How I work up a new reload

[SA Friday]

Well, I haven't had much time to do a new info thread in quite a while. Hell, for that matter, I haven't had much time to do much of anything I would consider fun. So, I ad to rebel a little over the last week and pull the trigger on something or risk my sanity. I figured I could talk about it a little too.

I have just started working up reloads for the 308 PSS I picked up over the summer. With the recent arrivals of the materials I needed to do this, I started working some reloads for the rifle. I chose to go with 175gr Sierra Matchking bullets for their weight and BC properties along with their reputation for accuracy. I chose to go with Lapua brass and Varget for powder as I can use this also with the 223 long distance reloads with heavy bullets. Lastly, I decided to go with CCI LRP's instead of benchrest or fru-fru fancy primers.

After researching the load, I found most were getting the best accuracy with this combo at around 44.0-45.0 gr of varget and an OAL of about 2.8 to 2.81. I checked my mag box and found 2.805 was about all I could squeak out without risking a round binding in it, so I limited my OAL to this. It just so happened to be the same OAL of Federal match ammo too. I checked my dimensions in the throat and found the box to be the limiting factor. I expected this, and wasn't too concerned as I was getting just shy of 1/2 MOA with the Fed match ammo.

After setting the dies and resizing the brass, I decided to test by groupings instead of a ladder test. I've never been too fond of ladder testing, and prefer to see the data from groups initially. I worked in .5gr increments from 43 to 44 and then tightened up the increment to 44.2, 44.5 and 44.7. I did this for two reasons. I wanted to see what kind of pressure signs I would get on the brass at a lower level of pressure initially, and I suspected I would find the best accuracy in the 44.x range so wanted to get as much data as possible in that range. Having a caliber that's so well mapped out and discussed on blog sites really helps out narrow the guess work.

The testing showed the rifle and ammo combo really likes the 44.0gr of Varget range. It shot just shy of 1/2 MOA edge to edge in the 5 round group. I had some weirdness at 44.2 that I have to retest and see if the accuracy started to open up or if it was just me anticipating instead of shooting. As this is an initial set of data, I know it will iron itself out with a couple more test runs.

You can see where the pattern literally tightens up and then falls apart again when looking at the targets. You can also see that a well made gun with the right components will still shoot sub-moa. None of the groups were bigger than an inch edge to edge in any of the tested charges. The smallest was 0.585". This is essentially a factory gun with a few asthetic changes, not blueprinted nor bedded. I shot all the groups off a bench at 100 yds. I started to see a little pressure sign on the primers at 44.7gr, but it had more to go if I wanted. Considering the accuracy results, there really isn't much reason to though.

I'll post the results after redoing the pics. It's too big to attach the photo of all 6 together. The results followed everything I have ever seen in working up reloads all in one session. The groups were circular and shrinking as it got closer to peak accuracy, then it strung the shots just past peak accuracy, and finally started double grouping as it got further away. I've see these results in other rifles I have reloaded for and they seem to hold fairly constant in determining where to go with the powder charge as long as the rest of the variables are within the range the rifle prefers. I have seen double groups when well below the peak of accuracy too. I probably would have seen this here also, but started high enough to not have it happen. Also, 308 is a fairly efficient cartridge. I believe the efficiency of the cartridge comes into play with just how precise the rifle will be when it comes to that peak accuracy. The more efficient the cartridge burns the powder the wider the peak accuracy range will be. Less efficient burning cartridges will be much more picky in their need to be exact in OAL, powder charge, and bullet choice. I saw this in the 270 Sendero I have. It drives tacks, but it gave me fits to find the exact combo of components and tolerances to get it to shoot accurately.

I'll work on the pics tomorrow night after class.

[coop68]

have you tried using a chrono?

From my experiences in High power and shooting .223 at 200,300 and 600 yards when ever i buy a new keg of varget. i work up a new load going by the FPS my rifle likes.

example: i load 24.5gn of varget i get 2750FPS with a 77gn molly coated bullet with one keg and the next one i buy to get 2750FPS i might have to use 24.3 or somthing in those lines. i would try going by FPS as burn rates can change from keg to keg as they aren't perfect they are just trying to get it into a ball park for that powder.

so fare what you have i think is in the right direction. The FPS idea has been given to me by other shooters who have been in the game way longer than me, so im still testing it as i go. might help explain the variation in groups as difference in FPS will change Point of impact if im not mistaken.

[Colorado Osprey]

have you tried using a chrono?

From my experiences in High power and shooting .223 at 200,300 and 600 yards when ever i buy a new keg of varget. i work up a new load going by the FPS my rifle likes.

example: i load 24.5gn of varget i get 2750FPS with a 77gn molly coated bullet with one keg and the next one i buy to get 2750FPS i might have to use 24.3 or somthing in those lines. i would try going by FPS as burn rates can change from keg to keg as they aren't perfect they are just trying to get it into a ball park for that powder.

so fare what you have i think is in the right direction. The FPS idea has been given to me by other shooters who have been in the game way longer than me, so im still testing it as i go. might help explain the variation in groups as difference in FPS will change Point of impact if im not mistaken.

I agree this is a great way to determine batch variances. You must also match temp or or results could be off quite a bit. Meaning, if your load on a 70 degree day was 2700ft/sec and you retested with a new batch of powder at 50 degrees and the velocity was 2650ft/sec it could just be the temperature and not the powder.

Lastly, I wasn't aware that others payed that much attention to velocity. Most shoot for group size and best velocity. I have found harmonic balances where certain velocities will give you good groups. 2700'ish, 2900'ish and 3100 ft/sec seem to be sweet spots for accuracy. I load most of my ammo for 2900ft/sec. Even different guns and different calibers.

[SA Friday]

Yes, I chrono my loads, but this being the very initial run the velocity is moot. I have nothing but factory to compare it to. If I was switching from one lot of powder to another, I would test over the chrono first and adjust accordingly.

In a peticular caliber, velocity is just one form of determining a general idea for the accuracy node (or nodes) for a rifle. But think about this; are you not typically using powders with similar burn rates in the same to produce the velocity and therefore oscillating the barrel at the same speed? The barrel harmonics are a function of Sine. If you graph sine, you get a general barrel oscillation during the bullet's trip down the rifling. The circular rotation of the barrel is essentially irrelevant, because your peaks (both the high and low ranges) on the Sine graph are your accuracy nodes. I suspect this is also why you see as a general rule a repeated pattern from targets as to if you are above, below, or near the accuracy node. The range that accuracy is found at, how big or small a variance in powder charge will still result in proximity to the accuracy node, is a function of a phase shift to the Sine function.

[SA Friday]

OK, pics. This is below the accuracy node.

[SA Friday]

At the accuracy node. 44.2gr is funky. I need to retest this area. There is obvious potential here.

[SA Friday]

Above the accuracy node. 44.5gr strung vertically. This was not my breathing. 44.7gr started to separate into two impact locations.

[jerrymrc]

I load for groups within a certain range then break out the crono. For the semi autos in .223/308 I start with .5gr differences. I also look at POI vs some of the surplus I have in .308

No good sitting on 3K of accurate surplus when the reloads are 10" off of your stash. And just for the record my .308 surplus is Aussie boxer primed 148Gr.

Most of the .223 guns like a little slower load for groups. My accurate 55gr loads crono at 2875 or so.

[Hoser]

Good info there Sean.

I cheat. I start by calling Sierra and asking what their pet loads are.

Breaking out the chrono is the last thing I do once I have settled on a load.

[Tim K]

Breaking out the chrono is the last thing I do once I have settled on a load.

Yup, same here. I really don't care how fast it's going as long as I know the number and the load shoots in my rifle.