sweet spots

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Ross Smith posted this 02 December 2022

Is  there more than one accuracy node or sweet spot when it comes to working up a load for a cartridge?

For those that want specifics: I look at the match results for 30BR shooters. When loading my 30x1.625 which is slightly more capacity I almost always find an accurate load at a much lower powder charge. ie; 30 br using 30 grains N135, me using 26 grains N135.

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RicinYakima posted this 02 December 2022

IMHO, it is pressure rate of rise, total pressure vs barrel contour and action bedding. Fred Sinclair and I used to laugh about "monkey see, monkey do" of jacketed benchrest shooters. Of course they only have barrels from three makers and all of the same contour. Ric

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Ross Smith posted this 02 December 2022

You have to admit that those match reports are a good place to start.

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Bud Hyett posted this 02 December 2022

Yes in my experience. Jacketed bullets sweet spots are easier to find. I am guided by P O Ackley's writings on bore efficiency, When the load begins to "smoke" at the muzzle, I think the load is most efficient and do not go above. Usually, this is at 54,000 pounds pressure or slightly above.

NASCAR drivers go as slow as they can to stay in first place. I also believe in setting the load where it shoots best and not to try to hotrod to the maximum velocity.  Good barrels are hard to find and should be shot at less than maximum to preserve.

I've found a good load usually at the 15% reduced load from where I start in my quest for a good load. This is empirical observation, not scientific. 

With cast bullets, lubricant smoke will interfere with this observation. We're not at pressures where the P O Ackley theory works. A lubricant star on the muzzle is a good indicator. However, I believe you can over-lubricate and get a lubricant purge shot. Usually this is the seventh or eighth shot in a group.

I guess this is the fun of cast bullets, there are no rules that universally apply. You just have to go to the range and keep trying. 

Farm boy from Illinois, living in the magical Pacific Northwest

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RicinYakima posted this 02 December 2022

^^^^^^^^^^^^^^^^ If it was easy, I wouldn't do it. 

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Shopdog posted this 02 December 2022

Yes on tiered "nodes".... with the caveat;

It depends,haha. It is somewhat dependent on the chambering. Certain calibers show it more than others. If I had to right an equation, it would start with the ability to hit a high node. Purely laziness on that one.... think about it.

My straight 6mmR cast varmint vaporizer IS most happy with full house 85g Saeco,IMR4831 loads about 1/2 way into JB book loads. But can do more moderate say,2200 fps(4895).... with no complaints either. And will lob 4198 loads at typical cast speeds with the best of them. This is my best example.... off the top of my pea brain head.

Be careful with the monkey see thing.... referring to what the "winner's" are running has been a guideline on this website for as long as I've been using it. Not pointing fingers...just sayin.

Another to be careful with; only counts if it's in competition. Used to beat that one to death racing M/C's. Just sayin,we have a range right out our machine shop door.

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John Alexander posted this 02 December 2022

Bud,

It a long time since I have read Ackley's writings and with the loss of brain cells I can't even remember the term "smoked muzzles."  How do you identify a smoked muzzle with JB loads? It sounds like something that might speed up getting to best load.

John

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Bud Hyett posted this 02 December 2022

It a long time since I have read Ackley's writings and with the loss of brain cells I can't even remember the term "smoked muzzles."  How do you identify a smoked muzzle with JB loads? It sounds like something that might speed up getting to best load.

John - "Smoke at the muzzle" is a better description. The shots as you work up a load from lighter to heavier will initially consume all the powder within the barrel. When the all powder is consumed at the muzzle, theory states this is maximum efficiency. You are getting maximum push on the bullet, more consistent barrel time and greater chance to have the same barrel vibration.

This is often not the highest pressure loading. Looking at the powder burn graphs in QuickLoad, this is where the powder burn efficiency stops being 100%. QuickLoad allow you to set a pressure level and then it calculates the velocity.

As an example using my .220 Swift: 

  • Powder: 37.5 grains of IMR 4064
  • Bullet: Sierra 55 grain soft-point boattail
  • Velocity: 3767 fps 
  • Burn efficiency:  98.27%
  • Muzzle pressure: 10,226 psi

I know the data from QuickLoad is  empirical, but the data mimics reality on the target and in the field. There is a very similar graph with the .22-.250 using 37.5 grains H380 and the same bullet.  

To me, this means the powder burn is still pushing the bullet. And the load shoots sub-minute 10-shot groups in both rifles when I do my part by steering it well. This happens with my other rifles as well. I have a Remington 788 built up as a benchrest rifle that is no longer competitive and is now a prairie dog rifle. Working up a soft-point varmint load, I quit when smoke appeared at the muzzle.

