shooting with a cant block

[Daryl]

A sand bag with a leather thong tied tightly in the middle (makes 2 wings) gives similar if not the same support as a rabbit ear sand bag as used on modern 3-legged bench rests.  This will help hold the gun vertical as the ram-rod and entry pipe would sit in the valley and the sides or 'walls' would give support to the barrel.

This is allowed, but not a bolt on device which changes the gun into a match rifle, just as the additon of a closed (peep) sight would elevate the gun to match rifle status. Seems to me, I noted that shaders were allowed as sometimes the sun is quite nasty at this range.

[Daryl]

A sand bag with a leather thong tied tightly in the middle (makes 2 wings) gives similar if not the same support as a rabbit ear sand bag as used on modern 3-legged bench rests.  This will help hold the gun vertical as the ram-rod and entry pipe would sit in the valley and the sides or 'walls' would give support to the barrel.

This is allowed, but not a bolt on device which changes the gun into a match rifle, just as the additon of a closed (peep) sight would elevate the gun to match rifle status. Seems to me, I noted that shaders were allowed as sometimes the sun is quite nasty at this range.

Proposed rule changes:
1/. --------- traditonal styled (CHANGE TO) hunting or trail-walk rifles with open, barrel mounted sights only. Your calibre will be noted on your scoring targets. (delete "any weight")
2/. change - "No match rifles, no false muzzles, no cant blocks."
3/.OK
4/.OK
5/.OK
6/.OK
7/.change  - "Preparation and practise time of 25 minutes for equipment settup and practise/zeroing."
8/.change  - "Patched Round Ball only - no exceptions."
9/.change  - "10 shot match - 5 per each of 2 scoring targets shot in 2 relays - 20 minutes per relay.
10/.OK
11/.OK
12/.OK

As yet - we don't have trouble seeing all 5 shots on each of 2 scoring targets (I scored CF prone & Pos. targets for years without trouble where prone targets were more tightly grouped than any ML targets I've seen yet). When 'holes' become difficult to score - we'll adjust the shooting regime as necessary.

[smokinbuck]

Kerry,
Okieboy has pretty much covered the "practice" time. At most matches I have been to the practice relay is determined by the shoot master.
Mark

[okieboy]

 Daryl, I am not taking exception to the sand bag, your shoot, your rules, but I would like to mention as information that the gun being movable side to side and forwards/backwards on the chunk (even with using cant blocks) has become an enforced rule at the York and they make plain note of it in their preshoot announcements. I think that the feeling behind it is very similar to your "hunting gun only" rule, that making the gun barrel captured on the chunk violated the spirit of what they wanted their shoot to be.
 NMLRA chunk rules specifically mention shaders and consider a globe style front sight to be a shaded sight as long as it does not contain an apperture inside. The longer a match takes, the more valuable that shader becomes, because of the light continually changing. At some old matches the targets were shaded for the same reason.
 Those rests are sure nice prizes.

[Daryl]

Thought I read somewhere that sand bags were allowed in chuck shooting - might have been NMLRA rule or thier description of the shooting itself - or someone elses - doesn't really matter much where I saw it or perhaps thought it up myself - don't know. Like you said, those are the rules at our shoot.  I don't even care if they use the front bag off a benchrest, on the log or chunk.  Just must use a hunting rifle or trail walk rifle.  A globed sight with a blade or post is not a peep sight. I see that as a shaded sight. Yes I know allowing buckhorn sights is almost allowing peep sights - at the stage where we are, with just over 7" winning, and 2nd and 3rd taking the measurements over 9", it will be a while before we have to get too picky.

[Paul Griffith]

Gotta join in the fun.

As to where to rest a chunker there's a couple of other factors that exist.

