How to determine proper Cast on/off, Drop, LOP for a rifle stock?

Mudduck

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Made a few edits to questions
Is there a (scientific) way to determine what the Cast on off and drop (and LOP) on the rifle stock is best for someone?
#1 I assume it is a bigger issue for a rifle with open sights ( even bigger issue with shotguns) but by using a scope the ring height removes that issue.
#2 I assume the drop of the stock affects the direction of recoil as it connects with your body which could make it feel like one rifle has more " kick" even if force is the same.
#3 Would Drop / cast on/off also affect the amount of muzzle jump?

If my assumptions are incorrect please feel free to enlighten me
my question - how would a person purchasing a hunting rifle be able to determine the best LOP for them?
 
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Is there a (scientific) way to determine what LOP on the rifle stock is best for someone?
#1 I assume it is a bigger issue for a rifle with open sights ( even bigger issue with shotguns) but by using a scope the ring height removes that issue.
#2 I assume the LOP of the stock affects the direction of recoil as it connects with your body which could make it feel like one rifle has more " kick" even if force is the same.
#3 Would LOP also affect the amount of muzzle jump?

If my assumptions are incorrect please feel free to enlighten me
my question - how would a person purchasing a hunting rifle be able to determine the best LOP for them?
If my memory is correct bend your arm 90 degrees and measure from the crease of your elbow to your trigger finger(where your finger touches the trigger), and position your trigger finger like you're going to pull the trigger of course. I don't see how using different height scope rings would change a firearm that doesn't fit you properly.
 
1) No, it doesn't. LOP is a stock fitting thing. Scopes and iron sights have nothing whatever to do with it. As mentioned, it has to do with the distance from your bent elbow to your trigger finger. Hold a yard stick like a rifle and see where your finger comes. That's as close to the right LOP for you as you can get without special measuring tools. Highly scientific, I know, but it works.
"...purchasing a hunting rifle..." Putting the rifle butt in your elbow and see where your finger ends up, on the trigger, will tell you if a rifle fits you. So does shouldering it with your eyes closed then opening 'em and seeing where your eye is in relation to the sights. Left or right, etc.
2) Not really. Felt recoil is subjective and the rifle matters, but the LOP on most of 'em(mattered on a C1A1 and other FAL's, but not on your typical hunting rifle. The C1A1's stock has a daft bump and if the butt was too short you'd get thumped on the cheek.) doesn't. A wide butt stock vs a narrow one will make a difference. So does the weight.
3) No. It's strictly about reaching the trigger.
 
Hi - Thanks for your feedback - I think I was mixing up LOP with Pitch angle of the stock
Found this article which is quite good about pitch angle

THE FIT OF A GUN by Bob Spencer
http://home.insightbb.com/~bspen/fit.html

Many factors are involved in shooting any long gun accurately. One which is not well understood by many shooters, and to which too little attention is paid by most of us, is the fit of the gun to the shooter. Since we don't usually have an opportunity to choose between different stock configurations, but must accept the gun as it was built, we tend not to give much thought to what is involved in gun fit, we just shoot what we have.

It's not nearly as complicated as casual consideration would lead us to believe. The various factors involved are easily understood, and every shooter of long guns should be on speaking terms with them. A few definitions seem appropriate to the discussion.


In the diagram, the dashed line extending from front sight to "C" is the line of sight. The heel and toe of the butt of the stock are indicated, as is the butt, with butt plate. Let's consider the measurements shown, and give them some thought.

If a perpendicular is dropped from the line of sight down to the point of the comb of the stock, as indicated at "B-B", that distance is called the 'drop at comb'. This is probably the most critical of all the factors involving fit. It is at the point of the comb that our cheek rests while sighting. If this distance is right, then when we "spot weld" our cheek on it, our eye falls naturally in line with the sights. We can throw the gun to our shoulder for a quick shot and not have to readjust the position before firing. It is obvious that this measurement is extremely important on a shotgun stock, or any long gun with no rear sight. The drop at comb IS the rear sight. If the comb is too high, the eye is forced high, also, and we will tend to shoot high. To counteract this tendency, we mash our cheek too hard against the stock, trying to lower the eye. This isn't a comfortable, natural way to aim, and, in addition, will lead to our being smacked hard in the cheek from the recoil of the gun. If the comb is too low, the eye is too low, and we will tend to shoot low. To avoid this, we find ourselves placing our cheek very lightly on the comb, or even raising our cheek off the stock a bit. Neither is good for accuracy.

