Seating Depth First Test of 105 Gungnir in 6 BRA, Thoughts?

[Buttstock-TX]

I've been shooting Bart's 105 Hammer for several months and recently purchased some 105 Bart's Gungnir bullets to test. I decided to try a seating depth first approach to load development because I've seen it advocated on this site.

Based on previous advice posts, I reduced my Hammer load by 0.2 grains and shot a spread of depths at 100 yards with the Gungnir in a blustery head wind (~12 MPH or so) with a small left to right crosswind component. On the target below, the upper left is a hammer group with the first three fowler shots from a clean barrel. The next group to the right starts the Gungnir test at -17/1000 (jump). I proceeded at 3/1000" increments into the lands. I skipped from -5 to +6/1000 because I've had a number of different bullets print poorly in that range.

My question is : The jumped bullets had the smallest groups but the worst ES's. Once I moved into the lands, the ES numbers dropped with increasing engagement and the groups started shrinking but were still not as small as the early jumped groups.

Intuition tells me I should explore the +12 to +15 engagement range some more and perhaps bump up charge weight up one or two tenths. Then, if that does not workout experiment with the -14 depth with some small changes in charge weight up and down.

Thoughts on this approach or any observations I may have missed? Thanks!

 

[JEFFPPC]

Before I put a lot of rounds down I would reshoot c in the first group. Round and small. ES doesn't win matches, good targets do. If it repeated I would shoot it at 300. If results were good I would take it to a match. Why waste your barrel when it counts for nothing?

 

[Buttstock-TX]

Good Point! The top left A group (fowlers) with the 105 hammers had an ES of 60 fps. I check at 550 yds once I've identified the best prospects at 100. Occasionally, I see groups that look good at 100 that don't hold elevation well a 550.

 

[JFrank]

I would not concern myself with es or sd as reducing the load could easily take it out of tune and possibly skewing the seating test somewhat.

 

[swd]

So if you didn't have a chronograph which would choose? Let the gun and target tell you what it wants.

 

[Bc'z]

I'm an advocate of seating 1st,
2 at 2.
If 2 ain't touching at 200 move depth .003.
I start .020 ITL and move backwards, I want to see where it goes out as well, then back up and confirm

 

[Gabe22BR]

I'm an advocate of seating 1st,
2 at 2.
If 2 ain't touching at 200 move depth .003.
I start .020 ITL and move backwards, I want to see where it goes out as well, then back up and confirm

Exactly!!!

 

[Fast14riot]

Your -7 and -14 loads had same poi. -17 started to move. Seating depth testing first is NOT about chrono numbers. Its about eliminating the noise while you tune powder, primer and neck tension.

Ditch the chronograph, develop your load on paper, then measure speed and see what it says. Go do long range and verify.

They don't give awards for best chrono numbers.

 

[ELR LVR]

Group C / 31.3 grns Varget / Seating depth of 2.730 (-.014") gets my vote
Looks like you are pretty much on the node
I'd try varying from there in .001" increments each way and see which direction it stays or shrinks

 

[Buttstock-TX]

I've always been a charge weight first developer and it's great to get all this thought and feedback! This is the first time I've tried seating depth first, but it made sense given the known performance of the two Bart's bullets. Thanks to all.

 

[Bottom Fodder]

Take your 3 best back to range and see if they repete if they do then you make the call which You like best and your happy your done if your not keep playing
Just my $ 0,02 which is not worth a dime

 

[Buttstock-TX]

I just made it back out to do the follow up tests of seating depth with Bart's 105 Gungnir at 100 yards.

I reshot depths that looked good before and added deeper into the lands groups. I also tried adding 1/10th grain of powder where I thought it might make a difference on the previous +12/1000 into the lands test.

Bottom line, the original -14/1000 still looked OK but, not as good as the first test. What really surprised was going deeper into the lands helped dramatically. The +15/1000 group was 39/1000 (0.039") and had a decent ES. This is the best group I've seen with this rifle to date. I am looking forward to trying it at 550 yds.

 

[Mark W]

I’m shooting a very similar load with Gungnirs in my 8 Twist BRA. I’m also at 31.3 grains of Varget, but I’m 0.012” into the lands at 2935 fps.

This load has given me 2.0”- 2.5” groups at 600 yards, which may be all I’m capable of…..lol. I plan to try to tweak it a little when I get a chance.

My phone flipped the pic when I took the picture, so this group actually had a more horizontal than vertical.

 

[Buttstock-TX]

I’m shooting a very similar load with Gungnirs in my 8 Twist BRA. I’m also at 31.3 grains of Varget, but I’m 0.012” into the lands at 2935 fps.

This load has given me 2.0”- 2.5” groups at 600 yards, which may be all I’m capable of…..lol. I plan to try to tweak it a little when I get a chance.

My phone flipped the pic when I took the picture, so this group actually had a more horizontal than vertical.

The barrel in this rifle is also 8 Twist. It's good to have further confirmation. I try to achieve ~0.33 MOA vertical at 550 yards for match loads when testing on the ShotMarker....

 

[JFrank]

I would follow up on each side of + 15 and it’s not just the group size but what’s happening on each side and how wide is the window. If you get my drift .

 

[Clancy]

Notice how 9 or more off the lands has never shot bad.

I’m glad you did seating first as I’m a big proponent of that, but I think you let the Chronograph pull you away from the whole point of the depth test.

That little dot looks nice, but it’s .003 of erosion away from disaster, assuming it’s repeatable anyway.

 

[JEFFPPC]

I just made it back out to do the follow up tests of seating depth with Bart's 105 Gungnir at 100 yards.

I reshot depths that looked good before and added deeper into the lands groups. I also tried adding 1/10th grain of powder where I thought it might make a difference on the previous +12/1000 into the lands test.

Bottom line, the original -14/1000 still looked OK but, not as good as the first test. What really surprised was going deeper into the lands helped dramatically. The +15/1000 group was 39/1000 (0.039") and had a decent ES. This is the best group I've seen with this rifle to date. I am looking forward to trying it at 550 yds.

I have shot quite a few PPC barrels at the square mark. Made itty bitty holes, just stayed there.

 

[boltfluter]

I have shot quite a few PPC barrels at the square mark. Made itty bitty holes, just stayed there.

This! .015 to .020 into the rifling has always been the one to beat in most of my rifles. I always start .020 in and only have one way to go. Easy peasy. Good luck and keep us posted.
Paul

 

[Bronsin]

In the recent testing I did with my PPC trying to get my powder sorted out, I found that lighter loads and light neck tension made my SD's go up dramatically when the bullet was out of the lands. With those corrected, it's now the same. I also abandoned doing a powder workup at 100yds and went to 300 instead. My rifle shoots so much better now, it feels like somebody swapped the barrel for a Dasher.

 

[Buttstock-TX]

Notice how 9 or more off the lands has never shot bad.

I’m glad you did seating first as I’m a big proponent of that, but I think you let the Chronograph pull you away from the whole point of the depth test.

That little dot looks nice, but it’s .003 of erosion away from disaster, assuming it’s repeatable anyway.

I do agree and plan to test the best jump load also.

But, since the subject of ES has come up several times in this conversation, I should explain my motivation. I used the Berger ballistic calculator and computed the elevation change at 500 yards for a 105 VLD on my home range at 500 yards. The ~23 fps extreme spread of the -14 group is 0.89" on the target. I would prefer not to build in that kind of elevation change if I can avoid it, since I am trying to shoot as many X's as possible. ;^)