6BR primer cratering

[Steve Ladino]

I reloaded some ammo for the new custom built 6 BR, 107 Sierra MK, 27.0 - 30.0 grains of Varget, virgin Lapua brass, and CCI 450 primers. Doing 3 round groups from 27 to 30.1 grains in .3 increments. At 27 grains I was already getting primer cratering. When I got home, I measured the boltface firing pin hole and it measures .076" and I also measured a boltface from the .308 that uses a standard large rifle primer, it measures .074" and it seems both boltface firing pin holes are for large rifle primers. I did some googling and I see that the small rifle boltface firing pin hole is .060" and would this be the issue? Send the bolt off to be bushed and get a small firing pin in it?

Here are the pics of the cratered primers.

When I use standard cci small rifle primers in my ,223 and in my 6 BR. they look like yours do and when I use 450's they do not crater unless I am way over the top with pressures.

I reloaded some ammo for the new custom built 6 BR, 107 Sierra MK, 27.0 - 30.0 grains of Varget, virgin Lapua brass, and CCI 450 primers. Doing 3 round groups from 27 to 30.1 grains in .3 increments. At 27 grains I was already getting primer cratering. When I got home, I measured the boltface firing pin hole and it measures .076" and I also measured a boltface from the .308 that uses a standard large rifle primer, it measures .074" and it seems both boltface firing pin holes are for large rifle primers. I did some googling and I see that the small rifle boltface firing pin hole is .060" and would this be the issue? Send the bolt off to be bushed and get a small firing pin in it?

Here are the pics of the cratered primers.

 

[Webster]

They look fine.

If you notice in the first post you will see a "lip" (not sure of the technical term and too lazy to look it up right now) forming on top on the crater. Yours are not doing that. At least they don't appear to be doing that from what I can tell in your photo. The first pic is a pretty good close on what the OP was seeing.

Some internet experts say it's OK, some say you have pressure. I have over 20,000 shots thru my Rem 700 action with different barrels. The size of the ridge around the primer indent is clearly related to pressure. The higher the pressure the farther the cup gets pushed into the hole. I don't care if bushing the hole makes the ridge go away.

 

[Whisky Tahoe Foxtrot]

Before I had my bolt bushed, I could crater and pierce factory Lapua 6BR ammo.
As soon as my bolt was bushed, the problem went away.
If primer cratering is the only pressure sign visible, it isn't always due to pressure.

If a non maximum load is experiencing primer cratering or piercing, reducing the firing pin hole aka bushing the firing pin is an excellent solution.

 

[Webster]

Before I had my bolt bushed, I could crater and pierce factory Lapua 6BR ammo.
As soon as my bolt was bushed, the problem went away.
If primer cratering is the only pressure sign visible, it isn't always due to pressure.

If a non maximum load is experiencing primer cratering or piercing, reducing the firing pin hole aka bushing the firing pin is an excellent solution.

50 years same REM action with slight cratering never had a pierced primer even with hot loads. I think that if the pressure is high enough to push the cup far enough into the hole that the center tears free resulting in a hole. Bushing just prevents cratering without reducing pressure. it's still there. If it isn't pressure what do you think is pushing the cup into the firing pin hole?

 

[243Mendoza]

What is the neck diameter of the loaded round? What its the neck diameter of your chamber? Tight neck? Do you turn neck?

 

[TackDriv3r]

Getting my bolt back next week, its being bushed.

I measured the headspace of the virgin / fired brass and it measures .004" between the virgin brass and the fired brass, will it cause high pressure, cratering and ejector swipes? If not, so how much headspace will it take?

I normally check headspace on fired brass, decap them, and try to chamber it as is, and see if its snug or closes without resistance. Then I decide to either bump back or not depending on how it feels when closing the bolt, mostly I bump at least .001" .

 

[TackDriv3r]

What is the neck diameter of the loaded round? What its the neck diameter of your chamber? Tight neck? Do you turn neck?

The rifle chamber is a .271" no turn neck, I believe my loaded round is a .2695" - .270" off the top of my head.

 

[Whisky Tahoe Foxtrot]

50 years same REM action with slight cratering never had a pierced primer even with hot loads. I think that if the pressure is high enough to push the cup far enough into the hole that the center tears free resulting in a hole. Bushing just prevents cratering without reducing pressure. it's still there. If it isn't pressure what do you think is pushing the cup into the firing pin hole?

None of my Remingtons have had pierced primers either.
It can happen with any rifle but seen often with Savage rifles that have a small firing pin diameter and the same old hole in the bolt that is considerably larger.

When the pin diameter is visibly smaller than the hole diameter, primer metal can flow with normal pressures during ignition. Fixing this won't cure loads that exceed maximum either.

All the bushing work does is fill in the gap so there is less room for metal to squeeze in when ignition slams everything back into the bolt face and expands brass into the chamber.

Another thing to consider here is the cartridge 6BR, which uses small rifle primers.
Some softer small rifle primers can flow more readily than others. I never had issues with primers till I started shooting 6BR in a Savage, though could have easily been 6BR in another rifle.

As long as the OP has what info they need we've done our good deed.

 

[sambo7]

check pm

 

[Webster]

I reloaded some ammo for the new custom built 6 BR, 107 Sierra MK, 27.0 - 30.0 grains of Varget, virgin Lapua brass, and CCI 450 primers. Doing 3 round groups from 27 to 30.1 grains in .3 increments. At 27 grains I was already getting primer cratering. When I got home, I measured the boltface firing pin hole and it measures .076" and I also measured a boltface from the .308 that uses a standard large rifle primer, it measures .074" and it seems both boltface firing pin holes are for large rifle primers. I did some googling and I see that the small rifle boltface firing pin hole is .060" and would this be the issue? Send the bolt off to be bushed and get a small firing pin in it?

