inaccurate new 6br

[cowboy924]

Hi all,
First time poster, long time lurker. I love this site, there is so much good information and so many helpful people here it is amazing.
Now my problem. I recently put together a 6BR with a Savage model 12 action and a McGowan barrel, bedded in a Shehane tracker stock,barrel and tang area free floated). I am using Lapua brass lightly neck turned just to clean up the high spots and flash holes deburred, CCI 450 primers, and Redding type S neck sizing die with a .268 bushing. I have tried 87 grain Hornadys, 105 grain Bergers and 68 grain Bergers with Reloder 15 and Varget. I have also tried bullets seated at the lands, jamed .01 and jumped .01. I chose this caliber because I read so much about its inherent accuracy and ease of load development. That being said I am not getting the kind of accuracy I expected.To make a short story long, I have 134 rounds down the tube and my best groups are around .75 to 1' at 100 yards.

I have a cheap borescope and I can see some very small blemishes in the first inch or so of the rifling. They look kind of like tooling marks, except they are irregular shaped, bad spot in the steel/pitting?,still a lot better than a factory barrel) Could this be my problem or is that something you normally see in an aftermarket barrel?
The barrel broke in easily and now shows no copper fouling but the powder/carbon fouling is worse than most of my factory tubes.
I don't want to blame the barrel if thats not the problem but I am out of other ideas.

This is my first semi custom build so I am not sure if this is all the better I can expect or if I should keep trying different components. Or something else I am not thinking of???

ps. I have been reloading for a couple years and can shoot way better than this with a couple of my other factory rifles so I don't think it is technique.

Thanks in advance for any and all help.
Luke

 

[Preacher]

For starters, what exactly is the neck size now ?
Twist ?
Seems to me that you need to tighten the neck down a bit more..

 

[eww1350]

What is the rate of twist in your barrel..???
What is the barrel contour..LV,HV, sporter..???
What are you going to do with the rifle Benchrest, or 300 thru 1000 yard..??


Eddie in Texas

 

[AlNyhus]

Two things:
1. What's the neck diameter of a loaded round and your chamber neck diameter?
In the common 'no turn' chambers the neck dia. is usually .272-.274. A loaded round w/o having the necks turned is in the .268 area. If you cleaned up the necks at all, a .268 bushing isn't going to give you much neck tension..if any. Keep in mind that neck tension is the difference between what a sized neck measures compared to what the neck diameter is of a loaded round.

2. Do you have a known good scope on the gun?

My 'baseline' accuracy test load in any 6BR is N135, a Berger 65 or 68,65's are on the .790 jacket and work better in barrels twisted 1:14), Fed 205m's, a neck bushing that sizes the neck .003 smaller than a loaded round measures and around .020 of 'jam'.

Setting one up this way for initial testing eliminates a lot of variables. My experience has shown me that if a 6BR won't shoot this setup well.... it has other issues.

If you don't have any N135, current H322 and Benchmark are also very good 'test' powders.

For what it's worth. -Al

 

[fdshuster]

cowboy924: As previously asked: what is your barrel twist? The answer will be at or near the top of the 'important things' list. I'm getting excellent results with Federal 205 primers, N133 w/ 58 thru 70 gr. bullet weights, 2 barrels w/ 1-14. Same primers, N135 w/ 75 thru 85 bullet weights, 1 barrel w/ 1-9.25.

 

[jo191145]

cowboy

If you used Mcgowens 'in house' reamer your neck should be cut to .271. I never trust internet reamer prints tho.

One thing that concerns me about the two prefit Savage McGowen barrels I have is the 'shiny' marks just inside the crown.
These seemed to be caused by either a crown cutting pilot or perhaps a buffing wheel reaching inside the muzzle. I do not know which.
Do you have this shiny area just inside the muzzle? I can see this clean or fouled.

As much as it concerns me my 243 Win 8 twist bull barrel has shot a couple of 1's,3 shot groups) during load development.
My 204 11 twist has gone below 1/4 moa with 5 shots.

Both these barrels have not been shot much but they do seem to perform. I'm always screwing something else on to try. Sort of like women and shoes

Loading to just touch works well in my 6PPC. Its always been the worse place to be in my 6BR's. Try some seating depth tests.

Deburring Lapua flash holes? I never have. I hope you did'nt use a deburrer with a standard flash hole reamer cutter.

As gunamonth said. Excessive carbon is usually a result of light loads.

My 14 twist will shoot both N-133 and N-135. My 8 twist loves N-135.

 

[cowboy924]

Thank you all for your help.

The barrel is an 8 twist.

gunamonth: that is basically how I set my seating depth too. I seat a bullet extra deep and then pull it and re-seat it a couple times to loosen up neck tension and then seat it extra long and chamber it, and call that my 'at the lands length'.
As for the fouling maybe I just am not running them fast enough? I usually do a ladder test up to a grain or so above what I can find for a max load. However I have not had to cut short a ladder test yet because of pressure signs. I went up to 31.0 grains of Varget with the Berger 105's and 34.0 grains with the 68 Bergers with no issues. I will have to try a few hotter.

eww1350: the barrel contour is a LV. I plan on mostly using it for punching paper, not competing with anyone but myself. Would like to take in prarie dog shooting, if I can ever get a trip planned. Maybe someday 300-1000 yard competition???

