Thread: What are you using for pressure estimation in your handloads.

one thing i will add here be very carefull with supressors, they give much higher pressure. I have seen loads shot with one on that pops primers out the back of the bolt face, and renders the pockets fucked in one firing!. Same load without can on is ok.... still hot, but ok.

I pretty much ignore primers now, except if they're pierced. They can be softer or harder. And different brass is also softer or harder...if a I get a stiffish bolt I will try another brand of brass with the load. PPU beats Federal etc.
And a case head failure is no big deal, I posted a photo of one I had last week. Didn't even notice it, and the bullet still fell in the group, but the case was blown in half.

But I listen to the Chronograph. If I am getting more velocity than the book, then I am getting more pressure. I will go over book loads, but I don't go over book velocities. And I pay attention to how much cases stretch. Not that I wont use a heavy load that pushes brass, but I am aware that the compromise is lessor case life.

Originally Posted by JohnDuxbury

I pretty much ignore primers now, except if they're pierced. They can be softer or harder. And different brass is also softer or harder...if a I get a stiffish bolt I will try another brand of brass with the load. PPU beats Federal etc.
And a case head failure is no big deal, I posted a photo of one I had last week. Didn't even notice it, and the bullet still fell in the group, but the case was blown in half.

But I listen to the Chronograph. If I am getting more velocity than the book, then I am getting more pressure. I will go over book loads, but I don't go over book velocities. And I pay attention to how much cases stretch. Not that I wont use a heavy load that pushes brass, but I am aware that the compromise is lessor case life.

Greetings all,
I am glad to see that some are using the chronograph to validate pressures. @JohnDuxbury first three sentences of his final paragraph cover it nicely. Velocity is the best indication of pressure the handloader has at their disposal. More on this later today.
Regards Grandpamac.

When I was young, foolish and new to reloading( ah memories) I once transferred the load for my m1 carbine to my 3030 for a good goat round thinking the difference in case etc wouldn't make any difference.
Fired one it was a bit thumpier than I expected and when I ejected the case the primer fell out.
It sat above my bench for many years but sadly got lost in one move

Greetings all,
In my earliest fumbling in reloading my .303 cartridges I just used start loads. Fast forward a few years a .308 had replaced the .303 and I had a subscription to Handloader. Early on, in the mid 80's, there were articles by Ken Waters and Bob Hagel, two of their top writers, describing how they assessed pressure. Each used a different type of case measurement which we will come back to later. Neither mentioned primer appearance. Much later, about 5 years ago, John Barsness wrote about using velocity as a method for estimating pressure. He suggested that most handloaders adding powder and looking for pressure signs wound up with loads with a pressure of around 70,000PSI or so. Far too hot. I've been using velocities from the Hodgdon load data corrected for barrel length and other factors as my max target often finishing a little below. I will dig up some of my calc's and try and post a summary.
GPM.

A method that I have found to be useful for rear locking actions is to measure. the length of the case over a series of firings of an individual case with a chosen load. If the case stretches (and it is totally obvious with calipers) then the amount of powder in the load needs to be reduced to the point where the case does not measurably increase in length. My 'series of firings' is usually 20 shots of the same load. An example is a miniature martini rechambered to 17 Ackley Hornet with a 25gr Hornady HP bullet. The chosen load of IMR4064 gives a velocity of 3,400ft/sec and the case lasts at least 20 firings. By which time the neck is very hard which affects velocities but the case integrity is still secure.

flat primers dont mean too much in my experience cratered primer dents can mean its getting a bit hot but unless its really bad i tend to let it slide a bit

mainly looking at ejector stamps and or tight bolt lift as signs I'm pushing my luck back of at least 0.5gn from the 1st signs of stamping or tight bolt lift
and call that my max for that combination in that rifle

i use data in loading manuals as a very rough Gide only even if the rifle shoots well in a low node I'm not all that interested I'm only interested in the high node
so, most of my loads are above the "max" load sometimes by a fair amount too i let the rifle tell me what max is just work up slow

loading data is piss weak these days

Originally Posted by rupert

A method that I have found to be useful for rear locking actions is to measure. the length of the case over a series of firings of an individual case with a chosen load. If the case stretches (and it is totally obvious with calipers) then the amount of powder in the load needs to be reduced to the point where the case does not measurably increase in length. My 'series of firings' is usually 20 shots of the same load. An example is a miniature martini rechambered to 17 Ackley Hornet with a 25gr Hornady HP bullet. The chosen load of IMR4064 gives a velocity of 3,400ft/sec and the case lasts at least 20 firings. By which time the neck is very hard which affects velocities but the case integrity is still secure.

