Question on finding pressure

[Koda_]

Well thank you guys I am going back to another promising node. 1.2 grains less. Will work seating depth to get my accuracy to back to .2 or .3 instead of the .4 .5 it was at.

There seems to be some different and conflicting experiences regarding seating depth and pressure in the above comments, so you will have to be the judge of that.
But I agree the best solution is stepping back at least a full grain of charge weight putting you back in the safe pressure zone you wont have to worry as much about seating depth affecting pressure (unless you jam the lands). Then you can play with seating depth to fine tune your precision.
I think your on your way.

 

[6.5x300 WBY]

I am not near the lands. Started at mag length and worked in from there. But yeah gonna drop my charge a bit and should be fine

 

[Louisiana Reloader]

Usually the velocity shelf will will be below the max pressure for a load. I load eight rounds of each different recipe before going to the range. (kind of like shooting 3 round groups or shooting 5 round groups, the difference is astounding) This gives me good data to track each particular load. One of the best things loading 8 does is it will tell me about deviance in each recipe, another thing is it allows me to shoot a hot barrel and it will cycle through a mag and into the next one. You will be surprised at the difference in the amount of things that more rounds of one recipe will let you know. I usually (used to are the key words here, age is creeping in) would take all day to shoot a ladder for a barrel. After shooting the eight I would leave rifle bolt open, barrel up, in the shade, mag out and by the time I walked down to retrieve my target and looked it over and returned, ran a brush and a patch the barrel would be cool. This let me start out with a cold shot and progress. Some particular recipes wouldn't be shot after a couple shots because I knew they were not what I was looking for. I would record the avg. velocity for each recipe as the particular shots would progress in powder volume, somewhere as I made the graph and at a point the velocity would fall or even out with more powder in the case. I usually would shoot another or maybe two recipes to make sure. Most of the time the last load before the flat or drop would be the best for powder efficiency and accuracy. Some times the accuracy would be a recipe or two under but not usually. Powder efficiency is very important because it gives a better burn and over this amount may give a few extra fps but at the cost of accuracy and shortened barrel life. After you have shot a few thousand rounds this will all make sense. I have shot out many barrels and I can tell you top velocity is not even close to top accuracy. If you ask most people who shoot .308 Win. they are shooting velocities less than 2650 usually around 2610 not nearly a max velocity. No use to shoot when you cannot hit a house when sitting inside of it. Happy shooting.

I totally agree with Arkansasdad. I have learned the hard way with my 6.5 PRC's that chasing and trying to beat the velocity in the loading manuals comes at a price. You can do it, but as I have said before--there are no free lunches. Out of all the guns in my safe (and there are many), I only have one that will still hold great groups with the upper end hot loads (Remington 700 Sendero Stainless in 300 RUM, 26" barrel). Those high velocities usually cost you accuracy and shortened brass and barrel life. I have absolutely come up with some remarkable speeds in my Browning Hells Canyon X-Bolt in 28 Nosler (greater than published with only slight pressure signs); however, I know if I keep it up I am asking for it with a short barrel life. Great discussion guys and one I wish I would have been a part of when I started reloading 31 years ago. Thanks

 

[RogerPA]

All of this reminded me of a thread by "Orcan" ( Primal Rights) in August of 2022, regarding false positive pressure indications. Along with several others, I had been going crazy trying to figure out why a brand new rifle, even with very low end start-up loads, was generating ejector marks on every case.
A good read going backwards! It saved me a lot of time, components, and grief, by defining the exact problem and solution. Probably not the OP's problem, but on occasion a mystery solver….

 

[N.Y.Arnie]

That would be wrong.
Seating a bullet deeper into the case increases pressure.

I agree with Koda, and I was told this by an old Kentucky veteran and gunsmith back in the mid 70s " The need for speed can drop you to your knees ".

 

[Csbc4fun]

Lots of "Advice" above. Randomly guessing at a powder charge, then tuning with seating depth is not for me. I can tune any powder charge and make the groups better, but why? Minimize the rabbit holes.

I will just state what works for me…

Load one round each in 0.5 grain increments. I write grains on the case with sharpie. Shoot until pressure signs are obvious, not maybe. If you are not sure, shoot the next round. Know for certain where pressure is for your load. Document where pressure was found. Discard pressure case and the two below it.

Drop down 3.0 grains and load one round each in 0.2 grain increments up to within one grain of pressure. Shoot, measure fps and graph out findings. Now you can see your node and logically select a powder charge in the flat spot node. Up to this point, I do not shoot for groups as that would be a complete waste of time and components.

Now load 50 rounds with that selected powder charge at the longest (closest to the lands) that you would ever shoot, 0.020" off the lands for me.
Take press and seating die to the range… seat three 0.003" deeper and shoot them for groups. Continue seating deeper by 0.003" and checking groups. Track each target group to the seating depth used for those shots. (Targets don't lie) When there is no paper between shots, repeat that seating depth to double check. Try another group 0.003" deeper, if it is a larger group. Done!

