Pressure question

[Idaho Trecker]

I recently did some pressure tests in my 300 Dakota and had some questions about how different powders exhibit different pressure signs. For the tests the same primer was used (CCI 250) but powder was different and I am seeing different signs. With one string I was loading with RL33 and the other with Retumbo. The primers on the 33 string were not flattening or cratering when below what I am assuming is max but when I started going over the "max" the primers started to flatten considerably but never cratered or flowed over. On the Retumbo string the primers were perfect until "max" then started to crater but never flatten. As the charge increased the cratering got worse but never flattened.

Does the burn rate or time of pressure peak determine the pressure signs seen on the primer?

Any thoughts why the signs are totally different when using the different powders?

Do you think I am reaching my "max" pressure with these signs?

Thanks for any input

 

[Idaho Trecker]

no thoughts?

Am I really getting max?

 

[Lefty7mmstw]

Primers are very subjective and most people won't want to tell you yes or no based on them alone. Personally I use chrono speeds as both a speed and pressure limit more than primers. Primers can be watched as you go up but other things like primer pocket looseness, speed generated, brass expansion, how the rifle behaves (if she's cracking instead of simply barking and has heavier than normal recoil) mean a lot more to me than a flattened primer. Cratering is often a matter of firing pin fitment on the rifle, but if it comes out of nowhere and/or you start blowing primers at the crater you are treading on thin ice for sure.

 

[Idaho Trecker]

I just found it weird that one powder seemed to produce cratering and the other didnt.
I agree with you on the chrono... unfortunately I dont have one yet and probably wont be able to afford one until fire season gets here.

Thanks for your thoughts i appreciate it

 

[royinidaho]

I've pretty much eliminated primer observations as pressure indicators.

I use only crummy Rem & Win brass. Though Win brass is better than Rem when available for the cartridge.

Pressure limits around my place are displayed by the case.

For max bullet performance and minimum barrel life pressures are kept only slightly below the point of a sticky bolt. I also try to get 6 firings from a case.

For reasonable bullet performance and zero probability of having to hammer open the bolt, which is usually due to inconsistent brass, I drop the charge a grain or two on the hottest day I figure to ever shoot. Then stick with that load. Cases last almost forever with these loads. However the magnums are not very extreme with this load.

Having said all of that every primer I remove from a fired case in the extreme magnums is flared to completely fill primer pocket. That is, the primer fills the slight bevel around the edge of the pocket.

I think cratering has something to do with firing pin size compared to the bolt's firing pin hole size, firing pen spring tension and shape.

I use Federal 215 mag primers. However all the above applies to the 270 Win with CCIs.

In your case I'd think that RL-33 may result in a bit higher peak pressure and reach that peak pressure sooner than Retumbo. Retumbo may have more area under the pressure curve which, for the most part, is a good thing. That is higher vel with less peak pressure.

 

[Idaho Trecker]

Royinidaho,

Thanks for your input it was very insightful. I think i will load up a few more working up til i get a sticky bolt lift.

I've reached 86 grains of rl33 behind a 215 berger and the bolt lift feels fine still just flat primers which havent flowed into the bevel. Wish i had chrono to have idea how fast they are going.

Ryan

 

[royinidaho]

Ryan,

You pay shipping and I'll loan you a crony.

Its a chrony crony but serves the purpose.

Roy

 

[Idaho Trecker]

Roy,

Thank you very much for that offer. I'll pm you this evening.

Ryan