Since a 16" bbl is short'ish for a .308win cartridge, I think it is fair to say a lot of the powder is not burned off before bullet exits muzzle and many ppl have experienced this (loud muzzle flash, etc).  So, I was thinking of using a magnum primer in my .308 loads that I intend to run through a 16 inch barrel.  Does anyone have any thoughts on doing this for the purpose of ensuring all of the powder is burned inside the barrel before the projo exits??   ..setting aside the fact I will have to reduce charge weights and re-workup loads for a given bullet.  Obviously, there is no real published data on this.  
I think this has three benefits:   a) burning all of the powder might be slightly more economical as it would allow me to reduce my charge weight with a slightly lower per-round cost (but meh, savings will be small for sure), and b) it might reduce muzzle flash since more (or all) of the powder would burn inside the bbl, and c) muzzle pressure would be lower, and thereby result in quieter and more controllable shot, since the max chamber pressure would occur earlier and diminish more quickly due to all of the powder burning faster (earlier max chamber pressure and faster burn of charge lead to lower muzzle pressure). I'm sure some ppl would be like "who cares if does all that," which is perfectly valid.  But my question is:   am I correct that these so-called benefits would result from using a mag primer, and are there other benefits or other effects that might result from using a mag primer to ensure burning of all the powder in short'ish bbl?  
Other factors to consider are whether I'm using a relatively light or heavy bullet (110gr v. 180gr), and am I using a relatively fast or slow powder or something in between (e.g., 5744 v. H380).   What if I did the same thing in a 12.5" bbl, would that make a mag primer and reduced charge more beneficial?  From what I can tell, ppl do not load mag primers in 308win simply bc there is no published data, which is totally reasonable.  I'm just looking to tinker a little bit, and intend to start low and work up all loads since I will be flapping in the wind on this.  
Anyone ever try this, or anyone have any armchair thoughts on this??
I have googled extensively, and can find no discussion on this.  

 
 
 
 
 
 
 
 

My armchair thoughts, for what they are worth.  (Their worth being exactly what you paid for them).

Using magnum primers won't help you to achieve your goal.

Short barrels and rifle cartridges are going to result in powder burning outside of the barrel.  

You can play with Quickload, but QL has no adjustment for different primers.  (At least my version doesn't).

You can go to a faster powder, but then you won't have the velocity of the slower burning powders.

If your goal is high velocity, (or relatively high velocity), then you will have to use slower burning powders that will result in burning powder outside of the barrel.

If your goal is to burn all of the powder in that short barrel, then you will have to use faster burning powders, which will result in lower velocities.

Like most of life, you are going to have to compromise.

An advantage of the slow burners is that the increased gas pressure at the muzzle appears to actually make the muzzle brake more effective. The downside is that the report will be louder.

Use  4895 IMR Or H  with  any std or mag primer. It dont matter IMO.

I think these all completely correct, and I do not disagree with them one bit.  So, lemme throw this idea out at you....what if I said my purpose was not simply to burn all the powder inside the bbl, but was to reduce muzzle pressure.  As was mentioned, reduced muzzle pressure reduces the effectiveness of a muzzle brake.  However, reduced muzzle pressure increases the effectiveness of a suppressor.    
Now, I do not know of a real good way for me to measure muzzle pressure, except I do have one idea.  
First, I want to point out a company that makes hardware to measure chamber pressure.  One thing that company says is:  " Efficient loads will normally have a faster rise time. It is also preferable to have a faster rise time because this helps ensure complete powder burn and reduced muzzle blast."  See https://www.shootingsoftware.com/pressure.htm  I think this statement says exactly what I am trying to figure out.  And, ostensibly, magnum primer would create a faster rise time...at least that is what I'm trying to test.  Also, it is common knowledge that high muzzle pressure is a often a necessary evil bc there are minimum required energy levels to push a bullet out the bbl and into the target area with sufficient force to kill the target....if we could drop an elk at 2,700 yards with the weight/recoil of a .22LR, we would but we can't and never will.    Slower burning powders allow the powder to impart more energy into the bullet without peak pressure exceeding SAAMI specs.  Regardless of what range you are working and the required terminal energy, it is ALWAYS preferable to achieve that minimum energy with the lowest possible muzzle pressure.  Lower muzzle pressure creates a decreased flash, noise, and muzzle rise.  It makes suppressors more effective, and reduces wear on the blast baffle...increasing longevity of the suppressor while--at the same time--making it quieter (more effective).    
Second, the only real way to test my hypothesis is to see if I can achieve the same muzzle velocity (with a given bullet in a given bbl) while having a reduced muzzle pressure...bc that is my goal for using a magnum primer.  Even if I did manage to achieve this, I am sure the benefit will be negligible...otherwise, shooting 308WIN cartridges with magnum primers would be standard, not abnormal.  There are a lot of smart ppl who would have already figured it out, if I was correct.  So I will need to think about testing muzzle pressure and do some more internal ballistics research.  But, I think in the end, using a magnum primer will just increase peak pressure up to the SAAMI pressure ceiling, and then will not allow any further gain in velocity...but I think if that were true, there would be no point to having magnum primers at all, even in magnum cartridges.  
So any armchair thoughts on this?  




