Blown out primers and pressure signs

[mikehill85]

I have been having issues with getting blown out primers with other signs of high pressures. My rifle is a Tikka CTR in 6.5 Creedmoor. The has happened with multiple types of powder, brass, bullets, bullet weights, and primers and seems to happen at random. By this I mean, I will have no pressure signs at maximum published safe charge but get a blown out primer, ejector mark, flattened case head, and primer cratering from a round that is 1.5 grains under maximum charge.

I have a borescope and checked for a carbon ring. There is none. I checked the bullet seating depth and all are at least 20 thousandths off the lands. I checked my headspace and the bolt won't close on a no-go gauge. I checked my powder charges with another scale (both give me the same value for my powder charges) and I am getting blown out primers and other pressure signs 1.5 grains under maximum charge for multiple powders.

I checked my base to shoulder dimension and it seems I wasn't bumping the shoulder back on my brass (at all really). Can not bumping the shoulder back enough cause pressure spikes?

 

[Fast14riot]

You can weigh loaded rounds to double check everything is about the same from round to round.

Aside from something being in the case or chamber, incorrect powder charge would be my guess.

 

[6MMsteve]

have u checked barrel bore size, maybe try a 6mm bullet it should fit right in, also chk barrel identification numbers just to make sure u have a 6.5 creedm simple things first

 

[Conaso]

What is your case headspace, how much bump?

 

[mikehill85]

You can weigh loaded rounds to double check everything is about the same from round to round.

Aside from something being in the case or chamber, incorrect powder charge would be my guess.

Yes, I have done this. I've tried checking all the charge weights with different scales as well. It would be nice if it were as simple as incorrect powder charge.

 

[mikehill85]

have u checked barrel bore size, maybe try a 6mm bullet it should fit right in, also chk barrel identification numbers just to make sure u have a 6.5 creedm simple things first

I am quite certain the barrel is the right size. I should mention that this only happens with reloads, not factory ammo, it is is definitely something to do with how I'm reloading.

 

[old codger]

Agree with Conaso. You could be setting the shoulder back too much and creating a headspace problem.

 

[243winxb]

blown out primers

Photo, brand? Could be defective primers ot loose pockets?

 

[dellet]

I have been having issues with getting blown out primers with other signs of high pressures. My rifle is a Tikka CTR in 6.5 Creedmoor. The has happened with multiple types of powder, brass, bullets, bullet weights, and primers and seems to happen at random. By this I mean, I will have no pressure signs at maximum published safe charge but get a blown out primer, ejector mark, flattened case head, and primer cratering from a round that is 1.5 grains under maximum charge.

I have a borescope and checked for a carbon ring. There is none. I checked the bullet seating depth and all are at least 20 thousandths off the lands. I checked my headspace and the bolt won't close on a no-go gauge. I checked my powder charges with another scale (both give me the same value for my powder charges) and I am getting blown out primers and other pressure signs 1.5 grains under maximum charge for multiple powders.

I checked my base to shoulder dimension and it seems I wasn't bumping the shoulder back on my brass (at all really). Can not bumping the shoulder back enough cause pressure spikes?

A couple things jump out. But a good start would be complete load data and actual measurements. Things like measured right, it fits, it closes have, little meaning. Here’s why.

You said it doesn’t close on a No-Go gauge. All that tells is that the chamber is not too long. It’s shot out if it closes. A Go-Gauge only tells it it’s too short. That’s more important for high pressure.

You said that you’re not bumping the shoulders back. That’s red flag #2. Depending on how your die is set up, screwed down to the shell holder, and not getting any bump, sounds like a short chamber. Normally a die adjusted like the instructions advise, ends up with excessive bump.

Excessive pressure and short base to shoulder length, really sounds like low case capacity, in a tight chamber is possible. If you have mixed headstamps, even more.

The more information with exact measurements, powder charges and bullets would probably help out. Especially some chronograph numbers.

 

[mikehill85]

Photo, brand? Could be defective primers ot loose pockets?

This has happened with both Remington 9-1/2 primers and Federal 210M primers. It is happening with both Hornady and Lapua LRP brass.

 

[gmr4]

You’ve got a good list of items checked. I’d double back and make sure the shoulders arent getting bumped too far on some cases. I strip my bolt and begin bumping fired case until bolt drop or has slight resisitence.

 

[mikehill85]

Agree with Conaso. You could be setting the shoulder back too much and creating a headspace problem.

