OCW Load Work Up Part 2- Varrying Seating Depths.
So in the last post, I talked about running an OCW test using 155 grain Nosler Custom Competition bullets in my 308 rifle. If you want to catch up on the original OCW test you can view that post here: Nosler Custom Competition OCW Work Up. I settled on a load of about 45.6 grains of Varget as being in the "sweet spot" for that rifle, bullet and powder. From there I decided to experiment a little with seating depth.
Personally, I have never really messed with seating depth very much. I typically set the bullets about where the manual suggests and leave it at that. I have a Hornady LNL overall length gauge and tried to figure out the length to ogive measurement for the Nosler Custom Competition bullet in my factory Remington 700 Varmint barrel. Unfortunately, Remington barrels are notorious for having long throats and mine was no exception. I wasn't very confident with the measurements that I was able to get, and that was because there was not even close to enough room to seat the bullet and touch the lands. With the bullet touching the lands, the boat tail would barely be in the case mouth.
With that in mind, I decided to use the manual measurement of 2.8" and increase in two separate .010" increments. That gave me loads with 2.8", 2.81" and 2.82". I decided to load up 20 rounds of the first and 10 rounds of each of the second two. That would give me enough to shoot at least two five round groups with each load and a few extras of the shorter load for sighting, etc.
The weather on this trip was a little warmer, the average temperature for this range session was about 40 degrees, so about 20 degrees warmer than the previous OCW test day.
Once at the range I set up two targets to fire the test loads at. One page of four targets took all of the 2.8" loads and the remainder of the 2.81" and 2.82" loads were fired onto the second page.
First, let's take a look at original 2.8" load target:
When I started shooting these groups I added about 1" of elevation to the turret to get the bullets to impact in the grid and not to affect the aiming point. Also ended up adding a couple clicks to the right as I shot, and still ended up hitting about a 1/4" left by the end.
First off, I will say that I was a little disappointed with the results. Even the smallest group is just over an inch. I also noticed that the velocity was a little faster over the previous OCW test, with an average of 2914 fps, vs the 2880 fps that I got with this powder load on the original work up. Now, the temperature was about 20 degree warmer and I fired a total of 20 rounds of this load, vs. only three the first time.
Another larger negative of this load was the standard deviation (SD), a whopping 25! Now, my chronograph has a simple display and I have to hand write all my results, so I generally have not been taking the time to figure out standard deviations, so I don't know exactly what my previous loads have been getting, but I know this number is high! While I may be able to get decent accuracy at 100 yards with loads that have a high SD, that will definitely hurt me at the longer ranges.
Before we go too far into any conclusions, let's take a look at the next target. This target shows the groups for 2.81" on the left and 2.82" on the right:
Once again, the overall accuracy wasn't especially impressive. I did manage one group under an inch (top left), but the rest are all over an inch. I decided I couldn't really pick a load from these tests based on group size alone. I decided instead to look further into the SD. The 2.81" load gave me an average velocity of 2897 fps over 10 rounds and an SD of 21. That was a little better, but still definitely lacking.
The 2.82" load on the right gave an average velocity right back at the 2880 fps mark and an SD of 12. While it still could be better (single digits please!), it was much better than the others. Now this was only 10 rounds vs. the 20 shot with the original load, so that could definitely have an affect.
What next?
After shooting these groups I'm not completely decided on what I want to do. I didn't have time to do any more load work up prior to shooting in a local 300 yard match, so I loaded up the 2.82" load with the better SDs and decided to try that at the match. I was able to hit all of the targets from the prone position, starting with a cold bore shot on a 3"x 4" steel rectangle. That seems to be adequate accuracy for the MOA size targets during this competition.
As I write this I am preparing to shoot the Cheyenne Mountain local match again tomorrow and I'll be able to get a better idea if the accuracy continues out to longer ranges.
Practical Accuracy
One of my big questions right now is what kind of accuracy should I be trying to get? I would currently say that my rifle shoots an average of one MOA. I actually started writing down my five round groups so that I could track and average the groups that I'm getting. Since that started more recently I only have about 40 groups written down so far, but I think that is a decent sample to start showing my capability and the rifle's over various range trips and loads. I have shot a few groups that are under .5 MOA, including three into one target, but I have also had days like today, where I was barely able to shoot a group under one MOA.
Tracking those 40 groups shows an average group size of just barely over one MOA. I think that shows me that while on a good day I am able to shoot a little better, that is what I should really expect from this rifle.
So is that my practical limit, or is that the accuracy limit of the rifle? Unfortunately that is the big question I am asking myself right now. I know there are definitely times that I pull shots, or just don't shoot well. But there are also groups that I feel really good about when the trigger breaks, but they still end up over MOA. That's how most of the groups above felt. I actually felt like my shooting was right on for this trip, but the groups didn't really confirm that.