The average American these days can do well with a drop at comb of somewhere in the range of 1.5 to 1.75 inches.

Drop a perpendicular from the line of sight to the heel, as at "C-C", and the measurement is called 'drop at heel'. This is much less important to gun fit than drop at comb. Whereas a small change in drop at comb can make a big difference, a fairly wide range of measurements of drop at heel can be comfortably accommodated by the average shooter. One thing which does change with this measurement is the perceived recoil. A gun with little drop at heel is said to have a "straight" stock. Recoil is more in line with the stock, more directly back into the shoulder, with a straight stock, and more comfortable for most shooters. Stocks with large drop at heel can be painful to shoot, because the comb recoils up against the cheek

Average Americans are comfortable with drop at heel measurements of from 2.25 to 3.0 inches.

The distance "D-D" in the diagram is designated the 'trigger pull'. This is a very important measurement when considering stock fit. It is defined as the distance from the center of the butt to the center of the trigger. It is easily seen that it is also a fairly direct measurement of the length of the buttstock of any gun. Too long a distance here will force the shooter away from the gun, move his cheek back from the point of the comb where it belongs, and cause him to "crawl" the stock in attempting to compensate. The butt will also tend to catch in his clothes as he quickly mounts the gun. Too short a distance is uncomfortable to get lined up, forcing the shooter to ease his face back, away from the breech, in order to line his eye up correctly. A too-short trigger pull will also result in having the thumb smack the shooter in the nose under the recoil of firing.

The average shooter can easily accommodate a range of trigger pulls from 13 to 14 inches. This depends very much on how tall the shooter is, and how long his arms are. Many old guns had trigger pulls as short as 12 inches, but most modern shooters will like one around 13.25 to 13.5 inches.

In the diagram above, there is a solid line from "C" at the heel, across the breech and into the air above the front sight. This is the line of 'pitch'. Pitch is simply defined as the angle of the butt to the line of sight. Give it some thought, and you will see that it is another important consideration of gun fit. Stand your gun on the floor, butt plate flat. Scoot it back until the breech area touches the wall. Measure straight out from the wall to the tip of the muzzle. That measurement is called the "pitch", and is shown as the distance "A-A" in the diagram above. A moment's reflection will show that the measurement depends on two things .... the angle of the butt, and the length of the barrel. The same gun with a 20-inch barrel will have a lot smaller pitch than it would with a 40-barrel. Simple geometry. So, if you ever need to describe a gun in terms of pitch, it is mandatory that you designate the length of the barrel, as in "a pitch of 2.5 inches for a 32 inch barrel". If there was a gap between the muzzle of your gun and the wall when you measured this, then the pitch is said to be 'positive' If the muzzle and the breech both touch the wall, the pitch is 'zero'. If the muzzle touches the wall, but the breech cannot, the pitch is said to be 'negative'. A gun with just the right pitch will stay firmly planted on your shoulder when mounted, and when fired. One with too much pitch will tend to slide up over the shoulder, and will tend to shoot low. One with too little pitch (zero or even negative), will tend to slide down into your armpit, and will tend to shoot high. A little positive pitch makes most of us happy.

It can be confusing to picture, but it's important to keep in mind that pitch has nothing to do with drop. A perfectly straight stock can have a small or a large pitch, and a stock with a radical drop, like some longrifles, can have a zero pitch.

The terms 'cast-off' and 'cast-on' are also used to describe stock configuration. Simply put, they refer to the deviation of the butt away from the center line of the gun. A gun with no cast is straight. A line down the center of the barrel will continue straight down the center of the butt stock, as viewed from above. With cast-off, the center of the butt is moved in the direction of the shoulder of the shooter. The opposite is true of cast-on, the butt deviating toward the center of the shooter's chest. The diagram at left shows cast-off in a right handed gun, by the amount between the arrows. Neither cast-off or cast-on are commonly built into guns, these days, and cast-on has always been fairly rare. The purpose of both is simply to make it easier to align the eye with the sights. Just as the height of the comb helps align the eye with the sights in a vertical direction, up and down, cast can make it easier to line the eye up in a side to side direction. A knowledgeable stock builder can use cast to cure alignment problems for people with particularly wide or narrow faces, for example. This curve in the stock can be accomplished either by steam-bending the straight stock or by carving the curve in as the gun is made, which is better.

