Load development: reading your target

T

TJUrban

Guest
(caution possible dumb question) When developing loads, I find that "bad" loads can have either/both vertical and horizontal dispersion. My better loads tighten up in both planes.

However, I was reading a book on precision handloading and the author concentrated solely on vertical dispersion as the factor that must be analyzed in load development.

So, using that system, you could have a load with almost no vertical, but lots of horizontal. That would not win a lot of matches.

Is the author assuming that all horizontal dispersion is created by wind drift?

And, is there a good book/resource out there on reading targets as part of the load development process?

thx

Tim
 
When I'm developing loads I'll start at 100 yards. If one or several loads shoot like I want, I'll move to either 200 or 300 yards. Once I've settled on a load I'll move it to 300 yards and fine tune with seating depth and slight powder adjustments like 1 to 2/10's of a grain of powder at a time. There are several factors to watch during load development such as case prep and the actual assembly of the cartridge, consistent neck tension, loaded round run out, wind, bag placement, shoulder pressure / placement and my favorite, shooter error. If the groups are round or triangular in shape I feel the load is trying to shoot. I've found that if my rifle is double grouping it's more of a seating depth issue. Vertical in the target could be high ES & SD, head / tail wind or shooter induced. Horizontal in the target could be wind or again, shooter induced. With the SMK's and or hunting bullets, I'll start my seating depth at .005" off the L&G's, with the VLD's, I'm .010" to .015" in the L&G's.

Try to test in ideal conditions, no wind and or mirage, use wind flags and pay very close attention during each shot as to remove as many variables as possible. Consistency is the name of the game.

I'm sure you'll get several tips and or techniques; this is just what works for me. :) Good luck

William
 
I could be wrong. But what I have been reading on BRC about barrel harmonics. The barrel moves in an up/down type whipping action which would give you vertical strings. Horzontal stringing for me has been the wind. If I am wrong Please somebody correct me. I hope this helps.
russell m
 
Do not test in calm conditions, I have rarely seen calm in a match and a load will shoot different in the wind than when there is no wind. Make notes on what a specific load does in certain conditions. A load that gives horizontal in crosswinds may shoot well in head winds and a load with some vertical may do well in cross winds. A good barrel and good load will get both good groups in either condition as long as you pick one or steer it correctly but not every barrel and load is perfect. There is a lot of value in sticking to a certain powder and bullet and getting to know what it will and will not do at any given condition. Only experience will give you your answer for the loads that you are using.
 
IMHO, if the rifle shoots well in vertical and loose in horizontal chances are it's not the rifle. Are you shooting over a good set of windflags??

Mike Swartz
 
Thanks John
I did experience what you are talking about on 1 occasion. MY pet load at 3270 fps gave me horizantal I went to my upper end load at 3400fps & the conditions were the same windy & switching & my groups tighten back up. What I dont know was it the extra velocity or just the load for those conditions. I am hoping with more experience I will be able to figure it out.
russell m
 
Hi,

wnroscoe

I find this thread very interesting on one very specific item. "Double Grouping" I do not have many folks to talk to locally. I have experienced the double grouping and I thought it was more likely me with different mounting on the bags, rest and different look through the scope.

I am trying to understand the seating depth issue, too long? Or too short?

I don't get the double group often, but I will keep much closer eye on the depths. I am using the Wilson seater cut with my chamber reamer.

Thanks for the great info!
Tony
 
Double grouping.

I'd be inclined to pay attention to your bag set up and watch the flags if you are getting double grouping. I haven't been at this BR thing for long but it has been my experience that these rifles are very easy to tune for since they are so much more predictable and repeatable than say a factory varmint rifle. I assume you are talking about a bench rest rifle ?

It seems to me that so long as the rest set up is good and the rifle is sound the loads that are miles away from a good load will just be big round groups, say scattery 0.5's. The same would apply to components that the rifle just doesn't like, say a certain bullet. Once you start to get close to a decent load the groups will tighten up and show mainly vertical spread to maybe 0.3 or so. Once you start to get the load going well the vertical will reduce and the rifle will shoot small round groups or hopefully "dots" !!

If you are getting horizontal double groups you are probably missing something in the wind reading or doing something on the rifle, pulling sideways on the trigger or not having the bags aligned with the target so the rifle is rested in a stress free state or any number of other possibilities.

