Gunpowder Burning Rate 

The burning rate of a gunpowder can affect how much recoil is produced.  Generally speaking, faster burning gunpowders produces less recoil than slower burning gunpowders.

Different gunpowders burn at different rates. People often put them in categories like fast, medium, and slow. However, there are no clear boundaries for these categories since the burning rates form a continuum from fastest to slowest.  Burning rate charts can be found at several locations on the web (for example: Ramshot Powders, Reload Bench, Vihtavuori Loading Guide). However, there is no clear agreement on the ranking of many gunpowders because the ranking for any given gunpowder varies depending on who made the chart. Therefore, burning rate charts should be used as guides and not as gospel. Never estimate gunpowder charges based on their ranking in a burning rate chart. Always follow a loading guide.

Principles

Okay, in very simplistic terms, here is the logic behind how the burning rate of a gunpowder influences recoil. 

1. Faster burning gunpowders reach peak pressure more quickly than slower gunpowders. Consequently, a smaller charge weight is required for faster gunpowders to reach a given velocity.

2. By inference, slow gunpowders require more of it (usually weight) to reach a given velocity.

3. More gunpowder means more gas.  More gas produces more recoil.

4. Therefore, slower gunpowders require more of it to reach the same velocity, and they produce more gas which results in more recoil.

Okay, let me put that in English. When comparing gunpowders with different burning rates, the faster burning gunpowder will produce less recoil when propelling the same bullet to the same velocity. An important feature is that the weight of the gunpowder required to achieve the same velocity is less for the faster burning gunpowder (see box).

Let me give an example to illustrate this point. Let’s say you have two gunpowders, a “fast” one and a “slow” one.  Let’s say that the fast gunpowder requires 5.0 grains to propel a 130 grain bullet at 1000 fps, and that the slow gunpowder requires 6.0 grains to propel the same bullet at the same velocity.  According to the logic outlined above, the fast gunpowder should produce less recoil.

The difference in recoil between a fast and slow gunpowder can be huge! The difference in recoil between two gunpowders with a similar buring rate can be small, but still noteworthy.

Ultimately, you have to test for yourself which gunpowders will produce the least recoil for your needs. But here is a real world example.  I tested two gunpowders made by Winchester: 231 and Super Target. Both of these powders are considered fast burning and both produce light recoil. Opinions vary on which is the faster burning of the two. I tested them to see which might produce the least recoil with one of my favorite bullets, the Remington 147 grain FMJ Match bullet (available at Midway). It takes 4.5 grains of Winchester 231 to launch that bullet at 950 fps from my Colt 5 inch barrel. It takes less, only 4.2 grains, of Winchester Super Target to achieve the same velocity with this bullet. So, there should be less recoil with Super Target since it requires less of it (in weight) to produce the same velocity. And there was. I noted a slight reduction in recoil with Super Target. The difference in recoil when using these gunpowders was very small because the burning rate and charge weight are pretty similar, but there was a palpable difference. I've tested other gunpowders (and in other hangun calibers) and the burning rate priciple has been supported every time. There are likely exceptions to this rule of thumb (see box) but if you're trying to reduce recoil, using a faster burning gunpowder might do the trick.

While there are advantages to using faster burning gunpowders to reduce recoil, there are limits to the velocity that they can achieve before reaching maximum pressure compared to slower burning gunpowders. Principle #1 above states: Faster burning gunpowders reach peak pressure more quickly than slower gunpowders. Consequently, a smaller charge weight is required for faster gunpowders to reach a given velocity. Another way to view this is that fast gunpowders reach their maximum safe pressure with less gunpowder than slow gunpowders do. And, generally, the velocity achieved by fast gunpowders is less than the velocity achieved by slow gunpowders at the same pressure. So, slower gunpowders often (but not always) produce higher velocities than fast gunpowders when both are loaded to maximum pressure. Another way to look at it is that slow gunpowders can achieve the same velocity as fast gunpowders, but at lower pressure.

Here is an example from Winchester's 15th Edition Reloader's Manual. The data in the table below is for a 130 grain FMJ bullet. Loads for two powders are compared, 231 and Winchester Action Pistol (WAP*). 231 burns faster than WAP. 231 achieves around 1145 fps when loaded to near maximum pressure. (Maximum pressure for the 38 Super is 36,500 psi. See the Technical page for more information.) WAP can produce that velocity at much lower pressure. When WAP is loaded to near maximum pressure, it's velocity is 105 fps faster than 231.

