RE: 308 accuracy load
 

This post has just come full circle. Nearly all the posters on here except you apparently understood that the downside of imr4350 in the 308 is too little case capcity not enough pressure. The purpose of the magnum primer was to bring up the pressure in the first place was it not?

You are just dead wrong above. If the powder itself fixes the burn rate explain to why some loadsoperate atsafe pressuresat 0 degrees but are overpressure at 90 degree and why changing primers can affect pressures and velocities. The answer is obvious. The powders burn rate is not fixed at all and varies based on many externalconditions well beyond the powder itself.

The above statement is a complete contradiction. If the burn rate does not change then neither does the pressure.

RE: 308 accuracy load
 

Because that is a characteristic of that particular powder.That characteristic won't change just because you change primers.At a given temperature,the powder will burn at a given rate.It will do that consistently,day in day out under the same conditions.Some powders have a very constant burn rate regardless of temperatures.

That may be true for the lighter bullets,but not with 180gr bullets.The Lyman 45th edition manual lists the chamber pressure at 51,600cup for imr4350 with a 180gr bullet.That is the same pressure that they develop with a maximum load of imr4064.
As for the lighter bullets,the best solution is to simply use a powder with a faster burning rate.

A primer adds fuel,or energy,which has a similar effect to adding more powder.A primer has enough energy to drive a bullet out of the casing,even if the casing has no powder.A magnum primer has more energy than a standard primer.
A supercharger adds powder to an engine by allowing it to burn more fuel,not by changing the burning rate of the fuel.

RE: 308 accuracy load
 

I am not sure what you are actually saying above. Do you belive the energy in primer is what is actually increasing the pressure and increasing velocity?

The original poster wanted a"load using a 150 gr sierra spitzer". That is what I based my suggestion on.

You are dreaming if you believe it is the energy difference between standard and magnum primers that increases the velocity. I have found the difference in velocity to be about 112 FPS in my 06. When you convert that to KE it is just over 200ft/lbs. When you also consider the efficiency of the 308 and 06 are around 30% it seems obvious that the primer differences alone has no where near enough energy toaccountfor the increase.

A supercharger adds air toan engine which allows it to aspirate more cfm.When maintaining the same fuel mix this allows more more fuel to be burned and more HP to be generated.

What you are failing to understand is how pressure also affects burn time. Since you seem to relate to engines I will use this example.

Take a naturally aspirated engine and increase the compression ration from 7.5:1 to 11:1. The HP output of the engine will increase also because the burn rate of the fuelgets fasteras the pressures increase. This will burn the fuel more completely at a given RPM and increase HP.It willalso allow the engines RPMs to be increased in most cases which further increases HP.

RE: 308 accuracy load
 

In going from an engine with a compression ratio of 7.5 to 1,to an engine with a compression ratio of 11 to 1,you need to use a fuel with a higher octane.Just like a magnum primer,the higher octane fuel burns slower,but it also burns longer,resulting in a longer power stroke, increasing the amount of energy released from the fuel.The result is more power.

RE: 308 accuracy load
 

Your attempting bring a variable into the disscussion (Fuel Type) in order to avoid acknowledging what must seem to most an obvious fact. Increased compression, speeds the burn time of fuel (and powder). The example I listed for a 7.5:1 to 11:1 compression ratio were for natual gas industrial engines that have I sold for the last 15 years. The sameholds true on diesel engines also except the ratios vary between 15:1 and 22:1. There is no need to change the fuel at all for either engine.You only need to retard the ignition timing as the compression increasesBECAUSE THE BURN RATE IS FASTER.

Your theorys on engine burn characteristics would probably go over big with the engine design engineers at Caterpillar that put on the techincal training classes at our industry trade shows. I am guessing theywould be forced to revamp their presentations to eliminate theeffect of compression on fuel burn rates based on your expert input:eek:.

RE: 308 accuracy load
 

By retarding the timing,you lose power.By substituting a higher octane fuel,you can advance the ignition timing and make more power,BECAUSE THE HIGHER OCTANE FUEL BURNS SLOWER and therefore produces a longer effective power stroke.
A magnum primer,WHICH BURNS SLOWER produces a longer burn,and adds more heat/energy to the combustion process,which increases chamber pressure,which in turn increases velocity.

RE: 308 accuracy load
 

This statement is nonsense. I have many power curves on several different engines that directly contradict that statement. We run the same fuel at higher compression rations with retarded timing and the result is higher hp in every engine.

It is apparent to me that continuing this post is pointless as you seem to just want conflict not honest discussion. In fact your past posts are littered with this type of never ending back and forth with out actually getting anywhere. It reminds me of my 7 and 9 year old in the back seat trying to get the last word.

I will leave with one last question to ponder. If pressure does not affect burn rate why does it take powder so long to burn when ignitedoutside a vessel?

RE: 308 accuracy load
 

I am talking about the same engine,with the same compression ratio,the only differences being timing and fuel.If you optimize the timing for regular fuel,it will make less power than the same engine with the timing optimized for higher octane fuel.Why is that?It is because the higher octane fuel burns slower,and provides a longer effective combustion stroke.
In the same way the magnum primer burns slower,and produces a longer,hotter burn to produce more chamber pressure.

The apple doesn't fall far from the tree.

RE: 308 accuracy load
 

??????

RE: 308 accuracy load
 

How are you igniting that powder?With a match?How much powder at a time?
The powder in a cartridge case is held in a narrow column just in from of a primer that releases a great deal of energy that blasts a flame into that narrow column of powder igniting much of it at once.Therefore you get very complete ignition,and a very fast burn time.

That is not at all the case if you throw a pile of powder on the ground and throw a match into the pile.A match is not even close to as hot as a primer,and it is not driving a flame into much of the powder at once.
Try an experiment if you want to see just how the method of ignition effects the burn time.

Place 100gr of powder onto the ground and spread it as thin as you can.Throw in a match and see how long it takes to burn.

Take another 100gr of the same powder,and pile it into as small of a pile as you can.Light an oxy-acetylene torch with a large tip and quickly hold the torch flame right over the powder.Notice how much quicker it burns when it is concentrated together and has a much more powerful ignition source that can ignite much more of it at once.