Effects of Recoil on Accuracy

[newton]

This is not really anything not already known, but it was a huge revelation for me. This is one of those nerdy, logical, mathematical type of threads. So I know it will be boring for some, but maybe it will help others. If you want to skip to the potentially most beneficial parts at the end(**) I understand. Also, don't think that I am a mathematician or engineer or anything. Just a guy who wanted to think about what the logical reason for my big groups was.

I know that from my past experiences and perspective, recoil has always been associated with how "accurate" a gun was. Most of the time its attributed to the heavier the recoil, the greater the flinch. Although, knowing that flinching will definitely effect accuracy, I have always tried to 'man up' even if it meant being bitten by the scope or having a sore shoulder. Meaning, I have learned over the years to control my flinch when shooting heavier recoiling rifles.

Never the less it never fails that the lighter recoiling rifles I own are the most accurate. I never gave it much thought, but my current project with a Ruger American in 308 had me contemplating it some more.

The gun is a relatively light recoiling gun. No flinch associated with it at all. It comes in, scope and all, around 7lbs. I have a 7-08 in the compact version, just about the same weight, maybe a few ounces lighter, and it shot a tad bit more 'accurately'. I was starting to wonder if it's just that I had not found the right load yet. I would sometimes get good groups, sometimes even one holing a few at 150 yards, just to have a few 'fliers'.

I know this is not untypical, so I did not put a lot of thought into it at first. What happened is I was just starting to search around for others ideas for why a group tight at certain yardage open way up at an unusual rate when shot at a longer yardage. I know there are many factors that go into why a 1" group at 100 yards will open up to 5" or 6" at 300 yards, but honestly, when you logically think about it, most of the reasons boil down to shooter error. Most centerfire cartridges will not de-stabilize at that short of a range.

I've always just chocked it up to me not being precise enough, but I honestly was feeling really good with the shots I was taking here lately. Atmospheric conditions were near perfect. Barrel was not getting even slightly hot. So on and so forth.

Then I ran across something that caught my eye. Someone talking about how lighter weight rifles are harder to shoot accurately at longer ranges. But why? Well a lot of times is because, as was stated before, the lighter the rifle the heavier the recoil force. Simple mathematics. However, it's not always a flinching issue, but rather what the effect of the recoil on bullet path.

I'll fess up, I have never given it much thought. I was one that thought the bullet was 'pretty much' out of the barrel before the recoil effected barrel movement. It's a pretty well known fact, with the lighter weight rifles, they will 'jump' more after a shot than one in the same caliber that is heavier. I did not give it much thought until I started thinking about it, and I also distinctly remember a few times I called a flier and realized that it was away from the group the same direction that my gun had 'jumped' after the shot. Coincidence?

In fact, when I go back and analyze a lot of my targets, the biggest bulk of the fliers going left of the 'group'. I shoot right handed. If the gun is going to move one direction or the other, it is going to encounter more resistance moving to the right, so naturally it's going to move toward the left. So does the rifle recoil effect bullet travel? I think it does. There is too much of a coincidence happening.

The very first thing we have to realize is that recoil begins the moment the primer ignites the powder charge. Of course, there are the nit pickers who will say, "actually, recoil begins the moment the firing pin starts moving", this is true, but the point is, every action has a reaction(equal/opposite). The firing pin has little to do with the type of recoil force that is going to affect bullet travel. The simple fact is we are generating over 55,000 pounds per square inch of pressure(with a .308), and that force is not going to start moving the bullet down the barrel without also moving the rifle.

......continued

[newton]

Here are some numbers to chew on. Let's take my 308 for example. Weight of the gun is just over 7lbs. Bullet weight is 169 grains. Velocity ~2675fps. Plug this data into a online recoil calculator and you get a recoil velocity of ~13fps. With my current load the bullet travel time in the barrel is ~1.129 milliseconds. Therefore, when you run the numbers, the barrel has the potential to move up to .176" from where it was by the time the bullet leaves the barrel.

13fps = 156" per sec. 1.129milliseconds = .001129 seconds. .001129 x 156 = .176"

At this point in the game you have to just start guessing at which way the gun is moving. In an ideal world, it would move straight back each and every time. But, since that only happens with rail guns, we can conclude that it also moves up and/or side to side. It is possible for it to move down, but that is dependent on what the guns forend is resting on. I would say the majority of the movement is rearward, however there is inevitably going to be some sideways movement. Let's just say that 90% is rearward and 10% is sideways/up/down.

