Tuning is the process of finding a load that shoots the best in a particular rifle. The more shooting I do, the more I realize there are not many hard and fast rules when it comes to tuning. The “exceptions to the rule” are endless. The general idea is to look for trends that point towards a forgiving load. In many ways, tuning is just as much an art as it is a science.
The main idea of this writing is to help you create a tuning procedure regardless of which rifle you are tuning. Keep in mind, tuning is much like editing a Blog article. Eventually, you just have to say it is good enough. The applications of the rifle and your own desire for precision determine when the tune is good enough.
Tuning Tip #1:
Some wind is needed to get a good tune. I believe that having zero wind is the second worst time to tune a barrel. The first would be in heavy mirage. Having no wind is when all the “gremlins” come out. Sometimes you shoot some really small groups and other times they are huge. The data on these no wind days is not reliable. A light wind keeps those “gremlins” away.
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Determining your Baseline Load
The first goal for tuning is to find a starting load for the rifle. Essentially anything that shoots semi-respectable groups will work. That first load is the baseline, a starting point. This load is rarely the final load, but you have to start somewhere.
A quick way to find the baseline is to shoot a load ladder. The main goal of a load ladder is to give an idea of where the powder charge tune window is going to be for the bullet you want to shoot.
Safety note: The shooter has to use his/her own experience in picking the correct powder/bullet combination. If you do not have experience with the cartridge you are loading, refer to a loading manual. By all means, if there is any question about how much powder to use, start low and work your way up looking for any pressure signs along the way.
Quick Tutorial on a Load Ladder.
I like to load between 5-12 cartridges. Less than that, and there simply is not enough data. More and the data gets confusing. My favorite distance is 200 yds for a ladder test. Less than that, and there is not enough distance to show the variance. Exceed 200, and the conditions play too big of a role in the group size. Only change one variable. All other measurements should stay the same. In this case, I chose to change the powder charge. In a Bench rifle I will load powder in .1 gr increments, in a hunting rifle .2-.3 gr.
There will be two targets; one target that is shot and another identical target at the bench. Click your scope so that the impact point is roughly two inches below the aiming point. While holding at the same aiming point for each shot, systematically shoot round #1 then mark the shot placement on the target at the bench. (A spotting scope comes in handy for this) Continue through all the rounds for that particular bullet/powder combination.
After retrieving the target, indicate which bullet holes correspond to the case number. There are no definitive answers given from a load ladder. It is simply the first step to determine a starting point for powder charge. That charge will be where there are chronological numbers that are close to each other on the target. Next, shoot a group with that powder charge. If the group is acceptable, you have found your baseline load.
The tuning example I will use in this writing is my Heavy Varmint (HV) competition rifle: BAT 3 Lug action, Kelbly stock, Krieger, 1/17 twist barrel, chambered in 30BR. I will be tuning the rifle to BIB 112-7 bullets, H4198 powder and CCI BR4 primers. Please keep in mind, this is a competition rifle. I would really like the final groups to be in the high zeros to low ones. A hunting rifle would not require this level of precision.
HV example: 200 yd 8 shot load ladder. I loaded BIB 112-7 bullets held in place with a .324 bushing at a seating depth of +.010 fired off with CCI BR4 primers. The only variable I am changing is the powder charge. I loaded 34.2 gr of H4198 in case #1. Case #2 = 34.3 gr. Case #3 = 34.4 gr., etc until I finished with case #8 at 34.9 gr.
On the Load Ladder Target, you will see that shots 1,2,3,4 (34.2 - 34.5 gr) were all close to each other and shots 6,7,8 (34.7-34.9 gr) formed their own separate group.
Based on this load ladder, I shot a group with a powder charge in the middle of the highest range (34.8 gr of H4198). The group was a mid .2” Not a bad start.
My baseline load is: BIB 112-7 +.010, .324 bushing, 34.8 gr of H4198, CCI BR 4.
Tuning Tip #2:
If the load ladder does not show any groups whatsoever that is a good indication that the rifle might need a different bullet/powder combination or your powder charges are way off.
Determining Tune Windows
Once the baseline load is found, start to make individual changes to find tune windows. You want to find the ranges of powder charges, seating depths, and neck tensions that the bullet will shoot in. These tune windows, or cushions, give margins of error when loading and also the final load will be able to handle changes in temperature, humidity, and altitude. You want to find the edges of these windows then go right in the middle for each one. These margins of error will produce an overall forgiving load.
