Finding the "sweet spot"

[Dai.S.Loe]

I may be preaching to the converted here but I thought I would pass this along to those interested.

A projectile passing through a barrel sets up vibrations.

The study of such vibrations is called harmonics.

There will be a spot on your barrel that oscilates less than the rest

This is the sweet spot.

If you are using cross sticks for your shooting or a rest it would be best if you place this " sweet spot' on the sticks.

Simple way to find the sweet spot. Especially if you have an octagonal barrel.

Dust the top of the barrel with lots of talcum powder.

Then in a standing position with no rest, fire the rifle.

The oscilation of the barrel will either throw the talc off or move it to the sweet spot.

Where there is the largest ammount of talc left is approx the spot.

Mark this spot somehow, i was told to use thin masking tape.

repeat the process a few more times. you shoud now have discovered an area where the talc seems to stay when the rifle is fired.

This is the place where you should rest the barrel on the cross sticks or rest.

There is less vibration or oscilation at this point and therefore you shoulds get less jump or disruption of the projectile when using sticks.


I hope i have explained this properly and that it makes sense. Also I hope I am not as I said, preaching to the converted\.

Dai.

[gw]

Had not heard of this method before Dai, I've always just shot groups to determine it. Some rifles seem more sensitive to this than others, which makes some sense I guess.  Have to give it a try sometime, just not on a windy day!

                                                        GW

[Silver Creek Slim]

Thanks, Dai. I'll have to try it.

Slim

[Four-Eyed Buck]

Hmmm, interesting..........

[john boy]

Dang Dai ... this is super!  All along, I been beating the barrels with a hard rubber hammer and listening to the harmonics.

Fer sure ... copied your post into my references.
Cheers

[Dai.S.Loe]

There is a much better explanation of the "sweet spot" on this website than I have been able to give.

Also another method od finding the spot is given but from my reading it is a lot more involved than the method I just stated.

It worth a look at this whole site.

I've actually printed the whole site off and the hard copy now resides in my information folder along with my shooting and reloading records.

http://www.longrangebpcr.com/Sweet.htm

This site has been mentioned here (I think) and it would be a great idea for anyone interested in long range BP to have a look.

As I work in the computer industry I spend a lot of time on the internet.(checking connectivity )

I'm always supprised at how much information is out there once you know how to look for it.

Dai

PS    The talcum powder method was shown to me by a gentleman over here who, dare I say it, lives for BPCR. He travels the world going to matches when he can and in NZ is one of the most knowlegable people on BP shooting I have meet.

I went to a training lesson with some mates one night. We spent almost 4 hours listening to him talking and I could have gone on for even longer. Unfortunately as he has just had a bad road acident he will not be able to shoot for about a year. I know he will still be involved and still help out us newbies over here.

[Bristow Kid]

very informative article but damn thats alot of loading and reloading.  I think I will try your method Dai sounds cheaper and easier.  And thats a very informative website too.  Thanks alot pard.

[Bristow Kid]

very informative article but damn thats alot of loading and reloading.  I think I will try your method Dai sounds cheaper and easier.  And thats a very informative website too.  Thanks alot pard.

[Dai.S.Loe]

very informative article but damn thats alot of loading and reloading.  I think I will try your method Dai sounds cheaper and easier.  And thats a very informative website too.  Thanks alot pard.

It sure is a lot of shooting but he explained "the sweet spot"  better than I had.

Went out yesterday with a mate and tried the talc method on his new rifle.

He has a John Bodine Rolling Block in 45-90.

Method worked fine.

He finished up with a piece of tape on his barrel where the talc didnt move as much.

Took him 5 shots to find it accurately.

Thats where he now rests the barrel on the cross sticks.

I have read that site from start to finish a number of times and I am still finding stuff I missed.

Dai

[reloader4410]

IF you used different bullet weights would that change the sweet spot? what about powders 2f 3f subs smokeless ect? thanks in advance.

[Dirty Dan Dawkins]

ok I just found this and have a question. You stated shoot standing, no rest. Am I to assume no support from the offhand on the forestock? Also, does this method apply and is it effective for offhand shooting?

[john boy]

Dan:  The shooting position is - standing offhand.  Yes, the forearm is held and do not grip the barrel in any manner.
If one does the test from bench rest or holds the barrel, the sine wave harmonics will be changed

The sweet spot (when determined) is rested on your shooting sticks at that point or on a forked bench rest.  If you are shooting from rest on sand bags ... lay the back of your hand on the bags and hold the forearm.

