Felt Recoil - an observation

[Nick_C_S]

For decades, I've loaded 200gn LSWC's for my 1911 ("'s," plural, these days).

My all-time pet load of 5.0 grains of W231 (45 ACP, of course). Chrono's at 840 f/s.

So I got into plated bullets the last few years and decided I wanted to make a basic range shooter with the same weight, with about the same velocity as my 200 LSWC with a plated slug. I decided on X-treme's 200gn FP's; these: http://www.xtremebullets.com/45-200-FP-p/xc45-200fp-b0500.htm .

I did my load work up with TiteGroup and 4.8 grains puts them pretty close to 840 f/s. So I've got 200 grains going 840 f/s; and 200 grains going 840 f/s - right? Seems to me, the recoil should be pretty darn close. Well, they aren't. The plated FP's have quite noticeably less felt recoil. About 10 to 15% less, if I had to quantify it.

Two things:

First, it wasn't a "hard" objective of mine to make the plated FP's recoil exactly the same as the 200 LSWC's. My objective in the load work up was to get them going roughly the same velocity; and by extension, should have had roughly the same recoil. If my priority was to mimic the recoil of the LSWC's, I would have used a plated SWC and W231 propellant. I'm writing this because I thought it was noteworthy how much different they are. It's was an eyebrow raiser that I found interesting and wanted to share.

Second, I know that felt recoil is a subjective thing. That said, I'm pretty sure that most experienced pistol shooters would agree with me on the recoil difference between these two loadings. Relatively speaking, the LSWC's have a "snap," and the FP's have a "spongy push" that translates to a much more tame feel. That's the best way I can describe the difference.

This was just an observation that I wanted to share with like-minded folks. Anything anybody wants to add or share is welcome.

 

[darkgael]

size

Are the bullets the same diameter?

 

[Nick_C_S]

No. The LSWC's are .452; and the PFP's are .451.

 

[tranders]

I would say it's more powder related than projectile. According to the powder burn rate chart 231 is a slower burning powder compared to Titegroup.

I load a lot with Titegroup,but have never used W231 so can't give first hand experiences.

 

[Nick_C_S]

I suspect it's powder related too. But . . .

According to the powder burn rate chart 231 is a slower burning powder compared to Titegroup.

According to Accurate Arms' burn rate chart, TiteGroup is slower than W231. Either way, they're pretty close.

I load a lot with Titegroup,but have never used W231 so can't give first hand experiences.

I load with a lot of both. And I can say with a great deal with certainty that TiteGroup is a little slower.

Although, as I said before: they are pretty close.

I suppose all of us could spend a lot of time speculating, and it makes for good conversation. But when it's all said n done, we'll never know for sure. I'm not really looking for an answer. I just found the two recoil impulses to be so much different that I felt compelled to write about it.

 

[tranders]

Not to argue, but in Lyman's 49th Titegroup is #9 and W231 is #21 on the burn rate chart. I agree, they are close.


Sent from my iPhone using Tapatalk

 

[T. O'Heir]

Powder lots always the same?
Hodgdon shows 4.8 of Titegroup is the start load for a cast 200. Running at 877 FPS out of a 5" barrel. Not 840.
"...the recoil should be pretty darn close..." The recoil should be identical with like bullet weights and the same load. Physics being physics and you not being able to change that Newton guy's laws. However, felt recoil is always subjective.
Mind you, there might be some sneaky 'lubricating' going on with the copper plating.
Hodgdon puts 231 at #29. Titegroup at #14. That makes the latter considerably faster. Close, they ain't.

 

[serf 'rett]

I've heard competition pistol shooters recite the mantra "fast powder and heavier bullets equal less felt recoil". Exit velocity can be equal between two differing loads; however, the applied impulse can be different. Fast powder applies impulse faster? My guess.

If there is any truth to the mantra, then it would seem that faster powder under the same bullet should have less felt recoil.

