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


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

Any ideas, or toughts?

 

[BallisticsGuy]

How are the velocities compared to what the "book" says you should be getting for that load? What bullet? How much neck clearance? Are you jumping or jamming? Folks will need some more detail. Do you know your bore and groove diameters? A too tight bore could easily drive pressures up 8-10K psi. With the data you've given I don't think a responsible diagnosis is really likely, though I guess it's possible.

 

[CVCOBRA1]

I'm guessing here, but a suppressed over bore could be the problem.

 

[ladebenken]

How are the velocities compared to what the "book" says you should be getting for that load? What bullet? How much neck clearance? Are you jumping or jamming? Folks will need some more detail. Do you know your bore and groove diameters? A too tight bore could easily drive pressures up 8-10K psi. With the data you've given I don't think a responsible diagnosis is really likely, though I guess it's possible.

Velocity is as expected. The same thing happens with 54gr of Retumbo also, so there is something strange going on. I have tought about carbon build up, but it should not happen in 5-10 shots. There is no copper either in the bore.

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.

 

[Trnelson]

It is the suppressor. I shoot quite a bit suppressed.

 

[Trnelson]

It is the suppressor. The suppressor is causing the gun to rapidly carbon foul. It is due to the back pressure. I had the same trouble with a 6.5/06 that I ran suppressed with 140's and Retumbo. Try H4831sc or pull the can off and everything will be normal

 

[Tangent]

I'm curious to the problem(s) some are mentioning here regarding the use of a suppressor. I typically shoot 200-300 rounds through my bolt guns suppressed between cleanings without any problems.

Can anyone elaborate to their suppressor problem(s)?

 

[ladebenken]

Can you explain how the suppressor is causing the barrel to carbon up? I Dont understand the physics behind it. In my opinion there wil allways be a higher pressure behind the suppressor than in front, causing all the gas to exit the muzzle. But maybe it is slowing it down?

Here in my country there is no licences or paperwork for buying a suppressor, many i know have shot every shot for 30 years suppressed. I have shot maybe 3000 shots a year with suppressor, and this is the first time ive heard about it or had this problem.

 

[Greyfox]

Just a thought, but you didn't mention the free bore of your chamber. I'd check it as well as the finish of your throat. Im not sure that this is your case, but I have seen what you describe with 6.5X284's which have been chambered with the free-bore of the 284 Winchester throat dimensions...a throwback from the 6.5x284's wildcat days. This is not a Norma spec barrel. There are some gunsmiths and barrel makers that still produce the 284W length throat, a short action design. This can reduce bullet seating depth to the lands compared to a Norma spec chamber by +.1". 56 gr of Retumbo, or relative charges of other powders will produce over pressure conditions compared to the Norma spec chamber
The diagram below is representative of a the Norma spec chamber by Pacific Tool. Note the free-bore of .188". I find it wise to confirm this dimension when having barrels chambered.

 

[BrentM]

I'm leaning toward brass issues regarding headspace. Maybe the brass is hard. How many reloads and have you annealed?

 

[willowwolfe1975]

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?

I have the same issue with my 7stw. It's nothing special, it's a 700 action trued up and an international 28" heavy barrel on a mdt ess chassis with a trigger tech diamond trigger.
I built it over the winter and the chamber was specifically made for the long Berger 195 eol bullet. I received my load data direct from Berger. I have 2 unusual findings with this gun.
1) like you my loads are running at the very low end of the recommended range and with 7828 it is actually below the lowest recommended load. A half grain more blows cases, leaves ejector marks, and makes the bolt nearly impossible to open. Further, at a half grain more it smashed the injector pin so hard that the spring was done and the pin was actually bent. However, with this light load my velocity is about 60 m/sec faster than top speeds expected by the hottest loads recorded in the available data.
2) As for the temperature insensitivity boasted by powder manufactures....BS!!!!
In this rifle regardless of powder tried (7977, 7828, H1000, and Retumbo) all of them require seriously reduced summer loads to avoid blowing cases. For example, with 7977 my winter load (still not max by the books, but max for my rifle) is 76g. This is anywhere from -30 to -50 celcius where I live in northern saskatchewan. My summer load with this powder is 71.5g but I have light pressure signs (slightly heavier bolt lift, ejector marks, and brass fails faster). This is in our current +20 celcius weather.
However, it's accurate so I shoot it that way.
I have sent the rifle out to 3 highly recommended smiths who have all returned the rifle saying that there is nothing unusual/wrong with it.
So, I have come to the conclusion that in the same same vein that we know know 2 rifles will not like the same bullet, some rifles may just be wildly atypical. Further, I've learned my lesson in terms of advertising as those temperature insensitive powders are anything but insensitive.
It is interesting to see the possible issues/causes posted in response to your post. Most seem very reasonable and logical. I tried it all to no avail.

 

[30BR]

I waited aprox 2 minutes for the silencer too cool down.
Same problem occurs over and over again.
Any ideas, or toughts?

Are you keeping round number 6 in the chamber during the cool down period?
Also, if the powder charge is on the low side (not sure about yours), and the cases are not utterly free of case lube, there may not be enough pressure inside the case to fully expand it and grab the chamber wall once the action warms up. Had this happen to me at a match one day.

 

[Sgt. grizz]

Are your rounds sitting in the hot sun if so this could be the problem depending on how hot it is. If not I would check you suppressor. Shoot the same amount of rounds with it off to see what happens.

 

[ladebenken]

Hello.

Free bore is to my spec. Its custom to fit the 147gr ELD, both angle into lands and length.

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.


WHAT THE F... is going on..


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