A strange problem with 6,5x284 - Pressure

[BallisticsGuy]

Well, your last post changed this one, so I'll just hush as it's now back to mystery land.

 

[30BR]

Today i went out again, the brass is new, only neck turned and length. Load is 47gr N160 and 0,5mm from the lands.

I shot 9 or maybe 10 shots before without any signs of pressure, everything seemed nice. I waited for about 3-4 minutes for the barrel and silencer to cool down. The first shot after cool down gave massive over pressure. This is the same issue as always, the first shot after a small "cool down" gives massive over pressure. Before these ten shots i have given it a massive scrub with all kinds of chemicals and nylon/bronze brush.
At the picture its todays shots. Down on the right is overpressure round.

The only oddity I see is the primers do not appear to be flattened. There is an arc that I can see on them, as if when seated, the tool is not centered. If the brass is flowing into the ejector, that primer should be dead flattened by the bolt face. Because it isn't, it makes sense that there is no overpressure. It it were, the primer would have backed out and flattened. I do not think your cases are expanding enough to get a good grip on the chamber wall for whatever reason.

 

[Sgt. grizz]

Maybe your chamber is a little too tight or too loose.

 

[Sgt. grizz]

Maybe your chamber is a little too tight.

 

[338 dude]

Hello

I am having some problems with a rifle in 6,5x284. The Rifle is a custom action on rem 700 footprint, and is fitted with a Krieger Barrel.

Brass is Lapua.

The problem is as follows:
When i work up a load i.e 55,5gr Retumbo, which is a light load, max should be around 57-58gr.
Ok.
After cleaning i can shoot 5-15 shots before i get problems with pressure, today it happened after 5 shots. First five shots gave me no signs of pressure. I waited aprox 2 minutes for the silencer too cool down. Shot nr 6 gave me extractor mark, and sticky bolt?

Same problem occurs over and over again. I have tried:
-Three different powders.
-Different brass.
-Checked neck cleareance, i have neck turned the brass.
-Checked overall length of brass


My tought at first was carbon build up, but it should not happen after five shots..

Any ideas, or toughts?

You mentioned a suppressor they hold in a great deal of heat they get hot and your barrel gets hot you didn't mention how long you waited between shots if you fire fast strings as heat builds it could raise pressures especially if you leave the chamber loaded for a while before you shoot it is called cooking off a round

 

[338 dude]

You mentioned a suppressor they hold in a great deal of heat they get hot and your barrel gets hot you didn't mention how long you waited between shots if you fire fast strings as heat builds it could raise pressures especially if you leave the chamber loaded for a while before you shoot it is called cooking off a round

I'm sorry you did mention two minutes that is not really very long and you will not dissipate all the heat in that time so gradually it is building

 

[ladebenken]

I Dont leave the rifle loaded when its cooling down. I think each cartridge is in the chamber for about 4-7 seconds, before fired.

Can this be a carbon ring, that grows very fast, and gets harder when it gets a few minutes to cool down? Before today i scrubbed like hell,,

arc on the primers is for seating tool.

I am one day from throwing this garbage in the ocean..

 

[30BR]

I Dont leave the rifle loaded when its cooling down. I think each cartridge is in the chamber for about 4-7 seconds, before fired.

Can this be a carbon ring, that grows very fast, and gets harder when it gets a few minutes to cool down? Before today i scrubbed like hell,,

arc on the primers is for seating tool.

I am one day from throwing this garbage in the ocean..

I will be happy to relieve you of your burden!!
But think about what you just wrote. The mark on the primer is from the seating tool. So the seating tool is applying more pressure to the face of the primer than the bolt is upon firing. So the primer remains seated below the cartridge base. There isn't enough pressure to back the primer up hard against the bolt face, yet the face is flowing into the ejector. The case is not sealing enough upon firing.
I suspect there is residual case lube on the rounds that becomes very liquid once the chamber is hot, causing the case to back up upon firing. Try wiping them down good with alcohol and try again. Make sure the chamber is squeaky clean and never lubed. if that fails to solve it, try bumping the powder charge until you see the primers begin to flatten.

 

[Bob Wright]

Send a picture of a side view of your heavy bolt lift spent catridges. Looking for soot marks from powder and how the case is sealing the chamber. It can tell a story as my son in law found out.

 

[30BR]

Just had another thought after looking at the fired cases...
Do you have a tool to check the brass headspace? Do you know how much you are setting the shoulders back?
New brass will always be short, and I like to soft pedal the first firing to fireform. The new brass looks like it grew quite a bit at the shoulder. If your chamber is on the long side, and you are resizing down to hit the die on the shellholder, it might be a tad too short and could be a contributing factor.

If you don't have a gauge, take the firing pin and ejector out of the bolt, and start resizing a fired case ever so slightly, and trial fitting it. the bolt handle should flop right down, unimpeded. Keep sizing until that happens, and lock the die down at that point.

 

[ladebenken]

Attached some more pictures of the over pressurized cases. No carbon back blow.

I always wipe my chamber with red etanol after cleaning my barrel. But the lug area can maybe have some oil still.

 

[ladebenken]

There is something on the cases, not shure what it is.?

 

[DUSTY NOGGIN]

im following the same lines as 30br , my question is, is your jump larger than your new brass headspace ?

re-read , its not what i was thinking , unless you are bumping that fire formed brass back down further than the distance of your jump .. it would be by chance that its all ways the 5th shot anyway ... weird dunno

you did alot of work to that brass , how is the case length looking after youve shot them a few times

 

[ladebenken]

The same thing happens with brass that is correctly sized. I also have a Neck bushing die. The same thing happens then also.