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

[StoneHendge]

The feed cones on that Odin throat look to be quite a bit deeper than the other 2.

[LRRPF52]

The feed cones on that Odin throat look to be quite a bit deeper than the other 2.

Since I don’t have anything in my hands, I won’t say anything definitive about the geometry of that chamber, but it does appear that way at least in the photos.

The feed cone appears to be more generous and at a different, shallower angle.

Could be the lighting, but that’s how it appears in those images.

Also, it’s possible that the tiny buffer and spring would work with 5.56 or .223 Rem shooting 55gr, but I don’t think I’ve ever seen buffers that light.

The only one I can think of off the top of my head was the nylon buffer KAC experimented with on the SR-25K back in the early-mid 1990s right as the Clinton AWB was looming.

It didn’t work out.

ArmaLite Inc. (Really Eagle Arms with lots of work done by Karl Lewis) developed a longer RET for their AR-10 carbines, now referred to as an A5 RET that has become popular in AR-15s with a longer-than-carbine length buffer, but shorter than rifle. That helped get reliability where it needed to be on 7.62 NATO carbines, which was very elusive originally.

The Dutch built some rare AR-10 carbines, but kept full-length stocks on them. Those buffers and RETs are larger diameter than AR-15 or SR-25.

[stonehog]

Stone,

Be aware that typical pressure signs on brass mean you are already overloaded in Grendel. As you know, overpressure in an AR is unforgiving. My point is, don't wait until you see indications on brass before backing off. Velocities and tables are more helpful in this calibre.

Definitely - all were under maximum published loads for the powder and bullet combo. To be clear - I'm moving to a mode of using the lower low-ES node for load development if there is one. No sense in living close to the edge.

[stonehog]

The feed cones on that Odin throat look to be quite a bit deeper than the other 2.

The PSA and Odin look the same to me. On the original pics and looking at them in person closely the PSA has even a bit larger cone cut.

[Zeneffect]

I'm wondering, did it feel like the buffer is slamming the tube when not kabooming?

[lazyengineer]

Definitely - all were under maximum published loads for the powder and bullet combo. To be clear - I'm moving to a mode of using the lower low-ES node for load development if there is one. No sense in living close to the edge.

I see. The two AR BBLs noted in the last 12 months that have kaboomed.

Sounds like something worth noting if shooting a brass with a shallow case head down there. Which happened to be the case in those 2 kabooms. Then again, we keep hearing that's probably just a coincidence.

[stonehog]

The more I have thought about this since yesterday, the more I am wondering about the bolt face depth.

If you had an out-of-spec bolt face depth that exceeds .136”, and a properly-cut chamber, it could also cause this to happen.

The fact that your extractor is intact, there aren’t any ejector extrusion marks or extractor pocket ledge shearing, and primer has a nice dimple on it all point to a well-within normal chamber pressure.

The flat primer is often seen in excessive headspace, when the primer backs out and slams against the bolt face, followed by the case re-seating over it due to brass expansion.

I need to go look at your headspace measurements again.



Click-no-bang is a telltale sign of excess headspace.

Firing pin hits the primer, which just pushes the floating cartridge forward in the chamber without activating the primer.

I measured bolt face depths which came out to in-spec per comments:
Odin: .135
Monster: .136
PSA: .133

FWIW - I also measured the length and lock tooth depths. Currently looking for the spec on all this, but someone mentioned it earlier:
Odin: 2.798" - tooth .278"
Monster: 2.814" - tooth .279"
PSA: 2.798" - tooth .278"

Firing pin length: 3.27"

[stonehog]

I'm wondering, did it feel like the buffer is slamming the tube when not kabooming?

I shoot this as a cheek pistol, so while it definitely needs a firm hold to keep the scope from denting my eyebrow, it didn't seem to hit harder than usual. My sensitivity in this area may not be refined yet, however.
[URL="https://youtu.be/87kKBaLI1f8"]https://youtu.be/87kKBaLI1f8
[/URL]
https://youtu.be/4-2cIhp12co
https://youtu.be/uFFJg62p2QQ

[BluntForceTrauma]

M16 dimensions per print are:

Firing pin overall length: 3.277

Bolt tooth length, more commonly referred to as a lug: .278 +/-.002

Bolt overall length: 2.800

[StoneHendge]

Since I don’t have anything in my hands, I won’t say anything definitive about the geometry of that chamber, but it does appear that way at least in the photos.

