Min OAL versus less powder

[lineofsight]

Started loading for the .30-06 with a 165 Spitzer BT using 47gr of Varget.

Happily sized a few to 3.375, 3.35, 3.3... and kept going past min. OAL of 3.3 for this bullet/powder combo to 3.25" and 3.2" then remembered the min OAL.

Now as I started at 47gr when the max is 50.5gr, how does the lower pressure because less powder compare to the higher pressure because of deeper seating? The min OAL for 150 & 168 is 2.25..., 165 is 3.3

Will likely pull the bullets and fertilize the lawn but curious just the same.

 

[stubblejumper]

how does the lower pressure because less powder compare to the higher pressure because of deeper seating?

Actually seating deeper can actually result in a reduction of pressure due to the bullet having a longer jump to the lands.The longer jump to the lands makes it easier for the rifling to engrave the bullet.

 

[Boomer]

I doubt if you would be able to determine the difference in pressure between a bullet seated deeply and one seated within spec with any bottle neck rifle cartridge that was loaded to a safe level to begin with. The cartridge with the bullet seated deeper would have a longer lead which would effectively reduce pressure. The only time I could see bullet seating depth being a problem would be with a small capacity straight wall handgun cartridge loaded with a fast powder like Bullseye. Even then, the shorter round will have more lead in the cylinder chamber of the revolver or the barrel chamber of a pistol. I doubt if a gun has ever blown up because a bullet was seated too deeply over a safe powder charge.

There were some stories about the .458 when used by PH's in Africa that might have some truth to them. What happens is that when a rifle is loaded 24-7, the bottom round in the magazine often has multiple rounds fired over it. Rounds are added as the rifle is fired, so over time, if the crimp is not sufficient, the bullet can push back into the case from recoil. This compressed load combined with the hot African sun was said to cause very strong recoil when that round was finally fired, but I never heard of a gun being wrecked as a result.

 

[lineofsight]

Thought with deeper seating there is effectively less case volume producing more pressure and more resistance to the bullet leaving the case producing more pressure.

 

[blargon]

I seat the bullets out as far as I can in to fit the mag and cycle reliably. Bullet depth aside, you may have better luck with 4350 or 4064 instead of Varget.

 

[Boomer]

Thought with deeper seating there is effectively less case volume producing more pressure and more resistance to the bullet leaving the case producing more pressure.

That is true to a point and might be a concern with a small capacity straight wall handgun cartridge loaded with a small charge of fast burning powder and a heavy bullet.

Consider though that the most efficient powder charges occupy about 95% of the total volume of a bottle-neck rifle cartridge. The bullet doesn't have much room to slide into the neck before it is stopped by the powder column anyway.

When the primer ignites the powder the bullet begins to move before all of the powder is consumed. As the bullet moves down the barrel the volume contiunues to increase. Looking at it like that, the amount a bullet extends from the neck doesn't make much difference from the standpoint of pressure, provided it was a safe load to start with.

 

[lineofsight]

Thanks for the feedback. Just measured 165gr Win Factory Ammo OAL of 3.15 so should be no issue with the 3.25 I loaded. Unrelated (hijack my own thread), read about OCW approach to finding optimum "resilient" charge by picking a median charge of the smallest group shot with incremental charges.

Tomorrow will try the loads with same charge and different depth. Next time will try different loads same depth.

Cheers.

 

[stubblejumper]

Thought with deeper seating there is effectively less case volume producing more pressure and more resistance to the bullet leaving the case producing more pressure.

The bullet will move in the case with very little pressure because it requires very little force.However it takes a great deal of force for the rifling to engrave the bullet,hence that is the point where the pressure will likely be the greatest.As such,the most important volume will be the volume in the case as the bullet strikes the rifling.

 

[lineofsight]

Well, was already to go this morning. Loaded a couple more cartridges the night before to try different charges as well. Telephone call... looks like daughter may be a little early, off to the hospital we go, box in safe, it will keep.

 

[H4831]

The bullet will move in the case with very little pressure because it requires very little force.However it takes a great deal of force for the rifling to engrave the bullet,hence that is the point where the pressure will likely be the greatest.As such,the most important volume will be the volume in the case as the bullet strikes the rifling.

With normal rifle powders, that is, powder that requires a nearly full case for full power loading, the peak pressure is reached when the bullet is about half way down the barrel.
It is still low pressure when the bullet is being engraved by the lands. This is why seating the bullet to touch the lands, doesn't increase the overall peak pressure of load.

 

[stubblejumper]

It is still low pressure when the bullet is being engraved by the lands. This is why seating the bullet to touch the lands, doesn't increase the overall peak pressure of load.

http://www.z-hat.com/Accurate.htm

Quoted from the link above.

Also pressure spikes can occur if the bullet is touching the lands. Testing had proven over and over that a bullet seated touching the throat can raise peak pressure by as much as 8000 PSI, that is substantial!

 

[H4831]

You should tell the world class bench rest competitors this.
They load heavy and they load to touch the lands.

 

[stubblejumper]

You should tell the world class bench rest competitors this.
They load heavy and they load to touch the lands.

From the same link that I posted previously.

I often hear shooters talk about seating out the bullet to touch the lands of the barrel. Bench rest shooter get away with this practice because they are normally loading at relatively low pressures. Conditions for bench rest shooting also allow the shooter to spot problems that a hunter could easily miss in the field.

 

[H4831]

I got the follwing line from a benchrest sight.
-----------------------------------------------

Many benchrest competitors load in the upper range of velocity and many seat the bullet touching the lands.
-----------------------------------------------------
This is the last of any comments I will make on this subject, as I have much better things to do with my time.

Cheers, H4831

 

[stubblejumper]

Many benchrest competitors load in the upper range of velocity and many seat the bullet touching the lands.

That still doesn't change the fact that seating on the lands can cause a significant increase in chamber pressure,contrary to what you stated in your previous post.
Below is actual proof of this using specialized measuring equipment.

http://www.shootingsoftware.com/pressure.htm

Look at the 6mm ppc data with graphs halfway down the page.

http://www.shootingsoftware.com/images/sampleseatingtrace.gif

Here's a classic good load for 6PPC. The only difference between all these traces is the first 3 were seated right on the lands. The last 4 were 30 thousands of an inch off the lands. Note the substantially reduced pressure and overall reduction in energy.

And the difference is in the 7000psi to 8000psi range,which agrees with the other link that I posted previously.

 

[lineofsight]

In conclusion... 3.375 (longest) with the same 47gr charge was the most accurate and of the varied charges all at 3.35 the 49.5 (largest) load was the most accurate. At 200m this low end Remy (SPS DM) was shooting less than 1.4" groups measured from the outside (so 1.1 / 2 = .55 MOA, was impressed (and a little remorseful of having sold it). Liked coolish barrel and some fouling best. Stringing tended to be vertical for the groups.