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Joined: 28 Aug 2014 Posts: 924 Location: Eastern Tennessee

I'm just curious what some of you consider too low of pressure and why. I typically don't load anything under 8,000 PSI so never really cared to ask before.

I was just day dreaming of the day I can let my boy take his first shot (granted it won't be a shotgun, but it will be someday).

I was reviewing some 3/4 oz rounds with PSI down in the 3,500 range. Is that even safe?

*Last edited by skeettx on Fri Oct 30, 2015 1:32 pm; edited 1 time in total*

Yes,

Safe is when the wad/shot exits the barrel, leaving the barrel clear of debris.

Good is when the wad/shot performs the expected task.

Mike

Joined: 28 Aug 2014 Posts: 924 Location: Eastern Tennessee

geez Mike,

I knew that much. Razz

When does that become a risk in most cases?

5000 PSI?
6000 PSI?

I figure it might be powder related to some point, but I figured there might be a good measure of generality.

It depends on burn rate, pressure rise and duration, and condition, bore diameter, and length of the barrel.

I would say 3500 would get the wad out of the barrel just fine if the wad was tight and there was no blow by. On the other hand if the wad was small and blow by happened .... well you know the rest of that story.

In some cases just the primer pressure will ALMOST clear the barrel of the wad.

Mike

p.s. what powder was the 3500 psi load you were reviewing using?

Why would you need a load with that low of pressure?

Member Joined: 16 Nov 2006 Posts: 1338

Joined: 28 Aug 2014 Posts: 924 Location: Eastern Tennessee

I just noticed today as I was reviewing my load data I had a few I'm interested in, for light loading (1,100 fps) I noticed pushed down to 6000 psi. I also noticed on the LPG sheets loads down to around 3,500 which just seemed crazy low.

For hunting I usually stay between 10,500 to 8,500 psi for 1250 to 1200 fps.

Member Joined: 09 Sep 2014 Posts: 105 Location: Virginia

I have been loading some real light loads for a FN 16g Hammer gun built about 1912.

It weighs about 6 lbs, recoil is a issue. Barrels are fluid steel it will handle stronger loads than I want to shoot. Was looking for a low recoil short range clay target load with RGLs DR 16 & Win 209 primers.

Started with 15.7 Green Dot clean burning effective loads using 3/4 oz. shot. Dropped the shot load to 11/16th and still got good crimps no filler wads using 14.7 GD, clean burn effective on Clays. Loaded another 50 and shot them using 14 grs Green Dot this afternoon, bores dirty with unburned looking grains. All 50 sounded fine though.

Will go back to 14.7 GD & 11/16 oz as the mimimum effective load. No bloopers breaks clays to 25 yards fine. Cold weather may make a difference, but it does not get real cold my area. No telling what the pressure is but it's probably not much.

If I get any strange sounding shots will bump the charge up just a bit more than 14.7

Boats

Just a reminder, pressure does not effect recoil. Load and velocity are the culprits.

Joined: 28 Aug 2014 Posts: 924 Location: Eastern Tennessee

I understand oh, but to get 3/4 oz or even less moving at around 1100 fps I'm dipping down in to psi levels that had me wondering when I should be having concerns. There are some in the 6000 to 6500 range.

Member Joined: 09 Sep 2014 Posts: 105 Location: Virginia

I understand recoil, light shot weights best way to reduce it. Velocity too, less important than shot weight though. Low recoil loads come with potential problems pattern density for one. Tight chokes tighten patterns and suit light shot weights best. Smaller shot improves density too, at the expense of range and penetration

Seems to me low pressure is least of low recoiling loads potential problems as long as the powder ignites properly. Way to judge is the sound and condition of the bore after it's been used. Published pressures on the low side not important. They are very important if working on the high end of pressures for a given load.

I could be wrong though.

Boats

Boats -- Recoil energy depends directly on the square of both the velocity and the projectile weight. Both are equally important in reducing recoil energy. Simplistically, the math goes like this:

First some labeling conventions:
Mg = Mass of the gun
Ms = Mass of the shot
Vg = Recoil velocity of the gun
Vs = Muzzle velocity of the shot

From conservation of momentum (Newton's 3rd Law):

(1) Mg x Vg = Ms x Vs

(2) Vg = (Ms x Vs)/Mg

(3) Recoil Energy of the gun = .5 Mg x (Vg^2)

Substituting (2) into (3) gives:

Recoil Energy = .5 Mg x ((Ms x Vs)/Mg)^2, which yields:

Recoil Energy = .5 ((Ms x Vs)^2)/ Mg

So recoil energy of a gun depends directly on the square of both the mass and velocity of the shot, and inversely on the mass of the gun. e.g. Making a ten percent reduction in shot weight or velocity has a little over twice the effect of increasing the mass of the gun by ten percent.

Of course this simplistic analysis ignores the masses and velocities of the wad and powder gases, which while not predominant, neither are they inconsiderable in regard to recoil. However, including them does not negate the fact that recoil energy is dependent on the squares of both the masses and velocities of all the ejecta. Including them makes an even stronger case for most effective reduction of recoil based on lighter and/or lower velocity loads.

Example --

If a shooter is comfortable shooting a one ounce 1200 fps load in a 6 pound gun (olde English rule of thumb), and then wanted to be just as comfortable shooting the 12 gauge standard high-velocity load -- 1.25 ounces at 1330 fps -- he'd need a gun that weighed almost 12 pounds.

Cheers!

Member Joined: 09 Jan 2013 Posts: 2169 Location: Florida

Member Joined: 09 Sep 2014 Posts: 105 Location: Virginia

Max Smoke,

Not doubting your formula but,

Practical velocity range shotguns is limited, all my loads look for about 1150 FPS. Velocity and muzzle blast more or less fixed reduction in recoil, assuming same gun weight, comes mostly from shot weight. I load 12s as heavy as 1 1/8 light as 3/4 oz. recoil difference one to the other is significant. That's why I say shot weight is the major factor.

For load comparison I ignore gun weight assuming the two loads will be used in the same gun, but gun weight differences are a major factor. My two 16 SxS guns one under 6lbs, other almost 7lbs big difference gun to gun same load. Have settled on target loads specific to the individual shotgun, otherwise the little FN is no fun to shoot.

It's all subjective anyhow. Some don't mind recoil others do.

Boats