The feed cone appears to be more generous and at a different, shallower angle.

Could be the lighting, but that’s how it appears in those images.

Also, it’s possible that the tiny buffer and spring would work with 5.56 or .223 Rem shooting 55gr, but I don’t think I’ve ever seen buffers that light.

The only one I can think of off the top of my head was the nylon buffer KAC experimented with on the SR-25K back in the early-mid 1990s right as the Clinton AWB was looming.

It didn’t work out.

ArmaLite Inc. (Really Eagle Arms with lots of work done by Karl Lewis) developed a longer RET for their AR-10 carbines, now referred to as an A5 RET that has become popular in AR-15s with a longer-than-carbine length buffer, but shorter than rifle. That helped get reliability where it needed to be on 7.62 NATO carbines, which was very elusive originally.

The Dutch built some rare AR-10 carbines, but kept full-length stocks on them. Those buffers and RETs are larger diameter than AR-15 or SR-25.

I used the 1 ounce Taccom Ultra Lite Weight buffers in my 16" 6 ARC with MLGS an adjustable titanium carrier. They worked great but I bailed on the whole system since the gas screw on the carrier would wander towards less gas. I'm guessing I had the gas open about 30-40% when it was dialed in. I'm sure the buffers would work fine on a .223/5.56. One downside though is that there can be feeding problems if you jam the mag against a barricade or bag and the mag moves in the well and tilts the cartridge nose down slightly. There may not be enough inertia to push it into battery and the round's nose can get caught up on the extension.

[VASCAR2]

Odin was one of the companies using the 2.80” length 6.5 Grendel bolt with standard firing pin length where pierced primers were encountered. With the shorter bolt I would recommend a firing pin no longer than 3.269”. The firing pin protrusion for an AR-15 is .028” minimum and maximum .036”. An out of spec firing pin protrusion can contribute to an out of battery ignition. The primer wasn’t pierced on the OP’s ruptured case but did the long firing pin set the cartridge off while the bolt wasn’t completely locked. Probably never know but in many situations a combination of events can contribute to a failure.

The specified maximum firing pin length I’ve seen for a 2.800” length bolt with a 1.25” bolt face depth is 3.279”-3.2800” with a tolerance of -.009”. With a .136” bolt face depth AA used a 2.810” length bolt so standard AR-15 pins could be used. So basically a standard firing pin needs to be .01” shorter to account for the .136” deeper bolt face, 3.279” - .01” = 3.269” maximum firing pin length for a 2.800” 6.5 Grendel bolt.

Op I’d recommend you measure the overall length of your Odin bolt from the face of the bolt lugs to the tail. The measurements I’ve seen reported on the length of Odin 6.5 Grendel bolts is 2.800” +or- .002.

I just reread the OP post where he measured his firing pin at 3.27, looks like the firing pin protrusion is in spec or very close. Looks like Odin supplied a shorter firing pin if the bolt is 2.800”. Sorry for any confusion.

[Tx264]

Stone,
Read my post on page5.
The skinny on bolts and pins.
I've got 5 bolts.2 monster,2 toolcraft,1 odin.When I tear them down and put em in the sonic cleaner.Odie's the special needs kid and takes a bath alone,non milspec pin.
Man l'm glad you didn't get hurt.
P.S. Who's the engineer that thought a 1.8 oz buffer in a pistol tube was a good idea must've graduated from Whatzamatta U

[LRRPF52]

I used the 1 ounce Taccom Ultra Lite Weight buffers in my 16" 6 ARC with MLGS an adjustable titanium carrier. They worked great but I bailed on the whole system since the gas screw on the carrier would wander towards less gas. I'm guessing I had the gas open about 30-40% when it was dialed in. I'm sure the buffers would work fine on a .223/5.56. One downside though is that there can be feeding problems if you jam the mag against a barricade or bag and the mag moves in the well and tilts the cartridge nose down slightly. There may not be enough inertia to push it into battery and the round's nose can get caught up on the extension.

Port pressure is less on MLGS vs CLGS, which allows more lock time on the action so pressure can subside to allow de-obturation against the chamber walls (spring back).