10% of .176" = .0176" Not much right?

Well, we can reverse engineer the algebraic formula for moving iron sights on a gun to determine how much .0176" of movement is translated at 100 yards. The formula is;



E is Amount of Error in inches
R is Sight Radius in inches
D is Distance to Target in inches
C is Sight Correction in inches
What we do is take C and use it as our barrel movement. D is 3600 inches, based on 100 yards(300 feet x 12 inches in a foot). R is the distance the bullet travels in the barrel, it starts at the case neck and ends at the end of the barrel. In my case, this is about 20".



Insert our numbers;



Keep in mind, this is not precise measurements. They are approximate numbers to show potential movement. In this case, with 10% non rearward movement, the potential bullet impact could be up to 3" away from each other if the barrel moves in different directions each shot.

Now, here is the kicker, rework the data with a heavier rifle. Let's say you "add" 6lbs to the gun. Recoil velocity slows to ~7fps. When you rework the formula with that number you get potential bullet impact that is lessened to ~1.5". That's around half the potential just by adding weight.

Think about this also, ever heard people say "longer barreled guns are more accurate"? I've heard it. There are many different opinions based around this that deal with velocity being increased, barrel thickness being increased, etc. However, for one a longer barrel on a given gun adds weight. BUT, it also increases our 'sight radius' in the formula. So, let's just say that you add 2" more barrel length, that cuts down the potential to 1.6". Not much more, but its more, and the longer the barrel the more it cuts down.

Again, these numbers are all estimates. Some are definite givens, but the rest is subjective. However, it shows you how the potential exists for recoil moving the barrel enough for those 'fliers' to be on target. If the barrel moved straight back, as rail guns do, then the only reason why bullets would impact different points on the target would come from wind and velocity.


.....continued

[newton]

**Here is the point or summation of the matter. Recoil plays a critical role in accuracy, even when you take flinching out of the equation. The more you can control recoil, specifically any movement other than straight rearward, will result in less potential fliers.

I tried something last night just to test this theory. I got out my 7mm-08 Ruger American, short 18" barreled, right under 7lbs total weight. I had worked up some hand loads a few years back for this gun that I was getting right around an inch at 100yards and little over 2.5" at 200 yards. Those are not bad at all and it is a hunting rifle so I am not concerned with sub MOA accuracy.

What I did is get settled in behind the gun, and put my off had on top of the scope. This effectively added about 5 or so pounds of weight to the gun(I somewhat weighted my arm on a postage scale before doing this), and it helped the gun not 'jump' after the shot. It still would move some, obviously, but I believe I increased the resistance for it to jump up or side to side.

What ended up happening is I shot 1/2" groups at 100 yards, and 1" groups at 200 yards. Yes, there were some fliers with some groups, but you could see the group size was definitively smaller than just letting the gun recoil normally without having my hand on it. I also was able to keep the target in sight after the shot, when normally it would be completely out of the scope view. This was just a small test, and there definitely is going to be some tweaking involved in it. But it proved to me my theory was correct. I honestly am looking forward to seeing how it effects the rest of my guns.

I know I am not the only one to have come to this conclusion. But I have not seen all the information packaged up in this type of way. I also know some are skeptical of this, and to that I would just say try it. It's not about trying to stop recoil, it's about controlling where the recoil 're-action'(think - every action has opposite and equal reaction) takes place. Adding weight slows recoil, and something moving slower is easier to control.

In the end, if you are having trouble with finding a load that is good, or you have consistent fliers, try adding weight to your gun. Of course, you never want to touch the barrel, so adding weight can be hard, but I found it easy by just resting my non trigger hand on the scope. This gives me a light weight gun for carrying around, but the ability to add weight to help control recoil and in turn help accuracy when I need it. Main thing is, if your gun is jumping when you shoot there is definite potential for it to directly affect shots on target. The barrel does move when the bullet is still in it. I suppose if it jumps the same way every time then the bullets will land in the same spot, but that would just be plain lucky - sometimes I guess I get that lucky.

