Stock drop questions

M

mshelton

Member
Going to be a pretty rookie question but not knowing the full details, I'm going to ask it anyway.

Stock drop, I know in 100/200 HV and LV classes there is a stock drop rule and this is why those stocks have the 1/2 to 3/4" of drop (guess on the number from what I remember seeing).

Long range (600/1000) do not have this requirement but yet I see both in long range stock, some with little to no drop and some with the same amount as the short range stocks, I know it may be possible to have a stock that one could use in both disciplines but seems that would be an oddball exception.

So I'm wondering is there any benefit to having drop in a stock even when rules say it's not required?
 
Your question isn't clear, at least to me. Which drop are you talking about? In Point-Blank BR, the only rule involves drop at the toe. For a picture

http://home.insightbb.com/~bspen/fit.html

AFAIK, there is no rule about the heel. You do want to be able to take the bolt out without a lot of hassle. And the drop at the toe is actually to get a certain distance below the bore center line (barrel, not bore in NBRSA), which is a rule.

As you've noted, there are no 1K rules on this. Whether or not "drop" is beneficial depends on the whole rifle -- the system. I have a couple 1,000 yard rifles that have no "stock" per se, so drop doesn't come up. But they were designed with that in mind. Remember, the butt in the rear bag is one thing that helps limit rotation from the torque generated by the bullet & rifling -- the other being the forearm -- flat & wide. There isn't much torque force generated by 6mm 105 grain bullets. There is a whole lot more from a .338 with 300 grain bullets.

Anyway, a competition rifle a system. What's important, outside adhering to the rules, is often a matter of design.
 
On the left side of the home page of this web site, are icons that lead to web sites of several bench shooting sanctioning bodies. For short and long range benchrest, depending on your area, you will be dealing with an IBS, or NBRSA sancitoned match, unless it is a club match. In any case, if you go to the sites that I have mentioned, you can take a look at their rule books. I think that what you are referring to is the requirement to have some minimum angle, relative to the CL of the bore, of the bottom of the butt stock. This is not specified in the manner that you used in your question, so you might want to look in the rule books to see what is legal. You are correct about it not being required for 600 and 1,000 yard rifles, ( I think.) and that it is for 1-200 yd rifles that are used in the classes that have weight limits.
 
if ya wanna be in with a bit of a chance contact Bob White and talk to him he does second hand gun and advice just my 2 bob's worth.wish Bob was in OZ.
jim
 
The drop rule I'm referring to is from the NBRSA rulebook #37 page 117.

4" down from the bore line at butt plate to 18" from the bolt face.
Bottom of stock may not be more parallel to the bore than a straight line between the above points.


Now to clarify, long range stocks do not need to meet that requirement and the stock bottoms can be parallel to the bore line if desired. Also I'm talking about the light gun (17lb and under) category here.
This is from my limited experience, what makes sense to me and in a free recoil configuration I would think a stock bottom parallel to the bore or very close to it would be more beneficial in that the rifle is limited to one direction of travel in recoil, straight back, as apposed to short range stocks which come straight back and angle muzzle up.

However I have seen some stocks designed for LG long range use that have stock bottoms that are not parallel and close to a short range stock, the McMillian EDGE for example. So that's what led to my question, is it somehow beneficial to not have that parallel stock bottom.
 
mshelton said:
short range stocks which come straight back and angle muzzle up.
Click to expand...

There are lots of issues. You have identified perhaps the biggest disadvantage of sloped heels. If the gun doesn't slide back in the bags exactly the same when the bullet exits the muzzle, there will be a difference in muzzle angle between shots. For a 30" distance between front and rear rest, each 0.001" of vertical difference causes 0.120" of vertical at 100 yards. With a 6 degree heel angle, this vertical difference would result from about a 0.010" difference in how far the stock recoils horizontally. For reference, it has been shown that bench guns recoil about 1/8" by the time the bullet exits. (Obviously depends on several factors, but this is a ball park value.)

Cheers,
Keith
 
Thanks Keith,

Reason I'm asking is that I'm building a rifle to compete in the 600yd matches, I recently received my stock from the maker. The stock was supposed to be a long range stock and after a call the maker is claiming it is but when checking the dimensions as described in the NBRSA rulebook the thing is pretty close if not conforming to the short range dimension rule and I'm left wondering what to do with it.
 