A problem with lower carrier mass is as you experienced, where lack of reciprocating mass doesn’t fully strip and seat cartridges into the chamber in various conditions in the field.

I blend, de-edge, and polish my extensions, trouble-shooting them to make sure the upper receiver’s feed ramp roots aren’t deeper than the edge of the barrel extension’s feed ramps.

It takes a long time to do if an extension is too proud of that junction.

[lazyengineer]

Please place any Lapua brass you don’t want on the EE.

Per request, this has been done by someone. In your hands I have the highest confidence of a long and excellent service.

Enjoy sir.

https://www.65grendel.com/forum/showthre...apua-brass

[Zeneffect]

Not the reason I'm selling it but sure why not.

I just have way too much damn brass. I'm keeping another 300 unfired stashed away still. I have 100% confidence in this brass in my rifles. So much so that the ones I still have will knowing receive over pressure several more times, repeatedly, purposefully, and I will have zero worries about an in battery blowout or early unlock and kaboom. My preferred load for matches where energy on target isnt a concern is a 123gr eldm and 28.2gr of 8208... pretty hot stuff. I'll run this until the primer pockets give out. I know it's over pressure, zero cares given. It's proven itself reliable and safe in my gun.

I'll be more than happy to pull them from the for sale section if this will be used as some illustration of customer distrust in the brand as this is not the case. I know they are rare as hens teeth right now and I have more than I need is all. That is it. Nothing else. I didn't post them ANYWHERE else for sale so the hoard could get at them exclusively. I can dump them on calguns instead if that makes you guys feel better, and they would be gone in moments. Either way no skin off my back, just don't use my ad as an example for this discussion please.

[lazyengineer]

Not the reason I'm selling it but sure why not.

I just have way too much damn brass. I'm keeping another 300 unfired stashed away still. I have 100% confidence in this brass in my rifles. So much so that the ones I still have will knowing receive over pressure several more times, repeatedly, purposefully, and I will have zero worries about an in battery blowout or early unlock and kaboom. My preferred load for matches where energy on target isnt a concern is a 123gr eldm and 28.2gr of 8208... pretty hot stuff. I'll run this until the primer pockets give out. I know it's over pressure, zero cares given. It's proven itself reliable and safe in my gun.

I'll be more than happy to pull then from the for sale section if this will be used as some illustration of customer distrust in the brand as this is not the case. I know they are rare as hens teeth right now and I have more than I need is all. That is it. Nothing else. I didn't post them ANYWHERE else for sale so the hoard could get at them exclusively. I can dump them on calguns instead if that makes you guys feel better, and they would be gone in moments.

Perfect - there we go.

[Zeneffect]

Off to calguns, some asshole will probably ruin them into 6mm arc now. Makes me cringe at the idea, but I'll make a few more bucks.

[lazyengineer]

Off to calguns, some asshole will probably ruin them into 6mm arc now. Makes me cringe at the idea, but I'll make a few more bucks.

I guess that answer was misleading. I wasn't suggesting you should sell elsewhere.

[stonehog]

Some recent testing and pics. I have another pistol lower with a regular carbine tube and buffer (2.9oz). I took the Odin 12" out with the Odin bolt (I re-measured headspace and it passed fine - no idea what was going on earlier) and shot some Hornady Black factory loads (same bullet) and then a couple of my A2520 reloads. One of the 2 A2520 handloads had the ring, but a few of the Hornady cases also had a less pronounced ring starting, so I'm starting to think that I need an even heavier buffer (H3) on this CLGS setup.

I also pulled the remaining 9 that were left in the kaboom box, and segmented a Hornady case, and the 40th pre-kaboom case that had a ring. There is definitely a ridge inside the Lapua case.

The first pic is left to right: Lapua A2520 shot in carbine lower, Hornady black shot in carbine lower, and Lapua A2520 shot in pistol lower (1.8oz buffer)

The second and third pics show the Hornady black case from carbine lower and Lapua case from pistol lower. I didn't segment the Lapua case from the 2.9oz buffer (yet). Interesting that the outside rings are forming in different places (just above where the web ends, I bet). I have an adjustable buffer that I'll set up this week and do some more testing. Next up are heavier buffer, and then a different bolt (monster).

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[Zeneffect]

What is length of a pre-kaboom but ring present case after firing?