Barrel Harmonics Demonstration and Questions

[oldracer]

I bought a new Armi Sharps 45-70 for a most excellent price just before New Years and yesterday got to try it out along with the full length scope that came with it. I had cleaned the barrel very well prior to shooting and also had wiped the outside with a light coat of oil since there was a chance of rain at the Dulzura range outside of San Diego. It took me about 8 shots to get into the black of the standard NRA triple bulls eye target at 100 yds. I had to move the front sight back to center of the dovetail which was different than the laser bore sighter pointed. I also played with the elevation adjustment to see that a full, half and quarter turn would do and then got down to some group checking. I was using the loads I had worked up for my Rolling Block and was happy they seemed to be working here too.

Just before I started, one of the other ROs said "hey look at the side of the barrel" so I did. I was amazed to see what looked like a sine wave starting from behind the fore end all the way to the muzzle. We looked at the other flats and they ALL had the same pattern in the light oil and were all in sync! He was an old time Army shooter as were a couple of others there but no one had ever seen the pattern like that. I checked my Rolling Block which had also been fired but it had no pattern at all.

The Rolling Block has an un-tapered, 34 inch Badger barrel and it is very heavy. The Sharps is a 32 inch with the standard taper that most Sharps seem to have. The RB has tang sights and the Sharps has a full length scope.

Any ideas as to what caused the marking? I am feeling it is pressure waves inside the barrel such as you see when a jet fighter turns on the afterburner but not why it showed up?

[405]

I wouldn't doubt that the evidence you're seeing in the oil coating is from the "wave". I know that some shooters will put a coating of baby powder on the barrel surface, shoot, then try to extrapolate some kind of "meaning" out of the patterns that show in the baby powder. Some have experimented with it and claim to be able to best position the front barrel rest based on the pattern of the wave. May have some merit. Too complicated for me to figure out.

[felix]

Typical barrel harmonics. Boolit should leave the barrel at a mid-point between nodes which is where the baby powder is heaviest. This is where the barrel is moving the LEAST. The nodes will change based upon placement of the front rest, or for that matter, any change in mechanical placement including personal. ... felix

[oldracer]

Thanks for the replies guys. For the present I am just happy that the bullets are leaving the barrel with a good amount of regularity and a fair amount of accuracy. I am still stumped why the Badger barrel showed none at all though with the same load? Possible much denser steel I would guess?

[Boz330]

The roller is a heavy barrel and most of the Italian Sharps (except Pedersoli) have much slimmer barrels so more barrel harmonics.

Bob

[cajun shooter]

Dead on Felix, While at the FBI Sniper School that was a part of one afternoons training. There is a spot on all rifles that will produce the best groups to over come the harmonics of each shot. I should have not said over come but working with would be a better statement. A lot of hinters don't realize how important it is. You can be in trouble fast if you take a wooden stocked rifle on a plane across country and then expect it to shoot to POA. This is even more important if leaving one temp range for another. The composite stocks might not look good but they will work better once the rifle is bedded as they will not react to the difference.

[John Boy]

Some have experimented with it and claim to be able to best position the front barrel rest based on the pattern of the wave. May have some merit. Too complicated for me to figure out. 405, piece of cake. Be sure to remove the forearm and shoot the rifle offhand. The powder looks like this
>>>>>>>>><<<<<<< Where the powder reverses direction is the NODE. Then put a piece of tape on the underside of the barrel and do it a couple more times. The mean distance between the pieces of tape is IT!

[405]

Yes, I understand the theory behind it- sine wave, nodes and all that. Have done it with a handful of Sharps and 85s. Seems to mostly work some of the time. But have noticed some exceptions. It's the exceptions and the some of the time parts that always get in the way of absolute statements on the subject. The usual and classic application for any such method is to predict the exact location of the front rest or forend pressure point when shooting. I've shot enough and some of my guns are accurate enough to be able to judge such things. If I powder the barrel and a or the "neutral" zone shows for example an exact spot 1 inch in front of the forend cap and I find by actual experiment by shooting, that exact rest spot DOES NOT yield the best accuracy then I WON'T continue to use that spot as the front rest location even though the gospel, as told by whoever, says it is. These types of things are academic for sure and are one of the reasons I load, shoot and experiment so much. Forces the mind to work and keeps the shooting sports interesting.

[John Boy]

Yes, I understand the theory behind it- sine wave, nodes and all that. Have done it with a handful of Sharps and 85s. Seems to mostly work some of the time.

So why did you post ...

Some have experimented with it and claim to be able to best position the front barrel rest based on the pattern of the wave. May have some merit. Too complicated for me to figure out.

Either you know or you don't!

[geargnasher]

Typical barrel harmonics. Boolit should leave the barrel at a mid-point between nodes which is where the baby powder is heaviest. This is where the barrel is moving the LEAST. The nodes will change based upon placement of the front rest, or for that matter, any change in mechanical placement including personal. ... felix

Barrel is stable AT the nodes, moves the most at the peak of the sine. I have had the best luck fine-tuning a "close" load to locate an actual node right at the muzzle. I noticed that ANY contact with the barrel by supports will change this significantly unless they, too, are at a node, then they seem to affect the amplitude. The problem I had was it was never the same way any two sessions. I would have had to load a "variety pack" for each range session or take my press to the range. But it can make a 3/4" 10-shot string into a 1/2" 10 shot string if it matters. These days, when I find myself obsessing over super-tiny 300 meter groups and fantasizing over building a bench gun, I take these little pastel-colored pills and in a few minutes I feel all better. :grin:

Gear