Thread: Signs of pressure in a 6.4x47

For 6.5x47 reloaders past & present please; when working up loads what sign or signs did you use as indicating maximum peak pressure had been reached - given that this case with its small primer pocket in Lapua brass is known for giving away few clues in this respect ?

Perhaps you could also please give your estimate as to what you thought the peak pressure might have been at the onset of the stated symptom/s and the reason that that was the point to back things off ?

As all chambers and barrels are different all traditional methods such as stiff bolt lift flattened primers etc. can be misleading at best dangerous at worst. Use a chronograph and note the fps velocity increase for each step in powder charge. You will note as you reach max there will be a diminishing increase in velocity. That is max do not continue. However in many cases your accuracy node will be below max. It really isn't about those last 50fps its about where it shoots the best.

I'm not sure I completely agree with @Dermastor comment above.

Diminishing increase in velocity is also an indication of a node. In a full spectrum of loads there are several of these as you progres thru increasing powder charges. If you stop below the first zone of diminished velocity increase, you may still be well below max....

Flat primers to me are often more a sign of poor head spacing on the case rather than pressure.

The 2 things I look for in terms of pressure are heavier bolt lift and marks on the case base. Without fail,me very single hot load I've had, has had extractor/ejector marks.

@Puffin, putting a 6.5 projectile in a 6.4 chamber WILL cause a pressure spike

Sorry dude, couldn't resist. Catch you at the range sometime, my bloody swipe card has stopped working, aargh !

If you're not seeing strain in the case in the form of ejector marks or heavy bolt lift, can the pressure really be considered dangerous?

Guess the "scientific" way would be to measure case expansion nof at the base / web, but even there you have a lot of variables in terms of the state of your brass, how old it is etc.

Not much help Puffin because my load development for my 6.5x47L was a doodle and I never stretched the envelop to find the last higher velocity node. Just wasn’t necessary and I had no desire to go there.

I was mindful however b4 I started of the very strong 6.5x47L SR primer case's ability to hide to a certain extent the onset of high pressure (within reason) also the Barnard action I have found doesn’t always present sticky bolt lift as early as some other actions. Plus that action has no ejector hole for brass flow. Have tried the head expansion measurements in the past but that is not always conclusive – I had an article debunking head measurements as the finite method but can no longer find it.

My loads gave 2900 for the 123gr Scenar and 2850 for the Berger 130gr VLD.

Cases have had 4 loads now and no issues detected with them to date.

I need to plug these into QL now that I have a copy so I can better understand where I am pressure wise with the loads.

The 130gr Bergers shot 5 shot 100yd groups of =<0.2 on good days and =<0.4 on bad (read me) days.

The equal most accurate rifle I own.

When it's stamping the cases you have gone to far, chrony the speeds that should give you an idea as well as bolt lift, etc there's plenty of data around on what speeds you can expect to get.

when the bolt goes past your right ear at a rate of knots .... you've gone too far.

Originally Posted by chainsaw

when the bolt goes past your right ear at a rate of knots .... you've gone too far.

That only applies to remigton actions

Puffin is using a Barnard. If the bolt from that comes flying back he has put in enough powder to create a small nuclear reaction !

Thanks Guys, some useful information.

Originally Posted by ebf

I'm not sure I completely agree with Dermastor's comment above.

Diminishing increase in velocity is also an indication of a node. In a full spectrum of loads there are several of these as you progres thru increasing powder charges. If you stop below the first zone of diminished velocity increase, you may still be well below max....

This is a great topic and now that we have grown tired of discussing ladders, OBT, OCW, and 3-shot groups, doesn't this deserve its own thread at some stage?

Originally Posted by ebf

Flat primers to me are often more a sign of poor head spacing on the case rather than pressure.

+1. I think most would find the edges do start to progressively square up though as loads are ramped, but with a good case-chamber fit then like yourself I've also found other pressure signs show up before full-on flattening. If things have been pushed to the stage where the head is just a smooth surface with a colour change then I can't help but feel that other indications would have been neglected long prior. Interestingly I can get slight but squashed looking cratering from moderate loads upwards from the pockets in the Lapua being slightly deeper than the CCI450 primers - a similar effect also caused by the primer having room to move during firing.

Originally Posted by ebf

The 2 things I look for in terms of pressure are heavier bolt lift and marks on the case base. Without fail,me very single hot load I've had, has had extractor/ejector marks.

Now I have to question this. Are you honestly trying to convince us that you have only ever fired off one hot load ? I bet it was in that rear-locking thing you owned too.

Originally Posted by ebf

@Puffin, putting a 6.5 projectile in a 6.4 chamber WILL cause a pressure spike
Sorry dude, couldn't resist. Catch you at the range sometime, my bloody swipe card has stopped working, aargh !

I fixed that up really quickly! You are either a true forum junkie or stalking my threads.

Originally Posted by zimmer

I was mindful however b4 I started of the very strong 6.5x47L SR primer case's ability to hide to a certain extent the onset of high pressure (within reason) also the Barnard action I have found doesn’t always present sticky bolt lift as early as some other actions. Plus that action has no ejector hole for brass flow. Have tried the head expansion measurements in the past but that is not always conclusive – I had an article debunking head measurements as the finite method but can no longer find it.

Cases have had 4 loads now and no issues detected with them to date.

The 130gr Bergers shot 5 shot 100yd groups of =<0.2 on good days and =<0.4 on bad (read me) days.

The equal most accurate rifle I own.

Thanks Zimmer, the above closely matches my situation and experience with this case. Bloody accurate but somewhat problematic for me as I'd like to explore the full spread of available velocities before picking my final load, meaning development up to some level that I remain uncertain about. QuickLoad points to a slow batch of 2209/H4350. It would be more reassuring if the program gave a better match as I'm already at 42gr behind a 140grVLD. I'm thinking I'll dig out the Pressure Trace and stick on a strain gauge - see what that has to say.

Originally Posted by ebf

The 2 things I look for in terms of pressure are heavier bolt lift and marks on the case base. Without fail,me very single hot load I've had, has had extractor/ejector marks.

Originally Posted by Puffin

Now I have to question this. Are you honestly trying to convince us that you have only ever fired off one hot load ? I bet it was in that rear-locking thing you owned too.

Finger trouble typing on the iPad. Meant to say "every single hot load", of which there have been several Funny thing is I can't remember any out of the 788.

Originally Posted by ebf

@Puffin, putting a 6.5 projectile in a 6.4 chamber WILL cause a pressure spike

Sorry dude, couldn't resist. Catch you at the range sometime, my bloody swipe card has stopped working, aargh !

Did you get to the range today ??

You could've made an @Norway video with real snow !!


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Originally Posted by ebf

Finger trouble typing on the iPad. Meant to say "every single hot load", of which there have been several Funny thing is I can't remember any out of the 788.

The brain has a tendency to discard the bad shit and remember the good ..


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