AlNyhus: I have tried two different scopes, both of which have worked on other rifles.

fdshuster: I have some N133, I will have to try it also. Do you have some starting loads I could try?

preacher, Al and fdshuster, I thing you all may have hit on something with the neck tension. I am embarrased that I didn't catch this. My loaded rounds measure right about .268. I am not sure about the chamber, I think it is a .272, but I bought it as a prefit so??? I have a .267 bushing, I will load up some with that and see. Can neck tension make this big of a differece acuracy wise? Or do I have other problems too?
As a side question, I have never really understood the bushing size, wouldn't the expander button stretch the neck back to the same size regardless of how far it is sized down by whatever size bushing?

No one thinks the small blemishes in the barrel are anything to be concerned about?

Thank you all very much for your help.
Luke

 

[cowboy924]

jo191145: My barrel also has the shiny marks at the muzzle. Almost like the lands are chamfered?
I tried jaming and jumping bullets by .01 each way and couldn't see any difference in group size,they all were poor). I haven't tried any other seating depths because I didn't think it could make that much improvement in group size. I understant seating depth can improve accuracy I just didn't think it could take it from 1' to 2's or 3's.,but I have been wrong before, a couple of times)
I didn't ream the flash holes I just cleaned up the inside with a lyman deburing tool. It seemed kind of pointless as the flash holes all looked good to start with, but it made a small improvement with some of my other guns, and I figured it couldn't hurt.

Thanks for your help.
Luke

 

[fdshuster]

Luke: One word jumped out at me: 'expander button'. When you use a neck bushing,die), there is no need to use the expander button, suggest you 'lose it' real quick. the only reason they are required for 'regular' dies, are because the neck is over-sized/ squeezed-down to a much smaller diameter than is required,, if you should be using brass with very thin neck walls), then they must be opened up, and in the process the neck can be pulled out of alignment), to approx. .002'/.003' smaller than bullet diameter- which is the same dia. we arrive at with our bushing. N133 is my powder-of-choice for the 'lightweight' bullets, N135 w/ the mid-weights. I have no idea how either would work with your heavier bullets. Hopefully someone with that experience can contribute. A 'late edition',after reading your previous post. The 6BR has a smaller than standard primer flash hole, so if you reamed them out with your Lyman tool, you may have opened them up to a larger diameter. I don't believe Lyman makes the tool for the ppc & BR flash hole diameter. Just something else to consider.

 

[cowboy924]

Frank, Thanks for your description of how the bushing dies work. That makes sense, I'll loose the expander.
I didn't ream the flash hole, I just used the tip of the tool to put a small chamfer on the flash hole inside the case.
Thanks again for your help.
Luke

 

[Obtunded]

A couple of thoughts...

First of all, neck tension. You have 'lightly turned the neck'. I would suggest using a 105 Berger or a 107 Sierra for this...

Seat a bullet in a re-sized case and measure the actual size of a working case. Choose a bushing that is .002 narrower.,I'm going to assume the chamber is a 'no-turn' variety... .272-.276)

Secondly, are you using a chronograph?

Ignore the barrel imperfections for now.

I would use the Berger 105 to start with as it is - from my experience - the easiest bullet to make work and works in every barrel I have used. Ladder test with 10 thou jam past first land contact. That will find you at least one really good node that you can make really great with some fine tuning.

 

[cowboy924]

Quick update, I have loaded up rounds for a ladder test with 105 Bergers, .01 jam, using 29.2 to 32.0 grains of Varget,hopefully find a hotter node to reduce powder fouling) I used a .267 bushing,with the expander removed) which made neck dia. .2655,why not .267???), loaded rounds measure .268, for neck tension of .0025.
As soon as we get a decent day to shoot, I'll post back with results.,hopefully positive, otherwise more questions)

One thing I forgot to mention earlier is that the throat seems rather long in this barrel. With the Berger 105's,at the lands) my oal is 2.435,+/- depending on the bullet). That puts the boattail/bearing surface junction about halfway down the neck and the base of the bullet at the the neck/shoulder junction. The 68 grainers are out a little further than half way in the neck. Anyone see any issues with this? I'm not sure what is ideal. What is the oal for Berger 105's in your guns?


Thanks again for everyones help,
Luke

 

[cheek9075]

cowboy, i just got my 6br shooting. had all kinds of problems, gruops were all over the place. i had a chamber of .269 and loaded ammo was .268. it was a REAL problem. turned necks another .001 inch. after playing with charge and seating depths, it will put 10 shots in the low 2's at 200 yards. fit was to tight in the chamber. just thought i would throw that out there.

 

[chris308]

Luke, on my br's i have .134 freebore which takes a berger 105vld boattail,bearing surface junction at 1/2 down the neck as well.A 108 match about 3/4 the way down. I have had no problems. i switched to a tighter neck bushing.,not as much neck holding the bullet?)I also agree with cheek. My neck is .262 and i turned my necks so a loaded round was .261.I now turn them to about .2602 or so and flyers disappeared...chris

 

[cowboy924]

Hi all,
I finally got out to shoot the other day. I shot a ladder with the loads I described in my last post, and got a fairly good cluster of four shots from 30.0 to 30.6 grains. So I loaded up five each at 30.2 and 30.5.
30.2 group measured .632' and 30.5 group measured 1.2',four in about 3/4' with one flyer) at 100 yards. Not much of an improvement.

I am thinking I will try 30.2 and jumping them by .01 and .02 and see what happens.
I will also probably order a .266 bushing and try that.

Any other ideas???

Cheek and Chris: I am not sure of my chamber dia. but my fired brass necks measure about .2715 so I am guessing .272-.273??? Seems like that should be plenty of clearance??? I am glad to hear that someone else has had success with similar freebore,one less thing I have to worry about!)

Thanks again for everyones help! I'll keep you posted with results.
Luke