Physics and a question of stability

[Lynn Otto]

Disclaimer: This posting has no intention to be personal, makes no reference to the rules and no animals were hurt in its making.

This question is not intended to dwell on topics previously discussed but is a geniune request for information. As I don't have a degree in physics can some one kindly explain to me why a rifle with say a 3" fore end supoorted on a rest should be inherently more stable than a rifle with an F Class bipod. Does not a bipod with feet spread to say 15" or more not effectively become a 15" fore end?? That is afterall the spread of the stability of that rifle.

I don't personally have a preference of either as they relate to shooting, either is fine, I simply prefer the bipod for the ease of managing my rifle, it's so much easier to put it down somewhere if it has a bipod attached (this may be a female thing).

But back to the physics of it, why should something that is 15" wide be less stable than someting that is 8-10" (the width of the stand) and if there is no difference then why are we making a fuss about it???

Lynn

[bully_eye]

A non-physics related answer..... I've used both a benchrest type stand then switched to a aluminium bipod and will be switching back to the benchrest stand. From my experience- and I do shoot a big kicker at the moment- the benchrest stand seems to enable the rifle to track much better under recoil as the stock has more travel than with the bipod- this advantage would be negated if the bipod had at least 6" of travel in the feet. Also the feet on a pedestal type rest could easily have a footprint equal to or more than a bipod and three feet would be more stable than 2 if properly leveled. I've also had more troubles canting with the bipod- this because the same mechanism which enables the bipod to level on uneven ground can allow it to tip to one side especially under recoil accentuated by the average top heavy rifle . The benchrest stand is certainly more trouble to set up well on uneven mounds but I will be switching back to one when my new rifle is finished- all advantages aside there is no way on earth I am having a rail installed on my new stock as it kind of negates the reason for buying an MBR type stock in the first place. I do think a lot of the advantages of a benchrest stand are somewhat negated if using a light recoiling rifle and the bipods certainly are more convenient.

My experience FWIW,

Michael

[bully_eye]

...... I guess what I was getting at was that it isn't just a matter of stability but tracking ability etc that MAY make a benchrest type stand a better option.

Michael

[Tony Q]

Physics 101 … I hope

If you look at a normal Benchrest rifle, the common type, you will notice 3 things.

1. The forend width is governed (3 ½” wide from memory?) and generally they are very thin, very flat and very slippy.

The thinness allows low center of gravity, the closer you can get the underside of the forend to the bore line the more stability due to center of gravity balance/mass, the wide forend creates a larger surface area spreading the weight of the rifle over a greater area.

I.e. The rifle is more stable and less subject to the twisting torsion of the projectile spinning through the barrel. Increased surface area reduces friction and the flat bottom allows smooth tracking.

2. Almost an absence of any sort of pistol grip .. most top benchresters shoot without even grasping the pistol grip as it can, under recoil, cause an imbalance to the rifle.

The idea is to get to a point where the rifle is just recoiling in a straight line backwards with no human resistance.

I.e. Free recoil removes, to some degree, the human resistance under recoil.

3. Almost no cheek piece or rise. This again is to limit and restrict the amount of human contact on the rifle itself, every bit of contact has the ability to produce uneven results as shot to shot consistency can be compromised.

A true Benchrest gun is shot in a way that is almost, but not quite, self supported with only the trigger finger making any contact. If they were allowed they would stand back and press a remote button to fire the round off.

A Long range Bench gun is a little different, it normally shoots something with more kick than a 6mmPPC and as such requires more weight a deeper an sometimes wider forend to keep the rifle stable and under ‘recoil’ control. This is why tracker stocks were developed.

The general rule of thumb with Benchrest guns is this .. the deeper the forend the wider it has to be. I cant remember what the formula is, but its basically an angular line drawn from the center of bore, so a thin forend (say 25mm) may only need 31/2” of width where a thick forend (say 50mm) may need 4” or 5” of width.

I’ll see if I can dig the diagram up from my resource files.

Bipods

A bipod has its stability a long way from the bore center and has other issues that can affect consistent shot to shot results. These include unlevel ground forcing you to cant the rifle over .. this changes the stability affect as the distance from the plumb point of the bore is now different on the left and right sides in relation the feet of the bipod.
(extreme case)

Also under recoil any lumps, bumps or changing dynamic of the ground has a direct input into how the rifle behaves shot to shot. This is why someone invented the bipod with the sliding feet … it helps to alleviates this possibility.

A pedestal or Benchrest does not have these issues as it is independent from the rifle and is leveled once and stays this way for the entire round. This allows it to stay in one place without having to move it. .. i.e. Consistency.

How many times has a bipod shooter been forced to alter their position due to recoil now putting the feet of the bipod in a different place on the mound?

Happens to me all the time.



Also … As with Lynn, no animals were hurt in writing this … and, if some one disagrees with what I have written .. go for it.

[Lynn Otto]

Hi guys

thankyou for responding, I'm about to run out of time so will get back to you later.

Tony could you reconsider your information not in relation to benchrest rifles, I was thinking standard rifle, do your ideas still hold the same?? That is, the way the rifle acts.

Lynn

[Tony Q]

HI Lynn

If that Standard rifle is of Benchrest design or Tracker design then yes.

If its a modified Std rifle, i.e. bolt on plates and butt rails .. then yes

If its a std rifle like your omark or my sako then no. your rifle and my rifle would act differently on a pedistal rest as the fore ends were not designed to track (added stabiliy wise) the same way as a bench gun.

