Load Development ES & SD

[Belton45]

Short barrel ? 2762 fps seems low using 44.9gr 8208 with a large primer.

20”

 

[Straightshooter1]

Lapua LRP, 210M, went from 44-44.9 today. 2762 was with the 44.9 load.

That velocity looks about right to me for a 20" barrel. . . with a COAL of 2.800.

 

[Martin52]

20”

Just out of interest I ran your load through GRT (the compact version). Assuming: 20 inch barrel (bolt face to muzzle) 56 grain H2O case capacity, 2.005 case trim length, 2.800 COAL, 44.9 gr 8208 and 2762 fps - the highest OBT node before getting too close to max pressure is around 43.6gr 8208 for 2687 fps.

Might be worth trying next time out - but as always, believe the target...let us know if this helps reduce your ES and SD.

 

[Belton45]

Just out of interest I ran your load through GRT (the compact version). Assuming: 20 inch barrel (bolt face to muzzle) 56 grain H2O case capacity, 2.005 case trim length, 2.800 COAL, 44.9 gr 8208 and 2762 fps - the highest OBT node before getting too close to max pressure is around 43.6gr 8208 for 2687 fps.

Might be worth trying next time out - but as always, believe the target...let us know if this helps reduce your ES and SD.

That’s wild!!! 43.6 was my best group… I had something odd between 43.6 & 44. Velocity dropped. Keep in mind I only shot these 4 per load but all the rest were increasing in velocity. These went flat.

43.6 2706
44.0 2703

 

[6.5 forever]

Even Lapua brass needs a few firings for consistency.

 

[mgunderson]

308s are stable and relatively easy to tune. 10 fps sd or less is your goal. Any of 155 class bullets with ready well with some seating depth adjustments. Look at seating depth with a new barrel and fire form brass. New brass can create sd/es variations. More roomy factory chamber often add to this. That doesn't mean it won't shoot.

 

[Belton45]

That’s wild!!! 43.6 was my best group … I had something odd between 43.6 & 44. Velocity dropped. Keep in mind I only shot these 4 per load but all the rest were increasing in velocity. These went flat.

43.6 2706
44.0 2703

Shot again today and 43.6 was best group again. Seen the same velocity go flat again at same charge. This was 2nd firing on that brass and was FL sized with .002” shoulder push back. Was slightly warmer by about 5 degrees and velocity dropped just a bit. I assume case volume is more with fire formed brass and caused just slight velocity drop?

43.6 2699 SD14 5 Shots
43.8 2693 SD 7 5 Shots

 

[Martin52]

Sounds like you're getting good groups using 43.6 grains. At this stage I wouldn't be concerned over the slight fall in velocity, I'd shoot some more at 43.6 grains to increase the sample size, keep a record of the ES, SD and group size and see if the load holds up.

 

[Stickflinger]

Without knowing your process I’m going to say you don’t have consistent neck tension. As far as new brass vs fire formed it will improve but you CAN in fact get pretty good numbers out of new brass depending on what brass it is. But I would run a mandrel on them before I shot them new and get a good chamfer on them. Another truth is some guns don’t like a particular powder. I have a 260 that I threw everything at with H4350 and it would do anything. Switched to H4831sc and the numbers and the groups got small in a hurry. Just my 2 cents.

 

[RabbitSlayer]

I do think you could do better with turned lapua brass. Those sd\es are about what I get in 6 creed with hornady brass with basically no tuning in a custom barrel. 3rd firing. My brass prep is similar to yours. .002 bump, anneal, creedmoor scale +- 0.02 gr. I should hope turned lapua would give you better results. I shoot larger samples 25+. Now sometimes more like 100 shot samples with the garmin. I think a lot of ES on the internet is small sample size BS.

 

[Belton45]

I have not switched to mandrels yet for setting neck tension, although I think I need to. Brass is turned to within a few tenths neck wall. Using a .334 SAC bushing. Necks turned to .014”. Loaded round all measure .336”. These are verified with micrometer and neck thickness micrometer. Been using 210M primers. I do have some regular 210 and some CCI I could try. Think I’m about to throw some Varget and see what those look like. Groups are .5 MOA so not terrible and it just a regular Tikka Proof prefit, not a custom chamber or anything.

