Flatenning the curve

[autoxforfun]

I went out yesterday morning to shoot an experiment.  I've noticed in my competition matches, especially in Heavy Gun where you'll shoot 50 rounds, that the groups tend to get worse as the match progresses.  As an example, I shot the Dasher last month at 1000 yards,  The first two 10-shot groups were in the mid 90's for score and 3-5 inches.  The third group opened up quite a bit compared to the first two.  So the experiment was to shoot 50 rounds like in a match and then measure each round/group to see what changed.  

This particular morning was cold (for CA).  it was in the low 30's and overcast.  The first thing I discovered was that RL-15 and RL-17 are indeed temperature sensitive.  As I shot both the Dasher and the 6 Grendel,   both rounds were a 100+ fps lower than what I expected and what I had seen working up the load.

I've attached a couple graphs from the data I collected for the Dasher.  I shot the 50 rounds in 7 groups.  The first 15 (3 groups)  were to represent sighters, then two 10 shot groups (record groups), a 5 shot sighter group and the final 10 shot record group.  From the average MV per group, the average gained roughly 20 fps from the start to the finish.  The 2nd graph is the MV of each individual shot.  There are some interesting excursions of a few rounds. (I didn't collect the first 2 cold bore shots).

I was thinking of either increasing the load for the first 30 rounds or perhaps reducing the load for the last 20.  This should have the effect of keeping all of the rounds closer to the same MV and in the node.

[jvw2008]

Every range and every day are different. However, four changes can usually be predicted as the day progresses. 1) With each round down the barrel your internal ballistics are going to change with possibly the greatest change occurring in the first 30 rounds down the barrel. 2) ambient temperature will usually rise affecting both internal and external ballistics. 3) The shooter focus and endurance decline. And 4) Wind patterns alter and wind velocity increases.

It is up to the competitor to adjust. The norm is we try but these changes during the day make all of us produce better groups in the morning than what we accomplish later in the day.

1) barrels are individuals. Some do better going into a match with 20 or more rounds already on the barrel. Some do better when cleaned as frequently as every relay. It's important to know what your barrel likes.

2) Temp stable powders can buffer the affect of increasing ambient temperature, minimizing adjustments required by the shooter. However, 30 degree changes stress that buffering ability and plays havoc with temp unstable powders. There are two readily available adjustments. One would be reloads with different charge weights for different times of the day. And the second is the use of a tuner. A tuner works extremely well for this purpose once you learn how to use it.

3) ALL competition is a mental game. This is likely the most difficult change during the day to control. Practice, good health, and maintaining a positive attitude go a long way towards winning the mental game.

4) Changing wind patterns and velocity are only conquered with practice with your chosen round. ?

[gman47564]

Could round count have a factor on what your seeing also bob.. for instance do you tune the load with a clean barrel ? And as the round count increases so does the fouling in the barrel causing increased velocity as the day goes on.. may help to tune the load with 40 or 50 rounds down the barrel.. i dont know.. 

[jvw2008]

Could round count have a factor on what your seeing also bob.. for instance do you tune the load with a clean barrel ? And as the round count increases so does the fouling in the barrel causing increased velocity as the day goes on.. may help to tune the load with 40 or 50 rounds down the barrel.. i dont know.. 

That's number one on my list of four.

[autoxforfun]

1) barrels are individuals. Some do better going into a match with 20 or more rounds already on the barrel. Some do better when cleaned as frequently as every relay. It's important to know what your barrel likes.

Jerry. I'm in agreement with what you said.  Part of addressing #1 is to understand the barrel.  That was the purpose of this experiment to get some data that would provide some insight into the barrel behavior.  When looking at the curves, it looks like the MV change is starting to level out after 40 rounds....hard to tell since I don't have much visibility beyond 50.  But it may be worth shooting 40 rounds and then either not clean it or do a very light cleaning.  Then do the 50 shot experiment again.  The challenge with a match is that fouling the barrel with 40 rounds is not practical.

[bikemutt]

I'm sure someone has already thought of this but, would keeping range ammo stored in a temperature controlled container more or less eliminate temperature sensitivity? Something as simple as a beverage cooler for example.

[jvw2008]

Yes you will see both BR and F Class shooters doing this on occasion. I've wondered about the possibility of condensation inside the case transitioning from a warm to a very cold environment. I don't have any personal experience with it so I don't know.

I've been satisfied using a temp stable powder and a tuner on the muzzle to compensate for the shorter or longer barrel time.

[mnbogboy]

In my 25-06 days i collected every velocity in load development and found cold bore "flyers" to have less velocity than others in each group.
To combat this slower speed I used my heavy weight culls in the sorted brass of which measured less h2o volume. With the same charge these boosted the velocity enough to get the groups back together cold. I marked the head end of these with a sharpie. I borrowed this gun to my second oldest son in a Wisconsin deer season after he broke the scope on his 06! He called me the next morning on the cell to help him get out a nice 8 or buck. First thing he said when I got there was I used a red one and he went right down. 200+ yards, a long wet drag across a swamp. ZERO must have held. THERE PROBABLY IS STILL some colored brass in those batches because I finally pulled them all down for the primers and necked that brass up to 6.5 for the 6.5-06

[autoxforfun]

It seems like I will need to load differently depending on the time of year.  Where I live and shoot, temps will range from low 30's to 100+ which is a lot to ask of any powder.  I'm thinking I may be able to get away with a load for 30-60, a load for 60-90 and then one for 90+.  I will need to pay attention this year and do some measurements to confirm.  This may apply to RL-15 mostly....RL-16 hasn't shown any issue but it would be worth testing that powder as well.