velocity issue in my 300WSM

[veezer]

I'm doing some load development for my 300wsm in a browning A bolt. A few weeks ago I went out with my chronograph and a 3 shot average was around 2980. I go back out this weekend and using the same ammo, I get a average of around 2850. And I say...what the hell? The temp on day 1 was about 85 and this weekend was around 75. Chrono set up the same. As far as the rifle goes, I did not fully clean it after the first outing. I just ran a couple of dry and oily patches.

One issue I have noticed is that when I seat my bullets, I notice that some bullets seat easier than others so I have some neck tension issues but could that account for 1000fps difference? The cases were annealed before the first firing (new Winchester brass) and this was the the second time I have fired the cases (no annealing before they were sized the second time).

Any ideas?

 

[jrob300]

Re: velocity issue in my 300WSM

I can't comment on much of your post except the annealing part.

I recently bought several hundred Win. 300WM cases. I did everything I could think of to make them shoot. I too noticed varied and difficult seating on first and second run through. I annealed a test batch and they tightened right up and seat like butter now. BIG difference. I shot a record for my rifle .585" c-c for 5 rds at 200 yds. out of that batch.

I don't know exactly what to make of it, but if it works...

Good luck,

John

ETA: did you mean YOU annealed them or assumed they were annealed because they were new???

 

[veezer]

Re: velocity issue in my 300WSM

No, I annealed them when I first bought them but only before the first loading.

 

[jrob300]

Re: velocity issue in my 300WSM

Got it. Then my comments would not apply...

John

 

[ColoYooper]

Re: velocity issue in my 300WSM

" I notice that some bullets seat easier than others so I have some neck tension issues but could that account for 1000fps difference? "

YES: but 100 not 1000fps (which is the situation you have)
Are you using a LEE Colet resizing die?

If so, I can explain your problems.

 

[mdesign]

Re: velocity issue in my 300WSM

It could be the ambient lighting or the distance of the muzzle from the chronograph, I've seen both of these cause a significant difference in reading.

I run mine a measured 15 feet from the end of my muzzle, any closer will cause a swing in the readings. I also noticed that a cloudy day can read different than bright sunshine and the angled sun of evening/morning can be different as well.

Just some thoughts, my chronograph is not an expensive one so your experience my be different.

 

[veezer]

Re: velocity issue in my 300WSM

I'm using standard RCBS dies.

On both days, it was sunny and the chrono was about 6 feet or so in front. I'm using a beta chrony with the sunshades attached. The first time it was around 10 in the morning and the second was from 1 to 2pm.

 

[jrob300]

Re: velocity issue in my 300WSM

My chrony will give erroneous readings when the sun is almost directly overhead. I made a sunshade and it completely went away.

John

 

[AQC440]

Re: velocity issue in my 300WSM

try moving the chronograph out to a measured distance, lets say 15 feet if possible. I think you are getting weird readings do to muzzle blast. The shockwave from your 300 is pretty big, plus the air it is pushing, even the volume of the air in the bore has to go somewhere.
I may be wrong, but it is worth a try. I think if you move it out to a measured distance and use that distance every time you will see better consistency...

 

[jrob300]

Re: velocity issue in my 300WSM

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AQC440</div><div class="ubbcode-body">try moving the chronograph out to a measured distance, lets say 15 feet if possible. I think you are getting weird readings do to muzzle blast. The shockwave from your 300 is pretty big, plus the air it is pushing, even the volume of the air in the bore has to go somewhere.
I may be wrong, but it is worth a try. I think if you move it out to a measured distance and use that distance every time you will see better consistency... </div></div>

This is a good point... a friend with a .338LM had to move his to 8-10 yards to get a consistent reading.

John

 

[AQC440]

Re: velocity issue in my 300WSM

John

I set mine at 30 feet on a regular basis...took me a while to figure it out!

 

[GRIM]

Re: velocity issue in my 300WSM

New battery in your chrono? Mine had that problem like that one time and I swapped in a new 9 volt and problem went away.

Might also be too close to your rifle and the muzzle blast is affecting the reading.

Does your chrono have sky screens on it?