|
Forum Rules | Firearms Safety | Firearms Photos | Links | Library | Lost Password | Email Changes |
Register | FAQ | Calendar | Search | Today's Posts | Mark Forums Read |
|
Thread Tools | Search this Thread |
April 6, 2012, 10:01 PM | #1 |
Senior Member
Join Date: February 27, 2011
Location: Michigan
Posts: 257
|
barrel pressure between different grains of bullets and recoil
I was wondering if the berrel pressure changes significantly when the weight of the bullet increases just just as the recoil usually becomes heavier. does heavier recoil indicate more barrel pressure or does recoil and barrel pressure not coincide with each other?
Last edited by mo84; April 6, 2012 at 10:08 PM. |
April 7, 2012, 08:16 AM | #2 |
Senior Member
Join Date: April 25, 2010
Location: Arkansas
Posts: 3,309
|
Yes. If you asked because you plan to reload, do buy a good reloading manual. It will have explanations and ballistics for different weight, and configuration of bullets.
A good manual is the first piece of reloading equipment a beginner should buy. |
April 7, 2012, 09:55 AM | #3 |
Senior Member
Join Date: July 26, 2011
Location: USA
Posts: 1,730
|
Substuting a heavier bullet, with the same powder charge used with the light bullet, will increase pressure and recoil. Possibly to a dangerous level. Heavier recoil does not always indicate more barrel pressure if using the correct powder charge. The burning rate of the powder comes into play here.
|
April 7, 2012, 11:14 AM | #4 |
Senior Member
Join Date: May 27, 2007
Posts: 5,261
|
That is a very complicated issue.
Momentum is mass times velocity. So the force felt on your shoulder is the product of mass and velocity. If you up the mass, or the velocity, you will feel more recoil if the product of the two is higher. There may be something subjective to this as my 190 grain loads in my 308 rifles always "hurt" more than my 168's even though they are both maximum. It might be related to barrel time. If you have a loading manual, you notice that the manual says something like "none of these loads exceed 50, 000 pounds". That is the same pressure limit for heavy or light bullets. Gunpowder has an exponential slope to the curve and you can easily exceed safe pressures, with light or heavy bullets, by adding too much powder.
__________________
If I'm not shooting, I'm reloading. |
April 7, 2012, 02:59 PM | #5 |
Senior Member
Join Date: August 3, 1999
Location: Houston, Texas
Posts: 2,991
|
Buy a copy of Quikload and play with it. Once you have spent some time with it you will see that it is not that easy of an answer. There are generalities but not many absolutes.
__________________
10mm and 357sig, the best things to come along since the 38 super! |
April 7, 2012, 03:11 PM | #6 |
Senior Member
Join Date: October 18, 2006
Posts: 7,097
|
Recoil comes in two stages:
1: Internal recoil as the bullet is being pushed out the bore the rifle is being pushed backwards, this can be as much as 1/16th of an inch. 2: "External Recoil" which is the "jet blast" as all that pressurized gas pushes out after the bullet leaves the bore. This is why a max load under a 140 grain bullet in a 7mm Rem Mag can "feel" more powerful than a sedate 175 gr Bullet at a starting load. When you add up the mass of the powder and bullet you get the total mass leaving the muzzle and pushing back through the rifle into your shoulder. A drop of 35 grains in bullet weight can be totally wiped out by an increase of 10 grains of powder giving back more felt recoil. Jimro
__________________
Machine guns are awesome until you have to carry one. |
April 7, 2012, 07:10 PM | #7 |
Staff
Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
|
mo84,
I'm not sure you were trying to say the same powder charge was involved. If not, if you are simply saying that you've noticed heavier bullets tend to recoil more, that's a true generalization. When the same pressure is applied to them they accelerate more slowly, subjecting the gun to the same equal and opposite force for a longer time. That accelerates the gun more to the rear. Because the nerve endings in the body tend to experience recoil in proportion to energy rather than the acceleration pushing on them, recoil calculations are often done to determine the free recoiling energy of a gun (recoil energy with no shooter or rest absorbing any of it; what it would have by way of energy if it fired free floating in space). SAAMI has a free downloadable00 document describing how to make that calculation, here.
__________________
Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle |
April 7, 2012, 09:53 PM | #8 |
Senior Member
Join Date: March 16, 2010
Posts: 733
|
In my experience, a heavier bullet will recoil more than a lighter bullet.
