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Bullet wandering to direction of rifleing twist.
sticks1
Member Posts: 12 ✭✭
I've noticed for some time now while working up loads for several rifles, that when the powder amount is increased the bullet will travel slightly higher and to the right. I assume this is due the the right hand twist of the rifleing. Is this why most benchrest shooters have slower twist barrels?
Comments
Ergo a lot of long range benchrest match shooters and varminters choose barrels with a somewhat faster than average twist if they are going to be shooting at predominantly long range- heavier bullets buck the wind better and have better downrange performance.
I don't own any match guns, this is just my understanding.
So far as your observation goes, it kind of depends on what range you are shooting at and what the ballistics of a given cartridge are as to whether higher velocity will move the point of impact up or down in terms of what you are seeing on paper. I have some guns that actually shoot LOWER with more powder as the trajectory gets flatter at higher velocity. I've not seen them wander right though it is certainly possible with a clockwise twist.
Benchrest shooters use rather slow twists because they are not shooting at great range, their bullets are short and light, and Harry Pope among other Scheutzen shooters and gunsmiths found long ago that the greatest accuracy was with a bullet spun fast enough to be fully stable, but no more. They don't care if the bullet drifts, as long as they all drift the same.
Edit MAYBE velocity is a big facto.The times I saw it was at 1000 yard range on super bright super clear days in Hawaii back in the mid 1960's I was spotting with a 100MM UNERTL spotting scope . the cork screw was about 300 degrees of a full circle I was sitting with the scope about 6 inches to the left and 3 feet above the bore line of the rifle. Just like when you were a kid and shot a BB against the sky line you could see the arc and the screw. With a 40mm round from a m79 this of course is very low velocity and the flight can be seen with the EYE I hope some of the BLACK POWDER long range will chime in on this subject . Where is Quigley when we need him[:p]
Be that as it may, my discussion of weights vs. twist rates is still true enough. Just to add one thing- like Perry shooter said, the bullet path is a bit corkscrewed, but there is supposedly a 'sweet spot' where, in a bullet's flight, that corkscrew tightens up.
The most common sort shoots at 100, 200, and maybe 300 yards. He uses something like a 6mm PPC with 14" twist and 68 grain bullets.
Then there are long range benchrest shooters and they indeed use heavier/longer bullets.
But a 100 yard gun would not be at all effective at 1000 and a 1000 yard rifle would not be competitive at 100.
I don't have perry shooter's long experience, but I have watched a few bullet traces headed downrange, and a few actual BPCR bullets wich are visible in flight. I have seldom seen a "corkscrew' path. And when I have, it has not generally given a good hit.
sticks1 - did the loads that had an increase in powder, even though they were high and right, "group" well?
There are several comments provided that I generally agree with. But, this corkscrew phenomenon has me a bit confused. I envision a corkscrew as just what the name implies. If this is true, then the amount of deviation in the amount of the corkscrew would indicate how the sucession of bullets fired will print on the target, regardless of the range at which they are fired. I personally have never seen a corkscrew in any of my spotting observations. The only deviations I have seen were wind deflection, the occasional "boo-boo" by the shooter and the occasional destabalized bullet that ended up on the paper but as a "keyhole" hit. Yes, there is a "bullet trace" that is visible through bino's or spotting scopes that is caused by the vortex caused by the bullet passing through the air. This I have seen. But as to the "corkscrew" effect, this one has eluded me in all my years shooting at Dam Neck (Little Creek Navy Amphib Base) Virginia and at Quantico Marine Base.
jonk - the twist rule is "the rule" but there are exceptions. My 1:8 twist match AR likes the 75 to 80 grain bullets but out to 300 yards will shoot 55 grain V-Max Hornadys right along with the heavier stuff albeit maybe a little lower. But, maybe I just have a gun that likes "everyone". Also, my 6XC will shoot the 115 grain Berger and Sierra match bullets so well that it's scarry. But, it will not shoot the 105 grain A-Max Hornady. Haven't bee able to figurethis one out yet. Outside of that, I stick with "the rule" depending on what bullet weight/length I plan to shoot.
sticks1 - I had and Interarms Mauser Mark X in 308 Winchester years ago. This rifle shot anything I put through it. 125's 150's 165' etc. Point of impact was different for each load/bullet but each one grouped exceptionally well. Even if I changed powders or powder amounts, that rifle would still print tight groups. I simply adjusted my sights to where the load wanted to shoot and never looked back. I am not really sold on the "out to the right" ideal, but I would imagine it is possible, though I have never experienced this happening as a general rule on any loads I developed for any of my rifles. There is a lot happening when a round is fired. Barrel harmonics, though not the only factor, is a major key to where the bullet strikes and how accurate each following round is. If the harmonics change, chances are so will the flight of the bullet, point of impact (high, low, right or left), and of course how accurate your load will be. (You may ask why I "used to have" the Interarms - A period in time where I suffered a lapse in intelligent decision making whereby I sold the 308 in favor of buying something "new". I have regretted that decision ever since.)
Hope this helps.
To all else, I hope I didn't step on any toes. If there is something that supports some of the comments provided, I am open minded enough to be "educated and enlightened". Until then I can only rely on my experience and observations. More info on pitching bullets out to the right on "right hand twist" barrels would be most welcome.
Cheers
Kinda deep (at least for my shallow mind [:D] ), but a good read.
The twist rate pulling the bullet to the direction of the rifling twist is called "yaw of repose". This happens as the bullet has become sub-sonic to a much greater degree. somewhere around 1200yds (from what I recall) is where your standard 30cal magnums will be noticeably affected.
and YES,..that is why as you increase powder,..you increase RPM, which will show up on target.
In benchrest we shoot for utmost accuracy. Physics has taught us through the years,..that the SLOWEST twist which will adequately stabilize a bullet of a given weight/length,..is the best choice. This way less intrusion into the jacket,...and therefore less chances of core seperation causing flyers or bullets being unexpectedly pulled one way. Remember,..it is all about the accuracy.
I use fast twist barrels so I can load anything I want,...light or heavy. best of both worlds. BUT,...I don't shoot 100-200yd class BR since I prefer 600-1000yds. In 100-200yds,..I shoot factory class to keep from building yet another competition rifle.
To all, I consider myself "educated and enlightened". Never knew there was that much to it all. Learn something new every day. Never too old (53) to learn.
Cheers
I understand the over stablizing problem with a faster twist and I too was, and still am bewildered about the cork-screwing thing. If the cork screw theory is real we all might have a problem hitting anything at any different distance other than what we were are sighted in at. Just when I think I'm starting to understand shooting I get a curve ball like this. Thanks again everyone!!
What you should have asked about is "barrel harmonics", which is another bag of snakes, but with handloading you can tune your loads to match your rifles needs.
Stick with the load tha gives you the tightest groups, and adjust your sights to match. Before you get to excited about 1 tight 3 shot group, run the same combo a few more times. If it stays consistantly tight, than you've found a winner.
Cheers