OBT and barrel length?

[jlow]

Boyd -
Interesting input, but not really on T with OBT.
Two seperate subjects with different effects - IMO.
Donovan

---------------------------------------------------------

jlow -
Simpliest way I can think of to explain it is: when the bell is ringing at one end, there would be echoing in the barrel and at the other end as well.
Look close at Chris' drawing. It tells the whole story well - IMO
Donovan

Donovan - you are in fact correct about the best time being "just before the pulse arrive". I think the reason is because as the pulse travels from the crown to the chamber and back to the crown. The period that signifies the crown having the most time to quiet down and relax is before the pulse comes back to the crown again. That period "just after the pulse leaves" is not as good as the crown is just starting to relax and don't have as much time to relax as the other node.

 

[jlow]

The location of the “best node” that is “just before the pulse arrive” has some ramifications, i.e. the top edge of the node is close to where the quiet crown is ready to “fall off the edge”….

 

[BoydAllen]

The original question did not contain any reference to OBT. He asked, "
If I have a very long barrel and I am running in a slower node can I cut the barrel back and adjust load to same velocity and achieve same precision/accuracy? Or does the accuracy node shift with barrel length?"

My while my example did not speak directly to the question, It does illustrate something of how a change to a barrel can influence accuracy node location. A shorter answer would have been that I don't know, and I am pretty sure that no one that I know of does either, at least not to a certainty. I would just love to see someone successfully predict the effect of cutting off a barrel based on the information that was furnished.

 

[Nvreloader]

Norm
Do you happen to know where this book could be obtain in the US?
I have not been able to find it in the states, with my researching, so far.

Tia,
Don

Strange you should ask!

A fellow in Australia, Graham Mincham, wrote a book called,"Optimum Barrel Length." This book outlines how to find the lateral resonance of a barrel by shooting a ladder type series of 6, 5-shot groups with each group having a different powder charge. Then, using a program like "On Target," plot the group size vs charge. The ES curve shows the charge you should use where the ES is a minimum, and the group sizes indicate what the barrel length should be for proper vertical resonance.
I believe this book can be obtained from the South Australia Rifle Association.

 

[Nvreloader]

Guys,
A question for those that know and understand OBT's,
just how close does the OBT nodes have to be,
to the BT as listed via QL load data?

Does having a muzzle break make any difference?

Tia,
Don

 

[savagedasher]

Guys,
A question for those that know and understand OBT's,
just how close does the OBT nodes have to be,
to the BT as listed via QL load data?

Does having a muzzle break make any difference?

Tia,
Don

No but a tuner does . I feel it is a waste of time . I have 5 all the same caliber and barrel size and length. None of the numbers align with each other. When I change powder and make the barrel time the same they don't shoot. Go figure. Larry

 

[jlow]

Guys,
A question for those that know and understand OBT's,
just how close does the OBT nodes have to be,
to the BT as listed via QL load data?

Does having a muzzle break make any difference?

Tia,
Don

I think you got it reversed. The question should be “how close do you have to get the BT in QL to the OBT node for it to work?” The reason being that you cannot change OBT since it is well the “optimal barrel time” which is determined by your barrel length. I suppose one could cut your barrel to get OBT close to BT in QL but generally it is much easier to change powder weight to change BT than to change barrel length. Sorry, it was just too good not to pull your leg…

QL is actually amazingly good and has worked for every one of my rifles first time out. On the other hand, it is never 100% and it can be off by 0.1 to 0.2 gr but that’s where you fine tune by running OCW.

 

[normmatzen]

NVreloader,

I don't think the book is available in the USA. I would google SARA or South Australia Rifle Association. They have a store where it is available.

 

[Nvreloader]

Jlow
Thanks,
It not the first time I have had my leg pulled,

I worked up a hunting load for the 284 Sp pistol,
21" bbl, w/muzzle break that add 2.48" more,
RL-26 w/Nosler 140 Part bullet @ 3000+ fps,
tested it out to 300 yds,
via adjusting the seating depth by .015" steps,
and the powder load amounts in 1/2gr steps,
went from 3"+ groups down to 1.125".

Have retested this load several times, stays the same,
QL shows a BT of 1.076,
The OBT table shows 1.0763

I don't think I can get any closer?
Not sure what OCW is or involves.
Suggestions?

Tia,
Don


QUOTE="jlow, post: 36768954, member: 1282775"]I think you got it reversed. The question should be “how close do you have to get the BT in QL to the OBT node for it to work?” The reason being that you cannot change OBT since it is well the “optimal barrel time” which is determined by your barrel length. I suppose one could cut your barrel to get OBT close to BT in QL but generally it is much easier to change powder weight to change BT than to change barrel length. Sorry, it was just too good not to pull your leg…

QL is actually amazingly good and has worked for every one of my rifles first time out. On the other hand, it is never 100% and it can be off by 0.1 to 0.2 gr but that’s where you fine tune by running OCW.[/QUOTE]

 

[Nvreloader]

Norm
Thank you,
Will look.

