When Does Recoil Occur?


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Jayhawker
December 20, 2004, 05:08 PM
Is it at ignition of the powder or when the bullet leaves the barrel?
Thanks for any input.

Pete

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Jim Watson
December 20, 2004, 05:31 PM
Best I can tell, recoil begins when the bullet starts to move.
Consider recoil operated automatics - something has to be going on as the bullet travels down the barrel to function the gun. Consider the sight alignment on a revolver - a straightedge will show that the stationary line of sight does not intersect the line of the bore, the barrel has to bring the exiting bullet up to the line of sight.

Domino
December 20, 2004, 05:36 PM
I would say that depending on what you are firing generally the projectile(s) will have the most influence on felt recoil.

R.H. Lee
December 20, 2004, 05:41 PM
Every action has an equal and opposite reaction. Recoil begins when the bullet starts to move. Heavier bullets (from a snubby, for example) will impact higher than lighter bullets, on account of the greater recoil before the bullet exits the muzzle.

cidirkona
December 20, 2004, 06:09 PM
I agree, but if you've ever watched slow motion shots... The firearms starts moving as soon as the hammer starts dropping due to the weight and movement of the hammer, even more when the bullet starts moving, and quite some more after the bullet leaves and the still-burning powder turns the barrel into a rocket engine -- but the largest part of perceived recoil seems to be when the slide reaches the rear of its movement. The slide is absorbing most of the "equal and opposite reaction" energy from the bullet accellerating in the opposite direction.

--- Or at least that's the way it looks in slow-mo.

-Colin

Jonathan
December 20, 2004, 07:10 PM
The thread on 1911 operating mechanism/recoil covers this topic really well. The recoil begins immediately, due to both gas and bullet.

However, on the issue of automatics such as the 1911, the slide does not immediately begin recoiling, since it is effectively being pulled forward by the barrel, under the influence of the bullet. So basically, things don't start to happen until the bullet exits.

Jim K
December 20, 2004, 10:56 PM
Hi, Jonathan,

The barrel and slide, locked together and forming one unit, begin to recoil at the same time the bullet begins to move. (Some additional recoil force is added by the mass of the burning gas moving forward*). But the barrel/slide unit is heavier than the bullet and moves more slowly, so the point at which the slide will unlock from the barrel is not reached until the bullet has left the barrel. From that point, the operation of the pistol is dependent on the energy stored up in the slide.

The barrel and slide are locked together by lugs which cannot disengage until an outside force (the link) pulls the barrel out of engagement. They are not held together because the slide is "pulled forward" by the barrel.

If the barrel is totally blocked so the bullet cannot move, there is no slide movement and no operation.

*On powder mass, note that the charge mass remains the same even while the powder is burning. So in calculations of recoil, the powder mass (weight) is added to bullet weight. In a rifle firing a 150 grain bullet with a powder charge of 55 grains, the powder mass is more significant than in a pistol firing a 230 grain bullet with a 6 grain powder charge.

Hi, cidirkona,

I have studied a fair number of high speed photos and never saw any indication that the falling hammer had a significant effect on recoil, providing the shooter was not moving the gun by flinching. In theory, the movement of the hammer forward should create its own "recoil", but since it drives the gun forward, the effects cancel each other out. I don't recall seeing any recoil calculations in which the mass or velocity of the firing mechanism was taken into account.

Jim

mete
December 20, 2004, 11:27 PM
As photos show, in a 1911 or similar gun,almost all the recoil [theframe moving] occurs when the slide goes all the way back and slams into the frame.

squirrelsniper
December 20, 2004, 11:56 PM
I guess it could be debated "exactly" when recoil begins (as in whether or not there's forward movement of the powder when the primer ignites), but for all practical purposes, it begins when the bullet begins to move.

As for semi-autos and such, it's exactly the same. However, with semis you have the mass of the slide assembly as well as a recoil spring that is holding the slide in the forward position until sufficient force is built up to move it rearward.

artherd
December 21, 2004, 02:52 AM
Is it at ignition of the powder or when the bullet leaves the barrel?

In a word, both.

Recoil begins when the burning powder first starts to move the bullet. It really gets going when the bullet leaves, and the rest of the gasses in the barrel start ejecting at speeds much greater than even the ~3000fps velocity of normal rifle bullets.

ks_shooter
December 21, 2004, 12:38 PM
Recoil starts when the bullet starts to move, but with high-pressure rifle ammunition, I would contend that most of what is felt as "recoil" by the shooter is due to the "jet engine" effect of the hot gases leaving the muzzle.

Consider the .50 BMG Barret rifles. Without the compensator on the muzzle there are not very many people who would enjoy shooting this round out of this rifle. Add the compensator and you have a rifle that kicks like a 12 gauge shotgun (or so I have read, I have never had the pleasure of shooting one myself).

