6BR tuning

[Ghansen]

I am trying to tie down a load for my 6BR, which is a switch barrel for my PPC.

Ultimately I want to use this as a 600yd gun (up to) and to that end I am using the 105gr projectiles.

Ingredients used are Reloader 15, Berger 105VLD's and CCI 450 primers in Lapua brass, in a Stolle Panda action with a Krieger 26" Heavy Barrel.

The chamber is not tight at .274 neck, and I am unsure of the free bore.

This link is to a target I shot today at 100yds, if you could have a look and have any advice to offer I would appreciate that.

https://www.dropbox.com/s/1x5yzifjnq6up2h/Feb202015_6BR002.jpg?dl=0

Geoff

 

[BenPerfected]

My thought is to pick one or two loads and then shoot (5) 3 shot groups and look for consistency.

 

[Sniper338]

10 thou is your money maker. Shot that load more and see how it does..

 

[Keith Glasscock]

I'm going to disagree here. It looks like you are not finding what you are looking for.

All of the groups are rather large for a 6BR. The .010" shows POI instability. The middle charge hits quite a bit higher than the other ones.

What does the velocity look like? What is the max charge in your rifle? That might give us a good clue as to which direction to send you.

 

[JamesnTN]

+.010 shows most consistent. Now change primer and shoot those loads again with the +.010 and see what happens. I've always had my best luck using the 450 primers on RL powder. Some do well with the BR primers.

Also if you have bushing dies try changing the bushing up or down by .001 but only try one thing at a time.

 

[Ghansen]

I'm going to disagree here. It looks like you are not finding what you are looking for.

All of the groups are rather large for a 6BR. The .010" shows POI instability. The middle charge hits quite a bit higher than the other ones.

What does the velocity look like? What is the max charge in your rifle? That might give us a good clue as to which direction to send you.

I haven't really evaluated what max load might be for RL15 and the 105's, and the loads haven't yet been chronographed. I have a friend with a chrono set up who shoots when I do, so I'll request a favour while he's doing some testing just to look at the velocity, SD and ES.

When I looked at the groups my initial thought was +.010 looked around the mark, but looking at the 30.4gr the +.015 and +.005 have comparative "fliers", except they are in reverse per relative shot position. A 5 shot group here would have sorted out the flier aspect. The other question is, perhaps my freebore isn't long enough to accommodate the 105VLD's? The VLD's seated at +.005 have the base of the bullet just at the Body/Shoulder junction. Without any complicated math, I know one or some of you would just know if that is too deep in the case for this chamber.

The group sizes for the +.010 sets measured .190, .198, .170 from lowest charge to highest, while it looks to me that 30.1gr had the lowest dispersion in group size for all seating depths, whether that is a factor in choosing a base load or perhaps not.

How high could I, should I go with RL15? No signs of pressure. If I cull the "flier" cases at .005 for 29.8 and 30.4 and re tested, the 29.8 is fairly relative in group position to 30.1gr, but not 30.4gr.

I guess that answers here might be relevant to other questions being answered first, like, nope; you are seated way too deep. AlsoI have annealed the brass after firing, is there something I may have done to cause the fliers? Necks are sized with .266 for .002 neck tension, .001 neck tension just doesn't hold the bullet firmly enough. Should I go and try neck sizing with .265 for 3 thou tension?

That's a lot of ponderance from my end, hope you can offer some advice,

Geoff

 

[Lapua40X]

My vote is for +.010 and a couple of five round targets to see where that vertical settles down.
(29.8, 29.9, 30.0, 30.1, 30.2, 30.3, 30.4, 30.5) at that seating depth is where I'd expect to find the sweet spot.

 

[comagutsa]

your doing better than me with 105gr hunting vlds and reloader 15 and pressure.. i start to get pressure at 30.2gr of powder , only difference in yours to mine is i'm using CCI BR4 primers and i'm using no neck turn .272 , loaded round is .269 and also using .002 neck tension
i just started to use 105gr hybrids so i am starting my load testing all over again

 

[Alex Wheeler]

Geoff,
You are doing load development for a ppc. For a long range gun you are going to have to go in smaller powder charge increments, same with your seating depths. Your powder window ill be .1-.2 and with a vld your will probably have a .003 window. If you have access to 600yds, I recommend a ladder at that range. If not, seat the bullets .010 in and go in .2 gn increments and cover a wider area. Post that target. Once you have that powder charge move the bullet .002 at a time. Also chrony numbers will help if you cant shoot 600. At the end of the day it will HAVE to be fine tuned at 600 for the best load. Picking a load from your target would be a guess at best, sorry.
Alex

 

[Ghansen]

Thanks guys,

Would it be a better test at 200 than 100? Given that is my best testing venue.

The longer range is not readily available for casual use and I have to say the conditions, when I have the opportunity, are going to be more skill related.

 

[Lapua40X]

Thanks guys,

Would it be a better test at 200 than 100? Given that is my best testing venue.

The longer range is not readily available for casual use and I have to say the conditions, when I have the opportunity, are going to be more skill related.

I only stretch out my newest test loads beyond 100 yards when I've got perfect, wind free or nearly wind free conditions. I can be difficult enough to read test prints on target without having to ask if some atmospheric factor might have influenced the shot.