Recently reloading for my uncles 300 savage, he was undecided between 150gr and 165gr. I recommended 150, but loaded some of both to test. The heaviest loaded 150 recoiled less than a mid loaded 165.... Of course, his gun has no recoil pad, just a metal butt-plate, so its easy to tell the difference in recoil, and a pain in the shoulder after 4-5 rounds ... On my savage edge which has a nice recoil pad, I didnt really notice a difference between factory 150 and 180gr factory loads..... My experience in handguns is the same but different.... With a lighter bullet the recoil is "sharper", where with a heavier bullet the recoil is more, but also more spread out, so easier to handle, if that makes any sense.... |
April 8, 2012, 08:23 AM | #9 |
Senior Member
Join Date: February 27, 2011
Location: Michigan
Posts: 257
|
thanks for the replys, its been a little while since I could get on. I was refering to just increasing the bullet weight and useing the right amount of powder. To get a little more specific. A 350 grain bullet with a max load of powder has less felt recoil than say a 700 grain bullet at a max load of powder. The barrel pressure could possibly be the same in both loads, just you have more mass pushing out against you with the heavier bullet which gives you the heavier felt recoil?
|
April 8, 2012, 08:57 AM | #10 |
Staff
Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
|
As I said, the difference is due to the difference in barrel time. If the pressure is the same, the 700 grain bullet will only be going half as fast by the time it gets to the muzzle. That means it has spent twice as much time in the barrel being pushed forward by that same pressure. Since essentially that same pressure pushes back equally and oppositely against the gun, the gun, being the same mass it was before, will have been given twice as much rearward momentum because it was pushed back for twice as long.
The concept you actually want is called impulse. It is the application of a force multiplied by the time over which it is applied. The longer the force is applied, the more it accelerates a mass (in this case the gun mass) to a higher velocity. Mass times velocity is momentum, and that's what the gun gets more of. It will feel closer to four times more recoil because your nerve endings will sense in proportion to kinetic energy rather than momentum. That's because your shoulder is stopping twice the momentum in roughly half the time, and that takes four times the force. Recoil should feel roughly doubled when the bullet plus powder charge is about half-again heavier. The force is just the pressure times the cross-sectional area of the bore. In a real calculation that part of recoil against the breech is actually the sum of the force against the bullet base and an average of about half the powder mass being pushed forward, too, plus you then get the rocket effect impulse added to it. Quite a bit going on there.
__________________
Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; April 9, 2012 at 08:30 AM. Reason: typo fix |
April 8, 2012, 11:28 AM | #11 |
Senior Member
Join Date: January 5, 2009
Location: Just off Route 66
Posts: 5,067
|
Unclenick, you never cease to amaze me on your knowledge.
Thanks Jim
__________________
Si vis pacem, para bellum |
April 8, 2012, 01:37 PM | #12 |
Senior Member
Join Date: February 27, 2011
Location: Michigan
Posts: 257
|
Thats a pretty good explaination. I pretty much understand what its all about now and how it works. Thanks alot
|
April 8, 2012, 03:42 PM | #13 | |
Senior Member
Join Date: October 18, 2006
Posts: 7,097
|
Quote:
Quote:
Momentum = mass*velocity. The peak rearward velocity determines peak rearward momentum. Change either velocity or mass and momentum goes up in a linear fashion. Velocity = distance/time, which gives us speed (but not an acceleration). So the LONGER a bullet spends in the barrel the LESS momentum you'll get. Combining the two equations give us; Momentum = mass*distance/time and the larger the time value the smaller the momentum value. Like I said before, you have to look at everything going out the muzzle of the barrel to get a handle on recoil. A heavier bullet will give you more recoil than a lighter bullet with the same powder charge because "for every action there is an equal and opposite reaction." Jimro
__________________
Machine guns are awesome until you have to carry one. Last edited by Unclenick; April 9, 2012 at 09:06 AM. Reason: oops. Hit edit when meaning to quote. |
|
April 9, 2012, 09:06 AM | #14 | ||
Staff
Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
|
Quote:
Quote:
To simplify considerations, assume you adjust powder choice and charge weight so the pressure profiles are the same with respect to distance down the bore for the light bullet and the heavy bullet. In other words, the pressure at the bullet base at any bullet distance along the barrel is the same for both the light and heavy bullet examples. a=F/m, so that as the mass of the bullet gets bigger the bullet's acceleration gets smaller, but the equal and opposite force is the same and the gun's mass is the same, so the gun's acceleration is not smaller. The gun's acceleration is just as big but now lasts longer because the heavier bullet takes longer to clear the tube. The result is the gun has more velocity, and, with the square of that, more energy at the end of the firing event. All this is spelled out in the SAAMI document I linked to in post #7. I recommend downloading a copy and working a few examples to satisfy yourself that it's true.
