6BR vertical stringing

[hbjones]

I just finished my first 6BR. 30" Krieger 1-8 HV barrel MBR tracker stock. Shot 8 five shot groups at 500yrds. The agg for the 8 groups was 2.505, the best 1.5" and the worst 3". I was very pleased especially since I have very little experience with this type of shooting. What I'm seeing is near perfect vertical string in each group. I'm shooting 107 MK with charges of varget from 29.8 to 30.2. It seems to be right on the edge of the sweet spot so i'm not sure if I should work with seating depth , neck tension, or powder charge to correct the vertical.. Also these results were with never fired Lapua brass. Any suggestions appreciated.

Thanks

 

[Eddie Harren]

Before I would adjust anything, I'd reload the brass, now that it is fireformed, and go back to the range.

 

[MarkS]

I would second Doc's post. If it still doing it, look at seating depth. Did you check you ES in speed? What it is doing in the fired cases?

Mark Schronce

 

[bohemR13]

Mark-

I'm not trying to argue with you, I'm trying to understand, so please don't take this as stomping toes.

I have been told a couple of times that horizontal stringing is more of a seating depth issue and vertical stringing is a powder charge issue.

Have I been mis-informed? It seems to hold water with some of the testing that I've done but I never sat down to run a specific test just to verify this.

When I first read the post my initial thought was exactly what Doc suggested, and if it persists, check the charge weights.

 

[hbjones]

Thanks Guys,

I have spoke with several very successfull competitors and the concensus is the same as what has been said here. Reload the once fired brass and shoot again. After that increase powder charge until the vertical goes away. I'm at 30.2g of varget behind 107 MK. I will try bump that .2 steps until vertical goes away or pressure signs.

 

[Klong]

If this persist during the next loading and EX spread of the velocities is not large, play with the parallax adjustment on your scope to be sure it is not parallax. Parallax is usually not in a single direction, but I have seen it this way before.

It would help to know if there is an order to the shots.

Also, it sounds like almost no wind. Was there mirage in a boil?

 

[skeetlee]

i think one thing we need to know is how much vertical are you having. A 1.5" group at 500 yards is pretty solid!! Can you show us? Lee

 

[hbjones]

Images attached in two post

 

[hbjones]

2nd set,

 

[hbjones]

3rd set

 

[hbjones]

Thanks for all the replies. I will be shooting again in a couple of days. I will load the same load for the bulk of the shoot and take 15 rounds with a little higher powder charge to see what happens. I have just started building rifles and really didn't know what to expect from a 6Br as my others have been 308s. Where I live no one shoots these kind of rifles or matches so I'm feeling my way through on my own. Thanks again, I will post the results from the second round.

 

[camac]

Great grouping - don't sweat it.

As everyone said (including yourself) try again with fireformed brass but also try and look at your velocities if you want to improve (hard to from there). A spread of around 40 fps for the 6BR will give you that much vertical on velocity alone ( around 2 inches+). Reducing ES can be never ending but some of the most important things are
1) seating depth and neck tension.
2) Accurate powder charges
3) Primer/powder combinations
4) weight sorted brass (and fireformed)

beyond that you need to start getting into neck turning, bullet sorting, annealing, flash hole and primer pocket uniforming, etc etc etc (many etc's).

Vertical can also be vibration nodes (tend to act more in the vertical) and bedding (have seen diagonal vertical but depends on where problem is) and others but I will bet it is mainly due to ES. 500 yards is starting to get out there.

 

[hbjones]

Got out to the range Monday. I bumped the powder .2 to 30.2 and shot 13 five shot groups. The vertical is pretty much gone as the groups were clusters instead of strings. Agg for the groups was 2.375 best was 1.375 worst 3.125. I'm just gonna a practice for while and see if i can catch up with the rifle. Thanks for the replies.

 

[MarkS]

hbjones,

I like to do my load work at 100 and 200 yds with wind flags, that way I can see what is going on, and not seeing wind effects on my groups. At 500yds a very slight wind could open groups up. wind can be seen as vertical if it is coming in or out, not right and left. I like to see sub 0.4" at 200yds, for my 600 yds benchrest guns. you did not say what type of shooting you are going to do, you are running 0.5 moa, that is good for most shooting

Mark Schronce

 

[hbjones]

I never really intended to shoot any type of specific dicipline, I just like to build rifles. However, I'm pretty interested in F class . I really like shooting the longer ranges. My 100 yrd groups generally run in .250-.300. I'm planning on loading 88g flat based Bergers for 100yrds and see what happens. With the vertical dispersion pretty much gone,I think that I've got to work on my end .

 

[Forum Boss]

There are many factors that can cause vertical stringing -- velocity delta being just one. As others have noticed, your results are pretty darn good already. Make sure the gun is placed in the same position on the rests every time -- a difference in bag placement can shift Point of Impact. Mirage can cause shift in true point of aim. Also read this article by Speedy -- it covers many factors:

Cures for Vertical Stringing
http://www.6mmbr.com/verticaltips.html

 

[hbjones]

Thanks for the link. Lots to work with there. I need a new rear bag but I don't want to do the trial and error as that gets pretty expensive. Any recommendations for a MBR Shehane tracker stock? Also in the article it mentions balance. How should the weight be distributed between the front rest and rear bag? Rifle weighs apprx. 15 lbs. Also at 500 yrds what are reasonable expectations in group size for a 6BR with someone that knows how to shoot?

 

[MarkS]

hbjones,
One more thing for For long range benchrest, I ran my bullets thru a David Tubb's bearing surface compairtor. sort bullets and shoot in lots. As far as groups long range. My 600yd benchgun (Bat action ) In good conditions would run in the low 2.0" aggs 4 - 5 shot targets at 600 yds. I shot 3 IBS records with this gun. In 2007" i shot the light gun small group 0.749", The chamber is a 6BRX, a 6BR imp. Sam Hall holds many records with a 6BR with the records aggs running around 1.5" now. check out the IBS web site for match results for group size. http://internationalbenchrest.com/results/long_range/index.php For 500 yds 1.5" would be a good group. I like to shoot groups long range on steel, so I can see the groups shot. just do alot of shoot, the more you shoot the better you will get.

Mark Schronce

 

[jamesh]

Mark,
You need to get rid of the period at the end of your link.

http://internationalbenchrest.com/results/long_range/index.php

Took me a little bit to figure out why it wouldn't work.

James

 

[hbjones]

Just the info I was looking for. Looking at the website everyone is using custom actions. Do you think there is a signifant difference on the target between these and trued Remingtons( which is what I'm shooting). Which BAT is best suited for 600yrd benchrest.There are so many models I get lost. I've also been looking at the Stiller Viper. I've held off customs because I'm tooled up to true Rems but If I keep at this I think I'll go with a custom.