[RED BEAR]

Some people can handle recoil better than others i don't agree that lighter recoiling guns are more accurate. The best way to help you to stop flinching is to let someone else load an unknown quantity of ammo and work the action on non semi auto guns. You will quickly see if you are flinching when you pull the trigger and nothing happens but a flintch. You know snipers use the 338 and the browning 50 two more recoiling guns i can't think of. Doing this little trick at the range with other people around taught me not to flinch with heavy recoiling guns. My old shoulders don't let me shoot them much anymore.

[newton]

The reason I posted in this forum is that most of my factory rifles are lightweight. I know some factory rifles are heavier, but lots of them are pretty lightweight. Even if they are heavy, unless they weigh a ton, they could benifit from this also I think.

[newton]

Some people can handle recoil better than others i don't agree that lighter recoiling guns are more accurate. The best way to help you to stop flinching is to let someone else load an unknown quantity of ammo and work the action on non semi auto guns. You will quickly see if you are flinching when you pull the trigger and nothing happens but a flintch. You know snipers use the 338 and the browning 50 two more recoiling guns i can't think of. Doing this little trick at the range with other people around taught me not to flinch with heavy recoiling guns. My old shoulders don't let me shoot them much anymore.

Right, but when you take flinching out of the equation, the lighter recoiling gun is going to shoot more accurately - or should I say tighter groups.

For instance, take two guns exactly alike, except one is significantly heavier - add some weight to the stock. Put them into the same rest(that allows them to freely recoil) and tie a string to the trigger so it takes flinching out of the equation. The heavier gun is going to have less recoil than the lighter one, and I would lay money on it having tighter groups.

[country gent]

Several things are at work here that also affect accuracy. The lighter gun is harder to hold steady than the heavier ones. Its amazing what a few extra pounds does to settle a rifle down from position or on bags. The lighter rifle normally has a thinner barrel contour while the heavier has a heavier barrel. This means the thinner barrel may have more stress in it from the extra machining done. Last is barrel harmonics and vibration nodes. These start at the drop of the sear and continue thru the firing process and continue shortly after the barrel leaves the muzzle. The lighter rifle and heavier recoil generate wider nodes thru the rifle and barrel. The heavier rifle stiffer barrel has smaller nodes.
Then there is flinch. Along with fatigue, the heavier recoilers just tire us out faster and increase shakes wobbles. Fatigue also affects eyesight and how well we see the target sights and conditions.
When I put the first heavy barrel on my M1A and balanced it for it with a set of stock weights it added almost 5 lbs weight to the rifle. It was amazing how much easier it held on target from position just do to the added weight. While I'm sure it made the rifle more accurate it also made it much more shoot able or just easier to use. A 13-14lb rifle isn't a hunting gun by any means but then the 7-8lb arnt target guns either.

[newton]

Several things are at work here that also affect accuracy. The lighter gun is harder to hold steady than the heavier ones. Its amazing what a few extra pounds does to settle a rifle down from position or on bags. The lighter rifle normally has a thinner barrel contour while the heavier has a heavier barrel. This means the thinner barrel may have more stress in it from the extra machining done. Last is barrel harmonics and vibration nodes. These start at the drop of the sear and continue thru the firing process and continue shortly after the barrel leaves the muzzle. The lighter rifle and heavier recoil generate wider nodes thru the rifle and barrel. The heavier rifle stiffer barrel has smaller nodes.
Then there is flinch. Along with fatigue, the heavier recoilers just tire us out faster and increase shakes wobbles. Fatigue also affects eyesight and how well we see the target sights and conditions.
When I put the first heavy barrel on my M1A and balanced it for it with a set of stock weights it added almost 5 lbs weight to the rifle. It was amazing how much easier it held on target from position just do to the added weight. While I'm sure it made the rifle more accurate it also made it much more shoot able or just easier to use. A 13-14lb rifle isn't a hunting gun by any means but then the 7-8lb arnt target guns either.

Oh yea, I agree, there are a lot of different things that can effect accuracy. The main point I was getting at is if everything is equal - top to bottom - except the weight of the the gun, the heavier one recoils lighter than the lighter weight gun does, and if all human error is removed, the heavier gun will shoot tighter groups - so long as each gun is allowed to move freely. This could easiely be proven with a synthetic stocked gun and a solid rest that allowed the gun to move(not a led sled with straps holding the gun down) but not fall off when shot. Just shoot the gun with it as stock, by tying a string on the trigger and pulling it. Then, take the butt pad off, fill with lead, and repeat.

