I have heard that a .5grain difference in charges will not make much difference. Is it true that bench rest shooters don't weigh at all? Do they have very accurate dosers?

I can't imagine that the driving force behind the bullet not being of great importance, if each bullet is not getting the same "push" from teh same amount of powder I'd imagine erratic results.
Can anyone clear this up for me?

Creighton Audette, an accomplished high power rifle competitive shooter, used what he called the "ladder method" of load development. This procedure is described in the NRA High Power Rifle Shooting Volume III. This method of
load development sheds a lot of light on the importance of weighed charges.

Mr Audette, using a .308 cal target rifle w/20 power scope on a good day, fired a 20 shot string over a chronograph @ 300 yards. The ammo he used was loaded in weighed cases which had squared heads. He loaded them starting at 37.0 gr. of 4895 (weighing each charge exactly), and increased each subsequent cartridge by .3 grains so that the 20th round contained 43.3 gr.

The group produced with this box of ammo measured 7.6� high by 1.8� wide (with a powder variation of as much as 6.3 grains!). The velocity was between 2259 fps and 2649 fps.

Wish I could post a picture of the group, but do not have a scanner or camera. It is interesting to note that there were actually three �groups� formed. Shots 1-10 (with powder charge starting @ 39.0 gr to 39.7 gr and velocity ranging between 2259 & 2384) formed a group only 2 1/2� high. Then there was a space and shots 11-15 formed a
second group about the same size (no measurements given), then shots 16-19 grouped �about the size of your thumb nail�. The 2 1/2� group equals less than 1 moa with a variation of 2.7 gr. of powder.

Using the ladder method allows the shooter to choose the flat spot or sweet spot in developing a load and makes weighing charges much less of a factor, especially as Bigdaddytacp said, most powder measures will throw charges in the +/- .1 grain range with ball or short cut extruded powders.

Regards,
hm

[ 02-15-2003, 23:22: Message edited by: hm1996 ]

An increase of .5gr. can certainly make a difference (and not a good one either!) if you are at a max. load; when your rifle and/or cartridges are subjected to high ambient temperatures; when case capacity is small[er]; when you use a heavier bullet; when the bullet has a long bearing surface; and when the bullet is seated at or perhaps touching the origin of the rifling. Also, bench guns are built around very strong actions (single shot, no magazine well and ergo, solid metal) so "hot" loads are less of a problem. Lastly, those benchresters that do load at the range use rather expensive and precise powder measures. Hope this helps, ...Maven

hm,

I've seen that write up on the Audette method, and I agree that if you can get things to stack up like that at 300 yards, you can get a pretty good idea of what powder charge to use.

In my own experience, and also in the experience of others, the Audette method rarely works out as well as was profiled for the NRA piece.

At this site http://www.windcharts.com/reality_based_load_development.htm you'll see an article which was written by Jeffrey G. Chosid, and it appeared in a recent issue of Precision Shooting. He has the same concerns with the Audette method as have I, and he has come up with his own way to offset what he refers to as the "shortcomings" of the Audette ladder test.

While Chosid's method is an improvement over the Audette method in my opinion, I still believe my OCW method is better yet--for the reasons I cite on my webpage. http://home.earthlink.net/~dannewberry/index.html
Chosid fires each group individually, and his method will cause groups fired late in the session to incur the effects of a fouled barrel. A heating barrel and a tiring shooter will also skew results fired near the end of the string.

Also, and very importantly, groups that are fired at these ranges may be wrongfully harmed or they may wrongfully benefit from the whims of the harmonic whip. A "friendly" harmonic whip node can cluster some shots with wider velocity spreads, while an "unfreindly" harmonic whip node can "string" shots that have relatively tight velocities, and which otherwise would have grouped well on the target. I believe that we'll all agree on that point.

Triangulated three shot "round robin" style groups at 100 yards will go a long way toward factoring out much of these and other variables.

I may never understand the fascination with chronograph data during load development sessions. In my opinion, velocity should not be a concern until the load is decided on. Since one must fire the shots in order for them to be chronographed, it would seem superfluous to assign any significant relevance to the chronograph numbers--especially in lieu of the fact that even the best chrongraphs have error factors that may mislead.
The targets should guide you entirely through the process. The load is either performing or it is not. And the ultimate indicator of the load's potential to group is not the chronograph, but the target itself.

