I had a partial case head separation using a 1.8oz buffer

[grayfox]

Definitely should check every case to confirm it is within OAL spec.
Sampling is not acceptable for this step.
What I do, to make it easier, is set my digital calipers to max, 1.520 in this case. Then lock it down with the setscrew. Now every case walks thru those jaws... if it passes, slips easily thru, ok. If not, and I mean if it does not easily slip thru, then off to the side for trim-down. No exceptions!
Maybe it's tight, or even just "stick" a tad at one spot... no exceptions - off to the trim bunch.
Then trim and chamfer inside and out. VLD for the inner chamfer. (This - do for all cases, whether trimmed or not).

OCD types will trim every case every time. If you use a crimp... then need to trim to equal length every case, every time.

ps, what are the OAL's of some of the ones that shot ok... for the record I mean.
And... can you get the shoulder datum for these, maybe not for the one kaboom but the others?

[Klem]

case neck dimensions are critically important. I learned this 2 years ago by blowing up a 300 blackout. I had worked up a good subsonic load with a cast lead bullet, and started forming brass from .223 range pickups. My load (7.2 gn Lil Gun) was just hot enough to cycle the action smoothly (pistol length gas, 16" barrel, std buffer and spring) but a case with a slightly thick neck snuck it's way into my magazine. It chambered, fired, extracted and ejected ok...but tore the lugs out of my barrel extension. left me a cute little 300blk belted magnum case in the brass catcher as a souvenir.

"if it seats, it yeets" is bad advice...even with those little pipsqueak loads!

Pashiner,

Your Blackout situation is interesting, but might not be related to bullet release.

Can I ask, how do you know it was an overly-thick neck that prevented the bullet from being released?

What thickness is your Blackout brass at the neck? For example, unfired Grendel Lapua is 0.0135" at the mouth (relatively thick). Gemtech 300BO brass is 0.01" at the mouth (about as thin as it gets).

A Grendel SAAMI chamber is reamed to .300" inside diameter (ID) at the neck. A typical cartridge will be about 0.290" outside diameter (OD). That allows 0.01" of space around the neck for bullet release - plenty of space. The other issue is not having too much space around the cartridge so it doesn't split on firing.

Not all Grendel chambers will be reamed to exactly 0.300". My Lilja neck is tighter. Spent cases measure 0.2925" OD at the neck. Fired cases will have sprung back slightly so the chamber will be maybe 0.2935". Still, plenty of space for shot release. As long as your loaded cartridge is not the same dimension or wider than your chamber then you are good to go for bullet release.

In this table due to slight differences in bullet diameters you get slightly different amounts of space around the neck when in battery; note the column 'OD Loaded'. With all the subtle variation from manufacturers there is still plenty of space for all bullets to be released.
table - Copy.jpg

FYI, 6.5Creedmore has a slightly tighter chamber mouth than Grendel at 0.2960". SAAMI specifies no more than 0.295" OD for loaded Creedmore ammo. That is 0.001" space for safe shot release - or in other words, 0.0005" between the cartridge and the chamber wall.

I have a tighter-than-SAAMI 6.5x47 match barrel with a 0.286" mouth. It requires all cases to be neck-turned so loaded ammo is no more than 0.2842" OD. I cannot use factory ammo in that barrel without kaboom. After all that, it is no more accurate than my other normal barrels.

Stone,
You can get an idea of the mouth dimension of your Odin chamber by measuring the OD of spent cases. Then measure the OD of those loaded unfired rounds in the photo. Check the difference for shot release and eliminate that as a reason for kaboom.
Note: Be careful of dings on the mouth from the spent cases hitting the receiver on the way out. the cases need to be perfectly round to get a good measurement.

[LRRPF52]

More photos. I was only able to find the slightest ridge forming on 2 cases. #9, and #36. #41 was the kaboom.

[ATTACH=CONFIG]19138[/ATTACH]
[ATTACH=CONFIG]19136[/ATTACH]
[ATTACH=CONFIG]19139[/ATTACH]
[ATTACH=CONFIG]19140[/ATTACH]
[ATTACH=CONFIG]19141[/ATTACH]
[ATTACH=CONFIG]19137[/ATTACH]
[ATTACH=CONFIG]19142[/ATTACH]

[LRRPF52]

This is pointless.

Kaboom 1 - Lapua in an AR15 with an Odin BBL by one user

Kaboom 2 - Lapua in a bolt action rifle by another user

Kaboom 3 - Lapua in an AR15 with a PSA BBL by yet another user


All other brass: No Kaboom.
Lapua represents a small portion of reloading brass in use; and has an engineering aspect different from all others, at the location of Kaboom's

Conclusion - Lapua can't be a component of that?

[LRRPF52]

I wonder if the Grendel is unusually sensitive to this issue. WAY back when the issue of Quickload predicting overly high pressure for the Grendel was first raised, a plausible explanation was that on this cartridge, the base of the bullet is so close to the primer that the ignition of the primer started the bullet moving. This resulted in a larger effective case capacity before much of the powder had started to burn. If the bullet is pinched in place by the neck hitting the beginning of the freebore, the pressure increase would be even greater (combination of smaller case capacity and higher bullet clamping pressure).

[LRRPF52]

* I wonder what your gas port diameter is, what carrier weight you have, buffer weight, and action spring type/length.

The discussion about Lapua brass has really distracted us from being able to focus on the real problems here.

That is even more likely using a medium-slow-burning powder like AA2520 with CLGS under a 123gr, which is a ball powder that will hit the port with higher port pressure.

[DeNinny]

Extraction contributed to the failure.

I have been thinking that but with extraction happening well after the bullet has left the mouth, I see it as the extractor did the damage well after the actual kaboom.