__________________
Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle |
||
April 9, 2012, 11:29 AM | #15 |
Senior Member
Join Date: February 9, 2005
Location: Owego, NY
Posts: 2,000
|
I love threads like this ... gives me something to think about when I kick back and pound down a few beers after a morning of cutting and splitting fire wood. Too windy to go to the range and shoot here in NY. You guys might force me to actually do some math for my 7mm Rem Mag with light and heavy bullets just so I can understand this better.
__________________
,,, stupidity comes to some people very easily. 8/22/2017 my wife in a discussion about Liberals. Are you ready for civil war? |
April 9, 2012, 11:54 AM | #16 |
Senior Member
Join Date: February 15, 2009
Posts: 8,927
|
Note that as long as the bullet's going down the barrel, the rifle and everything on it is moving backwards. After the bullet's left the muzzle, the jet effect adds a bit more recoil backwards. This is the main reason heavier recoiling hand-held firearms are more difficult to shoot accurately.
Even the recoil during the time the bullet from a .22 short rimfire round's in the barrel on target pistols used for international rapid fire events is minimized by the pistol's design. The barrel is aligned almost perfectly with the shooter's arm so it stays pointed at the aiming point while all things causing recoil doesn't move the sights up and off the target's center. 'Tis important when you're getting off 5 shots in 4 seconds and wanting all shots in the 4-inch 10-ring at 25 meters. |
April 9, 2012, 06:12 PM | #17 | |
Senior Member
Join Date: October 18, 2006
Posts: 7,097
|
Quote:
But you missed the point, VELOCITY is dependent on TIME. The longer the time, SPEED = DISTANCE/TIME the slower the velocity. Acceleration is not the same as barrel time which is a velocity. A bullet that leaves the bore at 2200 FPS will have a LONGER barrel time than the same bullet leaving the bore at 3200 FPS. The faster bullet from the same barrel had a greater acceleration to get to that final velocity, and therefore less TIME in the barrel. Acceleration is given in distance per time per time, such as feet per second per second. Newtonian physics again, the greater the acceleration on the bullet, the greater the acceleration on the rifle. Follow me on a thought experiment. Two bullets of different mass have the same barrel time. The barrel time being the same means that the recoil should be the same? Obviously not. It takes more energy to push the heavier bullet at the same velocity. Second, the "jet blast" effect of all that hot gas shooting out the muzzle at around 5,200 fps. This is where the bulk of felt recoil comes into play. That heavier bullet with the same barrel time as the lighter bullet is going to have more pressure behind it when it leaves the muzzle, and this is where you are going to get the biggest portion of recoil. E = 0.5mass*velocity squared, so that bullet with a 150 grain mass going 2800 fps pushed against the rifle less than that 45 grains of powder going 5200 fps. Lets take it to the other extreme, two bullets of different mass that never leave the bore, now we have a perfectly closed system where recoil is only a product of "internal ballistics." In this closed system we don't have to deal with muzzle blast so it becomes obvious that the longer the barrel time, the slower the bullet is moving down the bore, the less recoil there will be in terms of either Energy (because velocity is slower), although momentum equals Mass*Velocity, so if mass was large enough it could outbalance the disadvantage of velocity. Jimro
__________________
Machine guns are awesome until you have to carry one. |
|
April 10, 2012, 01:42 PM | #18 | ||||||
Staff
Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
|
Quote:
Quote:
Similarly, in the gun, there are two ways to increase the barrel time. One is to reduce powder charge, which lengthens barrel time by reducing the force accelerating the bullet, simultaneously reducing recoil. The other is to increase the bullet mass so the exact same increase in barrel time is needed to get it out of the muzzle, but that does not reduce the accelerating force. So now you have the same original force applied for a longer time, accelerating the gun mass more, increasing recoil. In the real world its not that simple because progressive powder will burn faster and make more pressure with a heavier bullet because it can't push the greater weight to increase the powder burning space (expansion) as quickly. So powder charge has to be reduced or the load has to be switched to a slower powder to keep the pressure profiles the same. Quote:
Quote:
Quote:
I will add that while it is true with some overbore guns that muzzle blast can be the majority contributor to recoil energy, with most common calibers, like a .308, it's responsible for about a third of the recoil energy. That's because it gets about a third of the momentum and only momentum, not energy, is equally and oppositely created in the gun. Quote:
Energy, on the other hand, is proportional to half the square of velocity times the mass, so square the velocity ratio and divide by the mass ratio (same magnitude) and also by 2. If the mass ratio is about 250:1, rearranging you have: 250²/(2×250)=250/2= or 125 times more energy in the bullet and gas mass than in the gun. The bottom line is the bullet gets more energy out of the powder than the gun does, basically as a result of having less inertia and therefore being easier to move. So, now we see momentum rather than energy is equal and opposite, let's run a calculation based on the momentum. 150 gr = 0.0214 lbs.That bullet had 0.5 × 0.0214 lb/32.2 ft/s² × (2800 ft/s)² or 2610 ft-lbs of energy. Lets switch to a 180 grain bullet also propelled to 2610 ft-lbs of energy by 45 grains of a slightly slower burning powder (so the pressure doesn't increase). It will be traveling at about 2560 fps. We now have: 180 grains =0.0257 lbsBottom line, firing the heavier bullet to the same energy level, as is common since the case only can hold so much stored energy, the heavier bullet recoils more.