Greetings @rupert and all,
Thanks for your post. I use a variation of this in my Martini and Lee Enfield rifles. I don't measure case lengths but do set loads so pressure is low enough to prevent stretching. Often the primers are backed out a little (a good sign) and the cases rechamber with ease. Only neck sizing is needed. Similar light loads were used in my .308 for short range target shooting with much the same results. Good training loads for the younger ones as well.
Regards Grandpamac.

Originally Posted by grandpamac

Greetings all,
It was all warm and horrible outside this morning so I thought I should find out what three of my oldest manuals had to say on pressure estimation. They were Reloading Simplified by Cyril Waterworth 1961, Speer No 9 about 1975 and Reloading Manual for Rifle and Handgun by Nick Harvey 1980. All included primer leak, hard extraction and case head expansion as signs (Speer also included primer appearance). All three did not consider primer appearance to be a reliable indicator of pressure. Interesting.
Regards Grandpamac.

Yes I was thinking you really need to know what you are doing using the primer as indication of pressure.....headspace is the determinator of primer flattening as well as hot loads. Too much headspace will "top hat" the primer even at minimum loads so primer shape is not going to be reliable....!

Quickload is a means to calculate the pressure but that will need to be reverse engineered from muzzle velocity. Relaoding manuals are quite conservative a probably where a new shooter should begin.

Greetings @Longranger,
Thanks for your reply. Julian Hatcher spent his whole career in the US Army working in interior and exterior ballistics. He described primer appearance as practically worthless for estimating pressure in 1946. Nothing has changed since then. There are many factors including headspace that make it unreliable at best.
Quickload estimates pressure based on velocity from what I understand and the two are linked. I think that the best data we have is the pressure tested data from the powder and projectile companies but these are kept a little low as a safety factor for variations in components and also the existence of older and supposedly weaker rifles chambered for the cartridge.
As stated in the OP this thread was started to give me a better understanding of pressure estimating techniques in use prior to some possible articles for newbies. That is still the plan although the path to the goal is getting longer and windier.
Next post there will be some data on my current methods.
Regards Grandpamac.

Hi @grandpamac...Yes we all need to read and re-read Hatchers Notebook.

Quickload is a very good analysis tool, but like all analytics BS in = BS out. So what I do for a new chambering is load somewhere in a mid range based on experience and research of that calibre from various sites on the internet. (Under-charging can be equally as dangerous as over-charging....research interior ballistics "Detonation" for an explanation of that.)

Obtain velocity from a reliable source like Labradar. Use that data to reverse engineer the software to align velocity with barrel length specs, case capacity, seating depth, bullet weight, charge weight etc. If the velocity doesn't align after setting all the other data some fine tuning of the powder burn rate is required or minor bullet weight adjustment to calibrate the output to match the velocity and powder charge. This calculation will provide chamber pressure for any cartridge listed and the pressures and velocities can be tailored from there to develop an accurate load. Once calibrated the progression is linear for powder charge and pressure.

Sorry,but it probably doesn't help much in explaining the basics to a new and inexperienced reloader. Without the facility to do the above one can only rely on published data and eventually experience like the bolt face engraving the cartridge base, tight bolt lift, tight cases, expanded primer pockets etc.

Full marks to you for your efforts to take some of the mystery out of this.....!

Greetings all,
Raining again in HB today so here is some more on my normal load development.
For various reasons I may need to do some load development for a 7mm-08 soon so have used this as an example. The rifle is a loaner so lets say I have no loading history for it. I have plenty of AR2206H, 145 grain Speer projectiles and the rifle is to be used for mid range target shooting. Hodgdon lists a max of 41 grains of H4895 (AR2206H) for 2,728 fps with this projectile so a start load of 39 grains is selected, a little above the Hodgdons start load. Previous testing with this powder lot has show it close to the data in my .308. The relationship of powder charge to both velocity and pressure is quite linear and the expected velocity for my initial load works out to 2,625 fps in a 24" barrel which is what the rifle has. A shorter barrel length could be adjusted for using a loss of 25 fps per inch down to an 18 inch barrel and more below that.
Next the load will be chronographed using my Oehler 35P and the result used to calculate the load needed to achieve the Hodgdon max velocity to validate the Hodgden data. The max could then be worked up to in a couple of steps.
For cartridges that are loaded to lower pressures like the 6.5x55 I would calculate the target velocity using the John Barsness Rules that I have posted and written about previously. The point here is that I work up to a maximum velocity rather than a maximum powder charge. More later.
Regards Grandpamac.