Cast-off and cast-on are used far less frequently than most other elements to affect stock fit. The British have always made a big point of the usefulness of cast, especially in shotguns, which must come to the shoulder quickly and without hesitation, lined up right the first time. Few modern American guns have ever had it, and most of the available black powder guns in today's market are made without cast, as far as I am aware.

The average shooter will find a gun with 1/8 to 3/8 inch of cast-off to be a comfortable one to shoot.

Drop at comb, drop at heel, trigger pull, pitch and cast are only a few of the elements which go into making a well-fitting stock, but they are some of the most important to be considered. To these must be added thickness of comb, width, position and angle of the cheekpiece, width of the butt and others. Of course, the size and shape of the shooter must be considered, as well as the shooting sport for which the gun is intended. A shotgun intended for trap, where the target is always climbing away from the shooter, needs to fit the gunner in a different way than that used for skeet or mixed small game, and both will be different from any rifle, whether used for off-hand or bench shooting.

Because of the fact that it is used in an almost automatic, instinctive way, the fit of a shotgun is most critical. The need for proper fit in an off-hand rifle is probably a close second. The fit of rifles used for bench shooting is not as critical, because we can adapt ourselves to any misfits fairly easily, given enough time before we shoot. It's the hand-held guns, especially those used for moving targets, or with no rear sight, to which closest attention to fit should be paid.

The support for a gun can be considered to be 4-point: butt against the shoulder, cheek against the stock, trigger hand at the wrist and the other hand supporting and guiding the barrel. If all these points are comfortably related so that you don't have to do anything radical to get into shooting position ...smashing your face against the stock to get the sights lined up, crawling forward on the stock, lifting your face from the stock, etc.... then painful recoil is not usually a problem, and you can do your best shooting.

A well-fitting gun is a joy to shoot, and can improve your shooting without your ever understanding all the elements involved. Think about a few of the factors discussed here the next time you buy a gun. It will pay dividends in the long run.

Copyright © 1999 B.E. Spencer, all rights reserved.
 
Also found this article on how different stock designs affect how you feel recoil

How to Reduce Recoil . . . . without using a muzzle brake
http://www.larrywillis.com/reduce-recoil.html

The shape of this Winchester stock really increases the amount of recoil that you feel.

Notice how the comb (top surface of this stock) slopes upward. This shape causes a rifle to recoil back - right into your face. This stock design almost always delivers brutal recoil. The 30-30 Win. is not a powerful caliber by any means, but just shoot one of these Winchesters, and you'll feel a whole lot more recoil than you should. It's mostly due to this stock design. The angle of the butt plate is another problem. The top of the butt plate is slanted to the rear, and that causes recoil to pound the upper part of your shoulder. This is the very worst stock design there is for comfortable shooting.


This particular Remington stock recoils straight back. It's much better.

Notice how the comb of this stock is perfectly parallel with the barrel. This allows the rifle to recoil straight back along (but not into) your face. This stock design is a major improvement, and you'll feel a great deal less recoil with this stock design. The angle of this butt plate is also much better than the Winchester. It's still slanted slightly to the rear, (but not as much) and it delivers recoil lower on your shoulder where it's more comfortable. A well designed recoil pad obviously reduces recoil even more.


Weatherby stocks are well designed, and you'll feel less recoil with this stock design.

Notice how the front of the comb on this stock slopes downward. This allows the rifle to recoil straight back, and away from your face. This stock design also delivers recoil to your shoulder the way it should. However, the butt plate is still not "perfectly" perpendicular to the barrel. The top of the butt is slanted "very slightly" to the rear. This puts recoil just a bit high on your shoulder. Changing this angle just enough to make it perpendicular to the barrel would make the recoil feel noticably lighter, especially when shooting from the prone position or from a bench.

Keep these two stock angles in mind the next time you refinish your stock. Even a slight change of these angles can reduce recoil considerably. One more note. I hate to see hunters use recoil brakes, because that increases noise to dangerous levels that can ruin your hearing with just one shot. A recoil brake can permanently affect your hearing (for life), if you're not wearing ear protection! The next time you install a recoil pad, be sure to maintain the correct length of pull (from center of the pad to the trigger), and improve the angle of your recoil pad. The reduction in felt recoil, with a well designed stock, is a tremendous improvement.


