A strange problem with 6,5x284 - Pressure

[ladebenken]

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
-Bullet is 147gr ELD-M

-Neck cleareance is .005" A bullet easily gets into a shot case.

-I have tried both jumping and jamming.

-I dont know my bore & groove diameter, but i guess its by spec. Its a Krieger.

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

Any ideas, or toughts?

 

[Country]

I think you are overloading for a 147 grain bullet come down to 54 grains of powder .
If the gun gets hot and you leave the round in the chamber for a while with that load over pressure .
Krieger barrel could be cut rifled and tight , also adding pressure and friction .

 

[ladebenken]

The same also happens with 54gr. At 54,5gr the speed is 826 m/s. At 57.5gr the speed is 886m/s. The barrel is 23 ". I see the Retumbo is burning i bit dirty.

 

[Steel head]

Not exactly a speed demon before you hit pressure

 

[SkyScrapin]

How many rounds down the barrel?

I had a similar issue with 300wm, 215 Berger’s and h1000. It seems to have settled after 50-60 rounds and a vicious cleaning.

 

[ladebenken]

About 500 rounds, but the issue has been there since about 30-40 rounds i think, but not as bad as now.

Today i went out again, the brass is new, only neck turned and controlled 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.

WHAT THE F... is going on..

At the picture its todays shots. Down on the right is overpressure round.

 

[Milo 2.5]

About 500 rounds, but the issue has been there since about 30-40 rounds i think, but not as bad as now.

Today i went out again, the brass is new, only neck turned and controlled 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.

WHAT THE F... is going on..

At the picture its todays shots. Down on the right is overpressure round.

If the right pic above is fired brass, you do not have any carbon anywhere on the necks. That tells me, either your brass needs trimmed, or you have a serious carbon ring at the end of the neck in your chamber. Case mouths are getting choked off.
If your brass is not too long, get a 7mm or 30 cal brush, either chuck a rod up in a drill or work that area of your chamber over by hand with a good carbon cutting solvent.

 

[ladebenken]

From the Retumbo rounds i get serious carbon layer on the necks.

Can it be the carbon ring gets harder when the barrel gets a few minutes to cool down? And this actually is a carbon ring issue.?

This rifle is a few days from beeing throwed in the ocean, or maybe melted into nails..

 

[Jerry m]

As Milo said above check for a carbon ring.

 

[Milo 2.5]

From the Retumbo rounds i get serious carbon layer on the necks.

Can it be the carbon ring gets harder when the barrel gets a few minutes to cool down? And this actually is a carbon ring issue.?

This rifle is a few days from beeing throwed in the ocean, or maybe melted into nails..

Ok, could be your retumbo loads not generating the pressure the other powder does, so carbon on the necks, but also, incomplete burns a big factor in carbon ring formation, more powder, cleaner burn.
But still, the cases in the pic do not look like any carbon present, need as much as faint line at least. I'd clean where I said to, maybe trim .008" of the brass, do one at a time and let's figure this out.
Rifles do funny shit at times, I cannot explain hot after a cool down. One day I was shooting a box of 50 through a dasher with a suppressor on, shoot 12, cool down, etc... Around # 40, stiff bolt, rifle not hot, load not hot, pulled the can and it went away, shot the remaining rds and never used a suppressor on the rifle again, problem solved.

 

[918v]

Have you tried jumping .100” ?

 

[ladebenken]

I have tried jumping 1mm. - approx: .050" i think.

Attached some more pictures of the overpressured cases. not carbon back blow, but there is something on the cases. I always use red etanol to clean the chamber after scrubbing the barrel. But it can be some oil left in the lug area..

 

[RampedRaptor]

Insufficient neck clearance between loaded round and barrel?

 

[FLIGHT762]

Will a bullet fit down the neck of the fired round?

 

[ladebenken]

Yes, a bullet easily fit down a fired case.

Neck cleareance is 0.005"

 

[Country]

The same also happens with 54gr. At 54,5gr the speed is 826 m/s. At 57.5gr the speed is 886m/s. The barrel is 23 ". I see the Retumbo is burning i bit dirty.

Those primers are not showing dangerous pressure . It could be the Krieger barrel . Scrub hell out of the chamber and the bore . Velocity does not seem to indicate dangerous pressure either . Polish up the chamber . The marks on the case look like a possible rough chamber that is causing hard bolt lift and extraction . Then run it with 54 grains for a while .

 

[ladebenken]

Well now i have got some new expirience.

I used to clean this rifle like all my others, including my comp rifles in 6,5 swede, which i shoot 4-5000 shots with a year.

Well it seems it hasn`t been good enough. It has now gotten what i call a judgementdaycleaning. About 5 days soaked with different chemicals, brushed like f... each day and polished 4 times with gold medallion.

Today i shot 35 shots with no problems. Same brass, same load, same bullet, with silencer.

5x5 shots at 430 meters - 480 yards.

Todays best group, and the worst.. Looks like that Krieger barrel is ready for hunting

 

[Country]

My work here is done . Judgement day cleaning I like that .

 

[FatBoy]

Carbon ring is a common issue on 6.5x284s. I have burned down 11-12 barrels shooting highpower. Now. They get JBd at 300 rounds then every 150 until they're trash, which is around 1k rounds.