Tell me what happened - Ladder Test

[keystone183]

Ok, going to try and get everything relevant in here but may not...

I have a good friend and experienced reloader who just got in to Grendel. He produced a ladder test and duplicated it for me. I'm shooting a PF 20" rifle gas 1-8 Bartlien barrel. Load was new Hornady brass, CCI #41, XBR8208, Hornady eld123, coal 2.250. Starting at 26gr in 0.5 increments to 28gr. Loaded 10 of each, first 5 over the magneto were thus...

26- 2445
26.5- 2481
27- 2525
27.5- 2571
28- 2602

No obvious signs of excessive pressure to ME on cases or velocities. So I ran the next 5 for groups. On the first round at 28gr, I broke a bolt lug and the case head separated leaving all but the base in the chamber. No blown primer or signs of pressure on the head, besides being seperated.

Is that load to hot? How do I get the rest of the brass out of the chamber? What's going on???

[keystone183]

Ok, on cell and can't edit.... Have pics but can't post them from cell. Will have to wait till tomorrow...

[tdbru]

KS183,
28 is probably a max load. of the several load manuals i have, for 120-123gr. bullets. max runs from 27 to 28.5 for IMR 8208 XBR. i wouldn't think that should cause a bolt lug to fail. maybe a faulty (incorrect heat treating) bolt? did the bolt indicate if it was MPI'd there's always the potential that in millions and millions of parts, a bad one get's through the various QA processes. Particularly now as demand is far out stripping supply are mfgr's taking short cuts on QA?? who knows.

to get the case out, a broken shell extractor is what is usually used. otherwise, through the upper in the deep freeze. once it's good and cold, push a tight fitting brush down the muzzle. as the bristles contact the case neck it might push what's left out of the chamber.

-tdbru

[Lemonaid]

I would inspect every Hornady case you have for internal flaws. A bore scope works quite well for that task. It might not be what is a fault but it may rule out that factor.
Very small chance of this but I'll include it for a safety tip... If you were loading with a different powder in the powder hopper last session it is possible for a small amount of powder to be present even after emptying it out. Tapping on the hopper/dispenser and working it while empty several times can dislodge the remaining powder and prevent possible contamination of the next loading. A small amount of residual pistol powder mixed with a max load of rifle powder could equal danger.

[StoneHendge]

I personally have never been able to get close to 28 grains of XBR in 2 barrels. I have had case head separation in a custom barrel. It was due to the case not being fully supported.

What was the temp? XBR isn't very sensitive, but it's not insensitive.

[keystone183]

Tbru - I am pretty sure the bolt is a PF bolt, and mpi. Could be wrong. I though I had a monster bolt in there, but when I took it out, it wasn't, and I can't think of anywhere else I've gotten a bolt from?

Lemonaid - These are all from my buddy, so he may, but do you think it may be a case problem?

Thanks for the replies!

[Lemonaid]

Tbru - I am pretty sure the bolt is a PF bolt, and mpi. Could be wrong. I though I had a monster bolt in there, but when I took it out, it wasn't, and I can't think of anywhere else I've gotten a bolt from?

Lemonaid - These are all from my buddy, so he may, but do you think it may be a case problem?

Thanks for the replies!

Many neither use ammo reloaded by someone else nor give reloads to others to use, so many liabilities (read getting sued) and troubles can happen. If you reload for yourself you are in control of the quality and most problems are on you.
I have had some Hornady brass that had external defects a few per 100, small vertical creases. That is why I would check them.

[Klem]

Key,

Sorry to hear about the bolt, but at least you're OK. I have done this twice in my lifetime and on both occasions the front half of the case came out by gravity. I'm thinking a barrel brush from a larger calibre will get that pulled back out.

According to QL that is a hot load but not by much. I have trialed that bullet with a slower powder (H4895) so have the bullet dimensions entered into QL. As you know, 52K lbs is the SAAMI max peak pressure and with 8208 that is also showing a compressed load at 28gns (102%) and compressed means it steepens the pressure curve.
26gns = 2,375fps - 46,330lbs pressure. for a 20" barrel
28gns = 2,550fps = 57,900lbs

That said, 102% compression is not very compressed and while it's a hot load it's not a bolt-breaking load, even in an AR15. If the pressure was too much the case wouldn't split, the bolt would just break.

I'm thinking it's all down to too much headspace. The case was too short, unsupported, and pressure that is normally contained by the case was taken by the bolt and chamber instead. Your case base will not show signs of overpressure (flat primers etc) because it did not contain the pressure. It split and the chamber took all the pressure; pressure that is meant to be shared between both the case and the chamber.

If any are left unfired check your loaded rounds for headspace. It is likely all those rounds were close to splitting and the one that did was the heaviest load in the weakest case. For the fired cases that did not split and were sized by the same die run a paperclip down the inside feeling for a trench in the same place as the one that split.

The solution is to unscrew the die to a .003" bump.

[grayfox]

[1Shot]

As has been said many times on this forum you will not see "pressure signs" until you are WAY over pressure with ARs in 6.5 Grendel. From looking at your velocities 27 grs would be about max. With 120/23 gr bullets out of a 20" barrel anytime you get 2550 fps don't go any higher because you have about reached max pressure with IMR 8208. As has been said this powder has a quick spike of pressure when at the top end but in my experience with it the trouble is right at max is where it gets the best accuracy. Also NEW cases have slightly less case capacity usually than fired and resized cases and with the small size of the Grendel case that can make a load go from mild to wild. As has been mentioned place your barrel in the freezer and then from the chamber end try using about a 35 cal or a little larger brush and run it into the chamber and pull back with a slight twisting motion. If that don't work put some penetrating oil in the chamber and let set for a while then repeat the brush pull.

[keystone183]

Thanks for all the replies guys. Going to look at the check out fired cases when i get home.

I know speed at 28 was a bit high, but velocity was not spiking? Did i miss something there? I was cautious about 28, but i've seen lots of reports here with that load and some a bit hotter. I know all barrels will be different, but what did i miss i should have been looking for?

[VASCAR2]

[SCJim]

Thanks for posting this. I keep a paperclip in my case prep tray but sometimes I neglect to do a simple test and inspection. You thread will keep me vigilant for a few months at least. A quick visible inspection after tumbling and a common paperclip can save gear and prevent injury. Light rings around a case is a sure sign that a further inspection is needed but as Klem posted a paperclip used to feel for trenches should be a part of every loading routine on every case every time. Here is a pic of the tool I use. Just a paperclip straightened and then the end bent up and sharpened a bit

[Klem]

Key,

If you can give us the headspace of a new unfired Hornady case, and a fired one that will clear up a lot.

QL is showing 27gns as max for SAAMI.

[Growler]

Key,

If you can give us the headspace of a new unfired Hornady case, and a fired one that will clear up a lot.

QL is showing 27gns as max for SAAMI.