Hello Fellas,

Update on my load development.

I Chrono'ed 8 rounds from my rifle just today and here's what I got:

7mm Remington Magnum
26" Benchmark 1:9 Barrel
168gr Accubond LR's
79.3gr of RL-33. Note: 106% Compression Load but is just below Max Load.

1) 3,096
2) 3,102
3) 3,109
4) 3,119
5) 3,141
6) 3,141
7) 3,152
8) 3,165

AVERAGE = 3,128
DEVIATION= 69 FPS

I used a RCBS 750 digital scale to weigh every powder charge and I seated every bullet exactly the same.

I was very satisfied with the accuracy of this load. Last week I shot several groups which were all SUB 1/2" at 100 Yards.....even with my 51 year old eyes so I am not complaining.

Is a deviation of 69 FPS "Normal"?

The groups were great so I am not worried about it but I would like to hear your thoughts on the 69FPS Deviation.

If it is a bit much, what are your opinions on what I could be doing wrong?

Thanks!

Frank

Your deviation is really extreme spread which is not too bad.
But I would also look at "standard deviation" which is a statistical term for something like the average deviation from the mean for each shot.

In your case sigma is about 25 fps. I think that is pretty good for a large case high pressure round like the 7 mm Mag.

You can tinker with that load a little but it may take a while to make it significantly better. Most things your do may make it worse.

You might raise or lower the charge a little and you might tinker with the primers like using a Fed 215M.

Now might be the time to shoot a ladder and see what that tells you.

Maybe my terminology is off sorry.

My slowest round was 3,096
My fastest round was 3,165

I am referring to the spread of 69 FPS between the two.

What is the proper term for that?

69 FPS is the extreme spread.
That can be caused by only 1 or two rounds.
One very high or one very low or a combination of the two gives the extreme spread. But that number says nothing about the uniformity of the rest of the rounds and they could all be very good.

quote:

Originally posted by Leopardtrack:
Maybe my terminology is off sorry.

My slowest round was 3,096
My fastest round was 3,165

I am referring to the spread of 69 FPS between the two.

What is the proper term for that?

Just because a load has a SD of 10 does not make it accurate. Havine a SD of 100,and your getting one hole groups at 100 yards is just fine.
I used to get hung up on the smallest SD I could achieve. An older shooter showed me his loads and asked me to try them in my same type rifle. They shot very well. SD was 150. I jumped off the band wagon of low SD over 35 years ago and have never looked back.
Shoot was is accurate at the range yorr rifle shoots the best. Stick with that load.

Since my accuracy is really good I am not going to change/tinker with it in any way.

So you guys don't seem to think that anything is out of wack with my numbers which makes me feel better and answers my reason for this posting...thanks!

Since it is a 106% compression load maybe the powder settled differently from highest to lowest velocity rounds??

Extreme spread and standard deviation are statistical predictors based on past performance.
Group size is a measure of what actually happened.
Put another way, do you want to talk about small numbers, ES,+/or SD. Or small groups on target.
As was said above small numbers don't equal small groups. And big numbers don't exclude small groups either.
If you enjoy the hunt for the small numbers have at the tinkering with your loads.
If you enjoy small groups find a load your rifle likes and stick with it.
Nuff said.

muck

quote:

Since my accuracy is really good I am not going to change/tinker with it in any way.

Yep I would leave it alone if the accuracy is what I want. Heck for years before we could afford a Chrony we would have just worried about accuracy.

If those are in order I wonder why the first 4 were the low ones.

Ramrod, I put them in order from slowest to fastest.

Seriously Fellas, this is one of the biggest reasons that I resisted reloading all these years....I new that I would become obsessive with it and that's exactly what has happened!

Now, I don't know how I could have been happy with factory ammo.
From my favorite factory load, Federal Premium 160gr Accubond, to this load that I did myself, I am shooting a bullet that is 8gr heavier, 100FPS faster, AND is more accurate.

There is also allot of pride involved in making my own loads as well.

Your spread is not bad and it is something I do not worry about; accuracy is more important. Don't fret over this small stuff; load, shoot; repeat.

