Too little neck tension? Virgin Lapua Brass? Cratered Primers

[RegionRat]

I was wondering about what @divingin was pointing toward as well.

I know that new Hornady and new Lapua can look very different, but I am wondering what the shoulder datum length looks like on cases that don't show the crater versus ones that do?

When cases are allowed to "move" forward, sometimes that primer cup is actually cycled back and forth so much that it produces a pattern like what you are showing.

 

[Bc'z]

Yep, this is the Ruger Precision rifle.

I've used this bolt for probably 4000 rounds now and never had a problem. However, I've always used Federal 210M large rifle primers.

If the issue is just my bolt and small rifle primers, is there a downside to cratering primers? Or can I eventually pop some if I keep this up?

I've seen the same thing on my Ruger American, but I've never ran srp's or magnum. I will say my primers are FLAT with the same crater. I've never pierced, but will be having bolt bushed once it comes home from Virginia.
I believe Jerry @carlsbad is set up to bush Ruger bolts.

 

[MagnumManiac]

I’m referring to the firing pin hole. If it is too large or beveled, it will crater primers no matter what load you are firing.
A bevel is a 45 degree chamfer usually used on the holes outer edge, it is an unnecessary and stupid thing rifle manufacturers do.

Cheers.

 

[KC MO]

I'm pretty diligent about making sure I get a good crush fit. Primers were relatively deep. Although this is the first time using primers other than Federal 210M


Hornady was shot with large rifle primers. Federal 210M


Was that just with the first firings? After the shoulders grew did you still get primer issues?

 

[CA_Shooter]

I was wondering about what @divingin was pointing toward as well.

I know that new Hornady and new Lapua can look very different, but I am wondering what the shoulder datum length looks like on cases that don't show the crater versus ones that do?

When cases are allowed to "move" forward, sometimes that primer cup is actually cycled back and forth so much that it produces a pattern like what you are showing.

That's a good question and I'll measure it out.

What I did notice, which makes me think this is due to the light neck tension is:

The more soot on the base of the brass, the less the shoulders grew. I'm guessing that brass had higher pressure.

 

[CA_Shooter]

Was that just with the first firings? After the shoulders grew did you still get primer issues?

I still need to fire them a second time. This was just the first time with virgin brass

 

[CA_Shooter]

I've spent an inordinate amount of time measuring the shot lapua brass and previously fired Hornady brass fired through this barrel.

Both brass started out the same size (Hornady and Lapua).

What I've found is that after 3 firings, Hornady is shorter than Lapua fired 1 time.

It seems as though many of the Lapua grew the size of my chamber after 1 firing. Could this be why the primers cratered? Large growth at one time?

 

[RegionRat]

Maybe.

The only way to see for sure is if a difference develops after the brass has more match to the chamber and then you size and load as normal. That will either show the crater disappears or it doesn't.

The good news is they don't appear to be piercing or damaging your firing pin.

 

[243winxb]

It seems as though many of the Lapua grew the size of my chamber after 1 firing. Could this be why the primers cratered?

Primer flow=High pressure. Watch for loose primer pockets.

 

[carlsbad]

Cratering is just a function of pressure and firing pin diameter. Your bolt face looks great. I don't see any chamfer on the edges of your firing pin hole. but ruger, for some reason, designed a modern rifle with an old fashioned firing pin diameter. The larger the firing pin hole, the more it will crater and eventually pierce the primers. cratering will eventually wear away at your firing pin hole and make things worse. cratering can cause hard bolt lift too.

I don't see any sign of primer leakage on your bolt (unless you cleaned it before you took the pic). You could post a photo of some fired primers and we could give you an opinion if your pressure is too high. You can get cratering long before you have excessive pressure.

yes, I can bush Rugers. PM if you want to eliminate cratering.

--Jerry

 

[CA_Shooter]

Maybe.

The only way to see for sure is if a difference develops after the brass has more match to the chamber and then you size and load as normal. That will either show the crater disappears or it doesn't.

The good news is they don't appear to be piercing or damaging your firing pin.

Cratering is just a function of pressure and firing pin diameter. Your bolt face looks great. I don't see any chamfer on the edges of your firing pin hole. but ruger, for some reason, designed a modern rifle with an old fashioned firing pin diameter. The larger the firing pin hole, the more it will crater and eventually pierce the primers. cratering will eventually wear away at your firing pin hole and make things worse. cratering can cause hard bolt lift too.

