I have a custom pre 64 M70 280 AI which I had put together 7 years ago. Right away I settled on an accurate load of:
nosler factory 280 AI brass
barnes 150g TTSX
federal LR primers
62 grains of RL22
It's typically at 3050 FPS.

I've always used new brass, same OAL and had great results but in the last couple practice sessions I've gotten some blown primers I'd say 10-20% of the time. I weigh every powder load and know I've not slipped up on the powder charge.
What other factors could cause a blown primer from time to time after all these years without issue. The rifle has a little less than 600 rounds through it thus far.

Thanks for your input.

The first thing that comes to mind that will raise pressure fast is if you may be seating them longer and they are touching the lands which can spike the pressure, or maybe you changed bullets and the ogive is different and again you are into the lands.
This would be the first thing I would check.

Can you check the head space? Maybe a different lot of powder? double check everything.
you are 6grs over the standard 280 load 150gr bullet. That's a lot of powder for a 100ft of velocity
if the case didn't expand due to high pressure. A blown primer will not fit back into the pocket.
if it was hi pressure the pocket should stretch and the blown primer should fall in the primer pocket.
Check your firing pin if it was damaged or has a sharp point it may pierce the cup. check the primers they could have a thin cup I saw a recall a while back don't remember what brand or size..

Soft primers, soft brass, different lot of hotter powder, thats about it. Not headspace. It just started happening, so what did you change? whatever you changed since 7 years ago, that's it.

If you are blowing 10-20% of your primers I'd say your loads are too hot. The ones that blow are just a touch softer than the others.

Have you always used Nosler Factory AI brass?

As hivelosity asked what is the condition of the pocket. I bet you a that even the non blown cases are loose or would be after the second loading.

Are the problems all with one lot of primers ?
That's the first thing I'd check.

Thanks for all the input so far guys. I always use new nosler 280 AI brass and my load of 62g has not changed.Same bullet as well, but obviously I've been through a couple boxes of brass and jugs of powder. But the load, OAL and primer have stayed the same. So really 6 years of non issue shooting and now the blown primers show up...

quote:

jugs of powder

Just to verify you are saying that you have used jugs of powder and the 62gr charge has stayed the same? Did you drop and work back up to 62 when you open a new jug?

Different lots of powder??? RL22 has had a lot of press as to the burn rates varying between lots. People talk about having to cut loads by a number of grains. I had a new bottle of RL22 years ago blow my first primer. I fuc!ed up got in a hurry and grabbed a new bottle and didn't test it. I ended up several grs lower. Lot to lot might match. Might not.

Just a quick run of QL shows using the normal burn rate for RL22 your load is around 61000 but bump the rate up by only 5% you are pushing 70,000.

What so the other primers look like? Have you checked to see if your pockets are enlarged?

Blown? Did primer fall out of the pocket after firing?

Is there a hole in the primer?

Where is the hole, if there is one.

You mention same primer. Is it a new box of primers? Primers have issues just like cases and powder lots.

I'm assuming that a "blown primer" means it fell out of the primer pocket.

If you haven't done so, check your scale with check weights.

I would also check the weight of the brass if it was purchased at different times.

I would drop the charge just a tad and switch to a magnum primer.