What's harder on revolvers: recoil impulse or pressure?

[sidheshooter]

I'm checking out loads for my .38 airweight, and I see that the buffalo bore standard pressure 158gr. LSWCHP (billed as safe in any older/alloy revolver in good shape) hits a claimed 854 fps from a 2" j-frame.

That's obviously pretty hot relative to the current market offerings; I'm fairly certain that there is no way that, say, Federal's version of the same load in +P "FBI" guise is going to even come close to that–IIRC, Federal's +P is probably just breaking 800 in a snub. My understanding is that Remington is faster than Federal, but I'd still be surprised to see their FBI load hitting much beyond that 854 figure.

Same bullet weight plus more velocity equals more pounding, and that strikes me as what stretches frames out of time.

What am I missing about the dreaded "pressure" issue here? I mean, so long as we are not so far above proof as to be blowing cylinders apart, I'd think that weight plus velocity equals wear, such as it is.

Or put another way, given the velocities, I'd expect the standard BB load to be about as hard (or easy) on the guns as the +P offerings from the big box manufacturers.

What do those of you that are expert in this sort of thing think?

 

[Oro]

I do not call myself an expert, but I do know basic physics pretty well and try to keep up on how it applies to firearms, both internally and with external ballistics. So my take is this:

recoil is what wears guns - stretches, pounds, etc.

Pressure is what blows up cylinders and chambers.

My rule: don't exceed SAAMI pressures. After that, I consider the trade off of heavy recoil vs. light recoil in individual cartridges and loadings. Then I go have fun.

 

[Jim K]

Well, like "love and marriage" in the song, you "can't have one without the other." (I am reliably informed that some people do, though.)

Bullet movement causes recoil but you can't have bullet movement without pressure, and under normal conditions, you can't have pressure without bullet movement.

More pressure equals faster bullet movement and greater recoil. Too much pressure equals blown cylinders. So one way or another, the issue is pressure.

As to frame stretching, the fact is that every revolver frame stretches on every shot. As long as the elastic limit of the frame material is not exceeded, the frame does not stay stretched and you are not aware of it.

Jim

 

[Daizee]

the pressure is likely different with the Buffalo bore, tho one has to wonder how much room there is for variation in 2" of barrel!

-Daizee

 

[Gary A]

Jim Keenan: You said

As to frame stretching, the fact is that every revolver frame stretches on every shot. As long as the elastic limit of the frame material is not exceeded, the frame does not stay stretched and you are not aware of it.

Interesting comment and it conforms to things I have read on this subject before but it raises the point of the difference between steel frames and the aluminum-framed airweights, especially the "pre-magnum" versions. I have read that steel is elastic and so it can flex and stretch repeatedly and return to it's original state as long as the elastic limit is not exceeded. I have also read that aluminum is different and does not have that flexibility and when it stretches, it stays stretched. I understand this is why aluminum is more subject to stress failure than steel and why springs are made out of steel and not aluminum. If this is correct, then a heavy recoiling load, even if not plus P pressure, might be more subject to stretching the frame of an older-version airweight than a lighter recoiling load even one of higher pressure. I don't think we can talk about plus P in J-frames without considering whether the revolver is steel-framed or an airweight.

I believe the concern in airweights is the topstrap, not the cylinder.

My understanding is that the topstrap on the plus P rated airweights has been thickened but I can't prove that, not having one.

 

[Redhawk1]

Back Thrust is what will destroy a frame, excessive pressure will blow up your cylinder and in turn destroy your frame as well.

Loading in safe pressures but shooting heavy bullets can destroy a gun, the back thrust from to heavy of a bullet.

 

[Shear_stress]

I have read that steel is elastic and so it can flex and stretch repeatedly and return to it's original state as long as the elastic limit is not exceeded. I have also read that aluminum is different and does not have that flexibility and when it stretches, it stays stretched. I understand this is why aluminum is more subject to stress failure than steel and why springs are made out of steel and not aluminum.

All materials are elastic to some extent. The key difference between steel and aluminum is that steel has a fatigue limit and aluminum doesn't. In other words, there is a stress threshold below which steel can be cycled and it will basically never fatigue. On the other hand, the fatigue life of aluminum is necessarily based on how many cycles it undergoes a certain stress. Whether or not a part will be cycled enough to reach that limit is an issue specific to the alloy, design and use.

 

[sidheshooter]

Great info, thanks for the responses so far!

So then, given that no cylinder is going to blow apart with any sane (or SAAMI) pressure, can we assume that–with the same 158gr bullet weight–that the fastest load will always be the hardest on a frame, regardless of pressure?