I thought this too, so I tried using neck sized only brass, I got the same random pressure issues.

 

[mikehill85]

A couple things jump out. But a good start would be complete load data and actual measurements. Things like measured right, it fits, it closes have, little meaning. Here’s why.

You said it doesn’t close on a No-Go gauge. All that tells is that the chamber is not too long. It’s shot out if it closes. A Go-Gauge only tells it it’s too short. That’s more important for high pressure.

You said that you’re not bumping the shoulders back. That’s red flag #2. Depending on how your die is set up, screwed down to the shell holder, and not getting any bump, sounds like a short chamber. Normally a die adjusted like the instructions advise, ends up with excessive bump.

Excessive pressure and short base to shoulder length, really sounds like low case capacity, in a tight chamber is possible. If you have mixed headstamps, even more.

The more information with exact measurements, powder charges and bullets would probably help out. Especially some chronograph numbers.

I checked and the bolt doesn't close on a Go gauge either (just to be clear, I took out the ejector and extractor when I check this). That said, I have never had any issues chambering factory ammo, so the chamber is definitely tight but it must be just slightly under SAAMI spec. Fired cases measure 1.5385" using the Hornady comparator tool with the D400 insert.

 

[243winxb]

It is happening with both Hornady and Lapua LRP brass.

Compare weight of both. Heavier, less capacity, , more pressure.

Tumbling media left in brass?

 

[coford]

Are you keeping your brass trimmed to length? You can create pressure if your case is too long. Either measure or trim each firing and this may go away. If you are using stainless steel pins to clean your cases it can cause thickness at the case mouth by peening the end of the case - that can also raise pressure.

 

[dellet]

If your chamber is short at the shoulder, and your brass is any where near max trim length, the necks will be too long and pinch the bullet in the neck.
This might explain the random spikes as you need the combination of short shoulder long neck.
chamber some of the sized brass and run your bore scope in from the muzzle. You’ll probably see the neck extending into the free bore.

You’re fighting a problem that should not have left the factory, if your base to shoulder datum is correct.

 

[mikehill85]

Below are loads where I got blown out primers and pressure. To be clear, my rifle has a 24" barrel.:

Primer: Remington 9-1/2
Brass: Hornady LRP
Bullet: 147 grain Hornady ELD-M
Powder: N555
Charge: 41.4 gr (max is 42.6)
Velocity: Unavailable

Primer: Remington 9-1/2
Brass: Hornady LRP
Bullet: 147 grain Hornady ELD-M
Powder: H4350
Charge: 40.9 gr (max is 41.8)
Velocity: 2,660 fps

Primer: Federal 210M
Brass: Lapua LRP
Bullet: 143 grain Hornady ELD-X
Powder: 6.5 Staball
Charge: 42.5 gr (max is 43.5)
Velocity: 2,717 fps

Primer: Federal 210M
Brass: Lapua LRP
Bullet: 140 SMK
Powder: 6.5 Staball
Charge: 42 gr (max is 43.0)
Velocity: 2,647 fps

Primer: Remington 9-1/2
Brass: Lapua LRP
Bullet: Berger 140 grain Hybrid Target
Powder: 6.5 Staball
Charge: 42.5 gr (max is 43)
Velocity: 2,711 fps

 

[mikehill85]

If your chamber is short at the shoulder, and your brass is any where near max trim length, the necks will be too long and pinch the bullet in the neck.
This might explain the random spikes as you need the combination of short shoulder long neck.
chamber some of the sized brass and run your bore scope in from the muzzle. You’ll probably see the neck extending into the free bore.

I thought the same thing, however, I trim my brass every time. I checked with my borescope and 10 pieces of brass and there is gap between the case neck and the chamber.

 

[mikehill85]

Compare weight of both. Heavier, less capacity, , more pressure.

Tumbling media left in brass?

I had considered that maybe there was media left in the cases. I checked all my brass with a borescope and there was nothing. The reason I tried Hornady brass was to try to rule out case capacity as the problem. Hornady brass has more case capacity than Lapua.

 

[mikehill85]

Are you keeping your brass trimmed to length? You can create pressure if your case is too long. Either measure or trim each firing and this may go away. If you are using stainless steel pins to clean your cases it can cause thickness at the case mouth by peening the end of the case - that can also raise pressure.

I trim every time and I don't use stainless steel pins. I also chamfer the inside of the case mouths and deburr the outside every time. I use walnut media in a vibratory tumbler.