Accuracy=seating depth or tenths of powder

[SidecarFlip]

Yes, I have just recently started to sort bullets=tedious. I was just curious of what's more important seating depth or a tenth of a grain difference. It sounds like seating depth.

So Next question on seating depth do any of you go and try to define the seating depth by 1000th of an inch?

Sorting bullets...tedious? How about pointing everyone in the lathe for uniformity and consistent BC, then sorting by weight (Bergers are unusually close in pill weight and runout is nill).

I point my Sierra's with a John Whidden pointing die btw. Gives an extremely cosistent tip to the Sierra ballistic tipped Game Kings (SBT).

 

[FEENIX]

So Next question on seating depth do any of you go and try to define the seating depth by 1000th of an inch?

lightbulbBerger has an excellent article/guide on CBTO vs COAL and VLD seating depth.lightbulb

 

[SidecarFlip]

...and you can apply it to any make or brand (of pill). Just keep in mind, the shorter and fatter the ogive is, the less impact seating depth has on grouping.

 

[Pdvdh]

Changing powder charges changes MV. Changing seating depths changes MV. Changing primers changes MV. Changing case capacity changes MV (different case weights = different internal volume).

Which causes me to revisit the possibility that what we're primarily doing is finding a MV that provides the best accuracy from our rifles. Both seating depth and powder charges affect MV. So how does anyone know which is what and what is which? Reminds me of the common Thermos. Keeps hot things hot and cold things cold. How does it know?

Historically I've primarily used different powder charges to find more accurate loads. I'm including seating depths more recently, particularly jammed 010" versus 0.010" jump for Berger bullets. Recently I changed seating depth in the search for lower ES and accuracy with RL33, which is known to produce higher ES with longer jumps - and lower ES with shorter jumps - to the lands. There is no change in the spectrum of seating depths that has a greater affect on MV/pressure than into - versus off - the lands 0.010". So I figured if shorter jump to the lands was the better approach to reduce ES, then jammed might be the best. The 215gr Berger Hybrids jammed 0.012" into the lands reduced my ES from 30-45fps to less than 10fps. This compared to a seating depth 0.005" - 0.010" off the lands. Accuracy was very similar at both seating depths. Of course, velocity/pressure both increased by jamming the bullets 0.012".

There are times when seating depth affects powder capacity to the point that I'm compressing powder charges (beyond my preference) to get to my preferred pressure/MV. And in those instances I prefer the longer seating depth if accuracy and ES is good. That was the case, and another consideration in the rifle with the 215gr Berger Hybrids.

I recently had another rifle where I was running out of powder capacity (excessive powder compression by bullet seating depth) prior to reaching maximum load pressures, so I switched from a standard LR primer (Fed 210) to a magnum LR primer (Fed 215). This was a 7mm Rem Mag. The change in primer had a similar affect on MV to a 1gr change in powder charge weight. The end result was all good. Accuracy was good and the bullets could be seated with very little powder compression.

 

[BountyHunter]

Changing seating depth changes volume just like adding more or less powder.

You will get max pressure with a bullet on the jam and less as you back off.

Yes changing powder will open and close a group sometimes dramatically. I was testing a dasher this week and a .2 change opened the group from Under 1/4 to over 3/4 and I reshot it 2 more times to confirm. .4gr later it tightened up again and the vertical disappeared.

Each barrel is a beast unto it's own.

I prefer working powder first and then tweaking seating depth off jam unless magazine gun and then I use max mag coal as starting.

 

[johnhhernan]

Ok, I'm back, computer down for a while. So thanks to everyone who has responded to my question it was fun to pick knowledge from all who participated in my question.

 

[BigSwede]

As a practical rule of thumb in my "hunting" rifles I start at max magazine length for my selected bullet and adjust powder charge. This allows maximum case capacity to be retained which hypothetically yields highest velocity. In a hunting cartridge this is good. Optimum accuracy and velocity at a functional magazine length works for me for long range hunting applications. That being said..... Most of us rarely need the second shot... and I have had numerous guns that loved em in the lands. If it's a tactical rig ..fit em all in the mag so you can get all the "bangs" out before you start hearing the "whizzes" !!!gun)

 

[SidecarFlip]

Changing seating depth changes volume just like adding more or less powder.

You will get max pressure with a bullet on the jam and less as you back off.

Yes changing powder will open and close a group sometimes dramatically. I was testing a dasher this week and a .2 change opened the group from Under 1/4 to over 3/4 and I reshot it 2 more times to confirm. .4gr later it tightened up again and the vertical disappeared.

Each barrel is a beast unto it's own.

I prefer working powder first and then tweaking seating depth off jam unless magazine gun and then I use max mag coal as starting.

Eric Steckler and others address that quite well. Myself, I'm not a fan of excessive pressure and what it can do (though most modern sporting firearms do have cross drilled holes in the receiver just for that scenario. Better to 'let the fire out sideways' than have the fire come backwards...in your face...lol (in case you wonder what those 2 drilled holes are for in your receiver....)

But then, I don't like cratered primers and or sloppy pockets after one load nor do I like metal transfer on the bolt face..... just say'in.