Point is, you can have your cake and eat it too. You can have a lightweight rifle that is easy to tote around, and then be able to shoot pretty accurately with it(again, as long as you're accurate yourself) as long as you add some more weight to it when it comes time to shoot. This is easiely done by using your own body weight in the form of your hand on top of the scope. Or, in the case of open sights, holding down on the forend with your hand.

I think the forend holding is tricky because some torque could be easier to induce than just simple downward weight on a scope. That's my opinion at least.

[newton]

I guess the second part of the point is that at some time in the past people were told that you should let the gun do what it does when shot. In other words, tuck you're off/nonshooting hand under the buttstock and don't touch the gun with it. Only be touching the gun with your cheek, shooting hand, and shoulder.

There are many articles on this, and the shooting community drifted away from using a sling and holding onto the stock. What I did was dig deeper into why doing those things were indeed good and not detrimental.

In digging I found a bunch of articles that state very clearly to not touch the gun with your off hand. I just found that interesting and wanted to prove that you can touch it with your off hand and done appropriately it will even help.

[JBinMN]

Along the lines of absorbing recoil & "weighting" a rifle to help do that, I am offering the following as another option for doing so that has helped me and countless others for many years. I only bring this up since so far no one else has and it helps to accomplish some of what is being addressed by this topic. So I am just posting to help inform for those who are not familiar with such things & just sharing what I can.

When shooting rifles, if it has a sling, I use it not so much to carry the piece, but I use it to hold the rifle steady & with downward pressure to stabilize it & keep it from moving much in any direction. I also use what I call, a "shooting sling", (Looks a lot like this one in the pic, but the 2 I have are pretty ragged as compared to this new one. )

which is an adjustable sling used in particular for shooting & it is designed to work not only as a "parade" sling ( which is what most folks use, IMO.) ,but as a way to "lock in" the rifle to your arm (I usually strap it in to my arm between the elbow & the base of my bicep, and sometimes above the bicep towards the armpit depending on how it suits me best for the particular rifle I am using.). Here is a pic of someone using the type of sling I am speaking of( Not me, I am wayyy uglier. ):

Once this is done properly, the rifle literally stays still & the only movement is when you breathe in & out. So, when I am shooting, I sight in on the target, then slowly breathe in/out & watch as the sights rise & fall on the target, occasionally stopping the in/out & holding my breath to find the point at which I am completing my sight picture & sight alignment to the optimal position to fire. Once that point is established, then it is time to shoot. It took me longer to type this than to do it, BTW. ( that method was taught to me while I was in the Corps.) I do not know if they still use those slings or not , unless perhaps for the Match teams & such. I don't know since it has been a long time since I was in and on a rifle range ...)

When used with the addition of sandbags, to enhance the stabilizing effect, that method works exceptionally well for me, but it works superbly well, even without any other support such as sandbags..

My point was that "stabilizing" a rifle using a sling to prevent rifle movement when shooting & to help absorb recoil, has been around a long time & the addition of that "shooting sling" basically adds the weight that was mentioned by downward pressure on the rifles fore end & upward pressure from your hand & arm to "lock it in", & you are basically trying to make the rifle an extension of your body, so that when recoil occurs, it is absorbed not just by the shoulder, trigger hand and arm, but also by the opposite "forearm" hand & arm, and depending on ones shooting position, other parts of your body as well. ( Kneeling, or sitting for example, dependent on what "style" you use, allows your leg that helps brace the arm with the sling on it helps absorb some of the recoil & helps to keep the sight picture & alignment on target.)



Perhaps, not using a part of your body to support the forestock of a rifle is fine , but it is not how "I" shoot. although it could be said that , "Well you are not a Bench rest shooter, so what do you know?". Well, I do know that while I do not shoot in competitions like some do, I am no slouch at shooting a rifle, and what works for me works for me. Besides, at least long ago, the Corps taught how to do this & IMO, No one in the Corps who qualified with a rifle was a slouch, when it came to shooting out to 500 yards(KD course) with open sights.


I suppose that those who are not using the forearm hand/arm on the forearm of the rifle are doing so to keep the "barrel harmonics" from being effected by doing so , or something along those lines. Then again they are likely also using some sort of a "Rest" contraption to shoot as well. Which might be great for being in competition, but is not suitable for hunting or military needs for the most part, Id reckon.

Anyway, Thanks! to the OP for the interesting topic/subject!