Return to see more Reloading Tech Tips
 
And one last which also gives so great information
http://www.fieldsportsmagazine.com/Shooting-Instruction/gun-fitting-with-simon-ward.html

Simon Ward on the simple route to better shooting - getting your gun fitted. Here he explains the benefits of having a gun that fits you properly and what to look out for.

The Greats always knew it, but increasingly more and more are discovering that gunfit holds an important key to good shooting.

But having a gun professionally fitted will only be of real benefit if you have learnt to consistently mount your gun smoothly and accurately onto a moving object. Your master eye is the backsight of your gun so good gunmounting is paramount to your success. I mention this at the outset in order that you get the most out of a gunfitting.

The fit of your gun comes in three stages.

STOCK LENGTH

There are three important stock measurements but the one which most people refer to is the length, which is the distance from the trigger blade to the centre of the butt of the stock, normally anywhere between 14½” to 15¼”. But while these are average lengths, it should be remembered that ¼” can make a lot of difference to both comfort and accuracy. You may be partridge shooting in a cotton shooting vest in early autumn, but by mid-winter you might be wearing thermals, a thick sweater and waterproof coat, which could add anything from 1/8” to ½”. To resolve this dilemma the simple solution is to have a recoil pad fitted into your shooting vest. This will automatically add anything up to ¼” which will compensate for not wearing your usual winter shooting garb. It will also give you kinder shooting on those hotter days.

Gunmounting is difficult with a short stock - the gun is not so controllable and likely to give the user some knocks. While a stock which is too long will result in the user mounting the butt onto the end of his/her arm as opposed to in the shoulder pocket. In which case both the cast and drop measurements will work against you, and definitely not for you.

Your master eye will be out of alignment at the breech, looking down the side of the rib rather than the centre. The eye will be lower than it should be, the drop measurement increased, the cast in effect reduced.

I mentioned that there were three stock measurements - centre, heel and toe. Reducing the toe measurement can be helpful for ladies or men who are fuller in the chest, and make it easier to achieve good contact in the shoulder pocket.

CAST

Cast is the sideways movement of the stock from the central line of the gun. Cast is referred to as ‘On’ for left and ‘Off’ for right, whilst there is cast at comb, face, heel and toe.

Cast on your gun adjusts the east and west movement of your pattern. The amount of cast needed on a side-by-side or over-under is determined by the use of a try gun to make and take accurate measurements so that when the shooter’s eye is placed centrally over the breech with a natural head position, the gun fitter will make small adjustments until he sees the perfect eye/rib correlation

The amount of cast on or off is wholly dependent on the shape and width of the Gun’s face, and what it takes to get the master eye in the correct position when the stock is correctly mounted.

You tend to find that someone broad in the face requires considerably more cast at ‘face’ than someone who is slimmer, with more narrow facial features.

DROP

The drop measurement on your gun adjusts the north and south placement of your shot pattern. There are three measurements in drop - at comb (top of the stock), at face (midway position between nose of comb and heel of comb) and heel.

This is one measurement which makers of off-the-shelf side-by-sides and over-unders frequently get wrong. Unless we are talking about trap guns, the majority have too much drop in the comb.

Generally the length is OK, and for cast they tend to opt for standard measurements of 1/8”at comb, 1/16” heel and ¼” toe. But drop at heel can be anywhere from 1½” to 2½” - and the latter is simply far too low for most people. Certainly for driven shooting. And remember just 1/8” out on the cast or drop measurement at face equates to the centre of the pattern being 6”off the target at 40 yards.

Too much drop results in the master eye looking at the top lever rather than the quarry, casusing headlifting and subsequently the stock banging the cheek and resulting in a stopped swing.

So therefore small adjustments such as 1/16” can make a huge difference to the point of aim of your gun - at 40 yards we are talking about the difference between killing a partridge and wounding or missing it underneath.

In my eyes comb height is a crucial measurement in gunfit.

But a word of warning... always remember that a little knowledge can be dangerous so before you start tinkering with your gun I suggest you seek the advice of a professional gunfitter who will tell you whether your gun fits or not. You will want to go to someone who has a good reputation and several years experience with a try gun and has the ability to give confident and accurate measurements at the end of a fitting session.

For the game Shot who specialises in grouse I would suggest the comb height be set so that half the pattern is placed above and half below the aiming mark at 40 yards. For the driven pheasant Shot I would suggest that the comb height is set a little higher ie. 2/3 above and 1/3 below. This results in the pattern being thrown a little higher than the aiming mark at 40 yards in the field, thus reducing the chance of wounding rising/crossing birds and enables the Gun to see a little more of the bird in flight.