Load laddering, I always go +10 past the lands (jam) and then right on Eric's regimen with one group loaded TTL as well but always with a medium powder charge, splitting whatever the recommended maximum load is, in half.

Interestingly, none of my rifles (including the one off custom built ones) like a LTL or +10 jump with VLD's.

 

[SidecarFlip]

Additionally, with no jump, concentricity, neck thickness and rounout play a big part in how the pill is presented to the rifling. It must be presented absolutely concentric and on the same plane as the rifling or the pill will cock slightly in the rifling, yielding an erratic group.

With some jump (between the rifling and the pill, initial movement decreases pressure and can (sometimes) allow the pill to align better with the rifling.

I find it interesting to gage concentricity of factory loaded rounds. You'll be amazed at the runout. Sometimes right on, other times, out in left field. Same apples to COAL measured on the ogive. Some brands are within 0.002 of Sammi spec, some aren't.

I guess my big issue with a factory round is, I have no idea what propellant is contained in the case, nor the primer and no factory is gonna tell a consumer anyway.

 

[txsendero]

So seating, then powder, then you should go back to seating and tweak it a few thou each way to 'shape' grouping. This final tweak is not tuning or developing(you're past that), and does not affect tune -unless you go beyond a few thou or into/off lands.


Mikecr, could you explain a little more in detail on what you mean by "shape" the group, and how you go about that? I'm interested.

 

[Kevin87]

That is the way I did my last load work up dsculley. I set my bullet at .030 off the lands, worked up to 90% of max load, then started playing with the seating depth one way then the other. Once you find that sweet spot on depth, the charge weight didn't change the group a whole lot. my bullet of choice is the 7mm mag Berger classic hunter hybrid, and this particular bullet really liked .060 off the lands--once I found it, worked up the charge to 2950 fps and called it good--can't argue with .30 in groups.
One the flipside, if I would have worked up to a max load at .030 off the lands, and then started playing with seating depth, there could have easily been an over pressure situation by seating the bullet further in to .060. I'm no expert, but learning things as I go.

 

[Pdvdh]

One the flipside, if I would have worked up to a max load at .030 off the lands, and then started playing with seating depth, there could have easily been an over pressure situation by seating the bullet further in to .060. I'm no expert, but learning things as I go.

Seating the bullet deeper, longer jump to the lands, would reduce pressure and MV, at the same powder charge. The running jump into the lands reduces the pressure spike when the bullet encounters the rifling.

 

[barefooter56]

I have a question for some of you seasoned LR accurate reloaders.

What is more important having the exact tenth of grain of powder or being within .005 to .010 of my seating depth.

The reason I ask is I loaded 51.8 grains of 4831SC powder and that seems to be accurate for my load so I then figure out my seating depth and I consistently come up with a group at 1.5 inches at 550yds which I'm happy with but I loaded up 51.9 by accident and I didn't see a difference in accuracy but if I shoot 51.8 grains of powder and my seating depth is .005 to .010 off of what i'm used to my accuracy grows to about 2.75 inches.

Now you see why ask what is your experience is in this situation.

Please enlighten me...

John Hernan

John,
Short answer is "both". MikeCR and SidecarFlip made very good suggestions and points as to why you start with seating depth testing first then powder charge. The trick is to do both in a set order in set increments so you don't miss the seating depth or velocity accuracy node(s). Keep a good reloading log book and only change ONE thing at a time then test! What I have found is that the seating depth accuracy node usually is found at only 1 certain distance on or off the lands. The velocity accuracy node usually repeats as you go up in powder charge. If you graphed it. It would resemble a sine wave as the group starts open or closed then opens or closes as the powder charge is worked up till it returns to the original (starting) group size. The target will tell you. Vertical dispersion will become flatter. SD (standard deviation) if you are chronographing will drop to single digits and the velocities will be very similar in speed. Once you find your accuracy nodes THEN step into the case weighing and so on. With lighter and heavier cartridge cases you will have to "tweak the powder charge up (light) or down (heavy) to stay on your velocity accuracy node. Same as you will have to do as you "chase the throat" and set the bullet out of the case neck to maintain your seating depth sweet spot. Get your basics down before stepping into the deep end of the reloading pool. And only go as deep as you want or to what makes you confident in your load weather you target shoot or hunt. Keep in mind however that once you get a load to a minute to half minute of angle. More accuracy can be found faster by working on reading conditions ( wind and mirage) and working on position and trigger control than by tweaking the load.
Hope this helps!

 

[SidecarFlip]

I follow the Walt Berger / Brian Litz school of thought. I use a median powder charge of any recommended for that particular caliber / pill weight that I have on the shelf, determine best grouping with stings of 5 loads in each of their recommended jumps from the lands and then any only then do I start adding propellenat or changing powder foir burn rate. Last thing I do is fiddle with primers and most times, thats unnecessary.

The ballisticians ar Berger, Sierra, Joyce Hornady and Speer don't get paid big bucks for nothing. They shoot everyday, a myriad of firearms so I tend to listen to their experience.

Why reinvent the wheel.

I have to say thet Berger VLD's have to be the most finiky, hard to get consistent pills on the mnarket today but once they are dialed in, they shoot lights out (so long as the shooter does his/her part.)