The usual order for tuning is: powder charge, seating depth, neck tension, then primers. Three shot groups at 100 yards are pretty standard. The goal is to notice any changes in group size. Remember, only change one variable at a time.
Powder Charge
To determine the powder charge, load charges above and below the baseline charge. In a competition rifle, I usually change in .1 gr. increments. In a hunting rifle I usually go .2 gr. to find the tune window. Shoot three shot groups with those different powder charges.
Look for trends in the targets. When you make a change, what does the target tell you? The targets will tell you which way you should be going.
Tuning Tip #3:
Many people say that you can not see a change in groups with small changes in powder. That is exactly the point. You want to keep making those small changes each way until you do see the change. That is your tune window.
HV example: Three shot groups with powder charge of 34.6, 34.7, and 34.8. Charges 34.6 and 34.8 both shot well. I am not sure what happened with the 34.7 gr. However, one bad group or one bad shot does not make or dismiss the load. I am looking for general trends. The overall trend shows that 34.7 gr. is safely in the middle of the powder tune window. Even though the 34.7 was an ugly, .3, I am not worried about the charge. There are plenty more “checks and balances” built into this load development procedure to catch false information
Seating Depth
Once you have your powder charge, follow the same process for seating depth. For all of my rifles (competition and hunting), I will change the seating depth by .005”.
Tuning Tip #4:
I am not opposed to jamming up to .025” in a competition rifle. In a hunting rifle, I do not like to go past .005” jam. The accuracy gain is not worth the risk of sticking a bullet in the field. Most of the time, clip length will determine your max C.O.L.
Tuning Tip #5:
If your groups are not even close to your expectations, do not mess around with little changes like .005”, make big changes such as .025” to see if that helps.
HV Example: These two targets are good examples of the trend that one should look for.
Target one I shot seating depths of +.010, +.005, and +.016. The trend was; the longer the seating the tighter the groups. I wanted to see if that trend continued so I shot seating depths of +.015, +.020, and +.025 on Target 2. The data clearly shows that any seating depth between +.015 and +.025 will shoot in this barrel.
Disclaimer: I do not own an official group scoring reticule. I simply take a caliper and measure the widest part and subtract the bullet diameter. When groups get this small, that process is not highly accurate. Regardless, those are small groups. In other words, 34.7 gr of H4198 with a BIB bullet set at +.020 is good enough.
Neck Tension
Next up to bat is neck tension. You should now know your powder charge and seating depth. Follow the same process as before, only change one variable and go both directions from your baseline load. For my competition rifles, I almost always start around .003” neck tension. Hunting rifles I start at .002”.
Tuning Tip #6:
Do not underestimate neck tension. Having the correct and consistent neck tension can make a difference in your tune.
HV Example: I tried .323 and .325 neck bushings. This would correlate to .004 and 002 neck tension. I already have plenty of repeating data for the .324 bushing so I did not shoot that. Not surprisingly, neither of those two bushings tightened up the group. I will stick with the .324”
Primers
Last, but not always least; primers. As always, keep your load the same but try different primers. Three shot groups should give you enough data.
Tuning Tip #7:
If you choose to try different primers you may consider doing two three shot groups with each brand of primer. It has to win twice to justify switching primers.
HV Example: I did not try different primers. I am a CCI BR primer fan. I do keep Federal Match primers on hand in case the CCI’s do not work. I have not noticed any “real” difference. Both are quality primers.
“Final” Load = Good Enough
The load that I am going to run with is 34.7 gr of H4198 set off by CCI BR4 primers, pushing a BIB 112-7 bullet at +.020 into the lands, held in place by a .324 bushing. Notice, the final load is not that far off from the original baseline load. The baseline load shot a mid .2”. The final loads’ last 4 groups were in the zeros. Based on the level of competitors I compete against, that could be the difference between bringing home some wood or finishing in the middle of the pack.
Conclusion
Regardless of your tuning application, there are some repeating themes in this blog. First, a single group does not determine or dismiss the load you should use. There should be repeating data with trends that all point to the same load. Second, you want to find a forgiving load. A load that will shoot well in many different types of conditions. You find this forgiving load in the middle of your tune window by only changing one variable at a time. Third, keep searching. Good is usually pretty easy to find, but if you want great, you have to dig a little deeper.
Hopefully, that was enough kindling to get the fire started and you are on your way to developing a process for having a tuned rifle. Remember, tuning is just as much an art as it is a science. Until next time, enjoy the experience.
