15 fps difference?

[Link]

6br 1-8t, 108 Berger, Varget do you think 15 fps average on 15 rounds, could make a difference in tune? 2715 to 2730 fps. If so how many grain drops do you think it would take to go down, .2 or so.
TY Don

 

[marchboom]

What do the targets look like? That's what I would use as a gauge. Also, nothing wrong with a 15 FPS spread with 15 shots.

 

[Alex Wheeler]

Your tune is not tied directly to velocity.

 

[DaveTooley]

I have never tuned for accuracy using a chronograph. The numbers will lead you astray. The target tells all.

 

[marchboom]

I have never tuned for accuracy using a chronograph. The numbers will lead you astray. The target tells all.

Yep. I have had great groups with high ES/SDs and low ES/SDs with not-so-great groups. Go figure.

The target reveals everything you need to know about your load development goals. At least for me anyway.

 

[TerryPohl]

Amen Dave. I have had shooters ask how fast I am pushing a bullet and my reply is always I don’t know and don’t care if it skips the ground before the target as long as it hits where I am aiming.

 

[searcher]

Depends.... If you are shooting at extreme distances, I'd try to find lower spread - but that alone, as others have noted, will not dictate all. Of course, the "perfect" option is one with low spread AND great target result. Seems there is always a bit of a tradeoff, as finding both can result in a bit more testing than a lot of folks care to subject their barrels to.

 

[RegionRat]

Agree with the others, tune isn't all about chrono numbers.

You must also watch the target.

Nothing at all wrong with also watching and recording chrono numbers, but we must add that folks who load in advance must also manage many other parameters like the round counts, cleaning, climate, etc., in addition to all of the above... in order to understand what the gun/ammo, target, and chrono are telling you.

It is an advanced shooter that understands how weather and tune should be used as feedback. Keep up the study and you will get there.

 

[Acyr]

Since the Garmin is so easy to use, I use it almost every time I shoot. I have been noticing a trend that my best groups tend to show up just beyond my best chrono numbers during load development.

 

[Olderthan dirt]

I was working a new 338ARC sub load down.
One load SD was 0.7( group was 2”)
Single hole group SD was 10.0

 

[6.5 forever]

Since the Garmin is so easy to use, I use it almost every time I shoot. I have been noticing a trend that my best groups tend to show up just beyond my best chrono numbers during load development.

My Garmin is always on when I shoot. It is interesting to review and set up. So why not!

 

[Tommie]

Agreed. And it makes my brain itch that a higher ES does not necessarily result in bigger groups. Baseline logic would say that inconsistent velocity results in inconsistent harmonics regardless of node. Ultimately it’s true that the target tells all. Ideally, of course, the pet load also results in low ES. Anymore I only keep track of velocity to calculate drops and windage.

 

[JEFFPPC]

After I have my load I SOMETIMES get the Garmin out so I can answer the inevitable question.

 

[CF Junkie]

It helps to recognize that most factory ammos chronograph with an SD of 15 to 17 fps which results in an extreme variation of about 45 to 50 fps.
My very best reloads have SDs of 5 to 7 fps which results in a extreme variation of about 15 to 21 fps..
The variation of my best reloads is probably due to the primer firing and resultant powder burn variations that occur naturally.
I still shoot groups with my best target rifles that average under 0.250 inches at 100 yards.
I have long since stopped worrying about chronograph measurement variations.
It doesn't seem to matter to my group averages. My lack of concentration on some groups, or my variations in set-up position create far more impacts than primer/powder burn variations,

To answer your second question, a 0.1 grain change in powder charge results in a velocity change of around 12 fps.