My 6BR and what I found with seating depth, powder charge, and sizing

[Bradley Walker]

I use a 6BR with a the standard SAAMI reamer. I am going to discuss what I found with Sierra 107s and R15. I use Lapua gold box brass and CCI450 primers. I clean my brass with stainless pin tumbling, and I size the brass to .0005" of interference using a .268 bushing.

I decided to go back to 100 yard load testing and I started shooting all my loads over the chronograph. After taking so much flack from saying that most "typical" bullet shapes shoot the best at right around .020" jump I decided to really wring out my seating depth with this rifle and load to see if I (and the techs from Sierra) were full of crap (I am being a little facetious... HAHA).

The high node I found with the R15 is right at 30.6 grains and that gets me between 2875 and 2950 depending on where I seat the bullet. I started at .025" out, and moved the bullet .010" at a time all the way to .020" ITL. I had dropped the charge to 30.3 and tuned from there previously to make sure I wasn't too hot in the summer heat. This load has shot very well at .020" of jump. The gun shot best at .020" at 30.3 and even better at 30.6. ES were right around 20 FPS at all seating depths out of the lands.

As the bullet went into the lands the accuracy did not exceed the accuracy of the loads out of the lands but the ES were cut in half. Now at 10 FPS. Accuracy was certainly pretty good, but the .020" jump shot the best, although the ES could not be improved over 20-25 ES.

All seating depths produced different velocities. The more the bullet is seated out the lower the velocity. Then as the bullet hits the lands the velocity goes back up. So, I would assume that has something to do with tuning the barrel node.... but what do I know...

So, if I were to shoot the rifle for 100-200 yard I would use .020 jump because it seems to just be very happy shooting small groups. If I were to shoot it at 600 I would use a ITL load and as much powder as the brass would tolerate.

 

[mbkmkk]

Mr. Walker

What was your COAL at .020 jump with the 107SMK?

Thanks

 

[ehkempf]

I use a 6BR with a the standard SAAMI reamer. I am going to discuss what I found with Sierra 107s and R15. I use Lapua gold box brass and CCI450 primers. I clean my brass with stainless pin tumbling, and I size the brass to .0005" of interference using a .268 bushing.

Is is safe to assume that with your standard reamer the the chamber neck size is .272? The older gold box Lapua has a little more neck thickness than the newer plastic blue box, so what is your loaded round measure. I ask this because I use the blue box and a loaded round has a dia. of .267 and I am using a .266 bushing. I am only using .001 of grip tension, have you played with a little tighter grip?

Ed

 

[Bradley Walker]

I use a 6BR with a the standard SAAMI reamer. I am going to discuss what I found with Sierra 107s and R15. I use Lapua gold box brass and CCI450 primers. I clean my brass with stainless pin tumbling, and I size the brass to .0005" of interference using a .268 bushing.

Is is safe to assume that with your standard reamer the the chamber neck size is .272? The older gold box Lapua has a little more neck thickness than the newer plastic blue box, so what is your loaded round measure. I ask this because I use the blue box and a loaded round has a dia. of .267 and I am using a .266 bushing. I am only using .001 of grip tension, have you played with a little tighter grip?

Ed

Yes. Sorry, the barrel is chambered for .272" neck.

I have a .267 bushing, and the new Lapua brass out of the box after run through the Sinclair expanding mandrel size the same as the brass using the .267". Seating tension is very comparable. I only have occasional cases that "feel" different when seating the bullet using .0005", and my seating depths are very consistent now... Which appears to be very important.

I am just wondering if using less tension and the least amount of sizing might be a good thing. I am not annealing, and I am getting very low ES already... soooo.... Maybe ITL with less tension is better and more consistent. My opinion is inconclusive at the moment, but I have never seen ES numbers this low out of one of my guns....

 

[fdshuster]

Ed: I use a .266" bushing with the older gold box Lapua brass and switched to a .265" with the "new" blue box. Both work exceptionaly well. Both work out to about .0015" of neck tension, with the difference of about 001" in neck wall thickne

 

[mod70]

Bradley, You know I believe you get better ES in the lands because you get better burn. When you are jumping I would try more neck tension and see what happens to the ES. I use the cardboard box with a .272 in 2 6br's and use .265 bushing jumping and depending on what bullet if I jump or jam, also tells me what bushing. Just my experinces.
John Roberts

 

[mikecr]

All seating depths produced different velocities. The more the bullet is seated out the lower the velocity. Then as the bullet hits the lands the velocity goes back up. So, I would assume that has something to do with tuning the barrel node....

It's not tuning, but standard internal ballistics, that is no doubt taking you from tune.

I wonder if you tweaked your experiment a little if you could improve on what you found.
What I read here is that you found your powder node first, -at 20thou off.
Then, you degraded your tune by messing with seating in large adjustments.
This is very normal.

Have you found any powder nodes with other seating?
You could do seating tests well away from where you expect to end up(mid load), then go to dialing in the top node with powder.
From here there is no need to adjust seating other than tiny tweaks to shape grouping.
And I wonder where your 'best seating' would be then.

Testing higher tension is a good idea, provided you can maintain seating consistency with it. But if your necks are too clean, this probably won't work.

 

[Forum Boss]

Many guys do find that the Sierra 107gr MK does shoot well .020-.025 away from land contact.

In my personal experience I also did find that in-the-lands seating reduced ES/SD with many bullets. Somewhere from .008-.015 in the lands seemed to be the "sweet" spot. ES started going up again at .020 in the lands. But keep in mind that every barrel, and every bullet shape may perform differently. Generally, when I start loading for a new 6BR barrel I'll try to find something that works ten to fifteen thou in the lands. If that doesn't work I go straight to .020 out.

Again, I caution that some guys have completely different experiences, and some guys have success five out or five in.

PM

 

[Bradley Walker]

Many guys do find that the Sierra 107gr MK does shoot well .020-.025 away from land contact.

In my personal experience I also did find that in-the-lands seating reduced ES/SD with many bullets. Somewhere from .008-.015 in the lands seemed to be the "sweet" spot. ES started going up again at .020 in the lands. But keep in mind that every barrel, and every bullet shape may perform differently. Generally, when I start loading for a new 6BR barrel I'll try to find something that works ten to fifteen thou in the lands. If that doesn't work I go straight to .020 out.

Again, I caution that some guys have completely different experiences, and some guys have success five out or five in.

PM

Thanks!!!