Or, to use the examples above, wouldn't the buffalo bore standard pressure load actually be harder on aluminum frames than Federal's +P version, given that the BB handily out powers the Federal +P?

 

[jad0110]

Or, to use the examples above, wouldn't the buffalo bore standard pressure load actually be harder on aluminum frames than Federal's +P version, given that the BB handily out powers the Federal +P?

Not necessarily. And in the case of BB standard pressure vs Federal's +P FBI Load, the standard pressure BB has a lower peak pressure ... hence it's non +P SAAMI rating.

The reason for this is fairly simple. There are a multitude of different powders / primer combinations on the market, each having it's own unique burning charateristics. Select a less than optimal powder for a given caliber, and you can actually end up with less velocity and greater peak pressure. I don't have my Lee reloading manual handy, but in it Richard Lee demonstrates how ideal powder selection leads to higher velocities (less bullet drop) and reduced peak pressure (longer gun life). Part of what you are paying extra $$$ for on the BB ammo is optimized powder selection, and that particular powder may well be fairly pricey (in other words, the powder Federal uses in their +P FBI Load is probably cheaper if not as ideal).

My guess is that the BB powder in the standard pressure loads burns more efficiently in handgun length barrels than the FBI Load; it's burn rate may be quicker overall, but without any big pressure spikes that other powders may create which would necessitate a +P SAAMI rating.

I suck at explaining this, maybe someone else can improve upon it.

It's kinda the same way with cars, power vs mpg. My parents used to own a 1980 Toyota Corona, 2.0L 4 cylinder. I think it made about 80 horespower (did 0-60 in a day next to never), and average only about 25 mpg at best. Fast forward to today and a standard Corvette not only weighs more, but makes 436 hp with it's 6.2L V8, gets to 60 in the low 4 second range and averages about the same gas mileage ... it is just a better (if obviously pricier) design.

 

[Vern Humphrey]

recoil is what wears guns - stretches, pounds, etc.

Correct.

Pressure is what blows up cylinders and chambers.

Pressure also erodes and cracks forcing cones -- one reason Smith and Wesson had so much trouble when cops switched from shooting .38 Specials to full charge .357s in practice and training.

 

[sidheshooter]

Jad0110,

I *totally* get what you are saying about the powders, and how buffalo bore's premium line does it at "standard" peak pressure; your explanation makes complete sense.

That said, I'd still think that the ultimately faster load (with likely more felt recoil) will be harder on frames, for our purposes, than the same basic bullet at a lesser velocity and FPE level; regardless of which load design had to go above the current standard peak pressure to be playing in the same ballbark.


Put differently, if BB still kicks harder and hits harder why do we even care about who's load is +P (a designation that also has a safety ceiling, unlike +P+...)?

I'm still not getting that one (unsurprising, since I'm no expert). Does a longer and flatter burn curve actually spread the recoil impulse out enough to make a difference in pounding on the delivery end of things?

The same question could be asked of the old RCMP loads (essentially duplicated by corbon in the 90s) at +P+ pressure versus buffalo's within-SAAMI +P; the corbon was, IIRC, good for more than 1050 out of 4 (I've still got some, I definitely feel well-armed packing that into a service model 64), while the BB is a claimed 100 fps beyond even that!

 

[sidheshooter]

FWIW, I stand corrected.

I sent a query to Tim at Buffalo Bore about this, since I figured that he would know. He was kind enough to reply the same day he got the email; here's part of it:



Without getting into long explanations jad0110 basically has it right.

Recoil is not going to cause any problems with alloy frames. Peak pressure and the curve used to get there will cause all of the problems with revolver wear. Powder/primer/bullet selection is the key to high speed loads that operate at relatively low pressures.

(emphasis mine).

I'm still not sure that I get it, but I will certainly abide by it, since I can have a carry load (BB) that dupicates "FBI" +P power within standard pressure for use in my model 12. May as well–there's lots of cheap stuff to practice with; I can swing for a few cylinders of something stout to carry with no worries.

 

[Jim K]

Actually, the elastic limit (Young's modulus) of aluminum is lower than that of steel, so it takes less pressure to stretch it permanently, but steel will stretch. Every shot.

Here is an example of elasticity of steel. There is (or used to be) in the Smithsonian in Washington a huge 14" deep, 10 feet long I-beam, with its ends on supports. It was attached to sensitive equipment that measured the amount a person could spring that I-beam just by pushing on it with one finger. I can truthfully say that I bent that huge steel beam. Not much, but I did bend it.

The same is true of a revolver frame under even light loads. It will bend (stretch), but its elastic limit is not exceeded, so it, like that beam, will come back and the temporary distortion will never be noticed.

Jim