Lt 32
- Thread starter r44astro
- Start date
Gene Beggs
Active member
It isn't easy to explain and it took me several years to understand it. It's a thing called positive compensation. I'm not very good at explaining things like this. I hope Keith Sharp (MKS) can help us out on this one.
Gene Beggs
This particular barrel looked real good, nice even finish. Very small tooling marks(might not be the correct term). The lands had very fine marks. Looked good. Cleaned up real good. At about 400 rounds. It would shoot 9-10 rounds and then you would get heavy bolt lift. Clean up good. Then heavy bolt lift. The group would also open up. A lot of 4 and 1 groups. Myself and several others checked equipment. Did this. Did that. At 500 rounds. I had had it. So being early spring. Let's get in there and get a good look. Looks good. Used patch out overnight. Looks good. Pulled out Iosso. Tried patches first. Cleaned up good. Looked good. Then I remembered seeing Jack N. using Iosso with a blue brush. So I did that. Scrubbed about 20X. A bunch of patches. Cleaned it out real good. Then took a real good look. nice and slow. same as always. I noticed 2 lands that the edges were not parallel. 2" in for about 8" the edges would get narrow. Just so ever slightly. The top and bottom.
The other thing. Fire cracking at about 400 rounds. Ever so slight. Thought that was normal. But, I don't load hot.
So the bore scope paid for itself.
I did shoot that barrel one more time in a score match. Same thing. 8-10 rounds heavy bolt lift.
Put the old barrel back on. Has over 3000 rounds. WE were back at it. Very happy at the last Score match. Last 2 Varmint shoots. 200-200. 192-200(But, 4 shoots were where I aimed sooo........). All good again.
Time to find a tune on the new barrel.
M
mks
Guest
Gene,
I'll give it a "shot." If every cartridge in a group produced the same muzzle velocity and bullet exit time, compensation would not be required. But if we take as a given that there will be a range of velocities and bullet exit times within a group, we know from external ballistics alone that if the bullets are launched at the same angle, the slower bullets will hit the target lower. To get them to hit the target at the same elevation, we want to point the muzzle higher for the slower bullets. How do we know which bullets are slower? They are the ones that also travel through the barrel slower and have a later bullet exit time. How do we achieve compensation without knowing a priori which bullets are slower? We tune the system so that the muzzle angle is rising throughout the interval when all the bullets exit. For perfect compensation, the muzzle needs to be at just the right angle to offset the extra drop that occurs for the slower bullet at the distance we are shooting. At longer ranges, we need the muzzle angle to be higher for the slow bullet than at short range. Thus the muzzle angle must be increasing faster, because the delay time for the slow bullet is the same. VarmintAl shows a nice graph of this principle for a 22RF at 50 and 100 yards. I hope he doesn't mind me attaching it here.
Geoffrey Kolbe wrote a nice article about compensation here: http://www.geoffrey-kolbe.com/articles/rimfire_accuracy/tuning_a_barrel.htm
I think of tuners as fine-tuning the high frequency noise out of the muzzle angle path. Changing yardages requires a substantial change in the overall angular velocity of the muzzle. In principle, this could be done by moving the tuner (a lot), but I choose to make the big change some other way (e.g., moving the forend in the front rest) and keep the tuner for fine-tuning, so that I don't lose track of multiple turns.
Hope this helps,
Keith
Gene Beggs
Active member
Thanks Keith
See what I mean guys; Keith can explain things perfectly while I'm thinking about it.
Thanks again Keith.
Later,
Gene Beggs
See what I mean guys; Keith can explain things perfectly while I'm thinking about it.
Thanks again Keith.
Later,
Gene Beggs
Tim Singleton
Member
Which direction do you move the forend? Further forward or move backward? What amount of movement ?
M
mks
Guest
No guarantees, but usually backward. My 200 yard position was 2" back from the 100 yard position. You need to do ladder tests at multiple positions to figure out the best position for each yardage.
H
HopeToBe
Guest
This helps, although I might be missing the big picture. Gene was kind enough to explain this to me a few years ago and this makes perfect sense to me. But to put it in another way. If we tune at 200 there is no need to re-tune it to 100. But a 100 yard load might not perform well at 200?
Or, of course, I might be a slow learner after all.
M
mks
Guest
Compensation does tend to work this way, i.e., proper tuning is more critical as yardage increases. A rifle tuned for 200 won't be terrible at 100, but a 100 yard tune could be awful at 200. The take away message, though, is that each yardage needs its own individual tune.
Apollo
Jason Stanley
"Compensation does tend to work this way, i.e., proper tuning is more critical as yardage increases. A rifle tuned for 200 won't be terrible at 100, but a 100 yard tune could be awful at 200. The take away message, though, is that each yardage needs its own individual tune."
Since this thread has turned into a tuning thread - I assume it is ok to ask this question:
One of my traveling partners and I always argue(discuss) about this; Are there separate tunes for windy vs calm days?
I think yes - but could be completely wrong. I can also see compensation working for this. If one tunes for "windy" days = it will still be ok on calm days (but not as good as the one who tuned in the calm). If one tunes on calm days = that same tune could be terrible on windy days. Again, this is just what I think and have not done any tests. Just looking for others who may have tested to confirm or disprove this idea.