Glass bedding the forearm also helps control the barrel harmonics but that is a whole different subject

[Loco Smith]

Ok Ok I got that sweet spot. What you're really saying is this is to find the spot where the barrel whips less with a particular load (while resting the barrel on an object), IE, bullet, powder etc. Now every one knows that it is said not to rest your rifle on a solid object due to it will jump and shoot high. What I just read is good info but that only applies to rest shooting or sticks. To clarifie for us learning types, when we are trying to find loads that shoot well we are changing and finding where the barrel whips or harmonics and the impact is consistent so we hit where we shoot. I for one never rest my barrel on anything, but get as close to the action as possible. I will have to try this then check my loads, to see what happens.. Did the 45 90 shoot well or ??Thanks Loco

[john boy]

For those that want to be totally conversant on the subject of barrel harmonics, read this .... http://www.varmintal.com/atune.htm

For those that want to provide increased accuracy shooting rifles offhand ... do a search on the Internet: How to glass bed a rifle

Happy Shooting!

[Delmonico]

Why John Boy are you suggesting that I should glass bed my Sharps?    To late I did that 8 years ago.

[Loco Smith]

Ok, I'm trying to put this in usable terma for me.. All material, barrels pipe etc have a natural point where the natural freguency can be set of, at that point the item vibrates like a tuning fork. From what I know you are trying to get at the right point on the sign wave so you don't increase the effect. But to change the harmonics (natural frequency) you either have to stiffen or add mass, to change this, Period, unless you change the the load for the paticlular rifle, then this all changes, again, and that point at which you refer to as sweet ain't sweet no more. That why when or if you glass the barrel in the forarm it added mass and stiffened)  and changed thesign wave raised the natural freg. All of this is of no help if you find the correct load and combination of bullet and powder, That is what people have been doing by changeing their loads (tuning the rifle to load)till they find one that works. But you can't shoot all bullets and loads by finding this spot. If so please send info to qualify data.How did the 45 90 go. This natural freq is why the longer barrels and heavier loads are hard to tune, either the barrel needs to be shorter or heavier and it would easier to tune loads.. Maybe, vibration has been used for years and is now being applied to rifles and its impact so time will tell..I read the other site, lots of high tech, but practical will be better..   Thanks for the info gave me more to think about Loco

[Loco Smith]

Ok Now I have reed all I can find, for sure good info but I have a question..Forearm? do you bed this? If so How. I relieved mine at the action and the sides only touching along the bottom.. It has taken a while to get it to shoot good groups(45 70). I will try the sticks and tape see i9f it gets better.  Thanks Loco

[Delmonico]

I did mine fully and relieved it at the action, I also did the butt stock fully.  Also did the same with my Lo-Wall that has been rebarreled to 22 Hornet.  Both shot much better.  I thing part of it is just plain dampining as much of the vibration harmonics ass possible.  The less vibrations, the more uniform things are from shot to shot.  That's why the benchrest folks like a short thick barrel.  Thats what they always tried to do, ellimanate the vibration.

The coming into sync with the vibration is something I never really heard put in such terms till Winchester/Browning put that ugly ajustable corncob on some of their rifles, the BOSS system.

Before that all I'd ever heard of was reducing the vibrations.

[john boy]

... I also did the butt stock fully

Aw Shucks, Delmonico.  Now EVERYONE is going to be shooting quarter sized groups.
Seriously, glass bedding the butt stock dampens Newton's Law of an equal and opposite reaction.  By doing so, the sine wave through the receiver and barrel is flattened.  Accordingly, shooters get a better feel for each reload whether to break the shot before-at or after the sine wave reaches the end of the muzzle.  An easy way to realize this process is ... at what point is better accuracy is obtained with the raised recoil of a revolver.

All this darn stuff is mind boggling.  I used to think - Point, Aim and Pull the Trigger for Accuracy.   Now ... 

[Delmonico]

Well it can get more bizzare than that, I have a 243 Savage 99 that is a tack driver with a proper load and it has a forearm relileived from the reciver and the forearm is pillar bedded.

I started with this about 20 years ago when I used to read gun rags, they had all kinds of articles on glass bedding bolt guns and I said, "Well why won't it work with single shots and lever guns.

By the way I in no way shape or form consider it any kind of cheating, some of the accuracy smiths of the time period use long hours of wood fitting and hide glue to create the perfect wood fit.  No any one with some amount of skill can aceive the same thing.

BTW if one does this, these single-shots and lever guns often need different parts bedded one at a time so you don't make the fit permanant.  Look things over well to make sure you don't bed to much at once.

Next project for me is a 375 Big Bore 94, non-angle eject type, I think I need a sledge hammer that has a surgeon's precision.