 

From my experience with QL the heavier bullets results in 100% powder burn with less chamber pressure.
For example:
a 210gr vld with be 100% powder burn in a 16" bbl at 57000psi with h335(10.0k psi muzzle)
a 190gr vld with be 100% powder burn in a 16" bbl at 62000psi with h335(10.8k psi muzzle)
a 185gr vld with be 100% powder burn in a 16" bbl at 64000psi with h335(11.0k psi muzzle)
a 175gr vld with be 100% powder burn in a 16" bbl at 66400psi with h335(11.5k psi muzzle)
a 168gr vld with be 100% powder burn in a 16" bbl at 69500psi with h335(11.7k psi muzzle)

Most if not all the powder that is going to burn is burned up in the first few inches if the barrel.

The Muzzle flash you see is caused by the gasses created by the "Burned" powder igniting when they enter and oxygen right environment.  It is not cause by powder burning it's way down the bore.

At first glance, this sounds like the opposite of correct.  Maybe I am not seeing the point you are trying to make.  Certainly, you would agree that longer bbls produce higher percentages of powder burn than shorter bbls and, therefore, higher velocity....it sounds like you are saying you get the same percentage of powder burn in a relatively short bbl as compared to a comparatively long bbl as long as both bbls are at least a "few inches" long.  Is that what you are saying?  Or am I just missing the point?  
Now, I would agree that "most" of the powder is burned in the first few inches..certainly.  But my point is that the higher this "most" becomes, the lower the muzzle pressure would be.  I am hoping that I can achieve the same muzzle velocities with a correspondingly lower muzzle pressure when using a magnum primer over a standard primer.  
I am also trying to sort out some ideas, which everyone here has been very helpful with.  My bad if my writing sounds jerky...women point this out, to me, regularly.
 

That is interesting, I should invest in this QL...ugh why so expensive.  



What are the charge weights for each of these?  
 

The powder is burned in the first few inches of the barrel

The longer barrel produces higher velocity because the bullet is continuing to accelerate as these gases push it down the bore.  The longer the barrel time, the higher the velocity.  The shorter the barrel the less acceleration time the lower the Velocity.

 Here is an Article by John Barsness of Handloader/Rifle magaizine.  He can explain it better than I can.
http://www.loaddata.com/articles/PDF/Bench%20Topics%20LR%20(2).pdf
If you cannot view the Article here is a Short Version.

One of the most frequently
encountered misconceptions
in handloading is that
a charge of smokeless powder is still
burning when the bullet (or shot
charge) exits the muzzle. As “evidence,”
many shooters cite the muzzle
flash, especially visible in dim
light. Nope, that ain’t burning
powder. Instead it’s the hot gas produced
by burned powder, re-igniting
once it strikes the oxygen in the
atmosphere.
Instead, almost all smokeless powder
burns within a short distance in
front of the cartridge. The exact
point varies with the powder’s burning
rate, the cartridge, the projectile
etc. But even in huge “magnum”
rifle cartridge, over 99% of the
powder is burned within 4-5 inches
of bullet travel.


Here is a discussion with "Gun Writers" on the subject.

http://www.24hourcampfire.com/ubbthreads/ubbthreads.php/topics/7851943/The_Article_How_Smokeless_Burn#Post7851943

Here is another discussion on the subject.

http://www.24hourcampfire.com/ubbthreads/ubbthreads.php/ubb/showflat/Number/8796385/gonew/1/Muzzle_Flash_vs_Unburned_Powde#UNREAD

First, I want to point out a company that makes hardware to measure chamber pressure.  One thing that company says is:  " Efficient loads will normally have a faster rise time. It is also preferable to have a faster rise time because this helps ensure complete powder burn and reduced muzzle blast."  See https://www.shootingsoftware.com/pressure.htm  I think this statement says exactly what I am trying to figure out.  And, ostensibly, magnum primer would create a faster rise time...at least that is what I'm trying to test.  Also, it is common knowledge that high muzzle pressure is a often a necessary evil bc there are minimum required energy levels to push a bullet out the bbl and into the target area with sufficient force to kill the target....if we could drop an elk at 2,700 yards with the weight/recoil of a .22LR, we would but we can't and never will.    Slower burning powders allow the powder to impart more energy into the bullet without peak pressure exceeding SAAMI specs.  Regardless of what range you are working and the required terminal energy, it is ALWAYS preferable to achieve that minimum energy with the lowest possible muzzle pressure.  Lower muzzle pressure creates a decreased flash, noise, and muzzle rise.  It makes suppressors more effective, and reduces wear on the blast baffle...increasing longevity of the suppressor while--at the same time--making it quieter (more effective).    
So any armchair thoughts on this?  


SNIP
Gyro Jet was supposed to be recoil free and would do what you want... HITTING that elk at 2700 yards is beyond my ability though.

