Seating depth's effect on ES

[montana_native]

Has anyone had experience with seating depth helping or hurting ES? I am working with a 300 Win Mag. I am getting good accuracy out of it, but my ES is hideous. Usually 30 fps or better. I've not experimeneted much with seating depth, just primers and powder charge.

Also, to add, I've neck turned, deburred flash holes and annealed. Everything has been trimmed to length. All powder charges are weighed as accurate as I can get them with 505 balance.

I've been shooting 215 Bergers with H-1000 and Retumbo, CCI250s and GM215Ms with not much improvement from one to the next. Brass is WW headstamp.

I've tried to elimate as many issues/variable that I could and ES doesn't seem to improve. Thoughts?

Thank you.

 

[mikecr]

What's your barrel length?

 

[ShootDots]

My "old" 6mmBR used, towards the end of it's life, 105 Hybrids. I found a great load and started a "ladder" test by going from 10 into the lands and moved it 5k from there back out to 20K off the lands. I was running about 17-18f.t. e.s.'s... However, when I hit 15OFF, my e.s.'s went down to 9-12 consistently.. My accuracy improved but almost to an imperceptible degree... Having said that, primers are a major source for cutting e.s.'s down. Powders probably the largest source of either good or bad e.s. spreads. I am wondering though, your 505, although a decent "beam scale", is nowhere near as accurate as a really good digital scale that goes down to 0.02grs. That MAY (not sure) be your problem.. H1000 in a .300 Win with the heavies is right on the money! You might want to try VV N560 OR VV N165 if you are so inclined>>>another excellent powder(s) for your purpose..

 

[broncman]

I did a load map for my 308 with 4 different powder charges, and four seating depths for each charge. Overlayed the results in an excel spreadsheet chart.

I found that there was a seating depth that produced the lowest es, sd and the same depth held true for all charges tested.

 

[montana_native]

What's your barrel length?

25". Thanks

 

[pmarauder]

Is this a factory rifle? what does your loaded round measure vs. your fired round..... Did you need to neck turn?
I would adjust your seating depth based on the average distance you anticipate your targets to be.... Once you know for sure what your rifle likes best in the way of seating depth. Adjust your powder charge up or down a tenth or so to tune the ES/SD numbers.
If its a big ol sloppy chamber......your limited on what you can do.

 

[RDavies]

Yes, seating depths can most certainly affect ES/SD. I have some barrels where the ES/SD comes down with more and more jam, others do it with more jump, sometimes over 0.100" jump. If you have to feed from a magazine, you might be restricted from jamming, but you could try increasing jump, it is 50/50 whether it will improve it or make it worse.

 

[montana_native]

Is this a factory rifle? what does your loaded round measure vs. your fired round..... Did you need to neck turn?
I would adjust your seating depth based on the average distance you anticipate your targets to be.... Once you know for sure what your rifle likes best in the way of seating depth. Adjust your powder charge up or down a tenth or so to tune the ES/SD numbers.
If its a big ol sloppy chamber......your limited on what you can do.

It is a match chamber. The way it's throated allows me to be 0.010" off the lands at magazine length so jamming isn't an option if I want to mag feed it. The action is a totally worked over 700 with a Rock Creek barrel.

The rifle was built to punch paper and shoot rocks to a mile+. I only neck turned enough to try an get uniform neck thickness. I'd say that I turned about 60% of the neck.

 

[mikecr]

What's your barrel length?

25". Thanks

BINGO
This isn't a 6br burning 4895, but a 300WM burning H1000 right?
Have you noticed that great big fireball at the muzzle?
That's way more than fractions of a grain -burning outside of the bore-

What do you mean ~'built to shoot rocks to a mile+'?
If I called a top gun builder and told him I wanna shoot at rocks over a mile away, will he say "well then,, I'm gonna need to cut 6" off your barrel"?
I think he would really ask: "Can you sneak up closer?"

 

[Keith Glasscock]

Ok, I'll bite.

Mike, rocks come a variety of sizes. I can shoot rocks at a mile + with a 223 and a 16" barrel. I might not be able to shoot the small ones though...

Back to the OP's question. Tell me more about your chronograph setup. What are you using, and how is it laid out? Also, what is the number of shots for that ES? I cut my ES down to one third of what I had before by changing chronographs.

 

[montana_native]

What's your barrel length?

25". Thanks

BINGO
This isn't a 6br burning 4895, but a 300WM burning H1000 right?
Have you noticed that great big fireball at the muzzle?
That's way more than fractions of a grain -burning outside of the bore-

What do you mean ~'built to shoot rocks to a mile+'?
If I called a top gun builder and told him I wanna shoot at rocks over a mile away, will he say "well then,, I'm gonna need to cut 6" off your barrel"?
I think he would really ask: "Can you sneak up closer?"

So are you saying that I should try a faster powder? To be honest, I suspected this, especially with Retumbo. It seemed that velocity increases stopped at about 2850 fps despite pouring more powder to it.

Shooting rocks at a mile+ means I bring this rifle with me to a gopher field and shoot at rock "targets" after the little rat-weasles get wise and stop coming out of their holes.

Thanks.

 

[montana_native]

Ok, I'll bite.

Mike, rocks come a variety of sizes. I can shoot rocks at a mile + with a 223 and a 16" barrel. I might not be able to shoot the small ones though...

Back to the OP's question. Tell me more about your chronograph setup. What are you using, and how is it laid out? Also, what is the number of shots for that ES? I cut my ES down to one third of what I had before by changing chronographs.

It is a little POS blue Shooting Chrony Beta Master that's been abused for many years. That being said, I feel confident it is giving me an accurate indication of the ES due to the vertical variation I get at 1500 yards and beyond.

 

[montana_native]

Maybe I'm crazy, but it seems to me that the real question is how does it shoot at long range? ES can be an important number, but in the end that's all it is, a number. Like any number, it can vary quite a bit for a number of reasons, such as the chronograph, the lighting conditions, and a few other things. You stated you are getting good accuracy out of it (I'll make the assumption you meant precision as well) so what difference does the ES make? How close the holes show up to where you aimed and to one another mean a lot more than the ES.

I am getting vertical inconsistency at long ranges.

 

[amlevin]

How close the holes show up to where you aimed and to one another mean a lot more than the ES.

Chasing the ES can often lead to excessive consumption of adult beverages and a sore but on your dog.

All it takes, no mater what the group size is, is for ONE round to be significantly faster or slower than the rest. I prefer to use the Mean Absolute Deviation when assessing a load. I don't think that the shooting chrony will calculate that number for you but there are dozens of online calculators that will. Just google Mean Absolute Deviation Calculator and pick one. If you have Excell or Open Office Calc, there are formulas included for MAD.

This will give you a better feel for your load rather than assessing it on the basis of one ornery case/load/bullet/etc.

 

[jlow]

Maybe I'm crazy, but it seems to me that the real question is how does it shoot at long range? ES can be an important number, but in the end that's all it is, a number. Like any number, it can vary quite a bit for a number of reasons, such as the chronograph, the lighting conditions, and a few other things. You stated you are getting good accuracy out of it (I'll make the assumption you meant precision as well) so what difference does the ES make? How close the holes show up to where you aimed and to one another mean a lot more than the ES.

In principle that is true but it assumes that you do all your load development at extended range which is not possible for most of us – this is where a good chronograph comes into play. The other way to look at it is that it is another piece of the puzzel that gives you confirmation that when you are getting verticle dispersion that it is your MV that is causing it.