How accurate is velocity in determining how close you are to the max chamber pressure? I'm concerned because I'm wanting to experiment with faster burning charges in .308 for my Striker with the 15" barrel. I can envision getting a pressure spike that may not be reflected in the velocity of the bullet, but may go beyong the safety margin. Was thinking about going to a magnum primer with less powder, among other possibilities.

[ 10-24-2002, 18:26: Message edited by: savageshooter ]

I think velocity does play a certain role in determining when one gets close to max pressures in his gun. When velocities start to level out then you are on the high pressure side generally. But one must remember that is only one part of the puzzle of determining safe and what isn't. One of the ways I do it is buy some factory ammo if available. Generally the high performance kind such as Hornady heavy mag, Federal High Energy or some equivalent and fire it and look at the cases especially at the expansion ring and try to get close to that if possible with my handloads. Also how the cases last is another piece of the puzzle too. If you are getting good vel. and the cases are lasting for a long time then that is a good indicator that pressures are ok. In getting factory ammo it is best to get the same brand as your cases you are loading. One must always remember that you are putting together a puzzle of many parts when trying to determine pressure and one can not only go by one thing because it is sorta like using one piece of a puzzle and then saying it is complete. Just doesn't work does it. You will lose roughly 10 percent of rifle velocity when going to handgun velocities. Some loads you may lose only 7 or 8 percent some maybe 11 or 12. Generally the heavier bullets will lose less. Get a standard such as a factory load and use that as a guide for determining pressure by case appearance. Other than that "Go by the Book" you will probably stay out of trouble that way. Generally speaking I have found that if you have been loading and an experimenter you already know what to look for if not "Go by the Book" until you have more experimenting under your belt. Proceed slowly and use good judgement.

Look at the maximum velocity in reloading manuals for your propellant. The max velocity for that powder is usually what they have determined to be near safe SAAMI maximum FOR THAT POWDER. In your case you will have to determine velocity loss for each inch of barrel length difference between their test barrel and yours. Anywhere from 25fps to 40fps per inch. Use 40fps for safety.

After this you will have to be very observant of external pressure signs, none of which are absolute, and back off the load if any are observed. Be very wary of faster propellants for which there are no published loads, such as pistol powders. The pressure spikes on them can be extreme at much lower velocity and can be quite dangerous.

savageshooter......if you are looking at a "faster" burning powder because you have a short barrel, it doesn't work that way.

Burn rate has more to do with case capacity and bore diameter than barrel length. It's hard to go wrong with either RL15 or varget in a 308 especially with bullets in the 150 to 165 grain weight.....180 grains and above you might check out IMR 4350 as a pretty good powder.

I don't quite understand why a faster powder wouldn't work better in the short barrel. It seems from the muzzle flash that some energy is being wasted, and may cause a disturbance on the bullet's exit. Aren't they determining how much powder they use based on a long barrel? Do you know of any books on the science of powder, chamber volumes, etc? Just seems to me that you could use pistol powder, working up from a pistol-size load until you reached the max chamber pressure.

Unfortunately some of the things we think we know by intuition aren't true. For example a load reaches achieves max pressure very quickly and certainly within the first inch or so of movement. The bullet continues to accelerate down the barrel but the big pressure is over.

Let me give you an example of tests others have done. Take a rifle with a 28" barrel and select 10 different powders of various burn rates and load them until you reach a safe maximum pressure for each and then rank them by the velocity achieved. Cut off 2" and reshoot to determine velocity...the result is the powders will still be ranked the same. Velocity will be lower and some may decrease more than others but the rankings fastest thru slowest will remain the same. You can do this down as far as you want but the relative rankings will always stay the same.

Muzzle-flash is another concept and is basically powder not fully burned coming out the barrel but the amount is insignificant as their is always some partially burned and/or unburned powder in the barrel after a shot....it has no impact on pressure or velocity.

If you can get a copy of the latest Nosler manual they have loads listed for pistols using rifle rounds...check out the powder they use and compare it to that used in the rifle section.

If you read magazines like "Varmint Hunter" which is very good for technical articles or "Rifle Shooter" which sometimes has good articles look for articles by Dr. Ken Howell and Mic McPherson as they rarely fail to satisfy.

Rick Jamieson of Shooting Times is also quite good.