Seating depth testing at 300m

[ProneKing]

Yesterday I worked up what I think is a good powder charge for my 6 Dasher 300m rifle. Today I did some seating depth testing. I don't really know how to interpret them.

All are 3 shot groups fired at 300m. I did a total of 10 groups, varying the seating depth from .005" off the lands to .027" off the lands. I picked what I though were the seating depths with the most potential. I had two other groups at .018" and .021" that were pretty good, but I forgot to take a picture of the groups. They both had average velocity of 3048, and 6 & 16 ES and 3 & 8 SD respectively. The X-ring, or inner dashed circle is 5cm (1.97") across for reference. By the end it was pretty warm out so the square piece of tape I was trying to aim at was bouncing around quite a bit from mirage, and I don't know if my bench technique was that great...

I've got some questions.
Can seating depth (all off the lands) affect ES and SD that much?

I'm using HBN coated bullets. Would it take a while to get an even coating of HBN and for velocity to stabilize and SD and ES shrink, or is that all the effect of seating depth?

What seating depth would you choose?

Thanks,
Eric

 

[dmoran]

The pictures are to small for me to even begin to see the groups, but I can see the velocity data at top fine.
With that said, yes the ES can very that much - IME
But your increases are on the high side then I typically see with a Dasher.
And the average velocity will continue to rise the deeper you seat them into the case (the increase to load density is why).

My 2-cents
Donovan

 

[ProneKing]

If you click on the thumbnail the pictures will get a bit bigger. The shots are plotted by "+"'s. The last shot is the + in bold. If you can see close enough, there is also a small square that represents the center of the group.

Just as a guesstimation, all groups are in the 3/4" - 1" range at 300m.
Thanks,
Eric

 

[dmoran]

I even downloaded the images to my PC and tried blowing them up..... still to distorted to make them out.
Place pictures in a photo suite online, then enter the direct HTML link to pictures, instead of resizing them down to attach them, is my suggestion.
Donovan

 

[BoydAllen]

Good shooting. I think that 300 M is somewhere shy of the point where small variations of otherwise good ESs need to be worried about. I would try to find the limits of my node width of weight of powder, at whatever seating depth gives you the best combination of accuracy, at a decent ES, and load in the middle. On the SD thing, with samples of three, it is virtually meaningless. I see where shooters quote small sample SDs all the time, and I think that this started because chronographs calculate it. I doubt that 20% of the shooters who refer to it could really explain what it is, or how to calculate it, and to tell the truth, it has been about 46 years since my last statistics class. (but with a little brush up, I would be up for both) If, on the other hand, one were doing quality control testing as a manufacturer of ammunition, I think that it would be useful, if samples were appropriately sized.

 

[ProneKing]

Boyd,

I figured there wasn't much statistical reason to do SD on a three shot group, but I threw it in like you said "because my chrono did it for me".

I'm about at the point where I need to settle on a load and start loading for practice and the ISSF world championships, which I leave for in two weeks... I've been shooting this gun the last month on a load I put together in a hurry in mid-July so I could shoot the Camp Perry mid-range nationals. I wanted to tweak it some on both powder charge and seating depth now that I've got three firings on the brass. The previous load workup was on just-fireformed brass, and like I said...in a hurry.

My first attempt at photobucket:
http://s216.photobucket.com/user/uptagrafft/library/300m%20Seating%20depth

Thanks for the words of advice,
Eric

 

[mgdietrich]

Eric:

I have never played with "close" jumps. When you are that close .010 and in I think that bullet variation can actually come into play- a bullet touching or not.

I would go with your .025 or even greater jump loads for consistency. I know 308 is different, but most all of my loads jump .03-.045 and that is for a 6br too.

I have not tried the Hbn, all naked for the last several years. I would not think that really should change your load all that much. Once a few rounds are down the tube it should settle right down.

Looks like you have a good load, any of them should win you another world champ!