Works for me, good luck and enjoy the journey!

 

[Odin6]

Keep loading and shooting, it's good to know where your max is, I generally like to stay 1 grain under Max or where pressure signs start, keep in mind ambient temp if your powder is sensitive.
How does the loads you already have shoot anyway, you may have already hit the node your looking for.

Agreed on finding the max pressure for your rifle. All are different and knowing how close you are is safer than guessing. SAAMI data is only a guide for most firearms chambered in that cartridge and the load data sources can differ drastically. I also want to ensure that my loads developed during milder weather, won't cause too much pressure when I'm shooting in the middle of the summer heat.

Key pressure signs to look for are: heavy bolt lift, flattened primers, extruded primers, and extractor marks on the case head. Just work up in small increments until you start seeing these signs then back off approximately a grain or so depending on the cartridge.

 

[6.5x300 WBY]

Agreed on finding the max pressure for your rifle. All are different and knowing how close you are is safer than guessing. SAAMI data is only a guide for most firearms chambered in that cartridge and the load data sources can differ drastically. I also want to ensure that my loads developed during milder weather, won't cause too much pressure when I'm shooting in the middle of the summer heat.

Key pressure signs to look for are: heavy bolt lift, flattened primers, extruded primers, and extractor marks on the case head. Just work up in small increments until you start seeing these signs then back off approximately a grain or so depending on the cartridge.

Pretty much did just that. Bolt lift easy as pie. Primers perfect. Just that faint extractor mark. Didn't even notice it till I had my +3 pharmacy glasses. So pressure isn't too terrible. But am backing down 1.2 grains to another node.

 

[fmuguira]

I d go down and work around that 1 grain less powder area if it's shooting good for you. Then get your 100-200 brass fired there and after 100-200 rounds check your velocity and accuracy again. I d expect to see 50+ fps increase in bullet speed.

Good luck and enjoy that 6CM.

 

[6.5x300 WBY]

I d go down and work around that 1 grain less powder area if it's shooting good for you. Then get your 100-200 brass fired there and after 100-200 rounds check your velocity and accuracy again. I d expect to see 50+ fps increase in bullet speed.

Good luck and enjoy that 6CM.

Yeah that's what I'm gonna do. Shot .325 for me so its not bad at all. Going to do seating depth testing next with that load.

 

[MagnumManiac]

I have a Pressure Trace II, it is a wonderful tool and told me things that most manuals don't tell you.
Pressure signs are just as much important as to case design as they are to rifle type.
For example, my Win Model 70's hold up well past 70,000psi without ejector marks, flattened primers or sticky bolt lift, but as soon as about 80,000psi is reached, the primers crater badly, still no sticky bolt lift, but well above max pressure. My REM 700's do not handle this type of pressure without sticky bolt lift, ejector marks & loose primer pockets or blown primers. My Ruger M77 will crater primers early on and have sticky bolt lift, my Ruger M77 MK II will not have cratered primers or sticky bolt lift until it blows primers, bulges case heads and has brass flowing into the ejector slot. This has been measured at 100,000psi and no discernible damage has been noted in the action anywhere.
80,000psi is a proof load, so all actions should handle this, however, HOW max pressure is reached in the curve makes a huge difference, which is why proof loads are regulated and that not ANY powder is suitable to do so with.
Anyway, trying to discern pressure looking at fired brass is a huge guess at best, sure, you can SEE flattened primers, cratered primers and ejector marks, but all 3 of these things can occur just from excessive headspace, not excessive pressure, although the latter will be blamed for the condition…

Cheers.

 

[6.5x300 WBY]

I have a Pressure Trace II, it is a wonderful tool and told me things that most manuals don't tell you.
Pressure signs are just as much important as to case design as they are to rifle type.
For example, my Win Model 70's hold up well past 70,000psi without ejector marks, flattened primers or sticky bolt lift, but as soon as about 80,000psi is reached, the primers crater badly, still no sticky bolt lift, but well above max pressure. My REM 700's do not handle this type of pressure without sticky bolt lift, ejector marks & loose primer pockets or blown primers. My Ruger M77 will crater primers early on and have sticky bolt lift, my Ruger M77 MK II will not have cratered primers or sticky bolt lift until it blows primers, bulges case heads and has brass flowing into the ejector slot. This has been measured at 100,000psi and no discernible damage has been noted in the action anywhere.
80,000psi is a proof load, so all actions should handle this, however, HOW max pressure is reached in the curve makes a huge difference, which is why proof loads are regulated and that not ANY powder is suitable to do so with.
Anyway, trying to discern pressure looking at fired brass is a huge guess at best, sure, you can SEE flattened primers, cratered primers and ejector marks, but all 3 of these things can occur just from excessive headspace, not excessive pressure, although the latter will be blamed for the condition…

Cheers.

Great explanation. Thank you