One factor, that might influence your decision, is how you intend to shoot the rifle. If it is almost any other way than free recoil, this may be a non functional difference.
 
Somehow, I got the idea that short range unlimited guns both rail and cruiser were also exempt from the drop? Or do I misremeber?
 
No, you do not, but of course you hardly ever hear of someone making a serious run at unlimited with anything but a rail.
 
mshelton said:
Thanks Keith,

Reason I'm asking is that I'm building a rifle to compete in the 600yd matches, I recently received my stock from the maker. The stock was supposed to be a long range stock and after a call the maker is claiming it is but when checking the dimensions as described in the NBRSA rulebook the thing is pretty close if not conforming to the short range dimension rule and I'm left wondering what to do with it.
Click to expand...

There are other here who can give you better advice based on their experience of actually trying different long range stocks. Short range BR stocks with sloped heels are somehow capable of shooting some amazing groups in spite of this possible problem. But the way I look at it is, why add a potential source of inaccuracy if the rules don't require it?

Keith
 
A stock with the sloped buttstock will shoot just fine at the longer ranges. It is just harder to use in some cases. If you are shooting at a range where sighters are taken at clays placed on the berm, the slope will make it hard to determine where you are hitting. When the rifle recoils backward, the muzzle goes way up and you cannot see the hit. If the bottom of the butt and the bottom of the fore end are parallel, then the gun recoils straight back. If you keep your head down and eye open, you can often see the bullet strike in your scope. This is probably not as important at ranges with pits where your sighters are marked on a sighter target. Additionally, for me at least, the parallel stocks seem to be a bit more forgiving of bench manners in the heavier recoiling rifles used in long range competition. But, I do use my 13.5 lb heavy varmint as my 600 / 1000 yard light gun. I simply put on a barrel chambered for a different cartridge. It only weighs 15 pounds or so but works pretty well. It does work better for me if I add a keel to make it a parallel stock.
Joe
 
mks said:
There are lots of issues. You have identified perhaps the biggest disadvantage of sloped heels. If the gun doesn't slide back in the bags exactly the same when the bullet exits the muzzle, there will be a difference in muzzle angle between shots. For a 30" distance between front and rear rest, each 0.001" of vertical difference causes 0.120" of vertical at 100 yards. With a 6 degree heel angle, this vertical difference would result from about a 0.010" difference in how far the stock recoils horizontally. For reference, it has been shown that bench guns recoil about 1/8" by the time the bullet exits. (Obviously depends on several factors, but this is a ball park value.)
Click to expand...
Help me out here Keith -- Let's suppose you are shooting at a single bull -- the target -- which is fixed for both 600 and 1,000 yard benchrest. You put the sight on the center of the bull. Now the scope and barrel (muzzle angel) relationship also fixed. If the muzzle angle were changed, it would seem to me the scope would no longer point to the bull. Restoring the sight picture in this case also restores the muzzle angle.

Obviously not true for score targets with multiple bulls, but that's not the case at 600 & 1,000 yards.

Where this does get you is when you sight in at clay pigeons set up at the bottom of the target frame. You can be busting birds-- or even small pieces of birds -- during the sightin period, but when you go up to the record target -- 3 to 4 feet higher -- you're shots will usually print low.

Or have I missed something?
 
Charles E said:
Restoring the sight picture in this case also restores the muzzle angle.
Click to expand...

Charles,
Maybe I wasn't clear on what part of the sliding I am referring to. What I am talking about is the rifle sliding back in the bags between the time that you pull the trigger and when the bullet exits. In this example, if the rifle recoils back 0.125 for the first shot, and 0.135 for the second shot, the second shot will be 0.120 higher on the target due to the heel dropping a different amount.

I think you are talking about sliding the rifle forward, right? You are correct, if you reacquire the same sight picture, the muzzle angle should be exactly the same when you pull the trigger.

Cheers,
Keith

A wild idea: As far as I know, it is not against the rules to also have an angle on the forend. The effect of the heel sliding down the rear bag could be largely offset by adding a 6 degree angle to the forend, assuming that the forend remains in contact with the front bag. However, there is evidence (Varmint Al's simulations) that shows that the forend may rise out of the front bag during recoil. If so, the forend angle doesn't matter.
 
I've seen a great many stocks with angle in the forend. Mine being one of them. They aren't 6 deg, though. I do wonder about the thought behind the angle that I see on them. Wonder if it like the famous story about the beef roast recipe in which a bit of the end was removed...
 
