speed vs tune
- Thread starter Link
- Start date
Since I shoot and hunt all year around, I have definitely experience changes in POI in elevation.
Using extruded powders instead of ball powders have minimize the affect but it is still significant enough for me, that I have make about 1/2 to 5/8 on average moa corrections in elevation.
I think it is the changes in air density, from cold temperatures to hot temperatures that has the most effect on POI changes. Then there is also the increase in image during hot sunny days.
I don't "get my tuned" back by monitoring fps changes, I merely do a sight in check at the range and adjust the scope accordingly. I have enough experience now with my loads and each rifle to fairly accurately predict the changes, but I always check the sight in when the seasons change.
Using extruded powders instead of ball powders have minimize the affect but it is still significant enough for me, that I have make about 1/2 to 5/8 on average moa corrections in elevation.
I think it is the changes in air density, from cold temperatures to hot temperatures that has the most effect on POI changes. Then there is also the increase in image during hot sunny days.
I don't "get my tuned" back by monitoring fps changes, I merely do a sight in check at the range and adjust the scope accordingly. I have enough experience now with my loads and each rifle to fairly accurately predict the changes, but I always check the sight in when the seasons change.
DaveTooley
Gold $$ Contributor
POI and tune are two different things. When I tune up a rifle I want know the high and low charge weight at that point in time where accuracy isn't affected. That way I have a baseline to work from as temps change. If I tune in the spring I'll be towards the low end knowing temps/pressure will go up. The goal is to stay in the window. If I tune in late summer early fall I'll be at the upper end. Depending on the width of the window I'll make charge weight adjustments as needed. This is comes from years of shooting 1K BR comps where we can't load and tune like short range BR can do during a match.
Bill Norris
Back in the Day
I don't believe tune is dependent on speed. Atmospheric conditions play a much bigger role in tune.
Basically, only in regards to "tune", I say YES. But it's not so much fps as it is barrel time, though there is a close relationship. In terms of any POI shift, atmospherics plays a significant role as Bill Norris points out, but not in terms of "tune".
Last weak I was tuning my 6.5x47L in the mid seventies velocities were running 2890 ish the tune was good, this week a cold snap came rolling in and temperatures drops to low 40's and velocities then dropped to 2850 with a 1.5 inches of vertical in the groups. Mr. Tooley you are spot on Sir!
Temp affects in bore time as well as velocity to some degree. Density also plays a role both in terms of internal and external ballistics, using internal loosely in this context. Basically, while the bullet is in the bore is what I'm referring to.
Tune, by whatever means, is timing bullet exit with optimal muzzle position. There are aspects of powder tuning that give the same results as a tuner er in regard to timing but they are not the same. For example, there is no reason why a tuner should give flat spots or plateaus, whereas powder does have velocity plateaus, where temp or charge increments have little effect on speeds. Every mark on a tuner is changing a constant and has a value where where every tenth or hundredth of a grain of powder does not.. linearly.
Link, am I wrong in saying this is just another way of asking the same question you have asked in at least one or two different threads and wording? No problem but the answer is not likely to change. Lol! I mean this in the best way. I wish it were 100% as simple as charting things out by a single factor, like temp but I've tried it...a lot. Three years in fact. Temp was the biggest factor but not the only factor and yes, there are parts of the country, like the PNW where Bryan Z is, where the pressure differences are much wider than the temp swings so yes, it's logical that he would tuner that way out there.
Tune, by whatever means, is timing bullet exit with optimal muzzle position. There are aspects of powder tuning that give the same results as a tuner er in regard to timing but they are not the same. For example, there is no reason why a tuner should give flat spots or plateaus, whereas powder does have velocity plateaus, where temp or charge increments have little effect on speeds. Every mark on a tuner is changing a constant and has a value where where every tenth or hundredth of a grain of powder does not.. linearly.
Link, am I wrong in saying this is just another way of asking the same question you have asked in at least one or two different threads and wording? No problem but the answer is not likely to change. Lol! I mean this in the best way. I wish it were 100% as simple as charting things out by a single factor, like temp but I've tried it...a lot. Three years in fact. Temp was the biggest factor but not the only factor and yes, there are parts of the country, like the PNW where Bryan Z is, where the pressure differences are much wider than the temp swings so yes, it's logical that he would tuner that way out there.
BoydAllen
Gold $$ Contributor
Simplifying that others have said, no.
If it's a terminology difference, speed vs in bore time...yes, for the most part if not entirely, then yes. But I agree with you that a chrono may get ya close but it is not velocity. Any tune method can be generally summed up as I said already though...optimizing bullet exit and muzzle position. Also like I said, and I might be wrong, it seems like he asked essentially the same question just not long ago at all. I do misremember from time to time so my apologies if not...and it's not a biggie anyway, to me. I'm happy to help if I can but if Link is just wording the same question differently, I don't see the answer changing unless there is a misunderstanding, very likely on my part.
tom
Gold $$ Contributor
No, but it may give you a clue as to what direction to look. Now to contradict myself I did shoot 2 different bullet weights the other morning as I learn my die. Now on the same morning, maybe 20 minutes apart, it did want the same speed.
Now more to your question. Let's say we stay with 103 3/4, and from this coarse test it's $ at 29.97. I find it perfectly normal to see the velocities change the next day, but 29.97 still be the $ spot. Over a lot of these type "ladders" it has been very common actually to never need to adjust the powder, even though the velocities with vary both directions somewhat. Now change elevation, humidity, YARDAGE, ect, and all bets are off!
Tom
Now more to your question. Let's say we stay with 103 3/4, and from this coarse test it's $ at 29.97. I find it perfectly normal to see the velocities change the next day, but 29.97 still be the $ spot. Over a lot of these type "ladders" it has been very common actually to never need to adjust the powder, even though the velocities with vary both directions somewhat. Now change elevation, humidity, YARDAGE, ect, and all bets are off!
Tom
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