Grain Count, Velocity Question
 

I asked this question in the Revolver Forum and though I might get some more answers here.

Please excuse the elementary question but, higher grain magnum loads are less powerful than lower grain loads? Why would higher grain magnum loads be better/safer, less hard on a model 66?

Also how does grain count affect power and recoil? Does higher velocity translate to more power and more recoil? I know very little about grain count and velocity. Somebody school me please!

-Dave

I assume you are referring to bullet weight, which is measured in grains. There are 7000 grains in a pound.

Typical .357 Magnum rounds have either a 158 or 125 grain bullet. The 158 is usually a little slower than the lighter 125 grain bullet. Recoil from both rounds is usually about the same, but possibly a bit less with the 125.

For your Model 66 either is fine, but I'd go with the 125.

May be confusing bullet grain with powder. Not sure though?

Yes I was. I thought grain count would refer to the amount of gunpowder in the cartridge. So it made no sense to me that higher grain bullets had slower velocities. I now know grain count refers to the weight of the bullet. Thank you.

Dave

125gr bullets at full power 1,450 fps are known to crack the forcing cones of K frame revolvers in the thin area. Since your model 66 is a K frame and S&W no longer makes or stocks the barrels for K frame .357 mag revolvers you run the risk of ruining your gun with no way to fix it short of finding a used undamaged barrel if you choose to shoot the light 125gr full power loads. A better option is to use the Remington Golden Saber at 1,250 fps which is less likely to damage your barrel.

Here is an article on the issue of the damage 125gr loads can do the any K frame .357 mag: http://www.gunblast.com/Butch_MagnumLoads.htm

Grain weight refers to BOTH.

The general rule of thumb is a heavier bullet requires a lighter powder charge.

The reason is a heavier bullet results in both more friction with the barrel, the heavier bullet is physically longer, hence more contact and friction, and the heavier bullet has greater inertia. Both result in more pressure, meaning a lower powder charge to stay within safe limits.

When you talk about POWER I believe your referring to muzzle energy, also known as kinetic energy. The issue with going by muzzle energy is the formula is MV(square), meaning energy increases at the SQUARE of muzzle velocity. This means a super light bullet at hyper speed has more energy then a heavier bullet at more normal speed. Impressive on paper but real world experience has proven in a lot of cases paper power is just that, paper power.

commercial ammunition
 

Commercial ammunition will state the weight of the bullet on the box, such as 125 gr. HP (hollow point). They won't tell you the weight of the charge of powder or the type. Sometimes the velocity obtainable will be printed on the box. If a cartridge is labeled +P it means it is loaded to a higher pressure and should have more velocity. How much more depends on the gun you are shooting. There will be variations in this information due to barrel length and some other factors.

An example would be: 125 gr JHP +P, which means a 125 grain jacketed hollow point bullet loaded to a higher pressure than standard ammunition.

Workable bullet/powder combinations for different calibers are found in books for people that make their own ammunition, like many of us here do.

Don't worry about the questions being 'elementary'. Do some homework and you'll learn fast. And if you are willing to help yourself, there are a lot of knowledgeable people here to help with the parts you don't understand.

Well , maybe yes , maybe no. That's if you ASSuME that the same powder is being used.

But if a handloader is using , say , HP-38 , yes , a heavier bullet would generally call for a lighter powder charge , due to the burning characteristics of smokeless powder.

But since we never know just what powder the factories use in which loads , , ,

An additional complicating factor is the type of bullet used, that is lead or jacketed. If a cast or swaged lead bullet is used, the barrel friction is less than a jacketed bullet of the same mass. By this I mean that a cast lead 158 grain semi wadcutter (abbreviated as LSWC) will have less bullet friction in the barrel than a semi-jacketed soft point 158 grain bullet. Accordingly, the lead bullet will have a different powder charge required for a given muzzle velocity than the jacketed bullet.

In addition, the powder (whose weight is also specified in grains) will have a different charge weight for a given bullet type and weight depending upon the burning rate or speed of the powder, and the barrel length used. For example, a slower burning rate powder can be charged to a higher weight in a longer barrel, since it will continue to burn and increase gas volume as the bullet moves down the barrel. A faster powder will burn up completely in a shorter barrel, and if a charge comparable to that of the slower powder is used, excessive pressures with potential damage to the firearm may result. In the shorter barrel, a lesser charge of slower powder will be used, otherwise excessive flash and blast will be observed as the incompletely burned powder burns as it leaves the muzzle.

The science of bullet acceleration, powder gas evolution and chamber pressures vs. muzzle velocity is called interior ballistics, since it occurs before the bullet enters free flight outside the firearm's muzzle. All of these factors, as well as bullet mass, bullet friction, environmental temperature, primer brisance, case volume and powder position within the case affect the final velocity, muzzle energy and recoil energy.

Since few of us have the equipment, resources, and time to determine these factors, we use the various reloading manuals on the market. The authors, editors and publishers of these manuals have done the grunt work for us, and as a result, have made handloading a relatively safe hobby.

JDBoardman,

You mentioned primer brisance. Do you have any good info on it?

Primer Testing Reference