ES Spread

bambambam

I'm still messing with my 7mm Rem Mag loads looking for a shooter.

I have a POS Remington Model 770 that I've worked over and got shooting better than I can.

I shot a batch of rounds the other day and I was getting about an ES spread of 25. Every now and then I will get a round that has a high # about 30fps more and moves my ES spread to ~55.

I have tried Fed 215 primers and WLR primers. I have used H4350, H4831SC, H1000 powders.

I've just recently got enough Win. W-W cases to use them exlusively. I've trimmed the cases to even perfect length. Cleaned all the primmer pockets.

I'm still getting this spread.

Is this spread normal for this class of rifle, or is it something I'm not doing right?

I don't trim the neck walls or clean out flash hole with a tool.



I don't expect this gun to shoot like a BR Model 700, but I just want to find a combination of componets that will shoot good in the gun. 300-500 yrd range for now.

charliemeyer007

I really like my 7mm Rem Mag. The only bullet I run it is the 162 BT Hornady on top of a case full to the neck of T870 lit by a CCI 200. I don't run a chrono but if I understand correctly you are running a extreme spread of 30 fps. 30 out 3000 is like 1% which I think is good. What kind of groups are getting? I'd start looking at seating debth and bullet selection. WW is my second favorite brass. I hand scrape the primer pocket every time and I only neck my used brass.

bpost

I never saw much effect from having a low ES on paper. According to the math you should have a balanced load when the ES is very low indicating that load should shoot well. I just never saw it on paper. I know mrbruce has posted some crazy low ES printouts when shooting a 6.5X284 experimenting with the Russian primers a few years back. Those loads did not SEEM to shoot any more accurately at 300 yards than some of his others. One hole is one hole. I set my bench up at 350 yards one afternoon shooting a 6BR 8 twist with JLK 105 VLD's and found three loads with different powders that shot well, all of them had ES readings above 40, all were under 2", that is good enough for me!

Hopefully a BR shooter will chime in and give a more learned opinion on the matter of ES and what it means to the flight of a bullet.

zimmden

Variation in neck thickness (if not neck turned) gives different neck tension on bullet causing velocity variation. How accurate is your powder charge? Do you weigh each charge? Can you throw each charge to within 1/10 of a grain? If not, velocity will vary. Match primers seem to help. Cases sorted by weight will help since internal volume will be the same resulting in the same height of powder in the column. PS: 25 fps ES should not affect accuracy very much.

MIKE WISKEY

#1. I'd be more conserned with sd (standard deveation) than es
#2. uniform and de-burr your flash holes (from the inside).

Rocky Raab

I have to disagree with you, Mike. Standard Deviation (SD) has many times been shown to have much less value than Extreme Spread (ES) as an accuracy predictor - at least in the sample sizes shooters usually use. Unless and until you start figuring SD over a hundred shots or so, it actually predicts very little if anything.

ES, on the other hand DOES show an immediate and positive correlation to consistency of the load. It has to do mostly with barrel time and harmonics, but bullets that accelerate to within a few feet per second of each other also have "transit times" within a fraction of a millisecond of each other. Thus, they exit at nearly the same point in the barrel's vibration pattern. That's good.

To this particular example, the 7mm Rem Mag is known to be a fairly poor round for consistency. Even the factories have trouble loading it to high standards, meaning low ES numbers. Any ES under 100 is pretty good, and threebam's numbers are surprisingly good. If I were threebam, I'd grin and not change a darn thing.

There are many, many reasons why muzzle velocity changes from shot to shot, many of which we simply can't control. Barrel temperature causes variable expansion of the bore, Barrel temperature also changes the powder burn rate. Then there's the different amount of fouling present for each shot, just to mention three such factors.

nononsense

bambambam,

This IS a Remington M770 after all. It's neither a target rifle or a rifle built for anything but light duty hunting. I don't get excited about small variations with statistics unless it should have a meaningful impact (expense and energy) on the outcome.

However, since you asked...

Unfortunately, sometimes numbers are simply numbers. That is until you choose to make them important. In this case, you have chosen to make a problem out of some numbers which have little or no bearing on your outcome unless you start working the entire process from start to finish with exacting precision. This can also be read as requiring some financial expenditure also.

Extreme Spread (ES) as used for reloading is just the range of velocities recorded for a group of shot represented as the subtraction of the slower velocity from the higher velocity.

Any variable which is present in the reloading process can have an impact on ES. This will include but is not limited to:

Chronograph
Brass condition and preparation
Powder and the method of weighing
Rifle barrel condition
Chamber dimensions as they relate to sized brass

If you don't have an exceptional chronograph and the conditions for gathering the data aren't consistent, the ES has little meaning.

If your brass isn't sorted and prepped to be accurate in volume and neck tension along with proper flash holes and primer pocket, the data will be less meaningful.

The type and brand of powder can lead to variations in ES. If you're using larger kernels of powder as opposed to smaller grains, the air space between the kernels can have an effect. The percentage of case fill with any particular powder will show variations also. Cases need to be full or nearly so, to demonstrate best consistency.

Using an electronic scale is guaranteed to give you enough error to show up as larger ES in your data collection. They are neither accurate or repeatable until you get up into lab grade.

The interior condition of your barrel can have a significant impact on ES. Fouling of any kind will degrade the data. But a perfectly clean barrel needs to be fouled to show consistency. It's a fine line to walk if data is critical because the condition of the barrel changes with every shot. That's why we look at statistical averages in the first place then study the aberrations for significance.

If this is a factory rifle then the chamber is suspect right from the start. This is not the handicap most folks think it is. Fire forming brass while working on loads will get you on the right footing but you need to re-size just to fit the chamber. The exception is if this is a hunting rifle then you need some slack in order to have perfect feeding under all conditions which is your situation.

The shape and size of the groups will tell you most of what you need to know.

Round groups are what we strive to shoot each and every time. If your rifle is shooting round groups with your ES, go hunting and enjoy life!

If the groups are showing vertical then the ES is having some impact of those groups.

If you're seeing horizontal spread then there is some physical variable showing up, wind being the primary.

Small groups, often referred to as 'one-hole', indicate the necessity of shooting at longer ranges for the variables to start showing up for assessment.

That's a long way around saying do some of the little corrections and get on with your hunting. Or switch rifles to something that will benefit from the cost and energy associated with these corrrections.

Best.

Rocky Raab

Except for the comment about electronic scales, I agree with nononsense 100%. (And that one is hardly worth quibbling about, because almost any scale is plenty good enough for reloading purposes.)

bambambam

Thanks everyone for your input. As always, you provide me with experienced infomation on problem solving.

I think I'm going to take the advice about complete brass prep and see what I get in my groups.

I know my powder charges are consistant, I use a 5-0-5 scale to measure my powder exactly.

I wasn't for sure how important the ES spread was for my rifle as I'm not an owner of BR quality equipment. Thanks for laying that out for me.

Time to get to work improving my brass.[;)]

Okie743

I don't use a chrono to get accuracy, I test the gun and find what it wants, then after it gets the accurcy it wants, and I want, I then check the vel and other chrony info.
I never could come up with any good reason for trying to make the chrony spreads less if the bullets are going into the same hole on the target.

Rocky Raab

If you moved the target out a ways, you'd have that reason, Okie.