Once you have been for a fitting with a professional then you can have adjustments made to your gun(s). But first, I would suggest a session on the clays under his guidance, just to make sure that both of you are happy with the result.

Then leave well alone and concentrate on some practice for next season.

THE FITTING

When you visit a shooting school for an appointment with a professional gunfitter be prepared for a 2-3 hour session. As soon as you walk through the door he will be making an assessment of your height and body shape in order to set up the try gun for an approximate fit to yourself.

He will ask you to dry mount the gun and if he sees any imperfection in your gun mounting skills his task will be to rectify them before using the try gun.

The try gun has three key adjustments - length, cast and drop. But the fitter will also look at your gun to check the measurements and if he finds that length and cast are OK, but spots that there is a little too much drop at face he may well opt to put the try gun to one side. Instead he will achieve the correct amount of drop by using comb raisers (easily attached to the stock with tape). Most fitters will agree that it is better to let clients shoot their own gun, if possible. They shoot more naturally.

PATTERN PLATE

Whether it’s your own gun or the try gun, once the fitter is satisfied that the measurements are OK he will then take you to the pattern plate, which is a big steel plate, erected upright and coated with whitewash. It’s a simple but tremendously effective and useful aid.

Typically the fitter will start you off at 16 yards from the plate and he might spend up to 15 minutes getting you to stand and mount correctly. It’s pointless proceeding if the mounting skills are not up to much - a full choke at 16 yards doesn’t lie and you can quickly see if the gun is shooting off point of aim.

Once he is happy with this then he will take you back to the 40 yard mark, which is a range that covers most driven game, and one which will highlight the quality of the gunfit.

You will then fire a sequence of shots at the aiming mark. The fitter may make small adjustments to the try gun at this point. And if there is still anything amiss, he will check that the gun is unloaded and ask his client to dry mount the gun. The fitter will then look down the barrels from the muzzles to check the position of the eye over the top of the breech. Only a fitter should do this - do not try it at home.

Once both the fitter and yourself are happy with what you see on the plate then it’s time to move onto the shooting ground to tackle a variety of angles of clays. When the session is complete and both of you are satisfied with the result, you will then retire to the gunroom where the fitter will take the measurements from the try gun and write out a fitting sheet for you (both parties will have a copy). The gun will then be adjusted to the measurements on the fitting sheet - a stock can usually be bent accordingly.

TRIGGERS

At some point during the appointment, it would be a good idea to get the fitter to check the trigger pulls on your gun. Again if these are too heavy it could be seriously affect your shooting, without you realising.

Standard pulls are: Single trigger 3½lb first barrel and 3¾-4lb second barrel. Double trigger 3lb and 4lb.

Anything heavier than this can induce a flinch or checked swing.

If you have been suffering with a bruised index finger due to the stock being too short or if you are holding the grip incorrectly, thus putting too much trigger finger around the trigger blade so that the index finger is butting up on the back of the trigger guard, it will cause a nasty swelling. But if you instead hold the gun a little further down the grip so you are reaching the trigger, pulling it with the tip of your finger you will notice a nice gap will appear between the trigger guard and the index finger.

But check with the fitter - your stock could possibly be too short.

BEWARE

When trying a different gun, new or second hand, it is easy to feel that it fits. Swinging it around in a room or gunshop, and away from the shooting field, you can make practically any gun seem the right one for you. But you’ll be very lucky if this initial judgement is correct.

One other word of caution... don’t be put off having a gunfitting because of cost. Compared to the price of game shooting it represents a remarkably good investment as well aiding you to kill your birds more cleanly. There are countless people out there in the shooting field with either the wrong gun or an ill-fitting gun and as a consequence will never shoot to their potential. But with a properly fitted gun their shooting and enjoyment from their sport could be transformed. What price on that?
 
I just want to add that these generalizations (while all true) will vary greatly depending on the shooters physique, height, fullness of face , etc. I find American Monte Carlo stocks very uncomfortable to use generally. There are "try guns" and "fitting stocks" out there, though the only ones I have personally laid hands on were from G&H and H&H. I don't don't know if anyone in Canada even has one. Martini and Hagn in BC, maybe. I find that what we think of as BR and precision rifles these days are less in need of a unconscious fit then a shotgun or DGR. FWIW - dan
 
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