Tuning loads for F-Class

[MikeMcCasland]

Hey Guys,

Something I've noticed over the past few matches is my velocity seems to increase in my 2nd and 3rd relays (about 15fps per relay, I'm attributing this to increasing temps), and I'm also seeing higher SDs as the match goes on.

Question: Any of you seasoned vets going to a match with varying powder charges for different relays? An an example 51.2gr Relay 1, 51.1gr Relay 2, and 51.0gr for Relay 3?

Or are you guys just in a more stable node to begin with, and not seeing this?

I know BR guys load for changing conditions; just wasn't sure how prevelent it is in F-Class.

Before someone jumps all over me for wanting to alter the load via FPS/SD, the load is accurate in all 3 strings. I just tend to get more vertical dispersion as matches go on, however I always feel like I'm actually shooting better.

 

[dcali]

I'm not saying you're not seeing something, but your chronograph really isn't capable of that kind of precision.

To answer your question - I load at one edge of a node so that if it speeds up, it's still in there. Sometimes it works, sometimes not. I don't think varying charge weights is a good way to go. Too many assumptions and too much to go wrong.

 

[MikeMcCasland]

I'm not saying you're not seeing something, but your chronograph really isn't capable of that kind of precision.

To answer your question - I load at one edge of a node so that if it speeds up, it's still in there. Sometimes it works, sometimes not. I don't think varying charge weights is a good way to go. Too many assumptions and too much to go wrong.

Fair point, these are observations from a Shotmarker over the course of a couple of matches, so I'm taking it with a grain of salt. That said, the system does seem to consistently report higher velocities as the day goes on (at least in summer conditions).

 

[ShootDots]

Hey Guys,

Something I've noticed over the past few matches is my velocity seems to increase in my 2nd and 3rd relays (about 15fps per relay, I'm attributing this to increasing temps), and I'm also seeing higher SDs as the match goes on.

Question: Any of you seasoned vets going to a match with varying powder charges for different relays? An an example 51.2gr Relay 1, 51.1gr Relay 2, and 51.0gr for Relay 3?

Or are you guys just in a more stable node to begin with, and not seeing this?

I know BR guys load for changing conditions; just wasn't sure how prevelent it is in F-Class.

Before someone jumps all over me for wanting to alter the load via FPS/SD, the load is accurate in all 3 strings. I just tend to get more vertical dispersion as matches go on, however I always feel like I'm actually shooting better.

I don't know what powder you are using. However, getting a temp stable powder can minimize this. AND finding a W-I-D-E window, where the point of impact does not change and groups do not open up and loading in the middle of that node is key. EXAMPLE: My .300WSM shooting 200-20X bullets with 61.1grs to 61.5 of H4350, there is very little difference between the loads. Maybe a few f.p.s. BUT accuracy does not change. I settled on 61.3grs and I always keep a flat waterline from match 1 thru match 3...

 

[David Christian]

Hi Mike,

No I do not bring different powder charges to the same match. If the lightest charge shoots well in the afternoon have you tried using just that load for all three strings? I find that my node is .4 to .5 grains wide and will typically load on the lower end of the window.

Do you think the vertical later in the day could be related to the visual effects of the sun/mirage?

 

[MikeMcCasland]

H4350 is the powder, and it very easily could be visual effects of sun/mirage. I don't know how much difference this makes either, but I'm usually developing loads at 1,000ft above sea level with relatively low humidity, but shooting at sea level in near 100% humidity. Perhaps thats moving the window around.

As far as taking 3 different powder charges to a match, I've never done it; always gone with the same charge for all strings.

 

[ShootDots]

H4350 is the powder, and it very easily could be visual effects of sun/mirage. I don't know how much difference this makes either, but I'm usually developing loads at 1,000ft above sea level with relatively low humidity, but shooting at sea level in near 100% humidity. Perhaps thats moving the window around.

As far as taking 3 different powder charges to a match, I've never done it; always gone with the same charge for all strings.

Mirage can have a detrimental effect on your vertical dispersion. However, I do not believe that it will cause say an 8-9" vertical dispersion of your load normally shoots a 3-4" vertical at say 1000 yards.. That does not mean that there are not some "conditions" out there that are causing some larger vertical dispersions. If you are shooting H4350 and loading it in a wide window, it is not your load>>>it is some other issue.

 

[F Class John]

Fair point, these are observations from a Shotmarker over the course of a couple of matches, so I'm taking it with a grain of salt. That said, the system does seem to consistently report higher velocities as the day goes on (at least in summer conditions).

FWIW even Adam would probably tell you the ‘chronograph’ function is largely anecdotal and in no way should be used for load development unless you’re shooting in a wind tunnel. This is because of how velocity is determined and there’s a lot of variables shot to shot that change and affect each velocity reading at the target. I’ve been shooting a Shotmarker for over a year and done a ton of tests with the chrono data and it’s mostly useless. You’d be doing yourself a disservice to use those numbers for any function of precision reloading.