Accuracy trumps SD and all of the rest of those terms.
Was you increase in velocity lined up as you posted them? If so, the increase could be attributed to the barrel becoming more fouled.

quote:

Originally posted by Leopardtrack:
Hello Fellas,



The groups were great so I am not worried about it but I would like to hear your thoughts on the 69FPS Deviation.
Frank

Not to worry , Frank. 69 is a great number. roger

Never thought of that

Your extreme spread is only 2% of your "average" velocity. That is fairly good. The big issue is that it is unimportant as long as you can shoot sub MOA groups. I always work up the loads for accuracy before I ever use my chronograph. The reason I do that is that the accuracy is the most important of all the characteristics of my ammo. I use the chronograph primarily to get the average velocity in order to predict trajectory, the standard deviation to predict the consistency of the trajectory and the extreme spread to predict the maximum expected deviation in that trajectory. As long as it is predictable at the ranges you will shoot at then the numbers don't mean much.
Sometimes I get an accurate load well below the maximum load and after making sure that load is recorded I have continued the process to see if there is a faster load with the same or better accuracy. If I find one that is at least as accurate as the lower velocity load I may use the higher velocity load.

In order to make sure the load is consistent I will shoot it for groups (5 shot) several times over a few months. If it consistently shoots sub MOA 5 shot groups then it is a keeper.

I fire five five shot groups in this way:
Place two targets aligned on top of each other for the first five shots. Take the top target down and replace it with another carefully aligned on top of the original target and fire five more. Remove and replace the top target and repeat. That gives me five individual five shot groups on individual targets and one target with an aggregate of all twenty-five shots which I record as the average group size for that load.
I always look at the first shots placement so I know if the impact changes much as the barrel gets fouled. I have found that with the right powder/bullet combination there is little if any difference in shooting with a clean bore and shooting from a fouled barrel.

Fellas your replys are full of great insight and I thank you all so much for your efforts

I think I got lucky with this loading.... A sub 1/2" group from a 7 mm bullet with an insane BC leaving the barrel at 3,100 fps Plus!

In working up a load for one of my center fire target rifles, I used to use the "ladder" method, which consists of selecting a fairly mild load and loading a series of cartridges, increasing the charge by either .1 grain or .2 grain each successive cartridge for 20 shots. Depending on which increase I used, the final load is either 2 or 4 grains above the initial load.

I then shot them in the order loaded, using a second target on the bench to plot the shots in the order fired.

My experience was that the points of impact would rise as the powder charge increased, but that at some point they would cease to rise and form a cluster. Five or more shots, with an extreme variation of propellant weight of up to a full grain would shoot into the same small group. A powder charge right in the middle of the charges which formed the cluster is the one I would select to use in that rifle.

There is a point in increasing a powder charge in which the harmonics of the barrel tend to cancel out differences in velocity of the bullets fired through it. Use a load within that range and differences of 1 or 2 grains of powder make no difference in the results.

You can use a powder measure and forget about laborously weighing every charge. An occasional weighed charge to confirm that the measure is still throwing the desired charge is all that is required.

Incidentally, weighing powder charges may not assure uniform loads if the ammunition is loaded on different days, because differences in humidity have been found to affect the weight but not the volume of smokeless powder granules.

Don't worry. The obsessive part is mostly because you are new. In time you will learn to ignore some details because it costs too much time to comtemplate their significance.

I have too many times worked on loads that performed well and shot tiny groups only to shoot much bigger groups with the same load on the next trip to the range. The major variable many times is just the trigger puller.

quote:

Originally posted by Leopardtrack:
Ramrod, I put them in order from slowest to fastest.

Seriously Fellas, this is one of the biggest reasons that I resisted reloading all these years....I new that I would become obsessive with it and that's exactly what has happened!

Now, I don't know how I could have been happy with factory ammo.
From my favorite factory load, Federal Premium 160gr Accubond, to this load that I did myself, I am shooting a bullet that is 8gr heavier, 100FPS faster, AND is more accurate.

There is also allot of pride involved in making my own loads as well.

That is a very good point

I'm at the point now that I don't chronograph a load till I shoot it 200-300yds and I have to do couple ranges trip before doing it.

In a perfect rifle it is acceptable to me if I don't intend to shoot past 300 yards.