__________________
Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; April 10, 2012 at 01:51 PM. |
||||||
April 11, 2012, 06:58 PM | #19 | |||
Senior Member
Join Date: October 18, 2006
Posts: 7,097
|
Quote:
Quote:
Quote:
I like the kid and fat aunt analogy, because both are being accelerated at -9.8m/s/s for 5 seconds. Time of acceleration is immaterial as the acceleration still results in a velocity of zero (providing the chair don't break). But here is another analogy, if two different balls are dropped from 20 feet up, the time it takes for them to hit the ground is exactly the same, the time of drop is exactly the same, but the impact is different, you can see my point that barrel time isn't the deciding factor in impact, but the energy required to get the balls to 20 feet to begin with. It all comes back to energy, not time. Sorry to argue so intensely over precision, but I hope some folks have found it amusing if not educational. Jimro
__________________
Machine guns are awesome until you have to carry one. |
|||
April 12, 2012, 05:12 PM | #20 | ||
Staff
Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
|
My second sentence should simply have been, "That accelerates the gun to a higher rearward velocity". That would have cleared the ambiguity.
Quote:
Quote:
You and I should get together and write a textbook. Between us we'll get it edited correctly in the end. Slightly OT, but relevant to the discussion: One of the confounding things for people trying to keep their rifle loads tuned is that velocity and barrel time don't always track well enough to do that. You can't just change powders and load to the same velocity and be tuned because the barrel times won't match. If you pick a charge of a fast powder and a companion charge of a slow powder that both produce the same velocity with the same bullet in the same rifle, the fast powder charge will produce the shorter barrel time. The above happens because, even though both charges have the same average pressure over the bullet trip down the bore, the fast powder achieves that average with a higher peak pressure and lower muzzle pressure. It therefore does a greater portion of its acceleration earlier in the bullet's trip, letting the bullet cover the remaining bore length at a higher average velocity. The slow powder has a lower peak pressure and a higher muzzle pressure, so it spreads the acceleration out more over the length of the barrel, and the bullet velocity just catches up to the fast powder bullet velocity at the very end of the journey. So barrel time has a pressure profile dependency, with average pressure being the integral of the powder pressure function with respect to either time or bullet base position in the tube. Since the average pressure comes out the same for both the fast and slow powder at the end, the resulting imparted momentum and transferred final energies are still the same.
__________________
Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle Last edited by Unclenick; April 12, 2012 at 05:18 PM. |
||
April 12, 2012, 06:30 PM | #21 |
Senior Member
Join Date: October 18, 2006
Posts: 7,097
|
An open source "XYZ's of Reloading" aka "the big book of everything you never needed to know explained in precise detail" sound about right? One of these days an enterprising young editor is going to comb the archives and combine the best of the most interesting.... Ever think that in a hundred years people might read our ramblings the way we read Hatcher's Notebook?
Anyways, when people want to talk "ballistics" and I ask "Interior, exterior, or terminal?" they usually look at me funny. But interior ballistics is a lot like magnets, they are pretty simple in concept but when you have to actually explain how they work.... it gets technical quickly. Then again the English language isn't exactly user friendly. Jimro
__________________
Machine guns are awesome until you have to carry one. |
April 13, 2012, 11:21 AM | #22 |
Staff
Join Date: March 4, 2005
Location: Ohio
Posts: 21,013
|
Yep. Esperanto, here we come.
__________________
Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle |
April 13, 2012, 12:18 PM | #23 | |
Senior Member
Join Date: January 5, 2009
Location: Just off Route 66
Posts: 5,067
|
Quote:
And Greek or Latin are? Jim
__________________
Si vis pacem, para bellum |
|
April 13, 2012, 03:31 PM | #24 |
Senior Member
Join Date: February 9, 2005
Location: Owego, NY
Posts: 2,000
|
I don't speak German but I usderstand it is pretty good for technical descriptions.
__________________
,,, stupidity comes to some people very easily. 8/22/2017 my wife in a discussion about Liberals. Are you ready for civil war? |
Thread Tools | Search this Thread |
|
|