 

[darkgael]

fast

Ignition times being what they are for modern propellants.....virtually instantaneous.....I am skeptical that anyone can detect a difference in the speed of ignition between one and another.
Take two powders with quite different burn rates....Bullseye and H-110. Shoot a cartridge loaded with each. Pull the trigger. The gun goes bang - you cannot tell the difference in speed of ignition. Even using very slow propellants in a rifle. Pull the trigger, the gun goes bang now.
Guns of the same weight loaded with equal weight bullets at the same velocity will have the same recoil figures. Recoil impulse, free recoil, rearward velocity of the firearm......the same. No formulas account for the type of powder used.
The load difference between Titegroup and W231 as cited is inconsequential.
The bullets used, however, are quite different.
Pete

 

[g.willikers]

Your results are not surprising and not uncommon.
Every component change makes a difference to some degree.

 

[Nick_C_S]

Your results are not surprising and not uncommon.

I would say so too. Always good input g.willikers.

The phenomenon was interesting enough to me to feel like sharing. So I did.

As far as propellant burn rates go: I don't have a pressure gauge or whatever hardware is used to track pressure curves. So I'm going to refrain from getting any deeper into a push/shove over which powder is faster than another or whatever (been there done that). I have my chronograph; my load work ups; my data; and 32 years of experience. I know which powder behaves in which way in my applications.

 

[Jimro]

Recoil has two components.

Internal ballistic recoil, when the bullet is moving down the bore, the firearm is pushing back with equal force. Heavier bullets here produce more recoil as it takes more force to push the bullet forward, so more force is pushing the firearm backward.

External recoil, when the bullet exits the muzzle like a champagne cork popping off and all the hot gasses behind it release like the pressure off a jet engine. The total recoil here is everything that goes out the muzzle, the mass of the bullet plus the mass of the powder. However the powder goes out much faster than the bullet once the bullet unseals the muzzle, and since energy equals half mass times velocity squared, the higher velocity of the gas add a disproportionate amount of recoil for the small mass.

If you aren't getting complete burn with the slower powder, as indicated by higher muzzle flash when unburnt powder ignites in the atmosphere behind the bullet, you aren't getting all of the external recoil force potential from the powder.

I think the odds are decent that if you swap bullets over those powders, you'll probably swap some of the recoil profile as well.

Jimro

 

[Nick_C_S]

Good post Jimro. These things, I knew. But your description was eloquent and gave a great visual. It's good to rehash the physics from time to time.

 

[849ACSO]

"fast powder and heavier bullets equal less felt recoil".

This has always been my understanding as well.

 

[Jimro]

"fast powder and heavier bullets equal less felt recoil".

Good reasons for that general rule.

Using less powder which produces less gas (and if you have 100% burn with two powders before the bullet unseals the smaller charge will give less recoil in the second "jet engine" stage), and the heavier bullet accelerates more slowly which increases the recoil impulse time for internal ballistic recoil. You get a longer "push" instead of a "slap" even though the total energy is as much or greater than a lighter bullet going faster.

Mathematically it is quantified as area under the curve, a light bullet going fast will have a sharper peak because it is pushing more energy in less time, and the heavier bullet will have a much more gradual peak spread out over more time. Even if the area under the curve is the same, the one with the higher peak will have more "felt" recoil.

If you don't get 100% burn, to make the equations balance you add the mass of the unburnt powder to the bullet to calculate the solid contribution to recoil, then the remainder of burnt powder to the gas contribution to recoil.

Jimro

 

[darkgael]

Difference

One cannot argue with the formula and the ideas as quoted.
I remain skeptical that the difference in the weight of unburnt vs completely burned propellant could have a detectable difference at the charge weights being used. Considering a charge of 4.8 grains....how much of that could be unburned and thus become ejecta. Even if 20% was ejected unburned, we are looking at one grain along with a 200 grain bullet. There may be a measurable difference but not a detectable difference.
Note also regarding the speed of the gas leaving the muzzle:

the powder goes out much faster than the bullet once the bullet unseals the muzzle, and since energy equals half mass times velocity squared, the higher velocity of the gas add a disproportionate amount of recoil for the small mass.

True enough, however, the speed of the gas is considered a constant for all types of powders whether the powder be Titegroup or IMR 4831. This velocity is often cited as 1.5 or 1.75 times the velocity of the bullet. 57So it is essentially a non factor in recoil calculations for loads thus small.
I will stick with attributing the difference in felt recoil to the difference between the two bullets used.

 

[Jimro]

If the same bullet gives the same felt recoil regardless of powder used, that would be a valid conclusion. If the powder gives the same recoil regardless of bullet that would support the opposite conclusion.

