Range Report COAL and POI

[Tempest 455]

Forgive me, I have used search and found similar topics but not exactly what I'm looking for. I'm hoping someone who has some experience with this can answer my question.

I did a ladder test last weekend on some .308 rounds with a Savage 10BA. They were 175g SMK and Varget powder with BHA brass. My son did all the shooting and we stayed at 400 yards. Everything went pretty much as I expected with regards to the various grains, POI etc.

However, when he was done, I had him shoot against a known standard we always shoot, Black Hills 175 SMK ammo. One thing I found strange was, the POI was moved over to the left. Elevation was the same as my 43.5g Varget loads (which I was trying to duplicate Black Hills). Got home and measured some BHA ammo and the COAL was around 2.79 give or take a thou. Mine were all 2.810 or so.

Can this little of a difference cause a left-right variation?

 

[melloyello]

Lots of different things could be playing a part in this. Is your neck tension the same as the BH ammo? Same powder, same charge? Same primers? The list could go on I am sure. It could come down to the timing of the bullet exiting the barrel and it probably will. If you only change one thing in the recipe it can possibly change POI. I don't know how much of a change you saw b/c you only stated it moved left. You didn't say how much. But, if you saw a 2" difference at 400yds then that would equate to only .5" @ 100yds. So, it's really not that much of a difference but something I would definitely note in my log book. I wouldn't worry about duplicating BH ammo. Since you were doing ladder testing, pick the node that suits your gun. If you pick the right one you won't be shooting anymore BH ammo.
Also, read up on OCW testing and you will see how only being 1/2-1gr off can make a difference in POI. Different lots of powder can make a known good recipe go awry. It might not be much at 100yds but it multiplies as you extend your range. 1/2" difference at 100yds equals 5" at 1000yds.

 

[Tempest 455]

Thanks for the response. No way of really knowing the powder and primer on the BHA?

I saw a 1 min difference at 400. That's why I was asking. Going to a 1,000 yard match next month and looks like it would be a pretty significant difference. If I have time, I will set some to the same length and go try this again. Thanks for the other comments. Yes I can see how a number of other variables can have an effect.

 

[melloyello]

If you make notes for the difference between BHA and your load then all you will have to do is dial in the extra windage for the shift depending on which ammo you zero with. If your zero is set with BHA then in your log book make a note that your load shoots x amount left or right at 100yds or in your case 400yds. I would verify that the 1" you are seeing at 400yds actually equals 1/4" at 100yds.
I like to zero for one round and make notes for any other round. But, I like to test more than once to verify. I do recommend though that you build a round for your rifle and zero for that round. If for some reason you run out of that load you can always shoot factory ammo. If you plan on shooting in 1000yd matches your best bet is going to be a load that you can control yourself. I wouldn't want to rely on a factory load even if it is a match load like BHA or Hornady.

 

[Enough Said]

Was the POI shift to the left the center of a group, or just one round?

 

[jthoffma]

COAL and POI changes

I just got through some of my load development for my 7mm rem mag. I am shooting 168 gn. Berger VLD's and followed the procedure found in Berger's reloading manual to find optimal cartridge overall length (C.O.A.L.). The procedure was as follows:

1. I found the COAL where the bullet touches the lands (which happened to be 3.440" for my rifle).
2. I loaded six rounds .010" off of the lands, six .050" off, six .090" off, and six .130" off (see all of my load data in the image below).
3. I shot two three shot groups of each COAL at 100 yds.
4. I evaluated the data to determine the most precise COAL (in my case the COAL with .090" jump happens to be the most precise. The group shown is about a 3/4 minute group.)

Notice that the 3.310" and 3.390" groups have a horizontal variation of about 2 moa!

 

[Sterling Shooter]

OP,

Here's the big picture, when anything is different you should not expect to get the same. But rather than wasting time pondering the difference, after all it's what you'd expect, and you already know what was different, concentrate on what it is you want to accomplish. which is hitting where aimed. What does it take to hit where aimed? It takes consistency. So, assuming your rifle is not broken, just make your ammunition consistent, make your position consistent, and adjust sight for trajectory need. What you are doing now will not get you to your destination.

About your ammunition, loading to win at LR is about loading to hold elevation and get to distance nose on. That means loading for a low SD and ES, as well as an average muzzle velocity that will get the bullet to target before the bullet begins to fly erratically. For a low SD and ES, component weights, and neck tension will need to be controlled; and, you will likely need to experiment with bullet seating depth. Concentrate on these things in pursuit of shooting zero dispersion and you will see progress instead of the ciaos you are now experiencing.

 

[HillbillyfromAL]

^^This X2


Also I'd suggest load development take place at 100yds/m. Then you are eliminating the wind for the most part. Also you'd have to shoot groups of ammo in which the COAL was the only variable to tell if its the source of the discrepancy.

 

[Tempest 455]

I was reading on this topic and forgot about making this post. Update on this:

My son and I went to another 1,000 yard F class match. He shot SWA ammo for the match. At the end of relay #3, he shot 4-5 of my handloads mentioned above.
I figured what better place to see how they shoot at 1,000 than actually shooting at 1,000 with someone marking your target. At the end of relay 3, he was shooting 9's, 10's and had 3 X's with the SWA. He shot the handloads above at COAL of 2.810 and 43.5g of Varget. Rounds were on target except 2-3 min high and to the right. Around 2 O'clock on the paper. Grouped pretty well in the same location.

So looks like the velocity is faster (I know I need to chrono) and need to back off a bit. Otherwise, they were consistent. It appears this load will work for this.

So my next question: Would you just leave as is and adjust. Or, continue to fine tune the amount of powder and COAL?