Home Forums Hunting & Shooting Ask The Gunwriters Bore Diameter and recoil: any relationship?

Taking two cartridges with the same parent case (say .308 and .358), loaded to the same pressures, with the same total weight of bullet and powder, will there be any difference in recoil? Assuming the same rifle weight. I'm thinking the amount of recoil energy produced would be very similar, but the velocity of the recoil would be different. Any thoughts?

My first guess on a quick reading of your question is that the recoil of the .358 would be greater. I don't make any effort to remember equations, but IIRC, the recoil equations use only half the weight of the powder charge -- therefore, equal weights of bullets and charges in the two cartridges would mean a significantly heavier bullet and lighter charge in the .358. I'm not sure how the different velocities would affect the relative recoil of the two rifles.

I'd have to consider this question a lot longer and simulate loads on the computer to derive a better guess. I never trust the accuracy of my first guess about a matter not already considered in depth, and this is one that I've never thought about.

I think you may have more variables in your question as what you propose would require different powders etc. Let me try another example to see if this is closer to what you mean.

Rifle #1 (.308) with a 200gr bullet
Rifle #2 (.358) with a 200gr bullet

Both rifles weigh the same, have identical stocks, identical barrel lengths, etc.

If the 200gr bullets are driven to the same velocity (and I would think you would need different powders) the pressure in the .358 should be lower than the .308....but muzzle energy would be the same.

Just ran the numbers for a .308 loaded with a 220-grain Sierra and a .358 loaded with a 225-grain Nosler -- both loaded to 60,000 lb/sq in., each rifle weighing 9.039 lb with scope and mount.



Powder charges: 46.2 gr H414 (.308) and 44.1 gr H335 (.358)

Bullet velocities: 2,525 ft/sec (.308) and 2,480 ft/sec (.358)

Recoil velocities: 11.89 ft/sec (.308) and 11.79 ft/sec (.358)

Recoil energies: 19.86 ft-lb (.308) and 19.53 ft-lb (.358)



See why I don't trust my first guesses?

DB- That is close to what I'm after. I'm just looking for equal weights of the mass component used to calculate recoil for each cartridge. If this requires a heavier bullet or powder charge for one or the other, shouldn't the recoil still be same/similar?


Maybe this will be better. If using an equation to calculate recoil, would only a difference in the bore diameter have any effect on the answer given that all the other variables are identical?

The knot in your problem is that you ask about equal pressures and different bores. Pressure and bore has nothing to do with recoil, (or at least it is not factored in any recoil equation I have seen)

If you look for a book maximum (from say speer #13) with a 180 gr. bullet in each rifle, and the same number of grains of powder, you can find these examples.

(We assume the pressures are the same because each is listed as a max load.) recoil # follows vel as....recoil enrgy/recoil velocity

180/308.....45gr/748.......vel/2553.........17/12
180/358.....45gr/RL7.......vel/2728..........20/13

In this case, the 358 will deliver more recoil because the velocity is higher. (pressure same)

If you load the 308/180 and 358/180 to the same velocity you get............

308/44 varget/.........vel/2591...............18/12
358/53/BLC-2/..........vel/2590...............20/13

In this case, the 358 delivers more recoil because the powder charge is greater. (pressure same)

Last example.....a max load w/308 and a starter load w/358 (lower pressure in the 358, but same vel.)

308/41gr/AA2520..........vel/2451...........15/11
358/41gr/RL7................vel/2456...........15/11

In this case the recoil is equal because the bullet, powder, and velocities are equal, despite the pressures being different.



Did this help?? or did I totally dense out on what you were asking??

JimF

Thanks Jim, that's what I was getting to. I didn't know that pressure wasn't included in any recoil equation! Seems odd to me, but I don't know much.

You have placed too tight a limit on the variables. If for example the bullet wt, the powder wt, and the peak
chamber pressure were the same, the .358 would have a larger expansion ratio making the muzzle velocities
different. Recoil depends on Momentum. Every mass x velocity componet forward has an exual mass x velocity,
or force x time to the rear. A recoil pad ror example takes a momentum and changes it into a lower force for a
longer time.
Take Care!

Whewww....now I know why I didn't do well in physics or algebra! <img src="/ubbthreads/images/graemlins/laugh.gif" alt="" /> Flinch

Recoil is the result of gas leaving the barrel and hitting the atmosphere. Newton's Law; for every action there is a reaction comes into play.

Pressure in the barrel isn't the controling factor; volume is.

If you load both to the same velocity, the larger bore will have to produce more gas to fill in behind the bullet as it travels down the barrel.

With a larger volume of gas hitting the atmoshphere when the bullet leaves the barrel, Newton's law comes into play; and equal and opposite affect. More recoil.

If recoil is the muzzle blast hitting the atmosphere then a gun would not recoil in space, or a rocket produce
any thrust. You are correct about the concservation of momentum however.

In order to make sure that this (correct) statement is not misunderstood.....................

