doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com I read it in a magazine...

In a one ounce load, the difference in the weight of the powder charge between those two loads is a tad under two percent, and you can feel the difference? I don't think it's the weight, others' opinions may vary.

Jim,
I can't believe a tough old bird like you could be bothered with the difference in recoil of those two loads. But I would chose the faster powder as well. Just for cleaner burning and more consistant pressures at low temps. My damascus load uses Hogden Clays. Clays is slower than Nitro 100 but still in the same range. My loads are consistant in velocity and report, but I don't know if they have consistant recoil, cause I don't think about it much.

Your math is as faulty as your logic. The difference between 15 grains and 25 grains is 40%.
And to my good friend, Chuck: I'm just an old bird, not a tough one. I'm very sensitive to recoil. I'm also allergic to bull-sh.. and theories that try to escape the physics involved. I know quite well the difference between true recoil and "felt" recoil. Some obvious examples being: an 8 lb. gas auto will deliver less felt recoil than an 8 lb. double, because the cycling of the moving parts spreads out the total true recoil. Same is true with two identical doubles, one with a good recoil pad, the other with a hard buttplate. The true recoil amount is the same, but the felt recoil will be less for the gun with the good pad, because the total recoil is spread out by the time it takes for the pad to compress against the shoulder. There are others but many situations explained illogicaly as "felt" recoil are pure bullsh.., used to sell a product or some barrel jockey's services that can not be proven or based on logic or physics. Also used to justify faulty opinions that have no basis in logic, or actual head to head testing.

Jim, back to math class, as well as physics class. We are talking the difference in the total ejecta weight. I will stick with my "under two percent" figure. You might want to delete the DUH! This is a discussion, not a fistfight.

Maybe what Eightbore meant was that the difference in total payload, due to a 10-grain increase in the powder, is 2%....because it is.

Assuming 438 grains of shot and 15 grains of powder, an additional 10 grains of powder increases the total mass by 2.2%.

I, too, questioned how, all else remaining constant, 25 grains of powder could make recoil more noticeable than 15 grains of powder. Expecting to find an increase in free recoil energy of only about 2%, I plugged the numbers into 2 online recoil calculators and got the same result....a 14% increase! how could this be? adding 2% more mass gave a 14% increase?

So then I kept the powder charge constant at 15 grains and upped the shot by 10 grains to arrive at the same total 2% mass increase....and the calclators showed a 4.2% increase in FRE. That's more like it. But why would 10 grains of powder count more than triple the 10 grains of lead?

Turns out the answer has to due with the ejecting powder gases that some doubt are real.
If you dig into the formulas used by people who programmed the recoil calculators, you'll find that powder charge is not trivial. I guess sometimes it really is rocket science.

Three elements enter in producing recoil. The first is the reaction to the acceleration of the bullet as it moves down the barrel until it leaves the barrel at it’s maximum velocity = muzzle velocity. The second element is the reaction to the acceleration of the expanding gas generated by the burning powder. The third element is the reaction of muzzle blast when the bullet leaves the barrel and the escaping gas gives a reactive push to the muzzle. As pointed out earlier, anybody who's ever used a muzzle brake knows this is real and significant....a .300 Win Mag is made to feel like a .243 with no loss of bullet velocity. As a general rule of thumb, the escaping gas velocity is about one and a half times the bullet velocity. A value of 4,000 is sufficiently accurate for practical purposes with small arms having muzzle velocities between 1,000 and 4,200 fps.

In general terms, this means that the Momentum of the gun (recoil) = momentum of the shot + momentum of the powder gases.
For a 1 ounce load at 1200 fps, the shot contributes 438 x 1200 and the powder 15 x 4,000 to the total FRE. You can see that adding 10 grains of shot isn't nearly as significant as adding 10 grains more powder, due to the big difference in velocity.

To test my understanding, I used a muzzle velocity of 4,000 fps so the projectile and gases had the same velocity. When I did that, increasing the shot or the powder by the same amount gave the same recoil increase.

Welcome to academia! A few of us shoot from the hip and a few of us are duds, but no live ammo was fired in the course of this discussion.

While you are apparently assumin' that your 2% increase in total ejecta weight will only increase the recoil by 2%, that is also wrong! Go here: http://www.10xshooters.com/calculators/Shotgun_Recoil_Calculator.htm and plug in some real figures. Try 15 for powder weight, 40 grains for wad weight, 382.8 grains of shot(7/8 oz.), gun weight of 8 lbs. and 1150 fps for velocity. That calculates to 10.56 ft. lbs of recoil energy. Then change only the powder weight to 25 and the recoil energy goes up to 11.4 ft. lbs. That's an increase in true recoil of 9%, not 2%. DUH removed for courtesy, not because you were correct. It surely is not a fistfight. On that, we agree.
I have a very good article about recoil, by Ed Matunas, that appeared in Sporting Clays magazine, in 2001. Ed Matunas is a real ballistician, not just another "gun" writer filling up monthly columns with thinly disguised factory release letters, and calling them personal reviews. It's too long to clutter up this forum with, but I'd be happy to email it to anyone interested enough to email me directly. My e-address is in my profile.
Thank you,

That's interesting Mike.

So that's the assumption the calculator programs use. I wonder if it's a valid one, and if so what experimental evidence it was based on. The dymanics seem problematical.

Upon shot charge exit, the barrel pressure of a shotgun approximates 500 PSI. Being pressure, it is of course acting in all directions until being released. After the wad clears the muzzle, at which time the leading edge of the pressure wave HAS to be moving at the exact same speed as the wad, the velocity of the expanding gas apparently is assumed to increase to 4,000 FPS as the pressure bleeds to zero from about 500 PSI.

I'm reminded of the stop action photos of the shot mass and wads immediatley after muzzle exit. Do we see any effects from the pressure wave acting on the payload after muzzle exit? I'd expect some scattering or at least random wad interference as the gasses out run the payload in the few inches ahead of the muzzle.

If anyone has any photos of such effects, or information on the actual dynamics of muzzle exit and pressure equalization I'd be interested in reading the info and seeing the pictures.

Interesting stuff, thanks for the discussion.

What I want to know is if Mike and Jim's recoil calculators give the same results. If not, then of course I want to see everyone fight--sorry "discuss" which one is correct.

You make a great straightman, McT.

Actually, I've already compared them and 1)no, they don't agree because 2)I suspect the one I've used (from 2 sources) is geared to rifles, but don't say so. The one Legg linked to has separate calculators for shotguns and rifles. Those two give different answers for the same values.

I suspect the reason the shotgun calculator gives a smaller answer is that it assumes an escaping gas velocity of ~2,000 fps as opposed to ~4,000 fps for a rifle (4-5x the peak pressure).

But, directionally, they are the same, though the magnitude is different. Whereas the rifle calculators suggest ~14% FRE increase with 10 grains more powder, the shotgun calculator suggests ~9%....still greater than the 4% increase you'd see from 10 grains more lead.

Jim and Mike have emphasized an important point. I used to think the same thing: how can a grain or two difference in powder make much difference in recoil, assuming velocity and payload are constant? It's because the powder carries more "weight" in the formula.

The felt recoil thing is tricky, to say the least. The late Bob Brister--another guy I think most of us would say was more than just a "gun writer" too--believed that backboring and lengthening forcing cones reduced recoil. He also refers to ear protection as being one of the most effective ways to reduce felt recoil--or, perhaps in this case, we ought to call it "perceived recoil". The louder it sounds, the harder you expect it to kick. We probably don't want to sidetrack into a discussion of those points, but they--and a number of other factors, like gun fit--impact "perceived recoil".