6mmbr losing primer

[kaduflyer]

Hi have been doing work development on my 6mmbr using hogden 4895 and 85 gr Sierra spitzer using 28.4 and 29 gr I found primers were blowing out of case and leaving mark on case head and hard to open bolt  when increasing load I found cases ok image shows 1 case minus primer 29gr of 4895 seated at 2.225 inch other case with prime was 30.4 gr 4895 same seat depth no probs 

[Laurie]

Bearing in mind how strong the Lapua 6BR case-head is, that load with the blown primer produced WAY over safe pressures. Pull any remaining rounds - don't fire them. Also, any case that has ejector marks / suffered hard bolt opening is almost certainly scrap, so don't reuse it even if the primer has remained in the pocket.

However, 29gn H4895 shouldn't be over-pressure, or even anywhere near this level with this bullet. So there is something else badly wrong that you need to sort  before  restarting. As a another round with a recorded heavier charge was apparently OK, that suggests your 28.5 / 29gn charges weren't those weights at all. In your shoes, I'd start by having the scales' accuracy  checked. Or were you throwing charges straight from a measure?

[kaduflyer]

Yeah definitely 4985 thou an old tub I had maybe need to chuck it start again also scales are Rcbs 1500 electronic calibrated 

[kaduflyer]

Must say velocities seemed down too 29gr producing about 2750fps thought it should have been higher with that bullet so maybe powder to old 

[Triffid]

The round with the blown primer has Norma headstamp. The one with the flattened primer is Lapua.

I'd follow Laurie's advice though.

Triffid

[Laurie]

10 minutes ago, Triffid said:

The round with the blown primer has Norma headstamp. The one with the flattened primer is Lapua.

I'd follow Laurie's advice though.

Triffid

 

Well spotted - I can hardly read that headstamp. That'll likely account for the apparent out of charge weight sequence issue, but I still suspect that something 'isn't right' here.

Remember that with Lapua 6BR (and 6.5X47L IME; and I'd imagine Creedmoor brass too) that an apparent 'no probs' situation quickly becomes a 'big problem' situation. There are often no intermediate stages  between apparent normality and a leaking or blown primer.

[kaduflyer]

Hi Laurie I had loaded 11 rounds only up from 28.4 gr to 30.4 all fired ok apart from 28.4 and 29 grain load these chuked primer out no others had tight bolt issues or ejector marks on cases thou as stated velocity’s seemed bit low over chrono the loads were in .2 grain increments 

[duey]

I wouldn't mix brass at any time, especially when load Developing, different brass different parameters of weight and dimensions can give different pressure curves etc 

 

 

 

[gunner]

On February 22, 2018 at 5:05 PM, duey said:

I wouldn't mix brass at any time, especially when load Developing, different brass different parameters of weight and dimensions can give different pressure curves etc 

 

 

 

+1 - uniformity is key , use just one brass batch , annealing it too helps accuracy / consistency as you probably know what primers btw ?