[RED BEAR]

I still don't buy that lighter recoil = better accuracy. As i said military snipers use some pretty heavy recoiling guns for some pretty extreme shots. Now it may be easier for some people to shoot a light recoiling gun better but in a rest i doubt that there is a difference . Some guns shoot better than others. Another trick i used to use is letting some one load a dummy cartridge some where in the mix. You can learn not to flinch. Just because a gun kicks doesn't mean you will flinch. Before my shoulder went bad i used to shoot some guns with a pretty good kick. I have friends who can handle some guns that just plain will stomp you know others will say a 223 really kicks. Its just a matter of what you shoot. My carry hand gun is a 23 oz 41 mag and with full power loads most of my friends want no part of it. And i will admit after a couple of boxes my hands have had enough due to arthritis.

[Hossfly]

The best accuracy I’ve ever gotten was .005 Dist. From boolit to rifling and holding my hand on top of scope. Once I got the powder right with harmonics of that particular rifle barrel combination. Watch breathing and shoot between heart beats.

[M-Tecs]

Accuracy and shootability are two very different subjects. The accuracy capability of the large artillery piece far surpass the capabilities of much lighter recoiling small arms.

As to the effect of recoil having on accuracy and point of impact this has been widely understood since conical bullets started being used in place of round balls. That is why slow heavy bullets tend to point of impact higher that lighter faster bullets out of handguns.

Heavier recoiling firearms require better technique to not be effected by shooter induced errors, however on the other hand, using equal type bullets and velocity heavier recoiling cartridges are effected less at longer ranges than lighter recoiling cartridges.

From the bench a 10 pound benchrest rifle is harder to shoot accurately than a 50 pound benchrest rifle yet offhand the lighter rifle is far easier to shoot.

[robg]

Triggers/recoil don't make rifles more or less accurate but make them easier for us to shoot ,good boolits and barrels determine accuracy. I find less recoil helps so does dryfiring .

[M-Tecs]

I still don't buy that lighter recoil = better accuracy.

It doesn't but lighter recoil accuracy is effected by bad technique less. I have built two 375 H&H with Krieger Barrels. They both will hold 1 1/2" five shot groups at 300 meters. That is about the same level of as much lighter recoiling cartridges like 6mm BR's using equal level of components.

[newton]

Along the lines of absorbing recoil & "weighting" a rifle to help do that, I am offering the following as another option for doing so that has helped me and countless others for many years. I only bring this up since so far no one else has and it helps to accomplish some of what is being addressed by this topic. So I am just posting to help inform for those who are not familiar with such things & just sharing what I can.

When shooting rifles, if it has a sling, I use it not so much to carry the piece, but I use it to hold the rifle steady & with downward pressure to stabilize it & keep it from moving much in any direction. I also use what I call, a "shooting sling", (Looks a lot like this one in the pic, but the 2 I have are pretty ragged as compared to this new one. )

which is an adjustable sling used in particular for shooting & it is designed to work not only as a "parade" sling ( which is what most folks use, IMO.) ,but as a way to "lock in" the rifle to your arm (I usually strap it in to my arm between the elbow & the base of my bicep, and sometimes above the bicep towards the armpit depending on how it suits me best for the particular rifle I am using.). Here is a pic of someone using the type of sling I am speaking of( Not me, I am wayyy uglier. ):

Once this is done properly, the rifle literally stays still & the only movement is when you breathe in & out. So, when I am shooting, I sight in on the target, then slowly breathe in/out & watch as the sights rise & fall on the target, occasionally stopping the in/out & holding my breath to find the point at which I am completing my sight picture & sight alignment to the optimal position to fire. Once that point is established, then it is time to shoot. It took me longer to type this than to do it, BTW. ( that method was taught to me while I was in the Corps.) I do not know if they still use those slings or not , unless perhaps for the Match teams & such. I don't know since it has been a long time since I was in and on a rifle range ...)

When used with the addition of sandbags, to enhance the stabilizing effect, that method works exceptionally well for me, but it works superbly well, even without any other support such as sandbags..

My point was that "stabilizing" a rifle using a sling to prevent rifle movement when shooting & to help absorb recoil, has been around a long time & the addition of that "shooting sling" basically adds the weight that was mentioned by downward pressure on the rifles fore end & upward pressure from your hand & arm to "lock it in", & you are basically trying to make the rifle an extension of your body, so that when recoil occurs, it is absorbed not just by the shoulder, trigger hand and arm, but also by the opposite "forearm" hand & arm, and depending on ones shooting position, other parts of your body as well. ( Kneeling, or sitting for example, dependent on what "style" you use, allows your leg that helps brace the arm with the sling on it helps absorb some of the recoil & helps to keep the sight picture & alignment on target.)



