Effect of fast vs. slow burning powders on semi-auto pistol recoil ope

[JonF]

I'm curious to know what actual effects a fast burning powder (like Titegroup, N320, etc) versus a slow burning powder (HS-6, longshot, etc) has on the *mechanical* recoil operation of a semi-auto pistol. Now, i'm not talking about perceived snap/push feel or how much gas to run a comp, rather, in a typical delay locked breech of a typical semi-auto pistol, what effect does a slow vs fast burning powder have on the actual recoil operated mechanism?

Most importantly for my specific curiosity, will one type of powder generate more overall force and cycle it much more strongly? Does the slower burning powder operate the mechanism more slowly? Is there a threshold for *TOO* slow a powder (like rifle powders)? What are some of the other important factors that come into play in such a comparison?

[superdude]

Slower gunpowders usually require a larger charge weight for the same velocity as a fast gunpowder. The larger charge weight (for the same velocity) will generate more recoil. The weight of the gunpowder figures into what comes out the end of the barrel with the "ejecta" so more of it for the same velocity means more recoil.

see the links below for more information.

http://en.wikipedia.org/wiki/Recoil#Including_the_ejected_gas

http://38super.net/Pages/Recoil.html

There is a threshold for too slow of a gunpowder for pistol cartridges, though I don't know how one would define that. Case capacity is one limiting factor.

[jmorris]

What are some of the other important factors that come into play in such a comparison?

What you feel. The law of "equal and opposite reaction" is pretty solid but "percieved recoil" or sight lift for open guns is what really counts.

[redial]

I can tell you that in a heavy-slide Bullseye gun, a 200 SWC at a given speed won't cycle the gun with a slow powder (4756) but the same bullet at the same speed with WST will reliably cycle the gun.

Maybe not relevant in Practical applications, but it's something I've found.

Mark

[Nitroexpress]

I was searching for, asking the same question myself. My research so far is summarized below.

 

Locked breech, recoil operated guns, as their name implies, depend purely on the impulse of the propelled projectile to operate the action. The complex dynamics of gas pressure build-up and drop down back to ambient pressure have little to do with this system.

 

Recoil is a basic property of every firearm. It’s a “product” of Newton’s 3rd law of motion, which states that for every action there’s an equal and opposite reaction. This means that when a bullet is expelled from the barrel by the pressure of the hot powder gases, the barrel (and the gun it is attached to) receives the same impulse, but in the opposite direction. This translates into a rearward movement of the gun, which is then felt by the shooter as recoil.

 

In a blowback operated gun the operation of the guns mechanism depends on the force of the reward moving shell casing to operate the action. In other words the casing "blowing back" against the breech block or pistol slide, which is not locked to the barrel. Blowback operated guns have the barrel rigidly mounted to the frame, the breech block is held in battery by a spring. Factored into the operation of a blowback operated pistol are the weight of the breech block, the spring tension and spring rate, the dynamics of gas pressure build-up and drop down back to ambient pressure, and friction between the shell casing and chamber. They operate at a relatively low pressure and use the weight of the breech (slide) and the power of the recoil spring to hold the action closed until the pressure level drops to an acceptable level.

 

As pistol design progressed, the barrel and breech (slide) were locked together for a portion of the movement of the slide. This removed the effect "blowback" had on the operation of the pistol. The barrel and breech were locked together long enough for the pressure in the barrel to drop too low to be a major factor in separating the barrel and breech. The only remaining force left to operate the action was recoil.

 

In the blowback design, the effect of recoil is a factor later in the cycle, does not play a major part in the pistols operation.

 

Recoil force can be calculated. Factors in that calculation are bullet weight, bullet velocity, powder charge weight, and firearm weight. In our case we are using the same gun, and powder will not vary significantly. What are left are bullet weight and bullet velocity, and that is defined in the handgun world as the "power factor".

 

Ammunition of the same power factor should in theory operate the same.

 

Therefore if a certain pistol is designed to function with ammunition having a 115 gr bullet at 1050 fps or a power factor of 120 (bullet weight in grains multiplied by velocity in feet per second, divided by 1000), it stands to reason that any load that has a similar power factor (recoil) will operate the pistol in a similar manner.

 

If the power factor is different, the recoil spring may require replacement, with a lighter or heavier recoil spring, to retain the same operating characteristics. As slide velocity increases, so does the strain on the pistol. The slide is "gently" slowed by the recoil spring, however the barrel is stopped abruptly by a lug or toggle pin, or whatever barrel retaining mechanism the pistol is equipped with.

[muncie21]

On 10/19/2018 at 11:05 AM, Nitroexpress said:

 it stands to reason that any load that has a similar power factor (recoil) will operate the pistol in a similar manner.

I understand where you're coming from, however there are limitations/exceptions.

 

While working up some test loads for 200gr .40S&W, I learned that at the same PF, my 200gr load needed a stronger recoil spring to bring the slide fully into battery.  I'm chalking this up to the slower slide speed (although PF was the same) from the 200gr bullet.  Changing the 11# recoil spring to a 13# one fixed the issue.

 

Aside from this, I think your other comments/feedback are pretty much spot on.  Oh and welcome to the forum!!