Thats the reason flat plates or tracking rods are added to std FS rifles to give them the same dynamics in stability and trackability that a bench gun is designed to give. Now Lynn, im not having a go at Trevs rifle here, im just pointing out that some modifications are taking away the alleged intended spirit of FS.

If we can come up with some guidlines for these guns that would be a plus i.e restricting plate widths to 2 1/2 inches.

Personally I dont have a problem with butt rods apart from the fact they look odd


The bipod issue would be the same for any rifle, regardless of design.

(to be honest, if it were up to me, all FS would be shot of a bipod. Even then the bipod would have limitations in design to counted those future creations that would be developed to create the Benchrest/Pedistal/Tracking/Self leveling/coffee making Bipod. )

[Guest]

Tony,

Just thinking about F-Std stock restrictions, the fact that we allow pedestal front rests and rear rests is the only reason why benchrest style stocks are preferred by some. A wide fore-end will be of no value if you're using a bipod, and a parallel butt base will be of no value without a rear rest.

Now the bipod certainly helps those who have trouble holding a rifle with sling, but the benefits of both pedestal and rear rest are in my opinion more towards enhancing accuracy than addressing physical handicaps. So maybe rather than trying to look at stock design, it is easier to restrict the allowed features which are causing the unconventional stock design!

So in otherwords, no pedestal front rests (bipods only), and no rear rests of any type. To me part of the spirit of F-Std should be portability - the pedestal and rear rests are separate and heavy items, and out of character. This would make F-Std (more than either TR or F-Open) a real world practical rifle for long range shooting.

Alan .

[bully_eye]

..... except you can get bags for pedestal rests designed specifically for rounded fore ends which negates the need for bolt on plates or tracker style stocks. Funny how every post seems to end up coming back to stock design and rules for FS.

[Lynn Otto]

As I've said I prefer the bipod anyway but would be against removing the use of the rear bag as I have a physical problem that requires me to avoid being hit with the butt of the rifle, that is I am unable to support it into my shoulder so a bag is essential.

Must rush, am between lecture at uni, best not be late for the next one.

Lynn

[Guest]

(he laughs)

It certainly is a revolving issue … and that’s a good thing.

And as such indicates that a control needs to be put in place for FS rifles. It has been mentioned before about making FS bipod only, and this I agree with.

Also .. Alan … wee will make a purist out of you yet, and I love your idea.

I and many others would like this concept, its as close as you can get to fullbore and makes the shooter develop control skills to drive the rifle. I also agree with Lynn that some conditions would require the use of a bag.

A bag is more stable and will provide better results… it’s a hard one to cover. One way could be to instigate fore arm or fist support under the butt (as military rifle is shot) this would provide the support for shooters like Lynn and would counter the free recoil positions.

This is not intended to make FS harder .. its to make it easier, more simple. FO is for the experimental rigs, FS should be as it was meant to be .. a fullbore rifle with a scope and a simple rest.

Bipod only would remove all issues in regard to stocks … but be warned, you would need to put in some control design issues for bipods.

[Guest]

(he laughs)

It certainly is a revolving issue … and that’s a good thing.

And as such indicates that a control needs to be put in place for FS rifles. It has been mentioned before about making FS bipod only, and this I agree with.

Also .. Alan … wee will make a purist out of you yet, and I love your idea.

I and many others would like this concept, its as close as you can get to fullbore and makes the shooter develop control skills to drive the rifle. I also agree with Lynn that some conditions would require the use of a bag.

A bag is more stable and will provide better results… it’s a hard one to cover. One way could be to instigate fore arm or fist support under the butt (as military rifle is shot) this would provide the support for shooters like Lynn and would counter the free recoil positions.

This is not intended to make FS harder .. its to make it easier, more simple. FO is for the experimental rigs, FS should be as it was meant to be .. a fullbore/ TR style rifle with a scope and a simple rest.

Bipod only would remove all issues in regard to stocks … but be warned, you would need to put in some control design issues for bipods.

[Tony Q]

What on earth did i just do

[Tony Q]

Alan .. there was a notion for FS a while ago that said:

'If its attached to the rifle it can be used' this is along the lines of your suggestion and its a good one ( in my view )

Again thismay come back to the issue of a 3rd class at some future point in time.

FS - the most purist form using just a simple bipod.
FSO - whatever you want but 308 or 223.
FO - for the developer and tinkerer.

Its almost like an A-B-C grade but grades equipment preference rather than shooter.

It could also be that F Open has 2 grades .. '308/223' and 'whatever caliber' this would lift the numbers in FO and still keep FS in an absolute purist format like fullbore is. As i have said before if you look at MBRC's 17 F Classers this would break down to:

4 - FO
4 - FSO
9 - FS

Either way, it still requires an extra badge for F Shoots and more cost. It may also encourage shooters to shoot local OPM's more often ???

[Tony Q]

Bully - eye

I know its FS dominated, but there isnt much wrong with FO in regard to equipment.

FO by default is an experimental class designed for tinkering and development with Ammo and Rifle design to get the upmost accuracy results.

Its an important class in that regard. Unfortunatly its a more expencive class to shoot and thats why we are seeing FO rifles and attitudes in FS.

This is why it needs correcting befor it gets so out of control it cant be fixed.

[Shane]

Getting back to the original question and not rules.
Depending on calibre and the way a shooter supports the rifle, a bipod may give vertical on the target. As in, when the rifle is fired with a bipod it recoils back and stops when the bipod feet run out of travel. If this travel is uneven or if a large calibre is running out of travel well before the recoil has finished vertical dispersion will occur. A benchrest will not show this if the shooter is consistant in their hold.
Regards,
Shane