I first noticed this years ago at Windhill on a rare windless day. Ed Doonan and I discussed this.Then Ed added he'd like to have Remington's load list they used for their 40X. They send a 5-shot target that this rifle shot that is sub-half-minute. They're not going to pay someone to spend a day developing a load for each rifle. They have a known load. I'd like to have this load list. I could then run their loads through QuickLoad to compare data.   

I've gotten to the point where I use this as one of the selection criteria in selecting a load. It often takes an observer to help see the smoke since this is smokeless and not black powder.

I hope my ramblings are an explanation. 

Farm boy from Illinois, living in the magical Pacific Northwest

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Tom Acheson posted this 02 December 2022

If you want some additional load info for 30 BR, check out page 78 in the Lyman CB Handbook, 4th Edition. These loads are pre 2010.

 

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.22-10-45 posted this 02 December 2022

I have been working with a .30-40 krag Al Story Sharps Borchardt and I have found working with H4227 and cast bullets in the 170 to 200gr. range,   There are at least two sweet spots.  First is with 14.5 gr.  Increasing charge in .5gr. Increments groups open up until 18.5gr.   Both groups are around 1/2" to 3/4"...my eyes can,t take long periods of this kind of concentration however and groups will be closer to 1".  But there is defiantly at least two sweet spots.  I suspect there is probably another one at higher velocity.

I am using a Leupold fixed power 12x with dot..a higher power scope might be easier.?  But I like the looks of the scope on the rifle.

I am not getting any leading..but then these are lower velocity loads, and only the space between gas check & bottom band & last lube groove are filled with my home-brew lube.  I am not seeing any type of grease as in a lube star..only powder marks on muzzle outlining groove pattern.  Inside bore at muzzle is black.

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Ross Smith posted this 03 December 2022

This is the conformation I was looking for. Same powder just different amounts giving good accuracy. All the answers have been very informative. In my ML days we always looked for the orange balls at the muzzle. They are sulfur . After that you get diminshing returns.

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Wm Cook posted this 03 December 2022

 I look at the match results for 30BR shooters. When loading my 30x1.625 which is slightly more capacity I almost always find an accurate load at a much lower powder charge. ie; 30 br using 30 grains N135, me using 26 grains N135.

There are a lot of variables that can mess up a head to head comparison between two people shooting the same powder.  Assuming both (or all) have match grade casting, reloading and bench equipment and match grade casting, reloading and bench practices it could be something as simple as the lot of N135 your burning. You probably know more than me on more than a number of things about cast and shooting cast accurately but if their velocity matches yours (and you're using 4 grains less N135) I'd guess that it would be a wild difference in the lot of powder you're using.  If your velocity went in the same direction as the reduction in powder charge you're using maybe it might not be a problem.  If it's shooting groups comparable to match results I'd work with it.

In my way of thinking finding the node/harmonics of the barrel are probably easier on a 66 grain jacketed bullet running at 3300fps than a 200 grain cast bullet running 1700 to 2000fps.  For my lack of experience in shooting cast the biggest takeaway from match results is velocities.  Within each class there are pockets of powders that are common but it sure ain't like jacketed BR where the only variation in powder is a few tenths of a grain of N133.  With cast I get a feel for the velocities being run with the cartridge I'm shooting and give a few different powders a shot at accuracy.  For the BR30 the most popular powders seem to be N135, Varget, 2495 followed by 3031 and 8208.  And there are probably another handful of powders that would shoot just as well.  That monkey see, monkey do things blinds us from seeing other options. But at least the results give you a starting point.

If I were starting out on unrestricted or Hvy I would go out to the range with N135 and Varget and work up the load to get in the vicinity of the 2000 fps most are shooting.  If it took a grain or two more or less to get that 2000 fps I wouldn't sweat it.  And 2000 fps is not magical either.  It may be between 1900 and 2100.  As Ken and others point out, there's only one rule to cast accuracy and that's bullet to throat fit.  I'm new to cast accuracy but that one variable, bullet to throat fit, quickly rose to the top of the "got to get it right" list.

As a side note I am a little amazed that 4 out of 5 competitors in this years nationals loaded at home and not at the range.  In jacketed BR that would be unheard of.  (setting aside the breech loaders and a unique peculiar species) J BR shooters will load at the range and they will tune their load group by group taking out the vertical.  But your talking about 4 grains of N135 not .4 of a grain.  So that has me scratching my head. 

For what its worth this is the 2021 and 2022 Nationals data.  In total there were 19 competitors those two years.  Of the 19, 16 shot three different powders; N135, Varget and 2495.  Bullet weight ranged from a low of 170 to 220 grains with the average being around 200 grains. 