Tia,
Don

 

[jlow]

Jlow
Thanks,
It not the first time I have had my leg pulled,

I worked up a hunting load for the 284 Sp pistol,
21" bbl, w/muzzle break that add 2.48" more,
RL-26 w/Nosler 140 Part bullet @ 3000+ fps,
tested it out to 300 yds,
via adjusting the seating depth by .015" steps,
and the powder load amounts in 1/2gr steps,
went from 3"+ groups down to 1.125".

Have retested this load several times, stays the same,
QL shows a BT of 1.076,
The OBT table shows 1.0763

I don't think I can get any closer?
Not sure what OCW is or involves.
Suggestions?

Tia,
Don


QUOTE="jlow, post: 36768954, member: 1282775"]I think you got it reversed. The question should be “how close do you have to get the BT in QL to the OBT node for it to work?” The reason being that you cannot change OBT since it is well the “optimal barrel time” which is determined by your barrel length. I suppose one could cut your barrel to get OBT close to BT in QL but generally it is much easier to change powder weight to change BT than to change barrel length. Sorry, it was just too good not to pull your leg…

QL is actually amazingly good and has worked for every one of my rifles first time out. On the other hand, it is never 100% and it can be off by 0.1 to 0.2 gr but that’s where you fine tune by running OCW.

[/QUOTE]

Glad you like the leg pull, it’s good to keep things light!

OCW is what Dan Newberry at BangSteel came up with for load development. It’s a wonderful and efficient way to find accuracy nodes. I honestly cannot do it justice with a line or two but you can read up on it here.

http://optimalchargeweight.embarqspace.com/

The nice thing about QL is because it is so accurate, so I basically cheat and instead of running a full OCW (i.e. if I have no idea of where it is..), I use the powder weight QL comes up with and just look at it and a few powder weight to each side just to make sure I am on the accuracy node. Once that is done, I then follow Dan’s suggestion as to fine tuning the load by adjusting seating depths.

BTW, there is a HUGE thread on this board that Eriik Cortina started up a few years ago that is based on OCW with 1,866 replies… So lot more stuff there.

http://forum.accurateshooter.com/threads/long-range-load-development-at-100-yards.3814361/

 

[Ned Ludd]

Have retested this load several times, stays the same,
QL shows a BT of 1.076,
The OBT table shows 1.0763

I don't think I can get any closer?
Not sure what OCW is or involves.
Suggestions?

Tia,
Don

All you need to do is change the charge weight by 0.1 gr in QL, then see how much the predicted barrel time changes. Unless you're willing to dispense charge weights in smaller increments than 0.1 gr, you won't get it any closer than you already are. In my hands, loads optimized without using QL, as well as several that were prepared using QL, almost always seem to fall just a tick slower than the OBT table value. For example, the Node 4 OBT value for a 30" barrel is 1.3684 ms. My best loads in 30" always seem to be in the 1.370-1.372 ms range as predicted by QL. This may simply be an issue of decimal places and/or data entry for other load parameters, but it is has been pretty consistent. Changes in predicted barrel times in the 5th decimal place aren't going to mean much in practical terms.

 

[savagedasher]

I have 3 dashers I shoot . One from the bolt face is 27 3/4 the other 29 1/2 the third is 30 9/16.
All 3 I load with36.6 GR of H4350 . I know BT must be the same because the will shoot .250 at 100. Larry

 

[dcali]

OBT is not the dominant effect (or even close to it) in barrel vibrations, and the fact that tuners work proves this. If an OBT node works, it's only by coincidence.

 

[Ned Ludd]

No, it isn't. If it were, it'd be a coincidence for every single load in every single rifle I own, several of which were developed completely independently of any prior knowledge about OBT theory or the use of Quickload. There's way too much support for it to be chance. Chris' explanation may not be the complete or correct mechanism that explains how it works, but it works nonetheless. I'm actually moving back to Omaha permanently in a couple weeks, and I'd be happy to go meet up with you at ENGC and demonstrate just how well it works with the various rifles I have. Perhaps I can turn you away from the dark side and change your mind about the OBT approach .

 

[dcali]

No, it isn't. If it were, it'd be a coincidence for every single load in every single rifle I own, several of which were developed completely independently of any prior knowledge about OBT theory or the use of Quickload. There's way too much support for it to be chance. Chris' explanation may not be the complete or correct mechanism that explains how it works, but it works nonetheless. I'm actually moving back to Omaha permanently in a couple weeks, and I'd be happy to go meet up with you at ENGC and demonstrate just how well it works with the various rifles I have. Perhaps I can turn you away from the dark side and change your mind about the OBT approach .