But to answer the OP question I do like the guys above, load to the low end of the node.

 

[MikeMcCasland]

Thanks for entertaining my dumb questions; appreciate it gents!

 

[Falfan2017]

Got mine loaded in the middle of a .4 gr node. Shoots the same from 30.4 to 30.8. If you’re running the ragged edge in f class you’re going to drop points. I think the vertical stringing later in the match could be happening from mirage and wind getting worse as the day goes on.

Also have you ever tried cleaning your barrel between targets? Just a few patches to get the worst out.

 

[ngb1787]

We had done testing on 4831sc about 4 years ago, we found that with every one degree rise in ambient temperature we saw a 2fps increase is speed. This was with approx 53 gr being used with .284.

 

[skibar_tx]

Thanks for entertaining my dumb questions; appreciate it gents!

Mike, I ran my numbers on a ballistic calculator, one at 80 degrees ambient, one at 100 degrees ambient. It showed a 33 fps increase in speed at the target. So the increase you notice is about accurate.

 

[Falfan2017]

Just need a tune that can survive a 20-30 FPS increase in speeds.

 

[rardoin]

Mike, are you obtaining your velocities from the Shotmarker data (velocity at target?). If so, on a hot day like we had last Sunday, the air density will fall as the temperature rises throughout the morning. You will experience less velocity decay over the flight time thus higher terminal V and less drop. Your load is not likely changing that much...just conditions. Also, the brighter the sun the higher shot impacts are because the target 'image' that we aim at is higher than the actual target. By the second match I was playing the vertical at least a half ring low when there were no clouds.

Robin

 

[MikeMcCasland]

Mike, are you obtaining your velocities from the Shotmarker data (velocity at target?). If so, on a hot day like we had last Sunday, the air density will fall as the temperature rises throughout the morning. You will experience less velocity decay over the flight time thus higher terminal V and less drop. Your load is not likely changing that much...just conditions. Also, the brighter the sun the higher shot impacts are because the target 'image' that we aim at is higher than the actual target. By the second match I was playing the vertical at least a half ring low when there were no clouds.

Robin

This makes perfect sense, and I think you nailed it. Exactly the kind of insight/explanation I was hoping for.

Thank you!

Edit: and yep, I was basing this off the shotmarker velocities. To answer a question earlier in the thread, I do load dev off a LabRadar.

 

[Ned Ludd]

As noted - measuring velocity at the target for this purpose is probably not the best approach. Changes in temp/air pressure/humidity could also be responsible for a change in velocity at the target. Although it is not legal to have electronic devices such as a LabRadar on the firing line during an F-Class match, I doubt your local match director would mind if you used one during a match but didn't shoot for record. Alternatively, you could plan to spend a good part of the day practicing at the range and collect velocity data through the course of a typical day. Ideally, you'd like to have data from both ends of the trajectory (i.e. LabRadar at the line, ShotMarker at the target). However, if only one is possible on a practice day, it needs to be the LabRadar.

IMO - one major difference between loading for F-Class and loading for LR BR is the long strings of fire in F-Class (typically 25+ shots) that occur throughout the course of a day's matches. This means that paying special attention to a load so that it maintains relatively uniform velocity during the course of the day's firing is more important than trying to achieve sub-quarter MOA accuracy. This is also why I believe that F-Class shooters that don't pay attention to velocity during load development, or possibly only check the velocity of the "final product" are leaving a lot on the table.

So let's say you were to find your load is actually increasing in velocity during the course of a day's match. The real question is - does it increase in velocity enough to put you out of the precision/accuracy window? And if so, what can you do about it? For obvious reasons, the first question is the one needs to be answered first. If the increase in velocity isn't enough to change the behavior of the load, nothing needs to be done at all, other than keeping your eye on it.

If the velocity does increase sufficiently during the day to negatively affect the load, then you have a few choices:

1) You can re-develop a load with a different powder that is less sensitive to temperature changes

2) You can load with the same powder to a point slightly below the middle of the optimal charge weight window such that it tolerates the temperature increase better.

3) You can drop the charge weight a tenth grain or so for each successive match (this is where QuickLoad can really help to expedite the reloading process).

4) You can sort your brass by volume and use increasingly larger volume sorting groups for each successive match. This approach is probably not sufficient for large velocity swings, but might be used in combination with one of the others for fine tuning, if necessary.

There are probably a few more approaches I haven't thought of, but you get the idea. The question you want to answer first is whether it is even necessary to change anything. If so, you can readily determine at the range which (if any) of the above approaches actually solves the problem, then apply them at a match and determine whether you think it made any difference. This last part is also very important...adding these kind of additional exercises to the reloading process makes it even more painful than it already is. It may be well worth it if there is a demonstrable gain, but the results need to be documented over time to determine whether there really IS any benefit.