I'm on the third firing of this 300RUM Rem brass and I believe that I've found that the third firing and on things seem to get a litte more consistent in terms of grouping and velocities--sound familiar to anyone?
At any rate, here's some chrono data (20ft. from muzzle) from an Oehler 33 at the range from a barrel that had three of the exact same rounds fired through it a couple of weeks ago and was left dirty. So cold, dirty barrel for first round. 200AB, 109g of US869, charges carefully weighed and generally very careful reloading. About 40 degree ambient.
10-3234-started to rain
12-3196-rain let up considerably
What concerns me is the lower velocity of the first round. To have more reliable data, I'd need to go to the range in the same conditions with a cold dirty barrel to check that 1st shot velocity, but at longer ranges that much drop in velocity on that first shot you're really relying on might spell trouble. Any thoughts on that data?
The second shot at 3244--not sure what that is all about. I wasn't real consistent with letting the barrel cool down or not during this string which is not typical of me but may have contributed to a couple of the higher numbers.
I'm thinking that the rain may have contributed to 10 and 11 being high.
I'm OK with the rest of the numbers. There's a great deal of folks on this board that have more experience than I and I'm hoping that someone might be able to make a little more sense out of the this data than I. Thank you!
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I've not found anything significantly different in accuracy or muzzle velocity between the first and even the 25th firing of the same case. But it's common that the first shot from a clean barrel will leave slower than subsequent ones because jacket and powder fouling increase friction over the first shot which makes pressure higher and that makes the bullet go out faster.
As for the swings in muzzle velocity, some of the spread is caused by holding the rifle tighter or looser. A looser hold lets more recoil energy push the rifle further backwards which subtracts from the energy used to push the bullet out; the bullet leaves slower.
I've always got the lowest spreads in muzzle velocity by firing each round exactly 60 seconds apart. Each round would be chambered 15 seconds before shooting so they would all have the same amount of "warm up" time. Barrel cooling isn't an issue. If the barrel's properly stress relieved, it won't change point of impact as it heats up. Even with 30 to 40 shots from 30 caliber magnums burning 65 to 70 grains of powder, a properly fitted good barrel will not change impact going from cold to hot.
As for shots 10 and 11 being faster, I'd bet an ice cream sundae you held the rifle tighter 'cause it was raining and that made the bullets leave faster. Then when the rain stopped, you relaxed, held the rifle a bit looser and shot 12 left slower than the previous two.
Well, after reading Barts explination I had to respond. You say shots 10 and 11 were higher in velocity but if you average the 11 velocity reading you recorded you get an average velocity of 3209 fps. Now shot 10 was 25 fps over this, shot 11 was 31 fps over this average velocity.
This is a bit higher but nothing that would alarm me as being out of the norm for using US869. I have found the very slow ball powders will in fact produce slightly higher extreme spreads in velocity compared to stck powders.
Was your first shot out of a freshly cleaned barrel? Whenever I do load developing I will shoot a freshly cleaned barrel three times before I start recording velocities because the first two are generally a bit screwy anyway from a clean barrel and from shot 3 on the rifles generally settle down. To make sure I start on shot 4 of a cleaned barrel.
Averaging your last 8 shots you get an average of 3212 fps and an extreme spread of 44 fps. Now this is nothing to right home about but no where near anything that should cause you to me alarmed.
Yes we all want extreme spreads to be in the single digit range but on the realistic point of view, when you use over 100 gr of a very slow burning ball powder this is just not going to happen in most cases. The smaller the bore the more extreme velocity spreads you will get on average as well. Larger bores tend to be more consistant in the velocity area which is probably why they tend to be less finicky then the smaller bore large capacity rounds.
Simply put, I would use accuracy and group consistancy as my standards for judging a good load over a bad one. 44 fps extreme spreads are not amazing but they are certainly nothing to worry about. Hell at long range that 44 fps variation will be down to half that.
As an example I have a factory stock Ruger heavy Varmint rifle in 22-250 AI. All I did was set the barrel back and rechamber to the AI chamber. Other then that its out of the box.
It loves the 50 gr Ballistic tip loaded to 4075 fps. This rifle will zip prairie dogs all day long at 500 yards with this load and it has several times. Funny thing, if you shoot it over the chrono for a ten shot string, you will get velocity spreads in the 125 fps range because I am using H380.