The compensator does nothing to attenuate felt recoil until the bullet has left the muzzle and the combustion gases are able to reach the compensator.

There is definitely some contribution to felt recoil from the acceleration of the bullet. This is simple physics. The difference can be felt when comparing loadings with different bullet weights. But I think the most of the recoil is from muzzle blast.

Tony Williams
December 21, 2004, 12:56 PM
The percentage of the recoil due to burning gas escaping from the muzzle varies a lot depending on the cartridge. For a standard-velocity pistol round only around 10% of the recoil force may come from the gas - up to 20% for a magnum. For a rifle round like the 5.56mm or 7.62mm NATO it will be 30-40%. For a powerful high-velocity military cannon round it may be as much as 50%.

Also for a given cartridge, the barrel length matters. A short-barrelled carbine will generate less bullet recoil (lower muzzle velocity) but more gas recoil (burning gas at a higher pressure) than if the same round is fired in a long-barrelled rifle. So in a carbine the percentage of the recoil due to gas goes up.

A muzzle brake doesn't just remove some of the recoil effect from the gas, it frequently deflects some of it backwards, so using it to pull the gun forwards. So if the brake can deflect 10% of the gas to the rear, it will reduce the recoil by 20%.

You can find a quick and simple way to calculate the recoil impulse of various cartridges from the article 'Basic Ballistics' on my website - it has a lot more stuff besides.

Tony Williams: Military gun and ammunition website (http://www.quarry.nildram.co.uk) and discussion
forum (http://forums.delphiforums.com/autogun/messages/)

williamcrane
December 21, 2004, 02:25 PM
WHen you least expect it? :neener:

Jonathan
December 21, 2004, 02:49 PM
Jim, thanks for the clarification. It appears my memory and causality were a bit muddled.

The key point I was trying to explain was that the movement of the slide (and thus apparent recoil on the shooter, since the minimum movement of the slide won't be noticed until more pressure is placed on the recoil spring) can be qualitatively described via lockup. It is my understanding that for safe and effective operation, the bullet is gone by the time the slide and barrel separate, so you can correctly conclude that the bullet is gone by the time the shooter notices the recoil.

It is correct that the slide is not pulled forward by the barrel (in fact the slide pulls the barrel to the rear), but it is true that the lockup is held solid (for a short time) by the effective forward force on the slide by the barrel: it is "pulling forward", but not to the extent that anything is accomplished. It just happens that the slide has more rearward force via the breechface than the barrel has in the forward direction from barrel/bullet friction (and momentum).

Contrary to my confusing previous statement, this interaction does not prevent recoil, but it does further reduce it due to the added weight of the barrel.

I hope that clarifies things, and that I didn't mess up anything else :D

Jim K
December 21, 2004, 04:11 PM
I guess the time the recoil is noticed depends on the shooter's nervous system, preception time, and all that sort of thing I really can't discuss, not being familiar enough with the human body. I do know folks have been badly burned because they were slow in recognizing that a piece of metal they picked up was hot, so maybe recognition of recoil is not that quick.

Let's look a bit more at that "pulling forward" business. If I said that the bolt of a Mauser rifle was locked to the receiver/barrel by the bullet pulling forward on the barrel, you would laugh at me. Yet, the barrel and slide of the 1911 pistol are locked together just as surely as the bolt and receiver of the Mauser. There is drag on the barrel when the bullet moves, but it is in a closed system and does not in any way affect recoil. Gas pressure is also in a closed system and has no effect on recoil other than to move the bullet. As I said, if the barrel is blocked, there is no recoil even though the gas pressure is the same (or greater) than in normal firing.

While the barrel and slide are locked together, gas pressure tries to force them apart, just as in the Mauser. And just as in the Mauser, the lugs resist that pressure by pressing against their seats. And, again like the Mauser, they can be unlocked only by an outside force. In the case of the Mauser, that force is the shooter lifting the bolt handle to turn the lugs out of engagement; in the case of the 1911, it is the link pulling the barrel down. If you remove the slide and barrel from the gun, then chamber and fire a round by driving the firing pin forward with a punch, the barrel/slide unit will recoil, but will not unlock since there is no outside force to do the unlocking. (Yes, it has been done, but don't try this at home, please.)

Jim

Jonathan
December 21, 2004, 05:05 PM
In no way am I confused about the reality of what maintains the relationship between the barrel and slide or receiver and bolt.

However, when you say "while the barrel and slide are locked together, gas pressure tries to force them apart, just as in the Mauser," there must be some mechanism for this resultant effect. As I previously mentioned, there are two components to this (when dealing solely with front/rear forces): the momentum of the barrel or receiver-barrel and the forward force drag force exerted by the projectile.

Without that interaction, the barrel would not recoil, and the result would be a faster recoiling slide. Without barrel drag on the projectile, it would accelerate faster and to a greater speed, resulting in more recoil. In a practical sense none of this really matters, but it's important to be technically accurate.

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