If you're trying to reduce recoil, faster burning powders will help you achieve that goal. But be aware that there are limits to the velocity they can achieve. If you want more velocity, use a slower burning powder. In all circumstances, follow a loading guide.

Light and Fast versus Heavy and Slow

There is often discussion among competitive shooters about the type of recoil characteristics that they prefer when it comes to selecting a bullet weight. The discussion revolves around the light-and-fast type of recoil versus the heavy-and-slow type of recoil. This refers to light bullets moving at fast speeds versus heavy bullets moving at slow speeds.

Now, for the sake of argument, let’s say that the gunpowder issue is neutral so it doesn’t get in the way of the point of this discussion – the difference in the type of recoil between light and fast bullets and heavy and slow bullets. This way we avoid the issue of the type of gunpowder being a variable in the recoil experience (see above).

Different bullet weights can produce different subjective experiences of recoil when both are loaded to similar power levels. For instance, lets say you’re trying to decide between your favorite 115 grain bullet and your favorite 147 grain bullet for an upcoming competition.  Let’s say that you have to achieve a Power Factor of 125 in order to comply with the rules (see the Box for an explanation of Power Factor). A 115 grain bullet has to travel at least 1087 feet per second (fps), and a 147 grain bullet has to reach 851 fps to reach a 125 Power Factor. So, the light bullet will be traveling fast and the heavy bullet will be traveling slow.

Generally speaking, the felt recoil of the lighter bullet feels “snappier” and harder than the recoil from the heavy bullet. It feels this way because the recoil event of the lighter bullet occurs over a shorter interval than the recoil from the heavier bullet (a more intelligent explanation of recoil can be found at: http://en.wikipedia.org/wiki/Recoil).  It’s a product of mass and acceleration. The lighter bullet has less mass but more acceleration. Many people feel that the heavier bullet has less felt recoil because the recoil event is spread out over a longer interval. Depending on the gun and cartridge, the difference in recoil characteristics can have a significant impact on how the gun handles. Ultimately, individuals differ on which recoil experience they prefer, fast or slow.

Recoil and Reliable Functioning

An issue when developing light loads for semi-automatic pistols is that there might not be enough recoil force to ensure reliable cycling. This can be corrected by installing weaker springs.  In the typical 1911 type pistol, two springs influence slide movement. The obvious one is the recoil spring. But the hammer spring also resists slide movement.

The usual factory strength of a 38 Super recoil spring in a Government Model (5 inch barrel) 1911 pistol is 14 pounds. My approach to light load development has been to retain the 14 pound recoil spring and make sure all my light loads will cycle with that spring weight. But some folks prefer lighter loads, or lighter springs. Installing a weaker recoil spring can allow the pistol to cycle with loads that won’t operate a 14 pound spring. Most 38 Supers will run fine with a recoil spring as low as 10 pounds in strength. But remember that the slide must have enough energy when moving forward to strip a round from the magazine. If the recoil spring is too weak, it can’t do that. A 10 pound spring will usually feed rounds just fine, but that might not work for every gun for a variety of reasons. Keep this in mind if you decide to install a weaker recoil spring.

The weight of the hammer spring is also a factor since it also influences slide velocity. The hammer spring resists slide movement only for the initial phase of rearward slide movement, until the hammer is cocked, whereas the recoil spring resists slide movement throughout its complete movement cycle. The usual weight of the hammer spring for typical factory 1911 guns is 23 pounds. But I know from personal experience that different brand-new 1911s have had very different hammer spring weights, some heavy, some light, so 23 pounds is more like a guideline rather than a rule. I put 19 pound hammer springs in the 1911s I build because that is my personal preference as part of my “trigger job.” This reduced power hammer spring allows the slide to cycle easier with light loads.

The 19 pound hammer spring weight has, in my guns, provided 100% reliable ignition with all pistol primers, including the so-called hard CCI primers. But keep this primer-ignition issue in mind if you decide to install a weaker hammer spring since primer ignition is directly related to hammer spring strength (and the particulars of the components in the fire control system) and your results might differ from mine.

There are several sources for recoil springs and hammer springs of different weights.  One place that has a wide variety is Brownells, but your local gunsmith might as well as many other places that you can find on the internet.