OBT and Quickload question

[JDNC]

This has probably been answered but anyway... in reference to Quickload and OBT do I use my instrumental velocity or calculated true muzzle velocity to tweak Quickload?

I know muzzle velocity is self explanatory, but I thought I had better ask.

Thanks, JD

 

[waldo1979]

Use your muzzle velocity to tune the powder burn rate until it matches the Quickload projections. Also, make sure your case capacity and other variables are accurate.

 

[Chuckhunter]

JD, Good info in = good info out. Make sure you have as many of Quick Loads parameters, such as, your actual case volume and length. The actual measured OAL of your loaded rounds and bullets you are using, (best to average several ). Then enter the temp at which your velocities were recorded,, then tweak your burn rate to give you your actual recorded velocity. Once all of that is done, check your barrel time and if your not close to a node, adjust your powder charge to get you either right on or extremely close to the OBT you wish to obtain. This has worked out very well for me so far, I'm sure others may do it slightly different but the key is getting your actual data correct. Good luck and good shooting.

 

[JDNC]

Thanks guys. I'm an old user of Quickload and understand the importance of having all of the parameters correct. What puzzles me is that it appears that most are calibrating QL to the velocity they get straight from their chronograph. As you know that is not the true muzzle velocity as the sky screens are not at the muzzle. For example the center between my start and stop screens is 12ft. I have been using a ballistics app to give me the corrected velocity from my 12ft instrumental velocity. I then make adjustments with QL to match this corrected velocity and compare barrel times to the chart. I guess my question is this necessary? I think it would be the most accurate way. I may be mistaken and that most are doing it this way. The other day it just occurred to me that the velocity my chrono was displaying was possibly 10-15 fps slow due to the location of the screens!

 

[Chuckhunter]

JD, I use a Magnetospeed Chronograph, so I get actual muzzle velocity. If you're using a chrono with sky screens, you must compensate for the distance from your muzzle to the 1st sky-screen. In my case when I used an old, Oehler 33 that would usually be 10 ft. The chronograph data was normally on average, 5ft per second slower than the adjusted muzzle velocity. So I guess to answer your question, use your adjusted muzzle velocity not the data straight from the chronograph.

 

[waldo1979]

JD, I use a Magnetospeed Chronograph, so I get actual muzzle velocity. If you're using a chrono with sky screens, you must compensate for the distance from your muzzle to the 1st sky-screen. In my case when I used an old, Oehler 33 that would usually be 10 ft. The chronograph data was normally on average, 5ft per second slower than the adjusted muzzle velocity. So I guess to answer your question, use your adjusted muzzle velocity not the data straight from the chronograph.

^^ MSC v3 here

 

[JDNC]

JD, I use a Magnetospeed Chronograph, so I get actual muzzle velocity. If you're using a chrono with sky screens, you must compensate for the distance from your muzzle to the 1st sky-screen. In my case when I used an old, Oehler 33 that would usually be 10 ft. The chronograph data was normally on average, 5ft per second slower than the adjusted muzzle velocity. So I guess to answer your question, use your adjusted muzzle velocity not the data straight from the chronograph.

Thanks, that was what I wanted to know. I purchased my model 33 brand new and still use it today when clocking down range. I also use a 35P. I guess I'm telling my age...OLD!

Thanks, again
^^ MSC v3 here

 

[JDNC]

One other thing that also puzzles me. Guys do I use the "Barrel time, 10% Pmax to Muzzle" or the the barrel time on the diagram/chart?

In my case the 10% Pmax to muzzle = .887ms and the X value at the end of the chart = .906ms. I'm old and confused here. The OBT node I'm trying to match is .887ms and I've adjusted QL to the 10% Pmax to muzzle. Then I later noticed the barrel time on the chart was different as its total barrel time. Anyway which do I adjust to?

Thanks JD

 

[Chuckhunter]

JD, I'm not sure weather or not I'm correct but I have found that all of my best loads were always extremely close to the total barrel time in QL, so I adjust my loads using those numbers to match those on the chart. For example my best load turned out to be 1.2788 ms according to QL while the chart showed an OBT of 1.2795. That is why I do it that way. I really don't know if that is correct but to date it seems to be working out very well using that procedure. Perhaps someone more tech savy than me can jump in here and help both of us out. Ultimately the target will tell the story.

