT. Test it with an actual round in the chamber.
With the bolt removed completely, I just drop a round into the chamber by hand and then I'll push on the primer end hard enough to "jam" it. If the round is jammed into the lands, it will not fall out of the barrel by gravity when you set the upper pointing straight up. And you'll have to use a cleaning rod to remove it. If it is not jammed, it falls out freely. I just did this to properly seat some 120gr ELD-Ms and it worked well. I found out they jam at 2.210" on my barrel so I set my COL to 2.190 which is much shorter than the Hornady book value.
BluntForceTrauma Wrote:Feed cone is completely separate operation from reaming the chamber.
Found a relevant thread on Sniper's Hide titled "Grendel-like Belted Magnum Problem" HERE.
I did not read the entire thread but based on the pics posted in it and this thread, I think this is a result of the feed cone area being unsupported and it could theoretically happen in any barrel (at high enough pressure). The belt as shown in the pics looks like it is in the same area as the feed cone. And it doesn't matter what the brass, there is going to be permanent deformation of the brass at that point provided the pressure to deform it is exceeded. In the Hornady case, the brass did not tear and instead formed that belt. In the Lapua case here, the brass literally ripped.
09-25-2022, 12:23 PM (This post was last modified: 09-25-2022, 01:53 PM by grayfox.)
Look at that snipershide thread, very interesting.
Note, for this comment, post #61, it's a pic of the Odin barrel chamber chamfer, a 2-step angle radiusing...
"[FONT=&]You can't really catch it with your fingernail like a step, but can feel it and measure it. It looks like Odin does a double angle chamfer and the step appears to line up with the steeper/deeper chamfer."
Would the OP ridge line up with that second chamfer in his Odin 12" also...
I'm still processing that thread. Might be a combo of lapua case design (not saying it's bad, but it is different at the case/web interface) and a double chamfer leaving the interface unsupported. Plus maybe other factors, like I said I'm still digesting that thread. Bill A and '52 are both in on those discussions.
Ledzep has some very interesting comments.
I have 4 6ARcs, 3 gas and one bolt. All of the chamfers are single radius, and appear to be shallower into the chamber depth, no Odin's, 3 mfrs among my 4.
I'm not getting any ridges, but then again I don't use any lapua.
Lapua's design, being earlier in grendel's product life, could it be its web/corner was not "exposed" (not unsupported) by the bolt face depths being 0.125 back then? I wonder, I was not into grendel at that time.
edit to add: in my early days of 6Arc I was actually loading just a "tad" too hot, and didn't realize it til later. But didn't get any ridges or belts that I remenber.[/FONT]
"Down the floor, out the door, Go Brandon Go!!!!!"
09-25-2022, 01:58 PM (This post was last modified: 09-25-2022, 02:15 PM by DeNinny.)
I'm still processing the thread too. It's a great read that complements this thread. There's a pic of the cross section of Lapua, Starline, and Hornady brass and it confirms the same thing as the pic here - Hornady has the thicker base and overall more sidewall at the head than Lapua. Starline is in between like Norma was in the pic here.
Another thing is that Alexander himself pointed out again that the feed cone shape matters. And there are some supporting posts stating that some barrels (I think Odin) show more of a ring than others.
And I'm still not convinced that early bolt release matters. If you think about powder ignition, it's going to literally start burning right at the primer, right there at the head first. Pressure will be the highest there, relative to the shoulder end. And that pressure is going to expand the brass there at the head more than at the shoulder. And as the powder continues to burn there will be a high pressure front that moves with it and continue towards the shoulder. It's like blowing up a hot dog shaped ballon where it expands near your mouth first and then keeps expanding out towards the tip as you blow more. Similarly, that ring or belt is going to form initially, given the pressure is high enough to deform the brass, at the head and into the unsupported space of the feed cone. And as the pressure wave propagates towards the shoulder, it will reach the areas where the case wall is supported by the chamber walls. And thus, no more belt formation.
Furthermore, in every pic I look at, the ring or belt is in a consistent spot. This is speculation only but it seems this will be hard to get that consistent if the breach is opening early.
So with all this, I still think that the ring or belt is simply the shape of the unsupported feed cone area. And it happens when the pressure is high enough to permanently deform the brass.