Perhaps, not using a part of your body to support the forestock of a rifle is fine , but it is not how "I" shoot. although it could be said that , "Well you are not a Bench rest shooter, so what do you know?". Well, I do know that while I do not shoot in competitions like some do, I am no slouch at shooting a rifle, and what works for me works for me. Besides, at least long ago, the Corps taught how to do this & IMO, No one in the Corps who qualified with a rifle was a slouch, when it came to shooting out to 500 yards(KD course) with open sights.


I suppose that those who are not using the forearm hand/arm on the forearm of the rifle are doing so to keep the "barrel harmonics" from being effected by doing so , or something along those lines. Then again they are likely also using some sort of a "Rest" contraption to shoot as well. Which might be great for being in competition, but is not suitable for hunting or military needs for the most part, Id reckon.

Anyway, Thanks! to the OP for the interesting topic/subject!

Right on. Yea, I kind of mentioned it a little in post #9, how the target shooting got away from using a sling like they used to, but my main revelation was just how much the gun moves before the bullet leaves and how simply adding weight will reduce that movement and make it easier to control.

I have used a sling to some degree, but I find myself more steady with the stock resting on something not connected to/touching my body.

I deffinitely think a sling is a way to control recoil. After all, that is the main point. Every gun will recoil, how you control it is key to accuracy.

[newton]

From the bench a 10 pound benchrest rifle is harder to shoot accurately than a 50 pound benchrest rifle yet offhand the lighter rifle is far easier to shoot.

This is what made me think of the whole hand on scope thing. I can carry a light rifle, which is easy to tote around the woods and be able to shoot it off hand easy if I need to. But then, if I wanted to poke out a bit further I can rest it on my pack(think benchrest), and use my body weight to increase the effective weight of the rifle, thereby reducing the amount of barrel movement before the bullet leaves the muzzle.

I used to, because it was said to be proper, to just rest my rifle on my pack and tuck my off hand under my other arm, being sure not to hinder the movement of the gun.

[newton]

It doesn't but lighter recoil accuracy is effected by bad technique less. I have built two 375 H&H with Krieger Barrels. They both will hold 1 1/2" five shot groups at 300 meters. That is about the same level of as much lighter recoiling cartridges like 6mm BR's using equal level of components.

I think maybe something is getting lost in translation. Often times when we hear "lighter recoil" we think smaller calibers. That is not what I am talking about. I am saying, to use your caliber for example, a 16lb 375 H&H will have 'lighter recoil' than a 8lb 375 H&H. The 16lb one will be easier to control the recoil, thereby easier to get better groups.

I am not saying that heavy recoiling guns are hard or impossible to get good groups with. My whole point is that it is easier to get good groups(accuracy) with a gun when you can control the recoil of it. Something lighter is always easier to control than something heavier, and in this case we are talking about recoil. It just so happens that a 'heavier' gun recoils less - that is simple physics.

[M-Tecs]

T if I wanted to poke out a bit further I can rest it on my pack(think benchrest), and use my body weight to increase the effective weight of the rifle, thereby reducing the amount of barrel movement before the bullet leaves the muzzle.
.

If you actually reduce the amount of barrel movement before the bullet leaves the muzzle you will change point of impact.

[Larry Gibson]

I think robg is close to the truth on this topic, particularly with reference to "triggers".

Realize the trigger is pulled well before (in relation to the barrel time from primer ignition to muzzle exit) the primer is struck. The trigger is pulled and the hammer/striker/firing pin all have to bang on the primer before it goes bang.......that means there is movement of/in the rifle prior to the cartridge firing. Perhaps imperceptible when shooting from unsupported positions but it's still there. Given an equal trigger pull there is a lot more potential with the lighter weight rifle for some movement of the rifle during the pulling/pressing of the trigger and the fall of the hammer/striker/firing pin. The use of a more solid shooting position helps considerably........."hold hard, shoot straight".......

Then there is always; "well, I had a perfect aim just before I close my eyes and yanked the trigger......." Then if they all went into one hole all the time this probably wouldn't be the fun it is........