Not sure if this will help but here is what the shooters put on the data sheets for 2021 and 2022 shooting those three powders chambered in BR30.  Good luck and if you have time give the velocity, weight of bullet you're using.  That and on what platform. Again good luck, Bill C.

 

My addiction to gambling starts and ends with me spending $ to try a powder I’ve never shot before.

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Ross Smith posted this 03 December 2022

Thanks Bill. When I got good accuracy at 26 grains, I didn't go higher. At that time I was still sorting out which bullet to shoot. I have that narrowed to 2. Both 190 grainers. I will load at home, but my next outing will have 26-30 grain charges. We'll see. Don't have a chrono.

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Ross Smith posted this 03 December 2022

Tom: Just re-read your article. I also made a similar list of powders and charges from the cba reports that I have. Good info. Next week I'll go looking for that second node. 

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Wm Cook posted this 03 December 2022

Ross, you gotta have a chrono. If you want I have an extra you can borrow. It’s one of those bayonet deals.

No good for shooting groups while it’s on but good enough to put three of each load down range to get an idea of what velocity you’re shooting. PM me if you want to give it a go.

I hate to burden you even further but a pound cast of your chamber will go a long way towards finding a mold you can work with.

A short cut to the pound cast is to drive a cast .30 bullet (not Linotype, preferably lead if your lucky enough to have it, #2 Lyman if you don’t) into the throat with a shaved down 5/16” hardwood dowel so you can find the diameter of the freebore and how far the lands are away from the start of the freebore. You just need to tap it in so you get markings from the freebore as well as where the lands start. Knock it out from the muzzle end. A hardwood dowel or a 1/4” brass rod with electrical tape in a few places will keep the rod off the lands and centered.

Through reverse engineering that’ll let you appreciate how the bullets from your two molds fit your throat.

Bore diameter is pretty easy by using a lead fishing sinker and a plastic mallet. That’s especially important for bore riders. Most recommend using a little oil first. Good luck, Bill.

My addiction to gambling starts and ends with me spending $ to try a powder I’ve never shot before.

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Ken Campbell Iowa posted this 03 December 2022

FWIW, twisting tuners on a 22rf will find you several nodes equally accurate ...  so barrels apparently have more than one node ...if that is the correct term.

but there we are not changing pressures ... if you don't have enough pressure, ignition gets goofy ... with too much pressure, the gun dissappears ...  so varying just the amount of powder might not give enough safe vibration range to find multiple nodes.

maybe changing powder burn rates would be the best way to find multiple nodes.

ken

 

 

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Wm Cook posted this 04 December 2022

maybe changing powder burn rates would be the best way to find multiple nodes

Valid point there.  One of the powders I worked with on a load was 4895. There was a grain difference between the 1700 to 1800fps velocity I was looking for. That one grain is only 4% of the charge so I had a lot of room to go hunting.  But trying to find a second nodes would have been impossible with the velocity limits I put on it. And that falls back on the burn rate Bud talked about.  Could I have found a second node at 1600 fps or 1800? Maybe.  But within individual competition classes accuracy has more in common with velocity then a specific powder.

I've learned a lot from this post about using burn rates as a variable for accuracy.  I should but I don't have Quick Load and I'd be new to reading the % of powder burnt but I do have a chronograph.  And I have registered match results whose equipment list I believe to be mostly honest.

So is this where I can ask whether I can find a successful node by speed dating different powders but limit the playing field to a targeted range for velocities?  I'm not advocating that match results are the end all for finding success but PBB are successful running near or under MOA with ~25:1 at 1450fps and Unrestricted shooting Linotype is running below MOA at ~2000fps. 

I'm certain using velocity as the dependent variable and swapping powders as the independent variable is not as good as having the skill set to understanding powder burnt rate. But for the lay person you could hop scotch across 3 or four powders to find a powder(s) that looks accurate if you were looking within a targeted velocity range. 

With any common sense handloading practices applied you can eliminate the powders that don't work. I believe that powders that continually shoot >3" groups using ladder increments of powder (example as with the 4895 I was using: 27.0, 27.3, 27.6, 27.9g) will never improve no matter what the seating depth is.   Once one or two powders are found to be somewhat tolerant (extrapolating that the belief that you are close to the appropriate burn rate based on the barrel length, bullet weigh, the charge etc.) it would bring you closer to adjusting seating depth, neck tension, bullet sizing to fine tune the load. 

But back to rule 1.  The bullet has to fit the throat.  I'd really appreciate your thoughts on this.  Thanks, Bill C.

My addiction to gambling starts and ends with me spending $ to try a powder I’ve never shot before.

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John Alexander posted this 04 December 2022

Bud,

Thanks for your answer.

John

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