Here are the pics of the cratered primers.

I would like to see a case head after they fire a proofing load at the factory.

 

[rogina]

Fixing a firing pin hole is not a "fix" for a hot charge weight. I'd back down the load first and see where the problem goes away and adjust from there.
For other posts on here about the primers, I did a lot of testing and the Rem 7 1/2 is the hottest small rifle primer going, it will add between 40 and 60 fps to a normal load and push some edgy loads over the edge.

Lefty, I tested 205 and 71/2 primers about 15 years ago. All four of my 6ppcs. 2 6BRs and 3 223rem barrels were 30 fps faster with 205s. All barrels were custom SS. I have an Ohler 35p. Have things changed?

 

[Lefty Trigger]

Lefty, I tested 205 and 71/2 primers about 15 years ago. All four of my 6ppcs. 2 6BRs and 3 223rem barrels were 30 fps faster with 205s. All barrels were custom SS. I have an Ohler 35p. Have things changed?

I tested a know good load for my rifles (6mm Creedmoor large primer and 6BRX small primer) here is the result with LabRadar...
Large test
Rem 9 !/2 Vel 3019 worst ES and worst group
CCI 200 Vel 2993 2nd best ES 2nd best group
CCI BR2 Vel 2980 best ES
Fed 210M Vel 2997 3rd best ES best group

Small Test
Rem 7 1/2 Vel 3017 sorry no ES data for any
CCI 450 Vel 2980
CCI BR4 Vel 2894
Fed 205M Vel 2974

 

[rogina]

I tested a know good load for my rifles (6mm Creedmoor large primer and 6BRX small primer) here is the result with LabRadar...
Large test
Rem 9 !/2 Vel 3019 worst ES and worst group
CCI 200 Vel 2993 2nd best ES 2nd best group
CCI BR2 Vel 2980 best ES
Fed 210M Vel 2997 3rd best ES best group

Small Test
Rem 7 1/2 Vel 3017 sorry no ES data for any
CCI 450 Vel 2980
CCI BR4 Vel 2894
Fed 205M Vel 2974

That is interresting.

 

[Drop Port]

I don't know if I missed it or not, but what action is this?

 

[Old Navy]

The photo of the cases I posted were two full grains under the proven load I had been shooting. The bolt/pin had fired 10K rounds. The primers were not blown and no black ring. The crater went from slight to what you see in a few hundred rounds. Don't have a clue why. And it did the same to several other bullet/powder combinations. My bad that I didn't find Gretan sooner.

 

[JEFFPPC]

Getting my bolt back next week, its being bushed.

I measured the headspace of the virgin / fired brass and it measures .004" between the virgin brass and the fired brass, will it cause high pressure, cratering and ejector swipes? If not, so how much headspace will it take?

I normally check headspace on fired brass, decap them, and try to chamber it as is, and see if its snug or closes without resistance. Then I decide to either bump back or not depending on how it feels when closing the bolt, mostly I bump at least .001" .

Getting your bolt bushed is a good move. Someone said they did not care if the primer extruded into the firing pin hole. They will when a primer is pierced and they get a piece of it in their face, not to bright. It is best to full length resize every firing. Take the firing pin out of your bolt. Insert a fired round in the rifle and close or try to close the bolt. Bump the shoulder until the bolt will startt to fall closed about half way and then finish closing with a very light touch. If you have a fitted neck be sure your loaded rounds are at least. 002 less then your chamber neck diameter, do this with a like not calipers.. Also keep your brass trimmed to spec as long brass going up into the leade creates high and dangerous pressure.

 

[JEFFPPC]

The photo of the cases I posted were two full grains under the proven load I had been shooting. The bolt/pin had fired 10K rounds. The primers were not blown and no black ring. The crater went from slight to what you see in a few hundred rounds. Don't have a clue why. And it did the same to several other bullet/powder combinations. My bad that I didn't find Gretan sooner.

A weak firing pin spring can also contribute. Some clip the firing pin spring to make the bolt cycle easier. Not a good idea as it also will show an accuracy decrease in a really accurate rifle plus the primer extrusion.

 

[Drop Port]

The newest varget is way hotter- like what used to be a 31.5gr load is now 30. Send that bolt to carlsbad and get it fixed cheap and fast.


The surface area of the pin is what makes the difference. You can blank a properly fitted .075 dia then properly fit it to low .060’s range and it wont

+1
With all the suggestions being thrown around it is important to know the difference in terminology and not mix them while trying to make suggestions there is a huge difference in diagnosis.
1 Blown Primers
2 Blanked Primers
3 Pierced Primers
are three entirely different issues. Without knowing anything about the rifle I wont speculate but will say I've seen identical issued with a stock Rem, crater, semi oval strikes off center, swipes from rough uneven burred bolt face and even Blanked primers with light loads. Other rems ran absolutely fine with out bolt work. Likely the bolt work will cure what is being seen.
Next address the the neck and make sure there are no issues or you might be chasing your next potential issue old BR gold box and new blue box have varied .001 release? Based off old box that you mentioned I had just enough release with a .272 neck

 

[RegionRat]

I will also chime in with a recommendation for GRE-TAN Rifles.

I lost count of how many times Greg Tannel has corrected bolt guns for this condition.

I now have had him do his bolt processing on my new custom builds up front.

 

[Dusty Stevens]

These days ill be sending mine to carlsbad. No games, cheap fast service, and an upstanding member here that contributes