Noob Alert - sweetspot to high?

[Wanderlust]

Ok noob question for all of you: is 46 grs Varget w/ 175 SMK too much?

I performed an OCW Test @ 100 yards @ 87 Deg F, with:
700P .308 26" barrel
42 - 46 gr Varget (.5gr increments)
175 gr SMK seated to 2.81" OAL (magazine max)
CCI BR2
LC Match Brass
3 round groups

There "seemed" to be a sweet spot at 42.5gr and 46gr, with 46 being the best. There were no signs over overpressure, at any stage.

The plan is to rerun the OCW in smaller increments around the 46gr node (45.4 - 46.3 gr)

So all thing being equal, is there any drawbacks to using such a hot load? I.e measurably reduced barrel life, danger in higher temps, etc. I'm a little leery of being a full grain + over book max of 45 grains.

 

[glock24]

Re: Noob Alert - sweetspot to high?

That's a little hot for me, so yes, I believe you are correct in being concerned.

I've run OCWs on three SPS-Ts, and the highest I've been able to go on all three was 45.2 grains before seeing pressure signs.

I'd love to see your OCW targets. 95% of the guys who load is combination report an OCW between 44.3 and 45.0 grains. My three rifles liked 44.5, 45.0, and 45.2 grains respectively.

Personally, I'd consider rerunning your test using 0.3 grain increments. I bet if you tested between 43.7 and 46.0, you would see another sweet spot in there somewhere.

Here's one of my OCW tests with the exact same load, except this one is running Winchester brass;


(Test 1 - charge weight, 44.5 grains chosen)

(Test 2 - seating depth, all at 44.5 grains)

 

[aggiesig]

Re: Noob Alert - sweetspot to high?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: glock24</div><div class="ubbcode-body">


(Test 1 - charge weight, 44.5 grains chosen)

</div></div>

I'm not the most familiar with the OCW test but why did you choose 44.5 out of that test bunch?

 

[glock24]

Re: Noob Alert - sweetspot to high?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: aggiesig</div><div class="ubbcode-body">I'm not the most familiar with the OCW test but why did you choose 44.5 out of that test bunch? </div></div>

OCW was explained to me by Dan Newberry. His website does a great job of explaining the gory details.

In short, the first stage of any OCW is to find the most stable point of impact (POI) in a progressive series of 3-shot groups. <span style="text-decoration: underline">Forget</span> about the smallest group, just examine POI. In my specific case, I was looking for the groups in the series that offered the most stable relationship between the center of the 3-shot group and the black square. As you can see from my picture, 44.3, 44.6, and 44.9 grains all placed their bullets just off the lower, right-hand corner of the squuare. By comparison, you can see POI drifting around in the other charge weights, both higher and lower. Yes, the group sizes look better in some cases, but I don't care.

The powder charge to choose would then be right in the middle of this most stable POI grouping. Why did I choose 44.5g specifically? I decided to stay just below 44.6 grains because I didn't like how my diagonal stringing changed slope between 44.6 and 44.9. See how the diagonal goes from high to low, and then low to high as you scan left to right? Dan says that is most likely a spot in bullet velocity where barrel whip is changing directions. I decided an OCW that kept my barrel whip moving in one direction would be a good thing, and still have a stable POI. 44.5 grains seemed like a good choice. Your mileage may vary.


And it is as simple as that. With 44.5 grains as my the chosen OCW, the second test simply varies bullet seating depth as a means of tuning in group size. Now I have the best of both worlds; 1)small groups, and 2)optimized long-range performance despite powder temperature and environment fluctuations that will ultimately affect my bullet's velocity.

 

[Wanderlust]

Re: Noob Alert - sweetspot to high?

On Saturday I'll be rerunning the .3gr test, I'll post up the scan. Oddly 44.5 was my worst node, both elevation and group size.

 

[glock24]

Re: Noob Alert - sweetspot to high?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Wanderlust</div><div class="ubbcode-body">On Saturday I'll be rerunning the .3gr test, I'll post up the scan. Oddly 44.5 was my worst node, <span style="color: #FF0000"><span style="text-decoration: underline">both elevation and group size</span></span>. </div></div>

It doesn't sound to me like you're conducting an OCW test, at least not the way I've described.

I guess I'll wait to see your results.

 

[aggiesig]

Re: Noob Alert - sweetspot to high?

Thank you for the explanation. I'm waiting for my Forster CO-AX to come in before I can start working up my own group size. Cabelas original delivery date of March 13 has now been pushed back to April 30

 

[vman]

Re: Noob Alert - sweetspot to high?

Perhaps Wanderlust is also looking for consistent MV which is an indicator of a good load.

Im no subject matter expert on the pros/cons and the best load development methods to use.

But i do believe that you can probably still identify an area of consistent MV using the OCW, even though it may not be the intended purpose of the test.

 

[Wanderlust]

Re: Noob Alert - sweetspot to high?

Well I wasn't able to run the 175 gr test, but I did run the 168 far more "normal" results.