Home Forums Reloading Big Game Rifles Velocity deviation

I load frequently, but do little "tinkering" with loads/guns once I find a recipie that works. I am a hunter, not a shooter. Most of my starting recipies come from my previous experience with the same cartridge or from friends and family I trust to be safe when loading/shooting and I work from there not having to start with a minimum load and work from there. I figure that practice to be safe using modern firearms from the big manufacturers, and 15 years of reloading bears that out...no incidents.

All that is to say: I buy a rifle, initially load bullets I want to shoot at game with a recipie garnered from my previous experience in same caliber, or a friend or family member's, find the bullet the rifle appears to like best and then I fine tune it. I try to make sure that the powder/bullet combo is capable from book specs of reaching my desired velocity for a given caliber/bullet wt. before I even start.

I recently decided to try 160 Accubonds in my Steyr 7mmRM. Due to having loaded and shot plenty of load with 160 and 150 grain bullets using R-22, I chose to start my loading with 66grs of R-22 behind this bullet. That is Hornady's book max load. As long as it gave me the accuracy and velocity I desired I intended to keep it right there.

For my purposes, I loaded 5 rounds to test. The particular range at which I shoot has the bench indoors shooting to a target outdoors. Due to lighting you cant use a chronograph to shoot targets with. Velocity testing must be done outside without benefit of a good bench. I shot a 3 shot group for the initial test. (when I do this I hope to just get something that shows promise that I can fine tune...my first hope is that the group is consistent and not 2 in one hole with one flyer...I can usually tighten any group that is a nice triangle by changing powder charge wt. or brand) Well this Steyr did what it usually does (its a right out of the box rig) and shot 3 shots in to one little shallow triangle measuring just under 1/2 an inch. Initial Success! I know this gun well enough to know that if if likes a load it will shoot it everyday, not just one in four, or tight one day with flyers the next. I need not screw with this load unless its extremely fast with pressure signs or too slow. I move outdoors to chrony with my final two rounds. First shot 3110fps. Pretty fast for a 160gr 7mmMag, but this gun has a 25.4"bbl, and thats not way out of the envelope in my experience with this gun. Also no classic signs of excess pressure. Second shot 3040fps. Unusual!

My experience with all all my rifles is that R-22 gives much more consistant velocity than that. Deviations around 10-15 fps. I know that is not off the charts deviation, and I know its precious little data to go on too. However due to my loading so few rounds a year I measure EACH round individually and using a digital scale that is routinely caliberated before and after each session of loading.

After all that to explain my questions are: taking into account that I trust this gun will shoot that load the same today as it did last week as far as accuracy is concerned, should I be concerned about that much deviation? I have shot many a book max load with 150/154s and 160/162s (though never any in large batches at one time) from this gun with no pressure problems in temps ranging from the 30s when I tested the load discussed here, to the 80s which is more common when I usually test hunting loads. Generally speaking this is a fast gun that does not require I push the envelope to get good velocity. That is a pretty fast load but not out of the box in my experience with this gun and Im within book max. However the deviation in velocity is unusual.

Suggestions, comments, warnings?

My goal is deviations in the single didgits. That being said, if it shoots well and nothing seems to improve the Deviations, then off you go. The problem comes up when your going to start reaching out to the longer ranges. Run a Ballistic profile on your bullet using the two extreme velocities and check the point of impact or trajectories at the longer yardages. Thats when velocity extremes can give you a real headache. I have had outstanding luck with the reloader powders, 338WM and rl19 or 21 consistently give deviations below 10. But one day i'll find a chamber that prefers some other powder.

JAMHO

It's explained here.

When I look at loading data, I like to see a load that has a small standard deviation. That load, if followed exactly, may well be an accurate load. I've found this isn't always so. Sometimes they don't shoot well in my rifles for whatever reason. The real test comes when you test it at various distances, and various temperatures. I've got loads that shoot fine at low temperatures and not so well at warm ones or vice versa. When this also affects my rifles zero - which it can - that load gets dumped. I am changing the ammo I load to temperature insensitive powders to avoid this. I understand Re-22 is one of the worst offenders in this regard. Hogden's stick powders, Ramshot's ball powders and Re-15 aren't.
BTW, For those who are interested, I've found that starting at a maximum book listed load is a good way to have problems. Cases have different capacities, powders vary a bit in characteristics by lot, bullets have a real affect on pressures of a given load, etc. What I've found is that the best accuracy is often 1-3 grs under the listed maximum. I've also discovered that loading manuels sometimes print loads which are too hot more often than too mild. Speer, for instance once published loads which were too hot in the .243, much of the current data for the 7 mm Remington Magnum is significantly milder than the original data. Hornady has also has problenms with their data being too hot, etc. On top of it all, rifle vary significanrtly. I can't use the listed data in either of my .308's that Speer has published. It's just too hot. I mean sticky cases on warm days too hot, for instances. Yet my reduced charge loads give the same velocity as their top loads.
As I see it, either load milder loads with cheap bullets just for practiceor take the time to do it right. You will end up shooting loads that more accurate, every bit as reliable and, if you use premium bullets, more effective than factory loads. E

I tend to worry more about extreem spread then deviation from norm. I feel the known overall variation is more important then the estimated variance from the avg.
An overall spread of 30 fps with a 15 fps SD means more to me then a 10 fps SD with a 60 fps spread.
JMHO

I would attribute your extreme deviation from too hot of primer, that is, assuming you're using one, like a 215 or WLRM. So, what are you using?
FWIW, Alliant uses the 9.5 primer for RE22. JAG

Denton's suggestion of statistical anomaly is one I would not discount.

However, as one trained in Economics, I have a built-in (perhaps better described as beaten-in) distrust for data. Lots of things go wrong when collecting data. I once threw away $100,000 worth of retail scanner data, because the computer concatenated it wrong. Numbers printed on a computer screens are just bits and bytes; they are not ordained truth. But, I digress.

A chronograph is a wonderful thing, but perfect it is not. I would START by throwing away the data, and shooting again. Sometimes, chrony's don't catch the bullet at the same spot, throwing off the reading. Short of building in redundancy a la Oehler proof channels, you can't blindly trust the numbers it prints neatly on the screen.

If your loading technique is sound, your rifle is clean and sound, your neck tension is good, one of those readings was simply wrong. JMO, Dutch.

Denton,

Amazingly enough, though it didn't appear so initially, that was simple and easy to get.

I know I have read many bench shooters dont give a hoot in hell about velocity deviations so long as it shoots. This gun and load shoots. Im going to consider it an anomoly, though I will check it again just to see if one of those two was a stray anomoly in and of itself, or is this particular load is one that shoots regardless of the high deviation.

Eremicus

To respond to one point in your post, and just FYI. I didn't "start" blindly with the max load here. I have shot that powder and powder charge with several other 160-162 wt bullets in this gun. I didn't feel it was a stretch to start there with this 160 bullet.

The other points you made were helpful. Thanks.

You already have some great replies.

Very carefully, change small things that may seem insignificant, allowing for possible pressure variations. A change of primer, for example, can make quite a difference regarding both performance and pressures.

I suppose the real proof of the whiskey, as Elmer said, is in the drinking... so, how are things downrange? Isn't that what's most important? You seem to be doing pretty darned well, it seems to me. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

Your welcome. My Speer No.12 lists 65 grs. of Re-22 w/ 160 gr. speers as max. Barsnes #2, on the other hand, lists 63 grs. as max. with their bullets. E