Velocity of the gas is directly related to the amount of pressure behind the bullet at muzzle unsealing. More pressure = more velocity in a pretty linear relationship. So if two powders produce the same amount of pressure, the velocity of the gas leaving the muzzle will be the same.

But pistols are generally pretty low pressure offerings (with a few notable exceptions) so "internal ballistic recoil" is probably the biggest factor in whether you feel a "slap" or a "push" from a given load.

Jimro

 

[Unclenick]

Nick,

If I interpolate Hodgdon's data, 5.0 grains of 231 with a 5" test barrel would produce 844 fps. A good Match to your data, assuming your barrel is 5", too. QuickLOAD, with defaults and the H&N SWC HS 200 grain bullet seated to 1.225", gets 842 fps. Pretty close.

Hodgdon's Tightgroup data, as Mr. O'Heir points out, says 4.8 grains gave them 877 fps from their 5" test barrel, and QuickLOAD, with all else the same, gives 876 fps. Again, very good agreement, but your result here differs using the plated bullet, as you say you are getting 840 fps from this combination.

So my first question is did you measure the velocities for both loads on the same day under the same conditions? I've seen optical chronographs get fooled by light conditions before. If it's a real difference, you might find Tightgroup is more position sensitive than 231 and distributes in the case less well, or if you simply used a different case (I've seen up to a couple of grains capacity difference in some makes) or a different primer, that might explain the low velocity. Another possibility is if the bullet seats deeper or has a sharper nose taper, you may get a larger gas bypass quantity past it.

But in the end, even if the Tightgroup got 30 fps more velocity, the effect on recoil, using QuickLOAD's fairly detailed recoil calculator, is only about 6% of recoil energy in a full size 1911. The way the human nervous system is wired, any change less than about 10% is very hard to detect, so I don't think actual recoil difference is likely to be what you are feeling.

Anything that changes the timing of the slide starting back can affect apparent recoil in the 1911 because it changes both muzzle flip and how hard the slide recoil spring tunnel slams into the recoil spring guide flange, and through it, into the frame. I used to swap different strength recoil springs into my Goldcup until I found one that was just slightly too stiff to allow the slide to quite make it all the way back to the guide flange, but still let fed ammo reliably. The recoil perception went from having a sharp edge (the flange impact) to being very soft and spongy. It was a night and day difference you would pick up on right away. And this was with the same exact load in every respect.

So I suspect your eject and load cycle timing has changed with the different load. I just don't see how the energy differences, much less the smaller momentum differences, would account for it.

 

[Nick_C_S]

Thanks Unclenick. You are always insightful.

So I suspect your eject and load cycle timing has changed with the different load.

Never thought of that. Seems most plausible to me.

I have three 45 ACP guns; and they are all full-size 1911's (5" bbl). The one at the range the other day was a Kimber Custom Target II with a Wolf 16.5 Lb (stock weight) recoil spring. The rounds of question were chronographed this past summer with this gun, in this configuration.

I've tested both load recipes more than once (different batches); and the 200 LSWC's more times than I can count. Results are always in the 840 neighborhood. I always test at the same range; at the same distance (4 yards); and when the sun is at roughly the same angle - bathing the diffusers in sunlight. If I can't duplicate that condition, I don't chronograph.

 

[Jimro]

So I suspect your eject and load cycle timing has changed with the different load. I just don't see how the energy differences, much less the smaller momentum differences, would account for it.

The energy differences are the only source of input for a timing difference once you control for how the shooter braces against the recoil. I think we've all seen someone "limp wrist" a pistol which cause the slide to not go back far enough and cause a miss feed, but as long as the shooter is consistent, then we can assume the vast majority of the difference comes in the load.

Unclenick, what does Quickload predict for final barrel pressure for the two loads? The 45 ACP is really a low pressure round, so the difference between 18,000 psi and 20,000 psi is much more significant percentage wise than say a 35,000 psi and 37,000 psi load in a different cartridge. If the pressure at barrel unsealing is the same, and bullet velocity is the same, then recoil "should" be the same, at least from a math perspective.

For sure there is an "accumulation of everything" from X% energy difference, Y% bullet to barrel friction difference, and Z% pressure difference all adding up to a different recoil feel, but my best guess is that it's the powder that is the largest contributing factor (although I'm totally happy to be proven wrong on that point).

Jimro