To your point, though, the casing might have ballooned into the extractor itself and the sharp edge of it actually cut into the brass and that is where the initial blowout occurred. Then later as the case continued to tear, it tore at the feed cone score "line".

Can you elaborate on your own failure model here and see if our thoughts line up?

[LRRPF52]

I have been thinking that but with extraction happening well after the bullet has left the mouth, I see it as the extractor did the damage well after the actual kaboom.

To your point, though, the casing might have ballooned into the extractor itself and the sharp edge of it actually cut into the brass and that is where the initial blowout occurred. Then later as the case continued to tear, it tore at the feed cone score "line".

Can you elaborate on your own failure model here and see if our thoughts line up?

[Zeneffect]

Page 4, post 71. You guys and your hate for quickload and immediate dismissiveness is a bit unfounded if you know how to use the tools appropriately. We all know where "in the curve" we should see the gas port. Regardless of what any number software says, it's relative position is the clue since peak pressure is already known. We are keyboard theorists and can never determine with absolute certainty the case of failure, but we can use ALL of the tools available to get to the same conclusion faster with lack of additional evidence. In cases for load development, I have recently experienced both published load, quickload, and verified from others load involving TAC. If I fif not have my magnetospeed attached, I would have happily shot everything instead of stopping to say wtf. This was for .223 remington, where software and published loads should be most refined.

I dont trust the software with absolute certainty as I know these cases exist, but to say it's useless is simply not true. It has its uses (especially quicktarget) when applied appropriately.

Hell I don't trust anything basically until I've tested it for myself. I've been told way too many things that are simply not true I've adopted the stance that nothing is true until it is proven to be so.

[DeNinny]

LapuaCase1.png

Ok so I was able to enlarge the photo of the first failed case until it was 37.5" across my monitor. then, per my blue arrows, I measured the unsupported head area (or feed cone depth) at approximately 2.25". Scaling this down to the actual casing size I get an estimate of 0.0915" for the unsupported head area. Here is my math:

(2.25"/37.5") x 1.5245" = 0.0915"

Based on the failure score line location, this is my estimate of both the feed cone depth and the unsupported case wall depth. This is fairly close, bigger actually, than what I estimated from Bill Alexander's statements about the M16 style feed cone design.

So now taking 30% of this, I get .3 x 0.0915 = 0.027". <- This is the estimated additional feed cone depth for a standard M16 feed cone from an Alexander Arms feed cone, assuming that at least 30% improvement was achieved when Bill Alexander redesigned it.

This still puts this failure model as more significant than the bolt face depth out of spec model which was estimated at 0.005". Instead of 4x difference from my earlier estimation, it is now 5x different.

As such, the feed cone depth issue is still a viable failure model. This shouldn't be a surprise since Bill Alexander acknowledged it was an issue to begin with.

[LRRPF52]

[LRRPF52]

[ATTACH=CONFIG]19151[/ATTACH]

Ok so I was able to enlarge the photo of the first failed case until it was 37.5" across my monitor. then, per my blue arrows, I measured the unsupported head area (or feed cone depth) at approximately 2.25". Scaling this down to the actual casing size I get an estimate of 0.0915" for the unsupported head area. Here is my math:

(2.25"/37.5") x 1.5245" = 0.0915"

Based on the failure score line location, this is my estimate of both the feed cone depth and the unsupported case wall depth. This is fairly close, bigger actually, than what I estimated from Bill Alexander's statements about the M16 style feed cone design.

So now taking 30% of this, I get .3 x 0.0915 = 0.027". <- This is the estimated additional feed cone depth for a standard M16 feed cone from an Alexander Arms feed cone, assuming that at least 30% improvement was achieved when Bill Alexander redesigned it.

This still puts this failure model as more significant than the bolt face depth out of spec model which was estimated at 0.005". Instead of 4x difference from my earlier estimation, it is now 5x different.

As such, the feed cone depth issue is still a viable failure model. This shouldn't be a surprise since Bill Alexander acknowledged it was an issue to begin with.

[LRRPF52]

Page 4, post 71. You guys and your hate for quickload and immediate dismissiveness is a bit unfounded if you know how to use the tools appropriately. We all know where "in the curve" we should see the gas port. Regardless of what any number software says, it's relative position is the clue since peak pressure is already known. We are keyboard theorists and can never determine with absolute certainty the case of failure, but we can use ALL of the tools available to get to the same conclusion faster with lack of additional evidence. In cases for load development, I have recently experienced both published load, quickload, and verified from others load involving TAC. If I fif not have my magnetospeed attached, I would have happily shot everything instead of stopping to say wtf. This was for .223 remington, where software and published loads should be most refined.

I dont trust the software with absolute certainty as I know these cases exist, but to say it's useless is simply not true. It has its uses (especially quicktarget) when applied appropriately.

[DeNinny]

We are aligned on the extraction happening after the bullet passes the gas port. That's what I mean by well after the bullet has left the mouth.

Also I understand your model, but the other failure model is also supported by this evidence that I posted earlier...

The case head expanded into the extractor and the blowout occurred while still in battery and it started at either the sharp edge of the extractor or it started at the score line where the unsupported wall starts.

Also remember...by the time the extractor is actually extracting, all the pressure is already released from the casing. The brass is no longer subject to the severe pressures as it was when the bullet was just leaving the mouth.

Also...note that there is zero extractor damage to the other two failed casings. To me these two earlier failures (but not blowouts) are an indication of a pressure issue at the head. The pressure is pushing the limits of the brass and there were two signs of this before the blowout.

I'm sorry but there are holes in the extraction failure model, and there are other models that still support the failure as shown in the picture.

[DeNinny]

I respectfully disagree. The other failure model is still viable and fully supported by the picture.

And I'm fine if we agree to disagree. It's been a great thread and I've personally learned a lot for my own reloading purposes myself.