A shooting buddy brought me a handful of 5.56mm cases he found on the range today...

Theres half a dozen, and each one is split cleanly in half (Separated into front and back) about 1/4th of the way up from the base.  There are no powder burn marks or dirt or anything like that on the halves of the cases, just clean breaks...

Is this from a super snubby like a Model 609 ripping the cases out quick and hard due to the short barrel, or some other type of problem (perhaps with a normal carbine) that I'm not considering?

More likely brass cases "stretched thin" from being reloaded too many times.  My 609 has never split cases.

I considered that, but the damnedest thing is that at least two of them have primers that look like they're crimped in and lacquer sealed.

This is what I'm thinking to.  Maybe MG reloaded brass, reloaded too many times, brittle brass, or possibly loaded a little hot.
Previous crimp marks can show up on re-loaded brass.

People always say something smart and look at me funny when I say that I only fire cases 3 times.

That is 2 reloads.

The smartass comments are " i wait until they start to crack before I chunk them "  
Well that is too late, is it not? They generally cannot come back with a witty comment because there is not logical debate here.
I am not the fool trying to fire the same case 33 times.


Sure, 3 firings might be a bit extreme on the marginally safe side..  But it is safe for sure.

How about a malfunctioning disconnector causing a second shot out of battery?

I've never had a problem with my 7", 7.5" 10", 10.5" and 11" SBR's.

is a 10.5 with a 4.5 FH a PC/sanitized SBR  ?

Nope.




Could be a couple of things. I'd look at excessive headspace first. Also check the chamber for foreign material or machining marks. I've seen a sliver of brass caught between the cartridge and the chamber wall in a Garand shear a case similar to what you describe.

OK, so it's stretched brass then.  I had assumed it came from an AR but you're right, I'm really not sure where it came from.
If this kind of thing happens in an AR-15, what's it do to the rifle?  Ka-Boom?

It just ruins your day until you get the front of the case that is stuck in your chamber out. Perfect reason to own one of these:

exractor

Let's also remember that carbines are overgassed - extraction is typically more violent than a 20" rifle, due to the larger gas port and the resulting relationship. This is why a lot of guys run heavier buffers. In FA weapons, it caused bolt bounce, which causes feed issues. Remember, the XM16E1 used the Edgewater buffer, which is very light and contributed to the high cyclic rate. They were notorious for tearing the case bottoms off, partially because of the violent extraction. One of the cures was the invention of the heavier buffer we are all familiar with. There was a reason you see pics of early Xm177s with A1 stocks - they didn't have H2 or H3 buffers then. IIRC, the standard rifle buffer is about the same weight as the 9mm buffer, thus slowing down the cyclic rate. LMT also makes a BCG with an extra gas port to bleed off gas for this reason. It's more of an issue in FA weapons of course, and I'd have to agree with jhud on limiting the number of times you reload a case as well. Even today M4s have more problems than M16s due to overgassing. Just my .02 and worth exactly what you paid for it.

ETA: I'd have to say however, that the split in the cases the OP referred to just sounds like dangerous reloads and/or bad headspacing to me.

Stretched brass is not necessarily the result of actual excessive headspace.  The sizer die adjusted to far down will shove the shoulder back too far and thus essentially causes a condition that acts like excessive headspace, with resulting stretch and case separation.

Cartridge headspace gauges are available for less than $30 to determine if brass is being over-worked or not:

http://www.sinclairintl.com/.aspx/pid=33287/Product/Wilson_Case_Gauge

It's usually not all that dangerous, folks have fired 308 in 30-06 and gotten away with it lots of times.  Separations are just damn inconvienient fishing the separated case out of the chamber and therefore not recommended.  Not the thing to have happen at a rifle match as a feller I know can attest who had several over the weekend.  I keep my brass in little "families" and keep careful track of how many times each "family" has been fired.  After four firings, I start sawing a few in half from each batch to see if there's a ring developing and toss accordingly.

You also generally want to keep brass fired in one rifle separate from brass fired in another.  Lasts longer that way.  As always, yer mileage may vary.

Is Entry level of SBR ANY BARREL LENGTH WITH BRAKE OR FH included in length of less than 16 .0 in.  ???

Ive had it happen while shooting auto. The FA would not budge the cartridge into battery. Then I had to pogo stick the thing to get the thing. When I picked up the live round it had the front half of the previously fired case stuck to it. Near the pile of brass was a brokem .223 case. Looked kind of like a 9mm case.
After checking a quick field strip and inspection I kept on shooting.

The case was a reload. LC 85. I was found alot of my 80's LC brass was splitting necks. That is when I adopted the 3 shot rule.

It is. A 10.5 in. barrel with a 4.5 in. flash hider is an SBR whether the 'hider is permanently attached or not. Even permanently attached your OAL would be about 14.5 in.

Maybe I misunderstood your question. You asked about a "PC/Sanitized" SBR, and yes, an SBR would be one with a barrel length measured from the bolt face to the outer edge of any permanently attached brake or flash hider of less than 16 inches. I thought your question was if the attachment of a 4.5 in. flash hider to a 10.5 in. barrel would make it a non-SBR.