PSI Calculator

[burch]

I`m looking for calculators or formulas to convert fps to psi. I`m trying to find out and maintain a safe psi for my guns.

Burch

[Larry Gibson]

There is no such conversion. Suggest reading a good reloading manual's section on "pressure" and to stay within the loads listed in the reloading manuals.

Larry Gibson

[82nd airborne]

there are too many factors to make such a conversion possible, to name a few, but not even scratch the surface: throat size, bore/groove dia., powder type, bullet type, neck tension, fillers or lack there of, compression, etc,etc....head size plays a large role too, (area that the force is applied. in my severely limited knowledge, there is no way to do this with a simple formula. fps really doesent have much to do with pressure when you think about all the other factors. consider a 12 gauge delivering a payload of 500gr at 1200fps. pressure is under 20,00psi. now shoot a 500 gr load out of a 500s&w and youre pressure will be substantially higher. someone more experienced please correct me if im wrong.

[burch]

Reloading manuals list a certain barrel length when developing their loads. If you use anything different than what`s listed everything changes. I don`t have a crono and that would help i`d imagine but was hoping to find some way to calculate a close psi number. Anyhow thanks for the help.

Burch

[fryboy]

read the chapter on pressure in the second edition lee book , but as stated the variables are endless and also note that lee's formula is only close and for use with certian ( read that much tested) powders

[mike in co]

just one more reason to buy a good chronograph

[lwknight]

While it is mathmatically possible to calculate the end velocity from a given barrel length and a given pressure , It is not possible in any reasonable mannor to estimate the average chamber pressures or bore drag.
With infinate varibles of burn rates and progression rates that vary with the tinyest change to anything , it would be virtually impossible to account for everything.

You can keep mental notes of supposed pressures and end results till you amass enough data to make reasonable estimates to be expected , but only a chronograph will prove anything.

I second the " Get a chronograph" idea.

[RobS]

Burch:

The best thing you can do is review your reloading manual or better yet a variety of manuals and stay with those guidelines for now. The variables extend all directions as been stated and because of this there is a safe margin for variables in reloading manuals. Reloading manuals of today are way more conservative than yester year. Published loads of the 60's and 70's and 80's with the same powder would be over max in today’s manuals. I am not saying to go over board and load up to a max published load either as all loads should be worked up gradually while looking for pressure signs.

A bit of info for you however............while working up your loads you will find a sweet spot where your groups tighten up and any more powder the groups start to open up. This is the point where your bullet/powder charge combo in relation to the specific firearm is topped out. More times than not this "accuracy load" is normally under the maximum published load data so if accuracy is your game then you'll be under the max charges anyway.

When you find a chance to save up some ding ($$$) and should you choose to purchase a chronograph it will tell you so very much about your load development. Some have no desire to work that far into their reloading and shooting practices, but it sure does reveal what is going on.

[burch]

Burch:

The best thing you can do is review your reloading manual or better yet a variety of manuals and stay with those guidelines for now. The variables extend all directions as been stated and because of this there is a safe margin for variables in reloading manuals. Reloading manuals of today are way more conservative than yester year. Published loads of the 60's and 70's and 80's with the same powder would be over max in today’s manuals. I am not saying to go over board and load up to a max published load either as all loads should be worked up gradually while looking for pressure signs.

A bit of info for you however............while working up your loads you will find a sweet spot where your groups tighten up and any more powder the groups start to open up. This is the point where your bullet/powder charge combo in relation to the specific firearm is topped out. More times than not this "accuracy load" is normally under the maximum published load data so if accuracy is your game then you'll be under the max charges anyway.

When you find a chance to save up some ding ($$$) and should you choose to purchase a chronograph it will tell you so very much about your load development. Some have no desire to work that far into their reloading and shooting practices, but it sure does reveal what is going on.

The load i`ve worked up for my revolver is in fact under maximum pressure. My issue is this. I have a S&W 696 no dash and if you even bring up the fact your using anything under a 200gr. bullet they freak out pretty bad at the S&W forum. The 696 has a thin forcing cone and pressure is a major factor on this gun. I`m using a 180 gr cast RNFP and my gun just loves `em. Now, as i`ve stated i`m way under the industry maximum pressure for 44 special which is 15,500 psi. The data i`m using is from one of my manuals but is for 180 JHP and has a max of 14,000 psi at over 1000 fps. I`m running this bullet somewhere around 850 fps.

[RobS]

Since your bullet is lead then there will be less resistence than with a hard jacketed bullet so pressures will be less if you are using the same charge weight.

Here is what I have in the Lyman manual for a 205 lead truncated style bullet (Lyman 427098) Firearm barrel length used was both a 4" and 7 1/2" for the loads in 44 special:

Unique: 7.0 grains 736fps 10,500 cup...............8.2 grains 869fps 14,000 cup
IMR 7625: 6.8 grains 761fps 9,700 cup.................7.7 grains 838fps 12,600 cup
HS-7: 10.0 grains 732fps 10,100 cup...............11.6 grains 874fps 13,600 cup
Blue dot: 10.5 grains 747fps 10,000 cup...............12.0 grains 855fps 13,300 cup
2400: 13.3 grains 734fps 10,800 cup...............15.2 grains 870fps 13,500 cup

With the above load data it looks that if you are thinking 850fps with a 185 grain lead bullet then you'll be in the mid range regarding pressures of the 44 special loads. However using the slower powders will build pressure later on in the barrel so it would be a better choice if you are worried about the forcing cone being the weak part of the revolver. Fast powders build pressures quickly and will have higher pressures vs the slower powder at initial ignition and into the forcing cone/start of the barrel.

Hope this helps

[Frozone]

Quick Loads.

While it's not perfect it does exactly the calculations you want.

[rhead]

You will get a different result for each powder for any given bullet, barrel, chamber combination. The velocity obtained from a lower sustained pressure may be greater than that obtained from a higher pressure that is more of a spike. Also velocity is the result of pressure but pressure is also the result of the resistance to acceleration. What would be the pressure if the bullet did not move?

Your question would have a near infinite number of answers.