i have gotten some data that has me confused and i am hoping for some comments. thanks in advance.

i am shooting a Rem 700 chambered for a 300 Win Mag. i have been shooting 175 grain bullets at about 2700 fps. my groups have been surprisingly good for me.

i have shot 12 groups at 100 yards at 10 shots per group. the largest group was 1.2" wide by 0.9" high. the smallest was 0.8 wide by 0.6 high. all of the groups fall between these two extremes.

i chronograph almost all of my shooting and this is where the puzzle arises. i have gotten some standard deviation figures that range as high as 70.0 and as low as 22.2 as well as some startlingly high extreme spreads ranging as high as 164 fps.

my question: if i am getting such a high standard deviations and extreme spreads, shouldn't my group sizes reflect that? this data seems like it should reflect larger group sizes than i am getting.

i have used both an Oehler 35 and a LabRadar chronograph to gather this data. i am confident that the data is correct. so, am i wrong in my thinking about this?

this is just a question. i have no intention of altering anything as long as i am getting groups like i am, but is this an odd circumstance or do some of you have similar findings?

again, thanks for comments.

quote:

my question: if i am getting such a high standard deviations and extreme spreads, shouldn't my group sizes reflect that? this data seems like it should reflect larger group sizes than i am getting.

Your group sizes are already reflecting it. The large SD reflects the big velocity spread and vice versa. Yet, with such a high velocity cartridge, the differences in time to target between all those shots is amounting to an imperceptible difference in drop at 100 yards. Even with your largest velocity spread, your looking at an extreme spread of less than .3" at 100 yards.

I have a 22-243 Middlestead, velocities are all over the place, but the gun shoots basically one hole groups!!??

Why??

Have no idea.

quote:

Originally posted by Grenadier:

quote:

my question: if i am getting such a high standard deviations and extreme spreads, shouldn't my group sizes reflect that? this data seems like it should reflect larger group sizes than i am getting.

Your group sizes are already reflecting it. The large SD reflects the big velocity spread and vice versa. Yet, with such a high velocity cartridge, the differences in time to target between all those shots is amounting to an imperceptible difference in drop at 100 yards. Even with your largest velocity spread, your looking at an extreme spread of less than .3" at 100 yards.

Yep. Extreme spreads aren't so critical at 100 yds, but there are at 1000.....................

A big question is "What do you view as the maximum range you will use that load at?"

Then, grab a ballistics calculator and check the difference in drop and wind drift at that range.

If you are happy with the result, keen on truckin'!

If not, work toward a load that has tighter SDs and extreme spreads.

Not necessarily; consider the "self compensating" factor that exists in rifles; the Lee Enfield is a good example. Bullets fired at higher and lower velocities tend to follow a similar ballistic path due to the way the rifle reacts to each shot. Recoil and barrel harmonics thing.
Not always. But I said consider it.
Which is why I do not measure nor care about velocity variations; just measure group size at whatever range you need.

All things being equal (which they never are) more consistent velocities tend to provide more consistent accuracy. However, there are much more important factors. As dpcd alludes to, barrel harmonics can, sometimes by happenstance, compensate for velocity variations. And as others have pointed out, POI changes due to variations in velocity show up more at extended ranges than at only 100 yards.

Disregard groups right now, too much human err to factor in, especially when all the groups are decent at 100 yards.

Some people are very happy with a decent group at 100 yards, and for short-range hunting that is perfectly fine.

Use velocity only to graph out each powder weight. You will find "flat spots", where the velocity will level out and might actually decrease a little. These will be your accuracy nodes where the ES's will also be the lowest. I start with Chrono work first, then go for shooting groups after I get my data to find my accuracy nodes.

You might even find that your barrel just doesn't like the bullet/powders you are trying to work with. Being OCD with your brass preparation also tends to shrink ES's a great deal.

Doing it the way you are doing it is a big waste of bullets/powder/brass/time. Graph out your Chrono data like this:



If you are happy with your accuracy/consistency for short-range hunting, just pick the velocity you want with what you have. If you are a perfectionist, like many here are, you are going to have to identify you accuracy nodes and work within those ranges. If your 35p is constantly telling you that there is a problem with your ammo, it is not lying to you.

2700fps is VERY slow for 175gr in 300 win mag. In my own loading with 175gr LRX, I am seeing my accuracy node at over 3000fps. You have a lot of room to spread the wings on that 300 magnum.

Also consider that your load is very mild. That is a basic velocity for a 180 gr 30'06.

You will get variations when you have empty spaces in the case and powder column varied.

Bill:

You'll burn that barrel out worrying about such trifles. A buddy brought his new "toy" bore scope by a few weeks ago. We scoped my 300Win/m.
The bore is cooked clear to the muzzle! Looks much like a charred board for all the cracks and craters. Strange thing though, it'll still put 200gr GK's in an inch at 200yds and all shots on a typing page at 300 with my shooting.

This is an original 1917 Eddystone Enfield '06, barrel is stamped 1918. It has to have 10,000 thru it. I shot thousands of prairie dogs with it as an '06. Quite a number of times I've had the barrel so hot it blistered my hand when touched slightly.

Don't over do it or you'll need to rebarrel.

Naki is right though, that is a mild load for the cartridge.

George

quote:

Originally posted by bill smith:
...some startlingly high extreme spreads ranging as high as 164 fps.

Try annealing the necks of your brass. This helped reduce ES for me.