I am working up my loads and my velocity is moving between 10 fps to 70 fps. What is an acceptable range between rounds? The powder is the same weight, bullets weigh the same, primers are the same, ammo temp is the same, cases are the same length, trimmed to length each time. Not sure what is going on, unless the norma cases are different thickness, but they are all out of the same lot. I have not weighed them yet. Any ideas?
First thought is how long are you letting the rounds sit in the chamber? Try to get the rounds off fairly quickly, especially the last two if you're doing five shots. I let a guy use my MagnetoSpeed last week and he had a round sit in the chamber for around 30 seconds due to another issue. I think it was number 7 of ten. That one was a heck of a lot faster than all of the others. Single feed the rounds and keep a set interval between shots and see if that brings your spread down. That would be the easy check and if you still get a high spread, you can move on to looking at a different angle.
Another thought is what chrono are you using? If it's optical, a change in angle of where the bullet crosses the sensors will give a different MV-I don't know about 70fps-but a change none the less.
What primers are you using? I hear tell some are more consistant than others, and try to keep the depth of the seating consistant. Are they all from the same lot, too?
Also, is your neck tension consistant? I'm using a mandrel to expand the necks on my 6.5 Creedmoor cases after resizing, so that I know the tension is consistant. Same with seating depth, but that seems like an unlikely problem.
I think the worst extreme spread I've ever had was 33 fps, but it's usually in the mid to high teens.
Be as consistant in your process as you can, and try to eliminate one variable at a time.
My chronograph is just a $100 optical kind that my great uncle bought me to replace the one that he shot a hole through when he had an AD as he was showing me the new .32 pistol he was carrying. The bullet made it completely through my chrono and the jacket lodged in the drywall, the lead core made it past the drywall and was stopped by a steel beam. . . he quit carrying the little junk. My powder is Accurate Mag Pro, primers are Federal Premium Match Lg Mag Rifle, Norma cases, and bullets are sierra match 300gr JHBT. The only thing that I can think is happening is that my barrel is not fully reached copper equilibrium yet as it has only been shot a total of 110 times, or that my bullet seating depth is not consistant. I did not check these last 20, but all the other rounds I have been loading has been pretty close. Granted I was just burning some 250 grain nosler partitions through it to break in the barrel some. Those actually shot pretty well at 100 meters. I haven"t done anything to the cases other than size and trim, I have no idea on the neck tension. I try to get the round off as soon as I"m on target, but I have been letting the chamber cool down so the chamber temp is consistant. Trying to figure out the problems is half the fun in starting a new hobby, I"m new to the long range shooting, I have spent most of my shooting time with pistols and AR"s, and sometimes hunting coyotes at no further than 300yds with a 308.
Thanks for your replies, and sharing your knowledge with me. I will go back to the reloading bench and play around some more!
I'm no expert, but I know where to look and I remember a lot from what I read and see. You're very welcome!
I'd still load single rounds as a start. That way you can get on target, load and fire. It's one thing to eliminate and has to be the easiest to check. Make sure that your ammo is not cooking in the sun, also! Then move on to the next item, whatever you decide that may be. I wouldn't worry too much about neck tension at this point, but it is something to consider, if all else fails.
Have you been to a seminar yet? Rex is just as he appears and his missus is a sweetheart! The one I went to lacked Lew and Kacie, but it was a blast anyway. I met some great guys and learned a thing or three. I highly suggest it!
Oh, and I measure to the ogive, as tips can be less than perfectly uniform.
Enjoy, and post how things work out!
My first chrono would on occasion display velocities 200 fps different than the preceeding shot. And that was in a bolt action with time between loading. I know that is wrong. So, then I have little confidence oin the rest of the numbers from that chrono. If you reload, measure your powder charge, the same charge, several times. Take it off the scale and then return it to the scale. I see a 0.1 grain variation between weighings. Every measurement you make has variation in it. Also variation in brass volume, bullet weight, bullet diameter, case neck tension, seating depth, barrel carbon and copper fouling, powder weight, etc.