Morgen

 

[BoydAllen]

Eric,
It looks to me like you have your equipment and load situation well in hand. If you can tell us, without revealing something that you would not want the competition to know, tell us about your rifle. I would be very interested to know what a top shooter uses, and since I know virtually nothing about 300 meter shooting, tell us a little about that. Good luck with the match. It seems to me that you have everything that it takes to win it. If you could point us to a link where we will be able to learn more about it, and the results, I would be grateful. I really like learning about things that are new to me that pertain to accuracy and shooting. Again, best of luck.
Boyd

 

[kcomeau10x]

Best wishes to you and all of the other members of the US contingent going to the World Championships. The shooting community is proud of all you accomplish on the world stage.

 

[ProneKing]

Boyd,

Here is a link to the ISSF World Championship schedule and eventually, results. The 300m stuff is toward the end. The 300m prone event that I'm shooting is on the 14th and 15th of September. http://www.issf-sports.org/competitions/venue/schedule.ashx?cshipid=930

There really aren't many secrets in 300m shooting. Probably 90% of the 300m shooters that will be shooting in Spain next month will shoot factory ammunition. This is unlike any factory ammo I've ever shot in that it is supurbly accurate. Norma and Lapua for the most part. Most shooters use a 6BR, with some using 6XC and some using 6x47. They mostly all use factory guns too. The most popular are Grunig & Elmiger, Bleiker, and Tanner. All use aperture sights with no internal optics. Think high dollar!

The different 300m matches are: Men's and Women's prone (60 shots, unlimited sighters for 15 minutes before you start), Men's 3 position (40 shots each in prone, standing, kneeling), Women's 3 position (20 shots each position), and Men's and Women's Standard Rifle (20 shots in each of three positions, with a more restricted rifle and 3.3 pound trigger). Outside of the world championship events, there is CISM, which is a French acrynym for military world championships. For that we shoot the Standard rifle event and also military rapid fire which is two 10 shot rapid fire strings in each of prone, standing, and kneeling. The target has a 10-ring that is 10cm across (3.94").

My rifle is considered a "free rifle" and is built off a BAT 3-lug action, 28" Bartlein 5R barrel, Anschutz wooden free rifle stock and Anschutz trigger. The cartridge I'm shooting is a minimum neck turned 6 Dasher. The Norma and Lapua factory ammo is loaded fairly conservatively with bullets that are easy to get to shoot. I'm using pointed Berger 105 Hybrids, going faster than the factory 6XC. Should give me a little leg up in the wind and possibly an edge in accuracy.

Most of what I know about loading I learned from Benchrest Central, and here. Like I said, no secrets, but few want to put in the extra effort of building a rifle and/or loading for it. I do have to admit that my life has been consumed by loading for this thing the last few weeks. For every 70-75 shots I shoot in a day I estimate that I spend two-three hours loading. To be perfectly honest, I'm looking forward to the 16th of September when I won't be loading for a while. The main advantage of shooting factory ammo is you spend more time shooting and less time loading with very acceptable results.

Eric

 

[FilippoMo]

I would choose the 005" jump and chasing the lands following throat erosion.I am afraid that 60 shots plus sighters in one hour and a quarter will be very rough on throat.
Filippo

 

[swimster]

I just did a 20 shot seating test at 500yds on 2 rifles with OCW proven charge weights. I read about this test on another site. Starting @ touching the lands backing off .005 for each of the 20 shots. I was using Hornady 75g Elds in my 22BRX and 88g ELDs in my 22/250Ai. The results were very interesting. There were 2 nodes on both rifles at about the same distance off the lands. The 75s had one from 0 jump to .030 off. And 1 from .045 to .060. The 88`a were 0 to .020 and from.045 to .060. I know this was just 1 shot at each @ 500 but winds were calm and these seating depths gave less than 1/2 moa. Vertical. SD`s on the 22 BRX were 14 over the entire string of 20. The 22/250Ai SD was 12. I will need another trip to the range to confirm.

 

[D-4297]

60 shots and sighters in that time frame would be rough on the whole "damn" rifle . And it is a beautiful rifle . For a "Slinger"

 

[swimster]

Let me start over. It wasn't 60 shots plus sighters. It's 44 shots total for 2 rifles counting sighters . That's 22 shots for each rifle. Done over a 3 hrs.