65 Kaboom

[motoxxx_ryder]

well my kb decided to kinda blow up. this reminds me of a out of battery but i know the rifle was fully in battery. Looking at my brass alot have a small belt after shooting and it looks like a 300WM belt. is that normal? the belt is gone when its sized and it happened with lower loads as well.

load data:
123gr amax
lapua brass (4th firing)
cci 450 primer
28.5 gr 8208xbr
2.24 OAL


the primer doesnt look flattened and no cratering like you would see with an overpressure separation.










Any ideas WTH happened? it blew out the mag so one mag down...

[kmon]

Never saw a case with brass curled back that way if it was in battery and supported by the chamber.

Action might be opening early and in this case, the rings/belts sound like a problem also. That is the area case heads separate at and brass from there is where it is coming from when brass stretched. If I see a ring the brass will be inspected with a paperclip tool before it ever gets reloaded.

[lead chucker]

Wow! That looks narley for sure. Whats the set up, barrel, bolt? I kinda looks like it may be a bolt miss match leaving the brass unsupported. How many rounds fired, any other problems before? But glad your ok!

[motoxxx_ryder]

Round count is 200 to 300 no other issues previous.

Upper is a complete upper I bought new. Will be talking to the builder and see if he's ever seen it.

[sneaky one]

Looks like early unlocking- in your case, maybe the buffer has no weights inside! Wow is right. Try a different buffer for 1 shot, heavier if you have one. Weigh your buffer if you can. Then compare to at least a std. buffer wt.

Many of us run with the H2 buffer.

Headspacing checked?-- Oops on the powder? Bad scale readings? Short chamber?

what were the initial 2-300 rounds, factory, or handloads?

Mine was a pain to dial in from day 1.

[LRRPF52]

the belt is gone when its sized and it happened with lower loads as well.

We don't re-sized cases that come out belted for this reason. You're setting yourself up for a case head separation, and you had a partial.

I'm guessing you have an 18" barrel with Mid Length Gas System and a .094" gas port. Either that or something with a very long dwell time or too large of a gas port for the barrel length and gas system length.

Another possibility would be hot loads in high temperature with a different chamber and lightweight buffer. That will cause early, violent unlocking.

For example, if you were loading 123gr with 8208XBR in a chamber that was a little tighter, the gun will handle it fine, but if you have early unlocking, the brass will belt like that.

Any brass that comes out like that gets tossed/recycled.

[motoxxx_ryder]

So what if every case is belted even when testing from 24 to 28.5 grains?

Asking what the cause could cause this.

Rifle is a 20 inch rifle length gas state

[sneaky one]

motoxx, that's the worst Grendel brass issue to date on here.

Check for a leak, in and or around the gas system- try a heavier buffer. Which carrier is in there? Std., or M16 wt.?

I have kept loaded ammo in car trunk on a hot day to see what happens== nada. Every powder reacts differently tho.

[BluntForceTrauma]

Another possibility would be hot loads in high temperature with a different chamber and lightweight buffer. That will cause early, violent unlocking.

The builder uses the .264LBC chamber but don't know if that's a factor.

SAAMI spec for 6.5 Grendel is a 0.293" cartridge neck diameter in chamber necked to 0.300". Don't have a drawing for the .264LBC so don't know its neck dimension, and don't know if that could have been a cause, anyway. But it sounds like something was tight from the get-go.

[sneaky one]

The Lbc is about 0.295-6

That's the chamber Bill A regreted drawing- and he produced a few---.300 is perfect for this app.


Lets wait to see if motoxx has a china made buffah... no weighters insidah..

[LRRPF52]

Jamming the lands can do it. I saw that happen with 120gr Scenar-L loaded to 2.260" in my chamber, whereas regular 123gr Scenar can be loaded longer.

If you spike the start pressure, it can also drive the BCG back violently, and the case will be under pressure still as it extracts, causing the belt.

Re-size the belt down and you will have a case failure even down in the low 40ksi range of pressures.

I've seen it happen in Bwaites' 28" Grendel with 8208XBR and 123gr IIRC. He would have to pipe in to specify the load, but that load works fine in his 19.5".

There are a number of factors that can create violent, early unlocking.

[motoxxx_ryder]

H2 buffer no manufacturer

Maybe I'll make a round for the tornado tool for this rifle and measure DTL. Maybe need to reduce it

[LRRPF52]

Sorry, just read the OP again. 2.240" should not be that bad.

This was simply a belted case that was re-sized when it should have been culled. If you are having this happen regularly, we need to diagnose what's going on.

What bolt carrier are you using, and do you know what gas port diameter you have?

[sneaky one]

Yeah, resizing the belt causes a thin spot on brass web area- which is do to fail on next firings. Sad you have this issue- time for a fix.

Check for a true sammie chamber firstly, then move on to reloads- primers- OAL's. ,, etc. THEN THE buffer!!!

[motoxxx_ryder]

Port looks like it lines up.
Port is .09
Bolt carrier is marked y/m. It's a full auto bolt with unknown bolt.