If you are getting double grouping vertically you might want to look at the shoulder position for consistent pressure or consistent gap if free recoil, also trigger hand on grip etc etc. If that all seems OK it may just be the load isn't right and the number of shots simply gives you a gap between 3 and 2 or 4 and 1 or whatever. If you had a double group to say 0.4 with 5 shots it may become a string of shots spread vertcally to maybe 0.5 if you fired 10 shots which would look more like a bad load than some other issue. See what I mean, the double group would become a string and no longer a double group at all.

It seems to me that once the load overall is getting close in terms of powder weight and seating depth changes in either will really only alter the vertical spread of the group. I wouldn't count on just changing seating depth to cut out possible double group scenario.

Get the powder weight close with the bullets on the lands, tune the seating depth to get the best depth and then fine tune the powder. Bingo !! Then you just need to keep the tune in different conditions !!

The only proper double grouping I have ever experienced was with a varmint rifle with a bedding issue.

Just my thoughts, like I said, I am no expert.

Bryce
 
russell m said:
Thanks John
I did experience what you are talking about on 1 occasion. MY pet load at 3270 fps gave me horizantal I went to my upper end load at 3400fps & the conditions were the same windy & switching & my groups tighten back up. What I dont know was it the extra velocity or just the load for those conditions. I am hoping with more experience I will be able to figure it out.
russell m
Click to expand...
Russel, I have solved it a few times with changing the seating depth, but not any one thing will fix a problem all the time. The biggest thing is experience, knowing what your load looks like out of your gun such as to hot or to cold and what a change in seating depth does to the group goes a long way in identifying problems in a match. Also it is good to experience playing with the front rest and bag to see how hard and how tight the bag should be with your rifle. Not every stock and type of rifle likes the same front rest settings
 
I can't even make up an answer to this question..

russell m said:
I could be wrong. But what I have been reading on BRC about barrel harmonics. The barrel moves in an up/down type whipping action which would give you vertical strings. Horzontal stringing for me has been the wind. If I am wrong Please somebody correct me. I hope this helps.
russell m
Click to expand...


How does a round barrel screwed into round threads shooting a round cartridge know which direction is vertical? If you shot it on its side would it still produce vertical? Not so much asking for an answer but it does bother me somewhat.
 
Wilbur said:
How does a round barrel screwed into round threads shooting a round cartridge know which direction is vertical? If you shot it on its side would it still produce vertical? Not so much asking for an answer but it does bother me somewhat.
Click to expand...

How do it know? Same way Billy Carters thermos bottle knew.

OK, take an 8' long 1/2" diameter dowel and hold it vertical. It is straight. Hold it horizontal and it droops. How much?? Probably a foot or so.

Take a 22" long LV barrel and hold it horizontal and it droops. How much?? Dan Lilja's barrel weight program says it droops 0.001266". That 0.001266" deviation at 22" is equal to 0.207" at 100 yards. A bullet hole almost.

Now then, put that 22" long drooped barrel under 60,000 psi from the inside and what happens??

Isn't this how a tuner works??
 
Pressure inside straightens out the droop !!!

That was always my understaning of why vertical is the main component of group spread.

The barrel droops and the pressure inside straightens the barrel out twanging it up and down. Just the same way an old style pressure gauge works, a Borden tube I believe it is called.

Imagine a barrel that is half inch round and 20 feet long and droopy, that thing would flop up and down like a crazy thing when pressure was introduced internally !!

Bryce
 
Seems the net result of the overall forces now acting on the barrel are such that the barrel is being deflected in the 8 - 2 direction, stresses in the bedding, barrel not being pushed totally vertically, rifling twist setting up a scenario whereby the barrel twangs slightly sideway ..........

The fact that the barrel isn't floating and free to do as it likes is a whole other situation. You could put a lot of forend pressure on a skinny barrel and very significantly bend it upwards. In that situation the barrel sag is actually negative but you will likely have some nasty stringing due to the stresses created and not because of the barrel droop.

Same as you can have stringing caused by action bedding stresses. There is no load on the barrel but the stresses will cause a deflection away from some contact point on the action creating stringing of the group.

My take on it anyway.
 
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Your Naderlogic is at least as good a bet as my assumptions are !! :)

I agree, I wanna see it actually filmed or measured in some way before I buy into any theory on how the barrel behaves on firing.
 
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