Chronographing after the load is finished is a good idea, I'll agree. This will give you an idea of trajectory and terminal performance in the case of hunting loads.

I'm still of the opinion that the three shot groups, fired initially at 100 yards in round robin fashion, are the best indicator of what I call the OCW zone.

After identifying the optimal charge weight, "depth tuning" of the bullets will get you onto a friendly harmonic node--then you'll have the best of both worlds: A load with a stable, consistent powder charge and a load that is tuned to your rifle's best harmonic node.

And such a load will be able to tolerate thrown charges of IMR 4350 if that be one's wish ...

Dan Newberry

[ 02-16-2003, 00:13: Message edited by: green 788 ]

One very good reason to use a chrono with load developement is to watch velocities rise as the powder weight charges increase. If one notices velocities getting above what should be expected from various load data books, they may be reasonably assured that they are going into higher presures than should the rifle should be operated at. If you use no chrono and just other pressure signs are used such as loose pockets, case flowing into the bolt extractor, case expansion, etc, then you have a very good chance of getting into proof loads or beyond. Of course this is only my opinion, as I have no pressure testing devices. It does however mimic the opinions of the likes of people with pressure testing equipment. I believe people like Stan Watson, Ken Howell, Ken Oehler, Brent Moffit, Chris F, JON A and other posters at this forum and other forums have said that without a pressure testing device, pressure signs are a crude guess at best and if you see any pressure signs you probably have gone way past the proof load range.

Lonnie,

I won't dispute what you say there, insofar as uncharted territories go...

However, I think that so long as we're not significantly above published maximums, we're going to be safe without pressure gauge data.

Considering the differences in velocity potential of various barrels, I believe it would be hard to discern from velocity alone when you were "getting warm," so to speak.

The publishers of load data have quite a bit at stake--especially in today's litigious society. I trust the manuals, knowing that those who prepared that data have certainly considered "worst case scenarios" throughout.

But again, if developing for a wildcat or other obscure cartridge that data is scarce for, or when using a not-so-well-known powder, a chronograph may be your best indicator. A poor one albeit, but in the absence of a pressure gauge, a forced choice.

Dan

Within pressure limits a full grain one way or the other will make little practical difference, that is why bench resters don't weigh powder charges...

Based on their findings I have tested this many times when working up loads and have found it takes 2 to as much as 3 grains to change accuracy or POI and then not by much in POI, but may in accuracy...

Also I found this to vary from gun to gun but again not by much except with barrels that just were not good in the first place, a fault that I remedy quickly by jerking that barrel off and installing another, I want no finiky barrels on one of my guns.

It depends on where that .5 grns difference places your load. The closer you get to critical mass, the bigger difference a little more is going to make. As mentioned above, one of the beauties of chronographing is being able to watch for sharp jumps in velocity. That is a sure sign that your getting into maximum territory and no two rifles get there identically. I like to get close to a max load and then leave myself a 1-1.5 grn margin for variation/"saftey cushion" with my hunting loads. A benchrest shooter might want to narrow that margin down much more.

[ 02-16-2003, 20:54: Message edited by: Wstrnhuntr ]

I have to disagree, with almost everyone. Last summer I decided to change from H-380 to Varget in one of my .22-250 rifles. The results were a disaster!

As you can see below, I used 0.3 grain loading steps, and look at the variations...

GRAINS VEL GROUP GRAINS VEL GROUP
30.7 ...2957 0.685 ....33.5 3316 2.184
31.0 ...3024 1.022 ....33.8 3361 1.701
31.3 ...3091 1.626 ....34.0 3373 1.801
31.5 ...3128 0.990 ....34.3 3408 1.610
31.8 ...3139 1.483 ....34.6 3447 2.174
32.1 ...3178 0.853 ....34.9 3458 2.128
32.4 ...3205 0.743 ....35.2 3503 2.188
32.7 ...3247 0.856 ....35.4 3527 1.608
32.9 ...3249 1.634 ....35.7 3551 1.609
33.2 ...3302 1.498 ....36.0 3575 2.328