 Note that your Pressure Trace Link has many references to Denton Bramwell.  Also note that the Links I provided to the 24 Hour Campfire have several comments/post by the same Denton Bramwell.  

 In short, he is an expert wit the Pressure Trace and he is one of many on the 24 hour Campfire that say, All The Powder That is Going to Burn is Burned up in the First Few Inches of the Bore.

Think about it like this, if ALL of the powder was burned in the first few inches, then slow burning powders would not produce substantially higher muzzle pressures than faster burning powder.  As any QuickLOAD user will tell you, faster powder = lower muzzle pressure, and slower powder = higher muzzle pressure..while keeping muzzle velocity the same.     I think that if ALL powder burned in the first few inches, this fact would not be true.
I agree with you that most powder burns in first few inches.  But there is just no way that ALL powder burns in first few inches..at least not when dealing with rifle-caliber charge weights.  Now pistol-caliber charge weights, such as 3 to 5 grains of powder, probably does ALL burn in the first few inches.  But not 25 to 50 grain charge weights.  I don't think anyone would contend that 50 grains of powder burns completely after the bullet has traveled only a few inches.  That seems fairly ludicrous, no??  It seems to me you are taken something that was said in one context and applying that same statement to other contexts, in which it does not apply.  Perhaps I am wrong, tho.  







 

Temperature on firing is almost  5,000 degrees for a very short period of time.  I dont think any powder will make it to the end of the barrel.   Only Black Powder will,  if to much is used.

Your theory was explained like this, by John Barsness of Handloader/Rifle Magazines.

Whoever posted that overlooked one major factor, the amount of powder in the charge.

A maximum charge of H4831 will burn a little further down the barrel than a max charge of, say, Benchmark behind a 180-grain bullet in the .30-06--but it will still all burn within a short distance in front of the chamber.

However, the charge of H4831 will also be considerably larger. Hodgdon's data list 60 grains of H4831 as maximum, as opposed to only 46 grains of Benchmark. 60 grains of H4831 produces more muzzle pressure because it results approximately 30% more hot gas than 46 grains of Benchmark. Thus there's more hot gas being released when the bullet exits, resulting in higher muzzle pressure.

This is also why slower powders typically result in more muzzle flash: There's more hot gas to re-ignite when it encounters the oxygen in the atmosphere. But hot gas is already-burned powder, not still-burning powder.

I agree with most of the other comments regarding a magnum primer... I am doubtful that it will help with a more through burn. If anything it would probably make for a more consistent ignition of the powder.

I will suggest using a faster powder, like IMR 3031.

One of the other forums ( M14forum.com ) has had threads using it with greater accuracy in 16.5" SOCOM's

Here is a Google search regarding that subject...

https://www.google.com/search?q=IMR+3031+in+SOCOM's&rls=com.microsoft:en-US&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1

And a general search....

https://www.google.com/search?q=IMR+3031+in+a+16+.308+barrel&rls=com.microsoft:en-US&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1

The 308 is an amazingly effecient cartrige,I have used TAC and Varget  as my go to powders  for both my 16 inch DPMS and
my CETME 17 inch barrel with very little flamethower effect. and standard primers.

New term to me. Had to look that up, learn something every day.

OP:  as you can tell thus far, there seems to be considerable debate about internal balistics theory.  As a theory, you'd expect that.

Back to your application and variables we CAN meassure (like velocity in a relatively short barrel for the .308, and accuracy):  here is what I would try (in this order)

-Federal primers.  Federal is the ONLY major U.S. brand to use a different primer compound ("Basic" vs. "normal" variation of L S compound).   It does not hurt to use Fed. Gold Medal primers for consistency sake, even if the compound type proves irrelevant.

-heavier bullets.  At least 175s (even heavier can be used in the .308) and

- a powder charge from PUBLISHED RELOADING SOURCES at the faster, rather than slower, end of the burn rate chart.

Ultimately, only you can answer what load yeilds the highest velocity and best accuracy in your gun.

The standard CCI #34s and CCI #41s used in federal military ammo ARE magnum primers according to CCI website:

Suggestion: Call up Springfield Armory and ask one of their SOCOM 16 experts about how to deal with muzzle flash, whilst maintaining respectable peak chamber pressure, and good tamed port pressure for driving the piston of the autoloader (not too high, not too low).  Ask them their advice on the best ammo to use to run the SOCOM 16, ie. which bullet weight in the myriad of commercial ammo offered in .308.

They did invent the little "pepper box" muzzle brake for that rig which, IMO, quenches (rapidly cools and disperses) much of the hot plasma and goes a long way to reduce the size of the fireball.

As fare as the handloader mag article in the earlier posts.  Anytime that particular gunwriter starts his article with "misconception in the reloader community" gird up your reloader loins.  I do not believe the hot gas, re-igniting and burning in the atmosphere outside the barrel is causing the fireball.   IMO it is the hot plasma disassociated atoms and electrons finding a more stable state as things cool off, and molecules reassociating, causing electrons to drop to a more stable orbit and releasing the stored energy in the form of photons, many of which are in the visible spectrum.