 

[Belton45]

Well I dug around and I did have a .306 mandrel and I had a .332 bushing. So loading up some with mandrel sized and will see if es&sd change.

 

[Evlshnngns]

Well I dug around and I did have a .306 mandrel and I had a .332 bushing. So loading up some with mandrel sized and will see if es&sd change.

Let us know how it goes.

 

[JEFFPPC]

Have you found a load that yields the group (dispersion of shots on target) that you need for your shooting discipline?

 

[Belton45]

It shoots good. Just playing with reloading technique to see if can get lower es and sd. Call this an experiment. Lol.

 

[D-4297]

I'm very likely going to get "TORCHED" for saying this , but personally , I think people spend way to much time worrying about SD / ES numbers . My opinion on this is it is more a "quantifier" of your actual Brass Prep , than anything else . Yes ; there are other variables involved , but the better , and more consistent your Brass Prep becomes , the better your SD/ES numbers will get .
A "noted & respected multiple National and world champion won a National with a S/D of thirty-two ! Go Figure !

 

[searcher]

About being concerned with your SD's, those numbers are quite high, but don't necessarily translate into putting you at a big disadvantage. There are so many little things that can cause high SD's - powder charge, neck tension, brass quality, etc., etc. In my own experience, I have (painfully) learned that I can try a dozen powders, bullets and primers, but if my neck uniformity is off (especially when using medium to heavy tension - going through all the powder ladders, powder changes and primer changes are just a futile exercise. So, if you want to improve those numbers, I'd start right off being sure your necks are TOTALLY dialed in, and I'd not use more than .002" neck tension. I prefer lighter than that. Then you can focus on the other elements of what you can do to improve them. I see bigger differences in powder charge settings and seating depth than I do from simply having fire-formed the cases - from which you will get the biggest result if using a custom die (or neck sizing only). I have noticed that I can get super-low SD's using a small base die, so in my mind that shows me that the biggest benefit from fireforming was likely just the brass getting straightened out during the fire-forming. The frustration of using a chrono is that it MAY show you that your "favorite" powder is just not capable of giving you the SD's you want with a particular bullet - regardless of what your target says is good. So, then you are faced with deciding to swap powders and start over - something I'd do if shooting long range. It depends a lot on your shooting discipline, I think.

 

[ORjeff]

For what it's worth I am, among other things, a professional experimental scientist and data analyst and just a little bit of a fanatic about careful load development with the 308 being what I have worked on the most. Ignore SD, the probability that anyone here is creating a data set where SD is meaningful is almost zero. Just because your Chrono knows how to calculate it doesn't make it meaningful. If you need to understand that take a class on statistics. ES can be useful but it's just one of many things that you need to dial in. The further you are shooting the more important it becomes to minimize velocity spread to get tight groups. Let the target tell you what matters for what you are doing. Focus on good case prep and finding the right combo of powder charge and seating depth to get tight groups. Max velocity is not interesting, consistent velocity is. To really dial it in you need a precision scale. You said you have some H4895, that has outperformed ever other powder that I've worked with but it's rarely available so I stopped using it and switched to N150.

 

[Belton45]

For what it's worth I am, among other things, a professional experimental scientist and data analyst and just a little bit of a fanatic about careful load development with the 308 being what I have worked on the most. Ignore SD, the probability that anyone here is creating a data set where SD is meaningful is almost zero. Just because your Chrono knows how to calculate it doesn't make it meaningful. If you need to understand that take a class on statistics. ES can be useful but it's just one of many things that you need to dial in. The further you are shooting the more important it becomes to minimize velocity spread to get tight groups. Let the target tell you what matters for what you are doing. Focus on good case prep and finding the right combo of powder charge and seating depth to get tight groups. Max velocity is not interesting, consistent velocity is. To really dial it in you need a precision scale. You said you have some H4895, that has outperformed ever other powder that I've worked with but it's rarely available so I stopped using it and switched to N150.

Thanks for the info. I have moved on from 8208 to N140 (I had some of that to try, also have about 6lbs of H4895….). I also ordered some expander mandrels to use for setting neck tension instead of using just neck bushing. Have had some ugly weather recently so have not had a chance to give new ideas a try.