The (bore) does not produce the gas volume, the burning powder does. Generally, when a larger and smaller bore are loaded to the same velocity with the same powder, the larger bore requires more powder volume to acheive the stated velocity, hence more gas volume and more recoil.

If a 30 and 35 are loaded to the (same velocity) with the (same volume) of (different) powders, the recoil will be the same (to the limits of calculation)

JimF

No one has mentioned the bore diameters. It was always my impression that the larger bore dia. released the gases faster and henceforth and had a lessor felt-recoil.

The reason for that is that the Bore Dia. is not a factor. Newton's third law says that for each action there is an (EQUAL) and (OPPOSITE) reaction. If the gasses left the bore faster, the recoil would be greater not less. (Just like bullet velocity).



In fact, the gas velocity is figured as a constant in most equations. It has a higher velocity than the bullet and has a greater relative effect on recoil than the bullet. Meaning, (assuming equal velocities) 10 gr. more powder would cause more recoil increase than 10 gr. more bullet)



JimF

Being that velocity is a variable in the calculation of recoil, bore diameter is then only an indirect effect. For instance, a 7-08 pushes a 120gr. bullet ~3000fps while a .260 pushes the same weight bullet at ~2800fps, in addition to having more powder capacity. Thus, the 7-08 recoils more according to the recoil calulator from PointBlank.

7-08 RE15 45.5gr 120gr bullet 3000fps = 16/13 (recoil energy/velocity)

260 RE15 41.0 120gr Bullet 2800fps = 14/12

**These are close to like pressures, but data was extrapolated slightly as barrel lengths and bullets weights were not directly comparable from Alliant's website.

Gentlemen:
Please excuse my nosing in. I'm brand new here. Two points haven�t been raised:
First, is that the 358 has 35% greater rear surface area for propellant gases to push against.
Second, is that for any given bullet weight, the 358 bullet will be much shorter than the 308 bullet, giving it a much shorter bearing surface, yielding less friction.
Both factors give the velocity edge to the 358.

The best example I can give is the 44 mag. Vs. 45 Colt in a Ruger Black Hawk. Given identical bullet weights, the 45 gives the same velocity at 30,000 (psi, cup?), that the 44 delivers at 40,000. The subjective part is that those who shoot both claim the 45 does it with less recoil. The fact is, different bore sizes, different pressures, same velocity.

Darrel

I thought that the amount of powder burned would be one of the factors.

Pretty interesting stuff!

One item that has never been adequately addressed by any recoil formula is muzzle pressure. Recoil is caused by two things: the bullet and powder gas. Each causes the rifle (or any other firearm) to back up in an "equal and opposite reaction."

The powder gas creates a "rocket effect" as the bullet leaves the muzzle. This is a big part of the reason a .300 Weatherby Magnum recoils a LOT more than a .308 Winchester. Muzzle energy is about 40% more for the Weatherby, when both cartridges fire a 180-grain bullet, but recoil is around twice as much, everything else being equal.

Muzzle pressure of a high-internsity magnum can easily be 12,000 psi or more, while a more moderate round like the .308 can be 6000 or so.

No formula I've ever seen adequately takes this rocket effect into account. I fooled around with a sliding scale, based on various bore/powder capacity ratios, a few years ago, but won't call my "formula" the answer.

But in general my observations (both subjective--getting the snot kicked out of me by many rifles--and "measuring" recoil by the amount various rifles push objects back during recoil) is that the rocket effect has more effect than any formula acknowledges.

At its most basic, this means that if two cartridges use the same amount of powder to push the same weight bullet to the same velocity, in a rifle of the same weight, the smaller bore will have more recoil, simply because of higher muzzle pressure due to the venturi effect. Push the same amount of gas through a smaller hole, and you produce more muzzle pressure.

I have thought about this also. I've also wondered if possibly chamber pressure has some effect (i.e. 416 Rigby with 100 grains of powder and 45,000 psi pushing a 400-grain bullet at 2400 fps compared to a 416 remington with 80 grains of powder and 60,000). I think the 416 Remington should have higher muzzle pressure and possibly kick the same or more. I have only fired Rigbys, so I can't prove this.

Concerning a larger-bore vs. smaller-bore scenario. If pressures were equal, powder charges were equal and bullet weights were equal, then the larger would have a higher velocity and kick more--at least I think.

As an example, at one time I was involved in working up loads for two FA-83 revolvers. One in .454 and one in .44 magnum. When the .44 was loaded hot (probably 55,000 psi) and shooting a 320-grain bullet at something like 1450 fps, it kicked noticeably less than when the .454 was loaded to a lower pressure (like 45,000 psi) and was shooting the same weight bullet at the same velocity. When the .454 was loaded to 55,000-60,000 psi, It, to me, borders on brutal, and takes substantial concentration to shoot, but at that pressure, it's shooting a 320-grain cast bullet at 1700 fps or so.

What all this proves, I don't know--probably nothing.

This is confusing; How does a muzzle form a venturi ?. And if it did, dosen't a venturi act to lower pressure?.
Take Care!