#1 is barrel flex. I got to thinking about this years ago & made up little fixture to measure it.  I attached a bar of steel (say 1/8' X 1"),on edge, to the top of the barrel. One end fastened at the back sight, the middle connected to the barrel mid way between the sights & the other end placed a dial indicator against the barrrel at the front sight. So it would show any sag or change in the straightness between the sights.  With the muzzle rested on a chunk & the toe of the gun settin on a concrete floor I pressed down with my thumb or finger at the breech.  With very little effort I could produce a bend that would amount to an error of 2 to 3 inches at 60 yds. Probably more as I just figured it as though the low point was a point of a triangle. In reality it's an arc & the ends point up more than if it were a triangle.  So the best place to rest a barrel with this in mind is directly between the sights. As what ever the back sight goes down, the front sight goes up & life is good.  This setup was probably with a 48"X 1 1/4"X .45.

But this brings us to the second problem. That is human error at the butt of the gun. Say a sighting error or a movement during recoil. This problem is exagerated the further back from the front sight you move the pivot or resting point. If we were to rest the gun three foot from the butt, any error at the butt would be 60 times worse at the target. By resting 6 foot from the butt the same error would only be thirty times at the target. So with this in mind the best place to rest a barrel is under the front sight.

For the most part I just split the difference between these two setups, which puts me a 1/4 of the distance between the sights back from the front sight.  I will say that the heavier the barrel is, the more you can slide out to the end for the rest. That & I think that they tend to flex somewhat the same from shot to shot.

Paul

[Daryl]

Gotta join in the fun.

As to where to rest a chunker there's a couple of other factors that exist.

#1 is barrel flex. I got to thinking about this years ago & made up little fixture to measure it.  I attached a bar of steel (say 1/8' X 1"),on edge, to the top of the barrel. One end fastened at the back sight, the middle connected to the barrel mid way between the sights & the other end placed a dial indicator against the barrrel at the front sight. So it would show any sag or change in the straightness between the sights.  With the muzzle rested on a chunk & the toe of the gun settin on a concrete floor I pressed down with my thumb or finger at the breech.  With very little effort I could produce a bend that would amount to an error of 2 to 3 inches at 60 yds. Probably more as I just figured it as though the low point was a point of a triangle. In reality it's an arc & the ends point up more than if it were a triangle.  So the best place to rest a barrel with this in mind is directly between the sights. As what ever the back sight goes down, the front sight goes up & life is good.  This setup was probably with a 48"X 1 1/4"X .45.

But this brings us to the second problem. That is human error at the butt of the gun. Say a sighting error or a movement during recoil. This problem is exagerated the further back from the front sight you move the pivot or resting point. If we were to rest the gun three foot from the butt, any error at the butt would be 60 times worse at the target. By resting 6 foot from the butt the same error would only be thirty times at the target. So with this in mind the best place to rest a barrel is under the front sight.

For the most part I just split the difference between these two setups, which puts me a 1/4 of the distance between the sights back from the front sight.  I will say that the heavier the barrel is, the more you can slide out to the end for the rest. That & I think that they tend to flex somewhat the same from shot to shot.

Paul

Barrel bending - interesting - certainly could be - especially a swamped barrel with narrow waist or very long, slim barrel. 

Point of matter is all guns will have a 'sweet spot'.

My 36" .40 cal . 7/8" straight octagonal barrel, probably much stiffer than a swamped barrel, still shoots best when rested on the second pipe when shooting prone, off a chunk.

When shot off the bags from a bench rest, I've always rested it on the stock at the entry pipe.  It has a VERY short forend- maybe 12" long from the lock, so that's where I've been resting it.  It's given me many 1/2" groups. Next time I bench it, I'll try the second pipe, etc.

Even modern rifles have a 'sweet' spot for resting on the stock.

[smokinbuck]

Paul,
Good to see you on the site. If you remember at the York a number of years back I "think" John Braxton brought a rifle with a 6' barrel, 2 piece, and when he put it on the block you could see it flex. I guess you could call that an exception. Thanks for the tips.
Mark

[Roger Fisher]

I was getting a 1 O'clock flier at times till I found thru trialand error the sweet spot abt a foot behind the muzzle.  
This is on my half stocked 1 1/16th straight 47 cal 40 inch barrel.  