Yes I could tame these down by switching to a stick powder but when I can get consistant 1/4 to 3/8" groups at 100 yards with a factory rifle and still consistantly hammer a pop can sized target at 500 yards in calm conditions, I figured why mess with things.
I think in many cases we can tend to OVERTHINK things with rifle loading and shooting. Yes velocity spreads are important, but not nearly as important as if the rifle actually shoots that load accurately or not.
IF you believe Barts theory that you tighten up when you shoot in the rain then all this will do is give you another mental block to overcome in conditions that are not perfect.
You will be lined up on that big bull elk at 600 yards and feel a drop of rain hit your face and mentally you will tighten up because someone told you that you tighen up in the rain.
Do not over think this stuff. Believe it or not, simplicity is still the best policy and far to many shooters get so wrapped up in the technical aspect of loading that they generally pass up just as many good loads as bad because they think they need extreme spreads in the teens or the load is no good.
Another example is my lightweight 7mm AM that I used this fall for hunting and has now become my GO TO rifle. When I started load development at 100 yards I was getting velocities in the 3150 fps average range with extreme spreads in the 45 to 50 fps range very similiar to what you were seeing.
Groups at 100 yards were also nothing to write home about averaging in the 5/8th to 3/4" range for three shots. I had pretty much come to the conclusion that this would be a general big game rifle with 500 yard limits for max range shooting on big game.
I came to this conclusion because of the 100 yard data I had collected.
Fortunately I took the rifle on a long range shooting outing where I had to test another heavy rifle. Shooting at 905 yards she popped three water filled milk jugs in four shots and had I not muffed the wind call on the miss it would have ran the jugs three for three at 900 yards!!!
Seeing that I realized that 100 yard targets and 50 fps extreme spreads mean basically nothing at long range. Since then I practiced with the rifle alot and developed an accurate drop chart and since then it has taken four big game animals past 600 yards and two past 700 yards. The only miss the rifle had this fall so far was my whitetail buck at 650 yards for the first shot because I messed up with the rear bag allowing the rifle to torque to the right.
The follow up shot 10 seconds later with a corrected rear bag was dead on through both shoulders at 745 yards.
That was the only miss so far with that rifle and remember that is a legit 3/4" rifle at 100 yards with 50 fps extreme spreads.
SO just get that load out and shoot it at long range and see what happens. I suspect if your rifle likes that bullet, you will never give those two slightly higher velocities a thought every again. I certainly would not.
Just do not over think this stuff as far as loading ammo. Even the most complicated loading is relatively simple and should be that way.
I have two diseases that I watch for in my customers. One is "Tinkeritis" and the other is "Paper bound".
Tinkeritis is when a shooter things he can always get a better load or a more consistant load or a more accuate load. Nearly 100% of all BR shooters have a serious case of this and alot of LR shooters do as well. It is not always a bad thing until you get into the class of round we are dealing with here for the most part on LRH.
Tinkeritis can burn up a barrel before you find that Sweet spot!!!
Set realistic goals for your rifle, define what you will be doing with your rifle and then find a load that will accomplish those goals consistantly and then get out and practice. That will be far more valuable to you then cutting 20 fps off your extreme spreads.
Being "Paper Bound" is when a shooter will not get off paper when testing a load. Initial testing at 100 yards is fine but I tell my customers to get off paper as soon as they can and get out shooting long range on more animated targets, water filled jugs or steel gongs or something like that.
Being "Paper Bound" nearly always leads to a severe case of "Tinkeritis" and both will result in you missing out on valuable practical LR practice time and eat up alot of your barrel life.
SO I would recommend, get off paper, get an averge velocity and start shooting at long range as soon as possible, I suspect you will totally forget about shot 10 and 11 if you do that!!!
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My name is RoyInIdaho and I'm a tinkeritus/paper bound aholic.
However, I am recovering, rapidly.
After much tinkering w/the 338 RUM selfproject rifle there is no more tinkering to do.
After arrival of the AM there never was any tinkering to do on it. Just load and shoot. However I did have to tinker with the bipod to get it up to par with the rifle as far as steadiness goes. Looks will come later [img]/ubbthreads/images/graemlins/blush.gif[/img]
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!