DN I am coming to the same conclusion, about the unsupported brass, particularly with a Lapua/Odin combination setup. But to your post, I believe near to the base, the heat/temperature may be higher early in the ignition process but pressure, probably not. Pressure increase won't really occur until the entire volume of the case/bullet interior has that pressure increase. That might be some microseconds after the heat towards the base increases. But that heat can still have an impact on the brass down there, which will accelerate as the pressure (and deflagration) proceeds. Pressure buildup needs to have some gas generation, and pretty much the entire volume will see that pressure. Any local pressure beginnings in that ignition wave, will propagate forward, not build up in place down at the base.
"Down the floor, out the door, Go Brandon Go!!!!!"
09-25-2022, 02:29 PM (This post was last modified: 09-25-2022, 02:58 PM by DeNinny.)
grayfox Wrote:DN I am coming to the same conclusion, about the unsupported brass, particularly with a Lapua/Odin combination setup. But to your post, I believe near to the base, the heat/temperature may be higher early in the ignition process but pressure, probably not. Pressure increase won't really occur until the entire volume of the case/bullet interior has that pressure increase. That might be some microseconds after the heat towards the base increases. But that heat can still have an impact on the brass down there, which will accelerate as the pressure (and deflagration) proceeds. Pressure buildup needs to have some gas generation, and pretty much the entire volume will see that pressure. Any local pressure beginnings in that ignition wave, will propagate forward, not build up in place down at the base.
grayfox I get what you are saying about pressure but I still think at the atomic and dynamic level there's going to be a gradient of it. The powder at the head end is going to burn first, thus the gas will form there first. The powder at the shoulder end is going to burn last. By this fact alone there is going to be a pressure difference. And I'm talking over a VERY short time interval. As you state the pressure overall in the case is going to get to an even expansion VERY quickly. Edit: And I'm not saying there's a "buildup" of it. I'm just saying that it will follow with literal burning of the powder that starts at the primer and that it simply follows alongside the formation of the gas and heat.
LOL I split hairs here with you, though. It doesn't matter in that the bottom line is that the case is going to expand the most where it is least supported...the feed cone area.
09-25-2022, 03:12 PM (This post was last modified: 09-25-2022, 03:15 PM by grayfox.)
Agreed. I don't have any instruments to measure down there, that fast, so could go either way like you said...
One other point I want to make here is, in partial deference to Lze's stance, there is now some indication that the Lapua design could be part of the issue. Not that Lapua is bad, and not that the Odin barrel is bad, but the combo of the 2 (in the cases I see here) leads to bulges/failures down at the web/wall interface, much as Ledzep in the other thread says. If anything is to be called "bad" or "avoid this", it would be avoid the combination. O and throw in an arguably hot or overpressure load -- didn't help any that's for sure.
Thanks to the discussions in this other thread there are now some handful of cases where this phenomenon has cropped up, all (if I read these correctly) with the Lapua brass and Odin barrel. At least, more examples so the brass failure in OP's case here is not due to a single defective case (as I originally thought). Indeed there could be other instances we don't know of, but I think this is what we have before us now. In the case of the sizing dies and relative base diameters, (whether "small base die" or not), the inverse but similar occurrence takes place with narrower dies. In the example of the die too small, the upper case is squeezed and the base is not, giving a ridge. In our cases, the walls are expanded but restrained by the chamber but the bottom portion is not, thus a ridge, line or blowout.
Physical processes, mechanical processes, gas, brass and metals, etc, are if you will, agnostic, unemotional and non-discriminatory -- they expand/retain, melt, flow or whatever purely in regards to the forces and thermodynamics upon them at the time. We try to arrive at the most objective and logical cause/effect conclusions based as much as possible on observable data -- convictions and feelings and beliefs aside.
"Down the floor, out the door, Go Brandon Go!!!!!"
Well said grayfox. To me that thread is a second "data point" on the issue of having too much pressure at the head for the scenario of Lapua brass combined with an Odin barrel. (All other things equal.)
If it's not something that's going to make you avoid Lapua brass, it should at least be something to keep in mind as you push pressure limits with reloads with it. Or one could chalk it up to "anecdotal observation" and keep doing their thing.