 

[JDNC]

JD, I'm not sure weather or not I'm correct but I have found that all of my best loads were always extremely close to the total barrel time in QL, so I adjust my loads using those numbers to match those on the chart. For example my best load turned out to be 1.2788 ms according to QL while the chart showed an OBT of 1.2795. That is why I do it that way. I really don't know if that is correct but to date it seems to be working out very well using that procedure. Perhaps someone more tech savy than me can jump in here and help both of us out. Ultimately the target will tell the story.

BTW, I was referring to the QL pressure barrel time graph as I think you're also referring. I have a OBT node of 0.887ms I'm trying to match and I just noticed the barrel time in QL (the little block below all the powder, charge weight stuff) was different from the QL's graph of pressure and barrel time. I've been using 10% Pmax barrel time inside QL also but I don't know if it's correct. I would hate to be adjusting charge weight to the wrong barrel time!

Thanks, JD

 

[Chuckhunter]

JD, attached is the OBT Chart that I use. It goes by barrel length, listed in far left column. If you look at 28" which is my barrel length the node that I strive to hit is 1.2795 as it is the only node that gives me the required velocity for 1000yd. competition. I match that node with the Barrel time 10% Pmax to muzzle, (the little block below all the powder, charge weight stuff). As I stated, this has been working out very well for me so far. Once your burn rate has been adjusted to agree with actual recorded chronograph data the results of matching barrel times with the nodes you desire will become extremely close at varying temperatures. They will never be dead nuts on at all variations but they will be close enough to give you the results you desire, at least I have found that to be true so far.

 

[jlow]

If you actually calculate the error of using MV numbers 10 feet from the muzzle, you will find that it is off only by 1-2 fps. I doubt any chronograph most of us use is that accurate.

 

[JDNC]

Thanks guys, I guess I've been doing it right. As for clocked muzzle velocities, I've been in the 2150-2200 range and when corrected I've only had to add maybe 8-10fps. Now at subsonic only 2 or so. Recently I purchased one on the Ruger American rifles in 300blk and it's so light on the bench I assumed most of my bad groups were bench related. Well, the very first load adjusted for OBT was hovering at MOA. So, I'm tickled and can't wait to fine tune this load.

Thanks again, JD

 

[Nomad47]

gstaylorg, I believe you meant to post a screen shot of the more detailed trajectory instead of the simplified version. IIRC, the detailed one has an entry for "distance to chronograph".

 

[Sheldon N]

gstaylorg, what chrono are you using to cross reference velocity against Quickload for purposes of OBT?

 

[Sheldon N]

Thanks, appreciate the info. Using a magnetospeed as well, so will keep that in mind.

 

[Hondo64d]

Use your muzzle velocity to tune the powder burn rate until it matches the Quickload projections. Also, make sure your case capacity and other variables are accurate.

How do you tune the powder burn rate? Do you mean pick a different powder that will give the suggested muzzle velocity at the suggested charge?

Thanks,

John

 

[Jeff A]

How do you tune the powder burn rate? Do you mean pick a different powder that will give the suggested muzzle velocity at the suggested charge?

Thanks,

John

No, change the Ba number for the powder used. You should get some hands on guidance for this.

 

[Sheldon N]

Here's a link to instructions on how to do it...

http://www.the-long-family.com/Tuning QL to achieve best results.pdf

 

[CH Luke]

I posted the exact JBM screen shot I meant to post. 12 ft is 4 yd, 15 ft is 5 yd. Both of those distance increments and their corresponding [predicted] velocities are listed in that image/table. I'm sure there are other ways to get JBM to output that info, but for me simpler is better.

I use a MagnetoSpeed to determine velocity. I really like the unit, but in my hands having it attached to the barrel absolutely changes both POI and groupings, so I shoot groups separately from velocity determinations.

Ahead of your time on this one. Using the V3 this fall I completely agree with the call on POI based on recorded data and tend to agree on group size (untested working hypothesis).

We exchanged messages a few weeks back. Would like to ping you again on some other topics soon.