 

[comagutsa]

hey guys have a look at mine could you and give us an idea on which way to go
i was shooting berger 105gr hunting vlds at 29.5 of RL 15 at .020 and .050 off the lands and they had been great (i hadn't finalized the end outcome because conditions haven't been the best)
but i have since swapped to 105gr hybrids
this was my 1st quick go at a load test
the sighters are .050 off lands as i was trying something but the rest are all ..020 off lands
the 29.4 one thats off is my fault as i lifted my head as i shot :


i have got hold of a chrony as mine is broken but i will be re testing again soon but i got my hunting vlds down to .2 inch groups at 100m

 

[MOShooter]

What twist is your barrel? Your will need a 1-8 to properly stabilize the 105 class bullet. The 105 hybrids 1-7.5 is recomended.

Scott

 

[comagutsa]

What twist is your barrel? Your will need a 1-8 to properly stabilize the 105 class bullet. The 105 hybrids 1-7.5 is recomended.

Scott

Hey Scott
yeah I run a 1.8
1st I have heard you need a 1:7.5 for hybrids. Even on berger web site they say 1:8
By my pic they look stabilize to me at 100m (no key holes there)
Anyone else heard this?

 

[snakepit]

What twist is your barrel? Your will need a 1-8 to properly stabilize the 105 class bullet. The 105 hybrids 1-7.5 is recomended.

Scott

Hey Scott
yeah I run a 1.8
1st I have heard you need a 1:7.5 for hybrids. Even on berger web site they say 1:8
By my pic they look stabilize to me at 100m (no key holes there)
Anyone else heard this?

It is a function of several variables. Go to the Berger Twist Rate Stability Calculator to figure your twist rate. Example: 6MM, 105 gr Hybrid, 70 degrees, 100 ft altitude, and 2870 fps the calculator recommends 1.75 twist. Change altitude to 2900 ft and the 1.8 twist just barely makes the stability factor. Plug in 105 gr Match VLD or 105 Match BT at 100 ft and 1.8 Twist is ok. I have used the 105 Hybrids with the first set of variables I gave you with good success even though the 1.8 Twist comes up as Marginally Stable. The sticker on the box says 1 in 8" Twist or Faster. Also on their Target Bullet Chart if you click on Store Link/Part# 2443 it says 1 in 8" Twist or Faster

Here is a link to the Berger Twist Rate Stability Calculator

www.bergerbullets.com/twist-rate-calculator/

 

[comagutsa]

Cheers

Well wish I knew about this before mmmm. It said my BC is compromised by 3% and a 1 in 7.75 barrel needed
Dam and I got 1500 of them too. Oh well I will see how they go and if they work all good if not I will sell them
Cheers again

 

[snakepit]

Cheers

Well wish I knew about this before mmmm. It said my BC is compromised by 3% and a 1 in 7.75 barrel needed
Dam and I got 1500 of them too. Oh well I will see how they go and if they work all good if not I will sell them
Cheers again

So far I don't think it has been a problem for me. The Marginal Scale goes from 1.0 to 1.5 and my numbers come out to about 1.35 and a loss of 4% BC but on a warm day of 90 degrees it goes to 1.40 and a 3% BC loss. Like I said, so far I don't think it has affected my accuracy and this has been using the 105 Hybrid in 2 barrels but the next time I get a new 6 BR barrel I may consider getting 1.75 twist. Or I guess I could move somewhere where the elevation is 3000 ft.

 

[Ghansen]

Conditions this morning were light breeze with moderate humidity at mid morning, the "flags" were a best guess of the ticker so some of the horizontal may be an errant wind read, but it was only maybe 3-5mph at the most with 105's at 100.

I shot some PPC beforehand when the conditions were thicker air and a shifty 4mph breeze, and it really showed on target. 200yds was double the fun :-X, but I am not that unhappy with the 6BR performance as far as conditions go.

I loaded several options to have a look at behaviour and these were the results.

 

[STS]

There is the possibility that this is not simply a tuning issue. There are flyers on that target that could be mechanical in nature. Are you 100% sure the bedding in the rifle is good? That can be checked with a dial indicator. Have you checked your loaded round runout? I assume you are using some sort of bushing resizing die. Not all sizing bushings are straight. I have a box with probably 35 or 40 bushings (those that are not currently in use) that are known good bushings. I also have a box with 5 or 6 bushings that the hole is not concentric with the OD of the bushing. One cannot assume that they are correct. Either of these issues will generate groups like you have.

 

[barefooter56]

Ghansen,
Go to our website To the INFORMATION tab on the home page and click "TECH TALK" in the drop down. You want to read "VLDs Making them shoot" and "Setting up your load for optimum accuracy". You may have to start over your load testing again and follow a more structured process changing one thing at a time to get the results you want. You are compromising the BC slightly with your twist rate but it should not be much of an issue. I shoot our 105 VLD target bullets out to 1000 yards with a 1-8" twist barrel with no issues except myself. Please feel free to contact us either here or at tech.support@bergerbullets.com for help if you have any questions. Thanks for using our bullets!