Please HELP!! Low pressure???

[Idaho Hunter1]

I read through this and was trying to understand/learn how a dented case equaled under pressure? I think I can understand the blackening and low velocity giving it away. Can someone enlighten me so I have this in my bag of knowledge?

 

[rammac]

I read through this and was trying to understand/learn how a dented case equaled under pressure? I think I can understand the blackening and low velocity giving it away. Can someone enlighten me so I have this in my bag of knowledge?

When the powder charge is too light the case won't expand tightly in to the chamber wall so hot expanding gasses will get between the case and the chamber wall which will dent the case.

 

[bullet man]

Sounds like a crimp on the bullet would help also, would let the loads develop more pressure before releasing the bullet.

 

[Bang4theBuck]

Tagging in to see results from OP.

 

[Traveling Tech]

I had the same issue with a 257 weatherby. The problem wasn't powder charge at all. The problem is that the bullet is jumping out of the brass before the pressure builds enough. This causes the bullet to stick in the start of the rifling and a secondary pressure spike forces the bullet down the barrel. The brass never seals and the pressure gets on the outside if the brass collapsing it. My cure was a lee factory crimp die. I use a light crimp. This gives me sufficient and uniform neck tension. The brass seals and my speeds are incredibly consistent.
Just adding powder doesn't help. You have to increase neck tension so that the pressure builds inside the case first. Also adding powder could be dangerous with that secondary pressure spike.

 

[cajun]

Run a 1 shot per charge weight ladder to find max pressure with each load. Watch your chrono and look for normal pressure signs. Save you a lot of components and tine.

 

[Colin78]

Yah I'd try h4350 and see what that does...

Couple of other questions that crossed my mind:
What are you using for a scale? Doubt that it could be your scale is reading higher than reality but it's worth checking vrs another scale to verify.

What make of barrel did you use for the build? Perhaps it's got a slightly oversized bore? Less friction/less pressure...

What is your headspace like? If you are a ways off on your headspace with virgin brass maybe that could be part of the culprit... if you were forming the brass from 7mm saum or 300 saum I'd say you could leave enough of a false shoulder at the neck/shoulder junction, just enough that you feel a sligh crush on closing the bolt, getting you a good seal on the chamber...

If you are 0.020" off the lands I'd say that's pretty much where I load mine to so I wouldn't say you are jumping them too far.

Have you tried with the Hornady brass yet?

Orch

I'm using a RCBS chargemaster lite. I calibrate before each use, as well as double check charge weights periodically on a RCBS 5-0-5 scale.

It's a Muller barrel.

Headspace seems to be fine.

Yes I did try the Hornady brass as well as more powder. Much better results. No more low pressure signs and my velocity is up in the range I was expecting. Going to continue the ladder texting next weekend to see what the top end is and see where my nodes are.

 

[Colin78]

I had the same issue with a 257 weatherby. The problem wasn't powder charge at all. The problem is that the bullet is jumping out of the brass before the pressure builds enough. This causes the bullet to stick in the start of the rifling and a secondary pressure spike forces the bullet down the barrel. The brass never seals and the pressure gets on the outside if the brass collapsing it. My cure was a lee factory crimp die. I use a light crimp. This gives me sufficient and uniform neck tension. The brass seals and my speeds are incredibly consistent.
Just adding powder doesn't help. You have to increase neck tension so that the pressure builds inside the case first. Also adding powder could be dangerous with that secondary pressure spike.

By switching to the Hornady brass I got more neck tension. I'm how using the Hornady brass for this beginning testing. If I feel the need to use the ADG brass I will order a different bushing to get more neck tension.

 

[Colin78]

Run a 1 shot per charge weight ladder to find max pressure with each load. Watch your chrono and look for normal pressure signs. Save you a lot of components and tine.

Yep, that's what I'm doing.