The wrench in all of this is still how well our brain is picking up on the conditions. Which (maybe) compensation fits also??? Our brain has to be so much more focused at the longer distances and/or when the conditions worsen. A slight loss of focus (missed an angle change - missed a tail movement, etc) could result in a "bad" shot which may lead some to blame on tune. I think knowing when you missed conditions verses having a "bad" tune is a huge hurdle to cross to be able to get to that "next level" of shooting. A lot easier typed (said) than done.
Very interesting thread - thanks to all those who are writing.
Since this thread has turned into a tuning thread - I assume it is ok to ask this question:
One of my traveling partners and I always argue(discuss) about this; Are there separate tunes for windy vs calm days?
I think yes - but could be completely wrong. I can also see compensation working for this. If one tunes for "windy" days = it will still be ok on calm days (but not as good as the one who tuned in the calm). If one tunes on calm days = that same tune could be terrible on windy days. Again, this is just what I think and have not done any tests. Just looking for others who may have tested to confirm or disprove this idea.
The wrench in all of this is still how well our brain is picking up on the conditions. Which (maybe) compensation fits also??? Our brain has to be so much more focused at the longer distances and/or when the conditions worsen. A slight loss of focus (missed an angle change - missed a tail movement, etc) could result in a "bad" shot which may lead some to blame on tune. I think knowing when you missed conditions verses having a "bad" tune is a huge hurdle to cross to be able to get to that "next level" of shooting. A lot easier typed (said) than done.
Very interesting thread - thanks to all those who are writing.
Last edited:
Dusty Stevens
Hollow Point Dispenser
lets get back on track- powder valley has lt32 in stock.
Dusty Stevens
Hollow Point Dispenser
I hate when good reading material gets lost in topics most may just scan by. If you opened this up and seen powder valley has lt32 in stock in 2014 you may not scroll on thru to learn that some people get so far out and seperated from reality they tune their guns different at 200 than 100. This should be in a whole new topic but anyway- yall carry on.
Dusty Stevens
Hollow Point Dispenser
And chris- i wasnt knockin anybody at all so dont take it that way. Just trying to make the site easier for visitors to learn from
M
mks
Guest
Jason,
Interesting question. There is a clear answer for headwinds and tailwinds. They both screw up the tune, because tune is based on differences in drop due to muzzle velocity differences at a particular range. Bullets drop more for a headwind, and less for a tailwind. The answer is the same for crosswinds if we include the magnus effect. The effect depends on wind speed and is different for left and right crosswind. Unless the wind were really consistent, it would be difficult to adjust tune based on wind. It isn't as simple as having one tune for "calm" and another for "windy." There is a different tune for each wind speed and direction.
Cheers,
Keith
I have some friends that shoot benchrest among themselves, and occasionally in a real match. Since it is close most of their matches were shot at Manatee, and when there are big matches at manatee it's always windy. They were benched close to a national champion shooter and noticed his windy day tune was the same as my friends decision was (Jon was the gambler of the group). The decision was to load as much powder in the case as they could get in, remember its a really windy day (way more than normal for manatee). Have any of you ever heard of this before? Long range shooters sometimes say that your only friends are speed and BC, this would support the full case theory, I guess.
r44astro
New member
Thanks Dusty!
If this is how threads evolve, I shall not again notify folks of powder, primers, bullets, being available.
Bill Greene
adamsgt
Jerry Adams
Don't do that
Bill. I know if someone posted availablility of Bullseye or Unique I'd be ecstatic. Of course, it's be gone by the time I got to the site. The evolving of threads is mysterious and wonderful at the same time. I understand Dusty's concern. Sometimes an important and significant topic pops up in the middle of a thread on something entirely different and you wouldn't know about it by the title of the thread. It'd be helpful if there was a way to tag threads by subject matter if there were more than one topic under discussion. My programming days are too far behind me to come up with a cute little algorithm to implement that.
Bill. I know if someone posted availablility of Bullseye or Unique I'd be ecstatic. Of course, it's be gone by the time I got to the site. The evolving of threads is mysterious and wonderful at the same time. I understand Dusty's concern. Sometimes an important and significant topic pops up in the middle of a thread on something entirely different and you wouldn't know about it by the title of the thread. It'd be helpful if there was a way to tag threads by subject matter if there were more than one topic under discussion. My programming days are too far behind me to come up with a cute little algorithm to implement that.
r44astro
New member
And,,,, your point?
I could care less what happens to a thread I start, will not be a problem in future.
Bill Greene
I am not a great shooter, yet. This year I shot, Cactus, Shamrock, Riverbend, Hog Roast, SuperShoot, Unaka, IBS Nats, Rattle Snake, Brocks Gap. I know how important powder and primers and bullets are to us that compete. That's all I have to say.
Bill
I disagree with the lets get back on topic thought. Some of the best reads on this sight have evolved from a basic question or statement. Lets face it, knowing that powder valley has LT in stock, really isn't all that interesting. Talking about tuning at different yardages in different wind conditions is much more interesting. To me at least. Lee
r44astro
New member
Lee Bite Me| Start your own thread about tuning at 100/200. See you at the NBRSA Groups Nationals which is the most important shoot if you want to qualify for the world next year at St. Louis.