Thanks very much, Keith.

As to the tapered forearms, I don't know of any matching the butt angle -- thought I did, made a post over on Rimfire Accuracy, & Jerry Stiller corrected me. He did go into a bit -- at least the most recent incarnation. See post #20 for those tapered forearms:

http://www.rimfireaccuracy.com/Forums/showthread.php/2815-Sloping-butts?highlight=butt

As to the general phenomena of muzzle angle during recoil, there is another problem area: the front (at least) sandbag. It's been reported -- Don in Redondo being one of several, IIRC, that an edge of sand can form &/or break away inside the front bag during a record string. That means the height of the sand in the front bag may change, and *that* would give you the same problem.

I do remember Varmint Al saying the forearm can lift completely off the bag during recoil. And bless me, I think I remember him saying the butt does, too. Too many recent examples of a once dependable memory (never had to take notes in school) no longer so dependable. If I'm remembering correctly, there is an FEM of the load on the butt somewhere, and I believe it dropped to zero at one point.

All this points up the futility of trying to make an over-simplistic determination on what's "best."

Here's a story: I have a .338 I'm currently doting on. It does come back fairly snappishly. To counter that, I take a lot of the recoil with my forearm hand, pushing forward against the stop, and pulling down against the bag. Some very good groups with that technique. Then, at the July match, an 18-inch group. Not "vertical stringing" as we usually use that term, not exactly a 3 & 2, just ... depressing vertical.

(1) The rounds were prepared a month before, the batch had 6-inch groups. It was a proven load, and no single round made the group so large. Odds are very high it wasn't the ammunition

(2) No other competitor on my relay had that sort of vertical.

My current thinking is that after the first couple shots, I pulled down harder on the forearm & unloaded the rear bag. I'll have to test to be sure, of course, but it fits, and with your numbers, that explanation fits even better.

* * *

It's easy to get our heads oriented to where we think everything is in the design of the rifle, bench technique doesn't matter. Don't believe that's quite correct.

So for the original poster, I wouldn't worry about it, unless for not very good reasons you're convinced it is a problem. If you believe that, it likely will be. Otherwise, there are enough other things to worry about. Maybe after a number of years, butt angle could become a significant part of how you design your long-range competition rifles, but that would be based on how you've developed your 1K components & technique over time, not on an "inherent problem" with sloped butts.

FWIW
 
I have developed a dependable technique for shooting a benchrest rifle with my non trigger hand on the forend. Granted, the recoil was a lot less than you are dealing with, but the lesson learned may still apply. I learned, by trial and error that for best results I should rest the back of my hand on something, and not apply any down force. If I did, inconsistencies would produce vertical. Charles, I think that you are experiencing what CF pistol shooters do when they try to eliminate muzzle rise.
 
So just to stir the pot a bit. Since the rules refer to a distance from the bolt face, are stocks made in the worst case scenario such as a Panda (not anything against a Panda) as apposed to a 6.5" BAT? The butt angle would/should be steeper with the S BAT than with a Panda where the bolt face is over a inch forward.

Wasn't it George Kelbly that made a stock "gauge" and said many stocks do not meet the rules?
 
First, several years ago a very expert mathmatican on this site, can't remember the name, calculated out the amount of gun movement when in free recoil of a typical 6 PPC L.V. bench rifle. A 10.5 lb rifle, shooting an fairly common 80 grain bullet and assuming no friction on the bags and the total rearward movement before the bullet exited the barrel was .038", not .125". If there is anyone here that remembers their math and phyics enough to re-work this you might check this.
Second, there is no such thing as an "illegal" stock for short range benchrest, only illegal rifles. The rule states that the bottom of the buttstock line must cross the center of the bore line at no more than 18" from the bolt face. This can only be measured on a completely built rifle, and since there are many different lengths of actions now in use, and different positions in the stock the action may be placed for trigger comfort, and different depths the action may be set in the stock, then all these items would change the required angle on the bottom of the butt. There is nothing on the stock itself that can be measured for this rule, only on the finished rifle. I think this rule is a hold-over from the days when most stocks were made of wood and this stock angle could be adjusted for each rifle. This is just not possible on todays modern synthetic stocks, at least not easily. A modern BR stock may make a rifle that is legal with one action in one position and illegal with another. This is something the riflesmith building the rifle should check.
 
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