Load development for same barrel length?

armybuck041

armybuck041

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Hey Guys,

I little while back I cooked up a nice load for my .308" Sig Cross with the 16" factory barrel. Essentially running a very spicy 130gn Barnes TTSX over 49.7gn of Varget at a COL 2.840". Was giving me a nice repeatable 1/2 MOA (5 shot group) at 100 yards and a nice velocity of ~3010fps with an SD of 8.6fps.

I love the Sig Cross platform enough that when the Sawtooth version of the same rifle with the 16" Proof Research carbon fibre barrel came out, I couldn't resist. It's just under 8lbs fully loaded with a Leupold Mark 5HD 3.5-18 in Leupold Mark 4 rings. A delight to carry. Shoulders beautifully.

So, got it all setup and headed out with a box of my pet load 130gn TTSX...

Long story short. Getting roughly 2 MOA with the same load. Fired about 40 rounds and called it a day.

Looks like I need to go through some load development again.

So my question is, given that it's the same length barrel, does the brain trust here at CGN think I skip the charge weight portion of the load development and just focus on seating depth? Or do I need to repeat the complete process of finding a charge weight node followed by finding the seating depth node?

Thanks!

Some gun ####:
dsOXZhf.jpg

tFHj5OY.jpg
 
Interestingly enough, I just checked the COL to jam on this barrel and it’s longer than the magazine length, whereas the original Cross wasn’t. I’ll start making up some ladder powder charge loads using the magazine length as the COL (2.885”ish) and go from there.
 
49.7 gr of Varget seems like a lot of powder and is .5 gr over Barnes published recommended Max compressed load. What brass are you using and what does a fired case look like?
Barrel length has nothing do with what load will work in one barrel and not the other. One barrel is SS the other is SS/carbon wrapped. Think about a tuning fork. Barrel harmonics have more to due with accuracy than max velocity.
You can have 2 barrels made one after the other from a manufacturer, same length, same bore, same groove, same twist, same chamber, one barrel will shoot faster than the other.
 
As Maynard has stated, two barrels of identical dimensions will not automatically shoot the same load well.
You may be able to use your original data as a benchmark in some instances, but I would start from square one, myself, especially since you are right t the upper end of the load for that combination.
Cat
 
Thanks for the comments fellas. This all makes sense.

Case in point; chamber (jump to the rifling anyway) is quite a bit different on this new one compared to the previous one, not to mention, the barrel harmonics changing from barrel to barrel as you guys pointed out.

I put together a ladder of powder charges from the bottom to the top of the table (3 rounds for each 0.3gn increment) in order to start the process over again. Loaded them all to the max COL that functions in the PMAG that comes with the rifle (2.882") which is still well off of the lands.

Never had any issues with the load mentioned above. Agreed it's at the top of the scale, but I've had no appreciable pressure signs and I've fired well over 100 at this point. When I was going through the load development last time, it was evident that these 130gn TTSX liked to be pushed hard, at least in that particular rifle. Got two distinct nodes; one at around 48.7gn and the other at 49.7gn. The latter picked up approximately 150fps and the SD dropped down to under 10fps consistently. Given it's a 16" barrel, I wanted every last bit of energy I could safely and accurately pull from this load.
 
nodes don't exist, so I wouldn't devote too much time and components in trying different seating depths or charge weights.

Every barrel can like different bullets / powders. If you're set on the 130 TTSX, I'd try a few other powders and see if one stands out. If nothing works better, try a different bullet
 
armybuck041 said:
Hey Guys,

I little while back I cooked up a nice load for my .308" Sig Cross with the 16" factory barrel. Essentially running a very spicy 130gn Barnes TTSX over 49.7gn of Varget at a COL 2.840". Was giving me a nice repeatable 1/2 MOA (5 shot group) at 100 yards and a nice velocity of ~3010fps with an SD of 8.6fps.

I love the Sig Cross platform enough that when the Sawtooth version of the same rifle with the 16" Proof Research carbon fibre barrel came out, I couldn't resist. It's just under 8lbs fully loaded with a Leupold Mark 5HD 3.5-18 in Leupold Mark 4 rings. A delight to carry. Shoulders beautifully.

So, got it all setup and headed out with a box of my pet load 130gn TTSX...

Long story short. Getting roughly 2 MOA with the same load. Fired about 40 rounds and called it a day.

Looks like I need to go through some load development again.

So my question is, given that it's the same length barrel, does the brain trust here at CGN think I skip the charge weight portion of the load development and just focus on seating depth? Or do I need to repeat the complete process of finding a charge weight node followed by finding the seating depth node?

Thanks!

Some gun ####:
dsOXZhf.jpg

tFHj5OY.jpg
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NICE RIFLES! I just picked up a cross 308 win. I am also going to use the Barnes 130's. Thanks for a load idea. Which muzzle brake is that on your original cross ?
 
Ganderite said:
You could have bought 2 identical rifles, one digit apart in serial numbers, and each would be quite different. Don't argue with the rifle. Give it what ever it likes.
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Wrapped up the load development a few weeks ago. I don’t have the recipe in front of me, but it was pretty close to the previous load. Slight adjustment to the seating depth and powder charge. The barrel also really settled down after 50 or so shots. Next time I do this, I’m going to plan to put a bunch of rounds through it before I start to obsess about the loads.
 
armybuck041 said:
It’s an MDT Comp Brake. Really like it. Actually moved it over to the new Cross a few weeks ago.
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So did you work up your load with the brake on? That is a good looking brake. Did you remove any of the screws in the top to reduce barrel flip? I know I am asking a lot questions but I am stoked to find someone who has tried the combos I have been researching. Thanks for the great insight.
 
Compressed Load said:
So did you work up your load with the brake on? That is a good looking brake. Did you remove any of the screws in the top to reduce barrel flip? I know I am asking a lot questions but I am stoked to find someone who has tried the combos I have been researching. Thanks for the great insight.
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If you work up a load and then add or take something off the barrel, you’ve wasted your time in my opinion. Develop the load the way the gun will be fired. I don’t think shooting a Spicey load out of a new rifle is a great idea either. Guns are like fingerprints, no two the same. Nice looking guns btw
 
Compressed Load said:
So did you work up your load with the brake on? That is a good looking brake. Did you remove any of the screws in the top to reduce barrel flip? I know I am asking a lot questions but I am stoked to find someone who has tried the combos I have been researching. Thanks for the great insight.
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Correct. I installed the brake prior to doing the load development. Didn’t want to insert any variables to the process. I’m running the brake with the top ports fully open for the time being. I need to spend some time taking offhand shots to dial it in.
 
barrel lengths aside, these are two completely different rifles and the ammo they will prefer likely will be different. Try a different powder under the 130TTSX and it could change things better or worse than Varget performed.

I've seen a rifle that shot a bullet terribly under the first 9 powders tried, I was ready to flog the 500ct box of bullets on the EE and move on. The 10th powder I tried will do 1.5moa ten shot groups! So powder can definitely turn things around in a good way

If the new rifle doesn't like 130 TTSX, try a 150gr TTSX with a few different powders under it, could work awesome. I wouldn't muck around with seating depth tweaks as I haven't found them to really change the accuracy of the load
 
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