Why do I get a speed increase after ever reload?

[Skyking]

So maybe this is common knowledge.

Does muzzle velocity increase with every loading on the same brass?

So I have noticed that my speed increases with every reload on the same brass. I don't keep track on how many times I have used the same brass. But the brass had been reloaded 7 or 8 times on Winchester 7wsm brass. I normally just shoot out at 1000 yards. So any change is really noticeable. My dope will be right on every time I go out, as long as I am still shooting the same batch of reloads. Once I reload 50 peaces of already fired brass again. I have to tweak my speed up just a little on the ballistics programs. I had never really thought much of it until the other day.

I started with 100 peaces of new brass. All prep ready to go. I full length size them using a Forester ultra die set. Same 8lbs jug of H1000. CCI-BR2 primers. Have not change a thing, other then new brass. Well we went to our 1000 yard spot. First shot was low, as well as the 2nd 3rd and so on. I can normally dial right at 22MOA and be dead on. It end up taking 23.5 MOA to get back on. So I had to tweak the programs MV for 2975fps to 2885 fps to get thing to match up. My buddy that was shooting the 7wsm was having the same problem. He is on is 3rd reloading of his brass. He is now 25fps faster then his first batch. So every time we go out we have to speed our MV up just a hair. We bump the shoulder back .002. Over time the neck tension does seam to loosen up. I would of thought this would make the speeds slower.
I just has me stomped.

 

[MarcusT_700ss]

Re: Why do I get a speed increase after ever reload?

Are they moving faster or slower ? Your're contradicting yourself if you need more elevation they are going slower and if you reduced the speed to get the numbers to match up they are going slower.

 

[supratt96]

Re: Why do I get a speed increase after ever reload?

It could be that your brass is getting harder each time you reload to to work hardening (I'm assuming you don't anneal since you didn't mention it). If this is the case, the neck may not expand as much or as easily when the powder ignites and this may cause higher chamber pressure. Higher pressure = more velocity.

Try annealing a batch and shooting those rounds back to back with some non-annealed rounds. If there is a difference in POI, you have your answer.

 

[Skyking]

Re: Why do I get a speed increase after ever reload?


No I don't anneal my brass. I guess I will start if that ends up being why I am getting the increase in speed with every reload.
I am going to do some testing this week.

 

[justapod]

Re: Why do I get a speed increase after ever reload?

Sky I am with Marcus it seems that your going slower not faster. I am not an expert but I have been reloading metallic cartridges for about 35 years and Lakeway seems to be right about your case necks work hardening. I would try annealing those necks.