Great. Just when I started placing in a match or two, you're going to show up. Would love to see the details of your setup/load dev. Obviously it's working! Still don't think it's OBT tho... I reserve as always the right to be totally wrong.

 

[savagedasher]

No, it isn't. If it were, it'd be a coincidence for every single load in every single rifle I own, several of which were developed completely independently of any prior knowledge about OBT theory or the use of Quickload. There's way too much support for it to be chance. Chris' explanation may not be the complete or correct mechanism that explains how it works, but it works nonetheless. I'm actually moving back to Omaha permanently in a couple weeks, and I'd be happy to go meet up with you at ENGC and demonstrate just how well it works with the various rifles I have. Perhaps I can turn you away from the dark side and change your mind about the OBT approach .

Just did the 5 th today same powder drop 29 1/2 barrel with .030 change in seating .
Nothing but a tuner change

 

[savagedasher]

I think the dark side is not using a tuner
Work a nodal point 2" from the muzzle a 1" change at 100 yards is.0005" at the muzzle
Larry

 

[Ned Ludd]

Great. Just when I started placing in a match or two, you're going to show up. Would love to see the details of your setup/load dev. Obviously it's working! Still don't think it's OBT tho... I reserve as always the right to be totally wrong.

I wouldn't be too concerned about match results. Shooting against the highest skill level competitors available and under the most challenging conditions is a very good way to improve your own skills. I will likely compete in Open class on occasion for those very reasons. There are several excellent Open shooters that compete at ENGC and I'm certain shooting with them will help me improve my shooting skills, regardless of where I might finish. I'm far less concerned about winning than about improving. With improvement, winning will take care of itself. Further, I am very willing to try to help anyone with their shooting/reloading that feels it may be of benefit.

Along that line, we have been shooting a monthly match here in San Diego referred to as a "Reduced Palma Match". It is 3 x 15 shots for record at 300 yd on the MR-63FC NRA target. Because this particular range has no pits, we position 12" Shoot-N-C targets over the NRA target so you can see your impacts at 300 yd. Scores are recorded from the NRA target underneath after each string. This is a very fun and challenging format. If you drop more than 1 or 2 points, you likely won't be in the running. Because there is one relay, the match only takes about 3 hr and is usually finished by around 11:00. I can tell you that shooting in this match has really helped me a lot with position, trigger control, holds, and other considerations. Plus, it is just a very fun match to shoot; a great bunch of shooters and very friendly competition. I think the folks at ENGC might really enjoy having another F-Class match in this format once a month and have been thinking about trying to get it implemented once I'm there. There might be a few minor hurdles to overcome regarding scheduling and implementation of the match with regard to the number of firing lanes on the 300 yd range, but I think it could be done. Do you think there might be interest in such a match there?

 

[dcali]

Along that line, we have been shooting a monthly match here in San Diego referred to as a "Reduced Palma Match". It is 3 x 15 shots for record at 300 yd on the MR-63FC NRA target. Because this particular range has no pits, we position 12" Shoot-N-C targets over the NRA target so you can see your impacts at 300 yd. Scores are recorded from the NRA target underneath after each string. This is a very fun and challenging format. If you drop more than 1 or 2 points, you likely won't be in the running. Because there is one relay, the match only takes about 3 hr and is usually finished by around 11:00. I can tell you that shooting in this match has really helped me a lot with position, trigger control, holds, and other considerations. Plus, it is just a very fun match to shoot; a great bunch of shooters and very friendly competition. I think the folks at ENGC might really enjoy having another F-Class match in this format once a month and have been thinking about trying to get it implemented once I'm there. There might be a few minor hurdles to overcome regarding scheduling and implementation of the match with regard to the number of firing lanes on the 300 yd range, but I think it could be done. Do you think there might be interest in such a match there?

I'd shoot a 300 yard match, at least once in a while. I think some guys tried something similar a few years ago, and it didn't really go anywhere. That was before I moved here though, so I'm not sure exactly what they were doing. F Class in general is getting pretty popular though. I think we had 43 or something like that last month, which is more than we typically had last year. Get your state championship registration in early - it will fill up. You'd have to talk to the powers that be, but my guess is that the 600 yard range might be best for it. The 300 yard range is a little awkward, and a good 1/3 of it is reserved for 50 yard shooting. Sort of depends on how many people would be interested. It might be fun to work in a rapid fire relay.

(Sorry for the thread hijack - I still don't believe in OBT!! )