Tuning loads for different weight bullets

R

Rflshootr

Member
If you tune a load in any given caliber for any given bullet weight there will be a node at a higher or lower velocity where it becomes back in tune.
Lets say for example that the velocity change is 150 fps. Now if you switch to a much heavier bullet that those velocities are impossible to obtain,
will the node for the heavier bullet to be in tune be in an increment of the 150 fps or will it be completely different?
 
This post has all the makings of a classic "hidden agenda" question.

First, no matter how intriguing node patterns may be, there is only one node that you "take to the match" because it produces the best accuracy without destroying your brass, your rifle and you. I have found that the "sweet spot" node is typically near or at max pressure in the system. I have also found that nodes at velocities slower than this sweet spot velocity are either prone to pitch shots out of the group (at all the wrong times), have poorer ES, or both. I know of no championship quality shooter that has done consistently well with loads that are not pushing the pressure envelope. An advertised velocity for a given bullet weight in the same case may be significantly "slower", but I suspect that is a function of the burn rate of the powder being used.

Now for the hidden agenda part.....are you wanting to try a different weight bullet in your system using the same powder? If so, accuracy will be "where you find it". What that means is that I urge you to have no preconceived notions of where accuracy will be, in this instance at some velocity increment below where you (may or may not) have found success with your current bullet weight. If you are intent on experimenting with a new bullet, I would suggest cutting down on the round count you will put on your barrel by focusing on seating depth with a powder charge within 1/2 grain or so of maximum. The velocity with this heavier bullet will be what it will be. If you look on the recent post started by "greenguy" concerning 240 Sierras, you will see where I have described the process that I believe is the most expedient for proofing your newly selected bullet. Ask your buds that have had success with the desired bullet where the seating depth was, and proceed accordingly.

Here is the kicker....I've only found one instance where the same powder produced reasonable accuracy for 2 dramatically different bullet weights, e.g. 250 and 300 grain 338 SMK's using Reloader 25 housed in a modified 338 Lapua case. Depending on the weight differential between your 2 bullets and the burn rate of your selected powder, there is a possibility that your system could barf on the heavier bullet. If you are currently using a "slow" powder, the risk of this unpleasant outcome is reduced, but may not be eliminated. I have an excellent match load with (30 cal) 210's that uses H4831SC. My system was "not happy" when I substituted 240's and tried to use this same powder. The ensuing load development resembled a card game of "52 card pick-up" or "go fish"..... you take your pick.

If your barrel twist supports the heavier bullet, I submit that this heavier bullet is the one you should consider focusing on for the best accuracy your system has to offer. The majority of whatever success I can claim has been with twist rates that "conventional wisdom" says should not have worked with the bullet weight (length) I was using. Bottom line: learn to like the game of "go fish", telling yourself all the while that you are "enjoying the journey". :D

Scott
 
Scott,
The question was because my rifle will shoot the 6mm 95 sierra very well. I've tried the 105 VLD's without much success. The barrel is an 8 twist Hart which should be fine for the 105's. I originally did exactly as you described & was shooting near max loads with both. I tried different powders with the 105's. I tried tuning the seating depth(everything from hard seated to .100 off)....I tried different primer combinations...I tried this & that & never came up with anything consistent that I was happy with. So I was wondering if I am trying to push the 105's too fast that I can't get to a velocity node where they will work. Hence maybe a slower node somewhere down the scale. Maybe it's the lot of bullets or maybe I just haven't hit on the right combination yet. No hidden agenda......I'd just like to take advantage if the better B.C. if I can.
 
Other possibilities include:
-what seating depth increment are you tinkering with? Much to my (frustrated) amazement, if I'm not honed to the nearest 0.001 inch, my accuracy goes to you-know-where. The real issue is my inability to measure seating depth with any precision/consistency. (I follow my geezer pills with klutz pill chasers) My accuracy windows have always been "knife edge". I am envious of folks who claim they have a "broad" sweet spot that has several thousanths leeway in seating depth.

-what powder increments are you using? I have repeatedly seen "garbage turn to gold" with a 0.1 grain change in powder charge.

A suggestion: take the combo with the 105's that you believe showed the best promise ( or, as I would prefer to say it, pi$$ed you off the most) . Do what I call a "3x3" array where you change the seating depth interval by 0.001 inch, and the powder charge for each varies by 0.1 grain. Load 3 rounds of each and shoot them at 200 yds. (27 shots total). You may discover, as I have on more than several occasions, that your seating depth measuring technique needs improvement. If the 3x3 shows you a group pattern that indicates a logical seating depth or powder charge progression, chase it to ground.

There is another possibility.....your barrel simply doesn't "like" 105's. :( Ahhhh.....the stories I could tell.....

Scott
 
I think 105's are MUCH harder to get to shoot than are 95's..... and 115's are another step in difficulty.

Regarding the near-max loads as best, this isn't completely true in the 6PPC realm as there are still quite a few folks shooting the 3250fps node in competition. Jim Carmichel for instance, but all in all I agree with Scott.

Ohhh, and while I've never gotten the 115's to really group, my "best" accuracy, around 1/2moa, has been well below max.

Also, it has been my experience that the longer the bullets get, the more guiding support they need. For me this translates into less neck clearance. To make 105's shoot 1/4MOA I keep my neck clearance at around a thou, total.

I don't expect your findings to match mine, this heavy bullet accuracy game is still in it's infancy.

opinionsby


al
 
Scott,


I did the "lower node" thing my first year in the IBS 1K with my first comp gun. 300 Wby shooting the 210VLD at WELL UNDER 2700 FPS. Had two other sweet spots....2850 and 3050. Had an ES of 6. Only shot 14 matches that year at Harris and Pella, IA....Made 75% of the shootoffs and won 66% of those!!! Against the likes of Lee Fisher, Al Forbs, Mike eshelman, Gordy Gridders, and a host of other top end shooters. Ended the year in third overall in the SOY points race and was Rookiy of the year.

My point...the "lower node" thing is doable. ;)

Don't ask what happend the next bunch of years!!! :eek: :eek:
 
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some barrels just hate certain bullets too...I didn't see how big your gaps in seating depth were, unfortunately with vld's, if they were over .003" you can miss it. you could try hybrids, I don't have a lot of time behind them but others had success with them. never seen a barrel that wouldn't shoot the 108's... so much so, if one exists.....unscrew, pound in ground, chamber another.

Tom
 
I never had luck with VLD's they would shoot good one day and so so the next. Went to the 115's they shoot right from the start .010 jump and they shot in a hole. Started with the 105 Berger hybrids,took a little more fooling around,jumped from.060 to zero, all seemed to shoot the same1/4 min. Started in and it came alive,.010 groups went into the zero's.I think the biggest thing if is you can miss the spot by moving too much,like Tom said .003 can miss it.......jim
 
Tom is right about some barrels hate some bullets, with seating I don't go more than .005 at a time. And Jim at a 1000 yards,I keep seating the bullet deeper till the vertical goes smaller with one gun I'm .105 off. Scott Your right about 0.01 Grains.both my guns liked that, and a lot of people say you have to go at least half a grain to see a difference. Hope you get a barrel that likes everything.

Joe Salt
 
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