[KNeilson]

Wow, thx for all the responses. All this has given me a heap of information to go thru and test. Don and Dan, I  think I understand what your trying to say, looking for the spot the vibration passes thru the barrels axis. This would be the dead spot or where the dust wont bounce. With the barrel out, I`ll give it a try, mark the spots, and then re-assemble and proceed to try on the rest to see what affects I get. Paul, I like your thoughts too. I have a barrel Ive spent some time on. It had enough tension in it that as you rolled it on a support in the middle, it would "droop" at one particular flat all the time. This being in the direction I would get strange fliers as I altered charges. For eg, the more powder you put in, the farther left it shot. At 100 yds sometimes 8 in. or more. fwiw the barrel is a .54, 38", swamped C weight transitional. Took a while to sort that one out. Daryl, I`d never considered some of your suggestions for a sand bag. I be giving them a shot (pun intended  ), I have a commercial sand bag, "saddle" shaped, and altho it softens the stock to rest connection I dont really like how it feels. The rifle kinda wallows in it. Okieboy, thx,

Those rests are sure nice prizes.

Some of my favorite "trophys" are like the chunk rest, a usefull hand made item that reflects the "heart" of the competition and competitors involved. I`m glad I got it. Anyways, from here I have a fair bit of work, thx again for all the help..      Regards..   Kerry   

[Daryl]

As to the vibration nodes in the barrel, once in a stock and pinned, they change from free held - they must change - have to change just as freefloating a modern barrel or adding forend tip pressure changes it's vibration patterns. I think you have to shoot the gun to find where the best spot is.

[T*O*F]

If the purpose of a cant block is to keep the gun from canting, shouldn't it be called a can't cant block?   

[KNeilson]

So I went home last nite and tried some of the suggested methods of finding out how/where a barrel vibrates. First, clamped by the breech plug, horizontally in a vise, I went up and down tapping with a soft screwdrivers handle. I could find several spots that were different. Tried again with coating the bar in powdered soapstone, no luck here.   Once again tried with the bar suspended from the tang, here it rang much louder and longer. Similar noise to a door chime or length of pipe (duh) . I stuck a strip of tape to the barrel, marking the "spots" using both my bare ears and also with a mechanics stethoscope. When I stood back and looked, it dawned on me. Ive marked the points the "wave" passes thru as it travels up and down the barrel. These same spots are what a guitar player uses to make chimes or bell sounds as opposed to a twang when plucking a string. As measured, they are approx 1/2, 1/3 and 1/4 barrel length, which is 18.5, 12.5 and 9.5 meausured on a 38" length. How this will affect shooting , I cant say. But at this point I do agree with Daryl that all this changes once the barrel is stocked. Starting to understand why some barrels "float". Having these points marked now, next is to see if what effects take place using them..btw, I discoverd this, an interested applet illustrating vibration in a bar...       Kerry

http://www.falstad.com/barwaves/j2/

[Daryl]

That picture of bar in action makes one wonder how a swamped barrel vibrates as well as the changes that take place in the pattern when it has a different profile. Then - what changes take place when held to the stock with 3 or 4 pins, 1 through 4 wedges, with soldered as opposed to screwed on underrib - no rib- ribs top and bottom jointing two barrels - what abotu calibre to outside dimension ratios  - round or octagonal.  The octagonal bar is much stiffer - how much? What changes take place when running tapered octagonal as opposed to straight octagonal - or octagonal to tapered round, what about tapered octagonal to swamped round?

My head's starting to hurt - I think it might be easier to shoot it for a day and find out the sweet spot?

[KNeilson]

I think it might be easier to shoot it for a day and find out the sweet spot?

Hey Daryl, I agree, and soon will be doing that. But, since I asked the question...I owe the respondants at least to check out some of the theory. Some of the things youve mentioned may mute, or amplify the way the vibrations travel, I was also considering the charge. atm it makes sense to me larger charges/calibers would also affect greatly how the vibrations are generated. Starting to understand why large, stiff  barrels are more (repeatably) accurate.     Kerry

[Daryl]

Nothing new there as to barrel weight - heavy usually shows better accuracy - I agree with the testing various scenarios too =  all interesting & with promise.  As with most firearms, theories & methods of arriving at a goal must be tested out with actual firing as usually some tweeking is necessary.