I have signed up for my first Precision Rifle Series (PRS) match, the Battle of Breakneck. Unfortunately I won't have the money and time to buy a new rifle, or barrel and get a new load worked up in time for that, but I am definitely considering if I am starting to run into end of the practical accuracy available from this combination. I mentioned in the first article in this series that I bought 1000 of the Nosler bullets to load and shoot. I think that when I run out of those bullets I will be seriously considering whether I should keep shooting this rifle the way it is, or have it trued and re-barreled.
What are your thoughts on load work up, practical accuracy and re-barreling? Let me know in the comment section below:
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| Loaded 308 in Magpul AICS magazine. |
With that in mind, I decided to use the manual measurement of 2.8" and increase in two separate .010" increments. That gave me loads with 2.8", 2.81" and 2.82". I decided to load up 20 rounds of the first and 10 rounds of each of the second two. That would give me enough to shoot at least two five round groups with each load and a few extras of the shorter load for sighting, etc.
The weather on this trip was a little warmer, the average temperature for this range session was about 40 degrees, so about 20 degrees warmer than the previous OCW test day.
Once at the range I set up two targets to fire the test loads at. One page of four targets took all of the 2.8" loads and the remainder of the 2.81" and 2.82" loads were fired onto the second page.
First, let's take a look at original 2.8" load target:
First off, I will say that I was a little disappointed with the results. Even the smallest group is just over an inch. I also noticed that the velocity was a little faster over the previous OCW test, with an average of 2914 fps, vs the 2880 fps that I got with this powder load on the original work up. Now, the temperature was about 20 degree warmer and I fired a total of 20 rounds of this load, vs. only three the first time.
Another larger negative of this load was the standard deviation (SD), a whopping 25! Now, my chronograph has a simple display and I have to hand write all my results, so I generally have not been taking the time to figure out standard deviations, so I don't know exactly what my previous loads have been getting, but I know this number is high! While I may be able to get decent accuracy at 100 yards with loads that have a high SD, that will definitely hurt me at the longer ranges.
Before we go too far into any conclusions, let's take a look at the next target. This target shows the groups for 2.81" on the left and 2.82" on the right:
Once again, the overall accuracy wasn't especially impressive. I did manage one group under an inch (top left), but the rest are all over an inch. I decided I couldn't really pick a load from these tests based on group size alone. I decided instead to look further into the SD. The 2.81" load gave me an average velocity of 2897 fps over 10 rounds and an SD of 21. That was a little better, but still definitely lacking.
The 2.82" load on the right gave an average velocity right back at the 2880 fps mark and an SD of 12. While it still could be better (single digits please!), it was much better than the others. Now this was only 10 rounds vs. the 20 shot with the original load, so that could definitely have an affect.
What next?
After shooting these groups I'm not completely decided on what I want to do. I didn't have time to do any more load work up prior to shooting in a local 300 yard match, so I loaded up the 2.82" load with the better SDs and decided to try that at the match. I was able to hit all of the targets from the prone position, starting with a cold bore shot on a 3"x 4" steel rectangle. That seems to be adequate accuracy for the MOA size targets during this competition.
As I write this I am preparing to shoot the Cheyenne Mountain local match again tomorrow and I'll be able to get a better idea if the accuracy continues out to longer ranges.
Practical Accuracy
One of my big questions right now is what kind of accuracy should I be trying to get? I would currently say that my rifle shoots an average of one MOA. I actually started writing down my five round groups so that I could track and average the groups that I'm getting. Since that started more recently I only have about 40 groups written down so far, but I think that is a decent sample to start showing my capability and the rifle's over various range trips and loads. I have shot a few groups that are under .5 MOA, including three into one target, but I have also had days like today, where I was barely able to shoot a group under one MOA.
Tracking those 40 groups shows an average group size of just barely over one MOA. I think that shows me that while on a good day I am able to shoot a little better, that is what I should really expect from this rifle.
So is that my practical limit, or is that the accuracy limit of the rifle? Unfortunately that is the big question I am asking myself right now. I know there are definitely times that I pull shots, or just don't shoot well. But there are also groups that I feel really good about when the trigger breaks, but they still end up over MOA. That's how most of the groups above felt. I actually felt like my shooting was right on for this trip, but the groups didn't really confirm that.
I have signed up for my first Precision Rifle Series (PRS) match, the Battle of Breakneck. Unfortunately I won't have the money and time to buy a new rifle, or barrel and get a new load worked up in time for that, but I am definitely considering if I am starting to run into end of the practical accuracy available from this combination. I mentioned in the first article in this series that I bought 1000 of the Nosler bullets to load and shoot. I think that when I run out of those bullets I will be seriously considering whether I should keep shooting this rifle the way it is, or have it trued and re-barreled.
What are your thoughts on load work up, practical accuracy and re-barreling? Let me know in the comment section below:
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