Today, only slow burn rate propellants are reviewed.

The damping effect of cold weather on slow burn rate propellants (also called magnum propellants) has is a bit murky. The constant pressure and burning speed of a propellant moves about in subtle relationships of physics and chemistry. This is an area nearly invisible to the reloader. In the laboratory there is equipment that demonstrates the firing process and places the burn in context for a visual review.

The Curmudgeon shot his mouth off by not going into detail when he indicated BLUEDOT may not endure cold weather firing with constant, even results. More detail was required. Hell, REDDOT is also subject to cold weather depression, but not as much as BLUEDOT. Everything is relative. Obviously, these fine propellants all have different burn rates and pressure expectations. The chemistry here becomes – burn speed and pressure curve in relation to resistance (mostly load weight) and the propellant’s temperature. While propellants do not freeze they can gradually grow "numb" with increasing cold. What revives a cold propellant is pressure – applied by resistance (weight).

To lessen the cold impact on slow burn rated propellants upon loads as the reloader heads into cold weather:

1. The propellant should be compressed to squeeze any air from the tiny "fluffy" particles.

2. Use a wad without a long "spongy" compression base.

3. A "hotter," stronger primer helps get the propellant going – (FED209A, CCI209M).

4. Good crimps: Hulls that are old, tired, lose the ability to maintain strong crimps; an ability to contain the shot load at the beginning of the burn progression.

5. Load weight. A substantial load of shot creates more resistance and helps burn all of the propellant. Think diesel! (A light-weight often "faster" load using a large amount slow burn rate propellant may not burn 100% in cold weather.)

6. Resistance comes from load weight, type of shot and the wad design.
Note: Steel shot despite being lighter weight creates more resistance when fired than lead shot of the same weight. Other metals do other "things".

If you can imagine, the propellant ignites and burns via an intense flame produced by the primer. A "fast" burn rate propellant burns almost instantly while a slow burn rate propellant drags its feet. The net result difference being a quick impulse versus a longer term of gradually increasing pressures within the barrel. The long term gradual pressure increase is capable of pushing a heavier (more resistance) load into acceptable velocity – without creating unacceptable internal pressures.

If you flick a small marble with your finger to get it moving you might snap it across the room. Fine, all you wanted to do was move that marble. Now you want to do the same with your bowling ball. Go ahead and snap your finger against it. It hurts like hell and the ball did not move. Now, rest your finger behind the ball and with a slow increase apply pressure behind the ball. It rolls away easily (and puts a hole in the Sheetrock). That is the difference between propellant burn rates and their relationship with mass.

What are you trying to get into motion inside your loads? All propellants require some level of pressure (resistance) to burn completely. In the open, in an unpressurized environment, they burn as slow as a match.

Under compression, fast burn rate propellants require less of a constant pressure to burn correctly than slow burn rate propellants. Temperature loss is a factor that has greater impact upon slow burn rate propellants because as soon as the mass (wad and shot) begins to move forward the impulse of the initial burn may drop off because the required resistance is too quickly reduced. The wad and shot move forward increasing the area being filled by expanding gases. What if the gases slow or cease to expand? Since propellants require pressure to burn, the drop in pressure may slow or stop the burn process. A "poof" load occurs. After a POOF you should note the unburned powder granules STILL IN YOUR BARREL.

Often, we use slower burn rate propellants to kick into motion lighter loads we wish to move along with increased velocity. This is an element of physics and chemistry that can be taken only so far – before poof! With shotshells, we have a ceiling and floor that we cannot fudge. We have a top PSI (pounds per square inch) of the shotgun’s chamber and the low end where pressure and load speed are useless. We operate between these pressures. This window is much smaller than that offered to metallic loaders. Our lightweight snappy shotshells of early fall may crumble with the onset of freezing temperatures. The combination of lighter shot loads and slow burn rate propellants to achieve an increase in velocity may "poof" in the cold. Bad load or misapplied load?

Sometimes reloaders don’t read load commentary, available manuals or instruction guides so as to comprehend propellant structure, wad differentials, shot weight influences – or anything else. They expect everything should operate the way they IMAGINE it should.

A fellow pointed out that he could not HEAR the the colder weather's effect upon his reloads. Well, by the time you CAN hear a difference – the show is over. Differences first appear in the laboratory – on the electronic screens. When loads are taken out of the freezer and fired, we see squiggly lines. We see ups and downs. Diminished velocities, pressure variations and nasty peaks and valleys. Some loads more than others. We note the most and least affected and make load notes, passing this information along to our customers in our guides and manuals. You can a great deal about powder character in BPI's Advantages IV Manual. Yes, you get what you pay for - recipes are more than the ingredients, sometimes knowing when to serve is just as important.

Other Factors:

All propellants are not equal in character or the speed and pressure they produce. Propellants are all designed to DO something special. Read the label! Air space between propellant and wad causes miss-fires. A soft cushioned wad is the next thing on the resistance ladder to air-space. Wad designs VARY with intent of use. You may need more than one type of wad too…

Adverse conditions eliminate some loading combinations while bringing others into play. If you read the instructions and commentary we provide, you will be able to discern which is which..