I don't see any sign of primer leakage on your bolt (unless you cleaned it before you took the pic). You could post a photo of some fired primers and we could give you an opinion if your pressure is too high. You can get cratering long before you have excessive pressure.

yes, I can bush Rugers. PM if you want to eliminate cratering.

--Jerry

Thank you for the advice. I'll try out the brass that ended up growing and if I still have primer issues I'll look into having you bush it.

The picture of the bolt was after I thoroughly cleaned it. There was a lot of powder soot on it.

I seemed to have multiple issues:

•loose neck tension for some brass, which allowed a bunch of powder soot to make it into the bolt and down to the rim of the brass. <--this brass did not grow to the size of my chamber
•brass that probably had more neck tension, because it didn't have powder soot on the rim of the brass: full growth to my chamber size from virgin brass. <--this brass seemed to grow from below the size of a go gauge all the way to my chamber size in one shot.
•brass with some soot on the rim of the brass grew in the middle of the brass with no soot and a lot of soot.

 

[carlsbad]

Soot coming all the way down the side of the brass is not caused by too little neck tension. It is caused by brass that needs annealing. When the round is fired, if the neck is appropriately ductile, it will quickly open up and seal the neck and very little soot will get on the outside of the casing. If the brass is the neck is work hardened, then it will resist opening up, it won't seal well, and you'll get soot on the outside. I think you said this was factory. Hornady brass tends to be hard and this batch may have been exceptionally hard.

As I understand this, it is all a function of the brass properties, not neck tension.

--Jerry

 

[243winxb]

Soot link increasing neck tension seemed to fix soot.

 

[LCazador]

For 6.5 creedmoor

I switched brass from Hornady to Lapua. Also switched to CCI 450s

With the Hornady brass, I mandrel using a .264. This gets me to PSI readings on the 21st century arbor press of about 70-90

Using Virgin Lapua brass, I mandreled it the same. But my PSI readings were 5-15 PSI.

After firing, I got some cratered primers. Just the primer strike was cratered, the outer edge of the primers looked normal. And also soot on the brass. I was below max loads. Are the cratered primers and soot from the necks being too loose?

I attached an image of the worst one

Updated images. On the same day I also fired:
•factory Hornady SSTs. These had the same base to shoukder size as the lapua brass
•some 2 year old Hornady reloads of mine. The brass has been shot a good amount of times. Primer is Federal 210M
•lapua new brass, CCI 450s with 38.5 H4350
•lapua new brass, CCI 450s with 42.0 H4350

Something I noticed: the more soot on the head of the brass, the less shoulder growth on the brass

Pictures reference which brass is which

Looks like you have a large firing pin diameter which doesn't work well with Lapua small primer brass. That's what's creating the crater on the small primers. You'll have to stay with large primer pocket or have your bolt bushed. Sooting is from not enough pressure and if you up your powder charge you'll blank the primer on the Lapua brass.

 

[carlsbad]

Soot link increasing neck tension seemed to fix soot.

I understand the neck tension argument...but it causes the pressure to build higher in the case before pushing the bullet out which can lead to overall pressure issues. Whenever you see factory brass exhibiting pressure signs it is usually too much neck tension. Nothing really good happens with excessive neck tension.

I anneal every time and have run neck tension so light you can move the bullets by hand (that was not on purpose) with no sooting.

--Jerry

 

[243winxb]

have run neck tension so light you can move the bullets by hand

Would the jump distance make a difference? Just asking to learn.

 

[carlsbad]

Would the jump distance make a difference? Just asking to learn.

I don't recommend neck tension that loose. I don't think jump affects pressure much but am not sure.

 

[Straightshooter1]

I anneal every time and have run neck tension so light you can move the bullets by hand (that was not on purpose) with no sooting.

--Jerry

Ditto

And when I fired mine, I was hand feeding my bolt gun, a .308, and they performed . . . ok and no soot. If they're that loose, I wouldn't mag feed them nor use semi-auto platform.

 

[Straightshooter1]

I don't think jump affects pressure much but am not sure.

Jump will affect pressure to the extent that it's a function of seating depth. As one seats the bullet deeper to get a longer jumps, pressure increases as the case's interior volume for powder is being decreased.

 

[LCazador]

Jump will affect pressure to the extent that it's a function of seating depth. As one seats the bullet deeper to get a longer jumps, pressure increases as the case's interior volume for powder is being decreased.

This is correct but the force of compaction is also going to change the seating depth by forcing the bullet out. Also as you seat further out into the lands the additional force required to chamber the round will push the bullet back into the case and change the seating depth as well as the interior volume of the case.