Long Range Load Development for F-Class
This article was written in 2014 for the Sierra Bullets Blog. It describes one method of load development that is commonly used. There are other methods that can work also. Some guys first isolate seating depth and then fine-tune velocity with charge weights. Other guys may aim for a known velocity node (speed range) and then optimize accuracy by adjusting seating depth. Still others look for smallest ES and tightest vertical to minimize 1000-yard vertical dispersion. There are many ways to skin a cat. Different rifles (and even different barrels) can demand different styles of load development.
In this instance the writer achieved desired results seating his bullets .007″ back from max “jam” length. For other applications (and other barrels) you may get the best, most consistent results seating off the rifling by .020″ or more. In disciplines with quick-fire such as PRS, it may be wise to develop loads that “jump” the bullet.
F-Class Long Range Load Development Methodology
by Mark Walker, Sierra Bullets Product Development Manager
Since I just put a new barrel on my F-class rifle… I figured it might be a good time to discuss load tuning for long range shooting. Getting the most accuracy out of your rifle is one of the most important aspects of load tuning. For long range shooting in particular, using a load that produces the least amount of vertical variation is vital. There are several steps to the process that I use, so I will go through the basics of each.
When I first get a new barrel installed, I like to determine what the loaded cartridge “jam” length is. I do this by taking an empty case (no powder or primer) that has been neck sized with the proper bushing (I like to shoot for 0.002 smaller than the loaded cartridge neck diameter) and seat a bullet long in it so that the throat of the rifle will move the bullet back into the case when I close the bolt. I close the bolt several times until the bullet stops moving back into the case at which point I use a comparator with my calipers and get a length measurement on the cartridge. This is what I consider to be the “jam length” for this barrel and chamber. I came up with 3.477″ as the “jam length” for this particular barrel. [Editor: In this instance, Mark is using “Jam length” to mean max seating depth he can achieve without bullet set-back.]
Next, I will fire-form some brass using a starting load of powder and bullets seated to “jam” while breaking in the barrel. My barrel break in process is not very technical; it’s mostly just to get the brass formed and the rifle sighted in. I do clean every 5 rounds or so just because I feel like I have to.
Once I have the brass formed, I use them to load for a “ladder test” to see what powder charge the rifle likes. With a ladder test, you take your starting load and load one round each with a slightly increasing amount of powder until you reach your max load for that cartridge. You then fire each round using the same aiming point to see where the bullets start to form a group. For this barrel and cartridge, I started at 53.3 grains of H4831SC powder and increased the load by 0.3 grains until I reached 55.7 grains. I always seat my bullets to “jam” when doing a ladder test. We will determine the final seating depth in another test later. It’s usually best to shoot this test at a minimum of 200 yards because at closer ranges the bullets will impact too close together making it hard to determine which load works best. I shot this test at 300 yards.
As you can see from the target, the lightest load #1 had the lowest velocity and impacted lowest on the target. Shots #2 and #3 were a little higher and in the same hole. Shots #4 thru #6 were slightly higher yet and all had the same elevation. Shots #7 and #8 were the highest on the target however pressure signs were starting to show. For some reason shot #9 went back into the group and the chronograph didn’t get a reading so I ignored that shot.
When picking a load, I am looking for the most shots at the same vertical location on the target. As you can see that would be shots #4 through #6 so I would pick a powder charge from those shots which would be 54.2 grains to 54.8 grains. As a side note, shots #2 and #3 are only 0.851 lower so I wouldn’t be afraid of using one of those loads either. I settled on 54.5 grains as the load I wanted to use. It’s right in the middle of the group so if the velocity goes up or down slightly, the bullet should still hit in the same place on the target.
Now that we’ve settled on a powder charge, I want to find the seating depth the rifle likes. I usually start at jam length and [shorten the COAL] in 0.003 increments until I get to 0.015 deeper than jam. [Editor: By this he means he is seating the BULLET deeper in the case, NOT deeper into the lands. He ended up at .007″ shorter than his hard jam length of 3.477″.]
I load 3 rounds at each depth using the 54.5 grain powder charge and shoot a group with each depth at 150 yards. As you can see from the target, the first two groups are not good at all. Next one looks good and is the smallest group on the target. The next three are not quite as small but the vertical location on the target is almost the same which indicates a sweet spot which will help keep the vertical stringing to a minimum on target. I went with 3.470″ which is right in the middle once again and should give some flexibility with the seating depth.
So after all of that, my load is 54.5 grains of H4831SC and a cartridge length of 3.470. I plan on loading up enough ammo to shoot five groups of five shots and see exactly how this load works on target as well as what the extreme velocity spreads are over several groups.
I sincerely hope some of this information helps you to get the best accuracy out of your rifle. I do not take credit for coming up with any of this, a whole lot of good shooters use this same method or a variant of it when working up their loads.
For more information about load development, please contact the Sierra Bullets technical support team at 1-800-223-8799 or by email at sierra [at] sierrabullets.com.
Disclaimer: Load data represented here may not be safe in your rifle. Always start low and work up, watching for pressure signs.
Similar Posts:
- Load Dev for .223 Rem Varminter and .308 Win Hunting Rifle
- NEW Rifle Load Development and Scope Testing Target
- Great B2B Target for Load Development and Scope Testing
- Dad Develops .223 Rem F-TR Load for his Daughter
- 6mm Creedmoor — How Velocity Changes with Barrel Length
Tags: .284, 7mm, F-Class, F-Open, Ladder Test, Load Development, Mark Walker, Seating Depth, Sierra Bullets
So you “jam”, and then jam more.
No attempt at zero, or jumping?
No. His jam length is 3.477.
The lengths of the rounds tested for OAL are all less than that. They range from 3.460 to 3.470.
The confusion is probably from the sentence “I usually start at jam length and move the depth in 0.003 until I get to 0.015 deeper than jam.”
Deeper, in this case, would mean ‘deeper into the case.’
I had to read it twice to avoid the same conclusion.
Editor: Jerry — You are absolutely correct. I added an Editor’s comment to clarify this. Walker move the bullet deeper into the case in .003″ increments, ending up with a COAL .007″ shorter than max jam length.
I’ve noticed that the majority of shooters who “jam” use 6mm , 6.5 , etc.
Yet .308 gunners like Brian Litz and others tend to recommend “jumping”. Maybe it’s got something to do with chamber pressure ?
Articles like this are excellent reference information , but I would suggest that including the caliber and case size could be invaluable to preventing some novice re-loader from a catastrophic accident . Sometimes it’s what is not said that can be dangerous .
Key point he did not point out is where the vertical node was, notice the closeness of the muzzle velocity and then the larger jumps before and after the mode. I have found the chrono is an accurate tool to help validate a node