Ladder rounds - the process

[Archeryrob]

I need some schooling on the process. I think I was doing okay and barrel heating started causing issues. I did not want to do this when it was cold and windy, but now I think I should have. I think the barrel was heating, stopping floating from swelling or just heat and being off. How long between shots or ladder steps? I am doing 4 rounds per step and I made a lot of steps as I am doing my first ladder with cast and seeing how fast and consistent I can get from them before it looses accuracy and I have to stop on speed. Rounds are wheel weights, water quenched and powder coated. This is a Bergara B-14 in 30-06 and using 4198 with a 175 grain spire tipped round, gas checked.

Started at 33 grains and 2171. Shoot 4 and stopped to change targets. walk out and back maybe 5 minutes between steps. The 5th step was 35.5 grains 2304 and first three rounds group and 4th shoots low, No fouling, but barrel is hot. Drive off to buddies house for water break/let gun cool.

Start again 36 grain 2329, 36.5 - 2354, 37 - 2378 and 4th one drifts some, 37.5 - 2403 and 4th pull right more and lastly 38 grain barrel allowed to rest some, shot one tight, follow by 2 pulled right. Let gun cool again and shot three on tight and shot 4 following three even farther off. Seeming the more rounds shoot the longer rest/cooling times need to be.

So it seemed velocity in cast rounds wasn't mattering but barrel heating was destroying accuracy. The longer the shooting went on the worse it got, but the cartridges were getting hotter with going up steps on the ladder too. So I am assuming I need a lot longer rest times between shots/ladder steps or a better way to cool the barrel back down. I think I could probably shoot one ladder step of 4 in sequence, but its going to need a long rest or cold air on the barrel.

What wisdom can you give on rest times and cooling the barrel down?

 

[GuitarmanNick]

My dad has a barrel cooler that he uses between steps when working up loads for his benchrest rifles. It blows air through the barrel to dissipate heat faster than if it just sits.

I saw some homemade coolers posted on another forum that looked promising a few days ago. Most can be assembled using items easily acquired online. Grab a rechargeable mini-fan, some plastic tubing, and make a chamber fitting from a piece of brass for the caliber.

I usually have another rifle to shoot while the barrel cools on the one performing the ladder tests. If I cannot hold my hand on the barrel doing the testing, it gets a rest. So far, I have had good results using this method. Just gotta remember to keep checking the barrel temp as you go.

In my limited experience with cast bullet loads, I think most calibers require a faster burning powder. Not sure if it may be a factor in producing more heat in the entire barrel, or perhaps just the breach end near the chamber. Either could affect accuracy.

Barrel profile is a factor. Heavier barrels take longer to heat up, and cool down. Thinner barrels may show problems much faster and require more vigilance on monitoring the barrel temp while shooting.

Anything in .30-06, even the reduced charges typical with cast bullets, is going to create a lot of heat, quickly.

When you finally get everything figured out and produce rounds that are consistently accurate, it is worth all of the effort, IMO. It is a process that consumes a lot of time and cannot be rushed. Anything that can save a little time may be worth a small investment.

Good luck on your endeavor, sir.

 

[Doco Overboard]

So I tell you what I would do.
I would determine what if any bedding deficiencies are present before proceeding, and correct them.
Sounds like you have a couple things going on at the same time.
Use jacketed bullets to asses what’s causing the bedding error to eliminate any problems you may discover firstly.
All the ladder in the world isn’t going to fix a mechanically unpredictable system.
Then, I would start by ensuring my cast bullet fits the unrifled portion of the chamber just before the leade and solve any discrepancies there.
Then do a ladder test and determine what charge works best and so on.

 

[Archeryrob]

I don't have any trouble with bedding but did not check it while it was hot. I am fully aware of this issue as I had a Remi 710 in my younger years and it shot different cold verses warm as it got older. I had to re-sand the stock to get it floating warm. I would get that gun sighted and then the col shot hunting was off.

Bullets are sized just over and fit the chamber. The cast bullets shoot great until the barrel gets hot. I am getting good groups until it gets hot. The question is how much time breaks and I'll look into the barrel is cooler. Or how to cool better or what other people do.

The first shots were always good and drift only started by 4th shoot or closer as it got hotter. So I know the trouble is the barrel heating.

 

[Speed3]

Seems you have access to a chrono? The last 2 loads I've developed fairly quickly, but they were jacketed bullets. I have zero experience with cast rounds.

If unsure start 10% below max charge weight. I load 1 round usually 1% increments, in this case .1gr increments. I shoot them back to back and record fps.

I'll then chart it in excel looking for a "node". Easy to see the node at 38.7gr. I want to see little variance left and right also. That way when shooting in the morning @ 55 degrees, I can still group well when its 85 degrees later in the day.

Once i figure out the charge weight load based above, ill then move to seating depths. I usually start 20 thou off the lands and move in
003" increments. Again looking for a node in seating depths (.006") same POI and tight groups. Ill then load as long as I can to fit in that node, so as the barrel wears im in the node for the longest period I can.

Hope it makes sense, typing from phone .

 

[Archeryrob]

FPS listings are GRT generated assumptions. I do not have a Chronograph.

What does the chart and graph mean? Just increasing after the dip is the go to load?

 

[Doco Overboard]

I don't have any trouble with bedding but did not check it while it was hot. I am fully aware of this issue as I had a Remi 710 in my younger years and it shot different cold verses warm as it got older. I had to re-sand the stock to get it floating warm. I would get that gun sighted and then the col shot hunting was off.

Bullets are sized just over and fit the chamber. The cast bullets shoot great until the barrel gets hot. I am getting good groups until it gets hot. The question is how much time breaks and I'll look into the barrel is cooler. Or how to cool better or what other people do.

The first shots were always good and drift only started by 4th shoot or closer as it got hotter. So I know the trouble is the barrel heating.

Of course you are until the barrel gets Hot.
What goods a ladder with a hot barrel?
Idk. Sounds like a bedding problem to some extant.
Don’t look through your scope more than for how long it takes for the powder to heat up your cartridges then maybe.
Because powder/ cartridge temps affect burn rate/ external ballistics , pressure and so on.
Maybe you have a kinked barrel too if it really got hot one time or it’s just not a [Hot one]
Maybe I just misinterpreted your post asking about a ladder.
Good luck with load development and hope you get it figured out.

 

[erwos]

You need to do a statistically significant number of groups per ladder step. A single group per step does not really prove anything, even if it's five shots. Suggest looking up what Bryan Litz has to say about this topic.

 

[outrider58]

Paging @Melnic

 

[Russ D]

You need to do a statistically significant number of groups per ladder step. A single group per step does not really prove anything, even if it's five shots. Suggest looking up what Bryan Litz has to say about this topic.

This is where I am now. I will shoot 5 shot groups just to eliminate the bad ones. Any 5 rounds groups that show promise and I’ll shoot 20 round groups to verify. If I get solid 20 round group performance I’ll then shoot them at distance to see if they hold up. The vast majority of my load development is just to eliminate what’s bad. I also put the majority of my emphasis on group size and then I’ll care about ES and SD.

 

[atblis]

The version of the ladder test I am familiar with is simply shooting a sequence varying powder charges from min to max in an appropriate increment using the same point of aim. You’re interested only in the vertical point of impact thus wind drift isn’t really important. What you’re looking for is a window of powder charges that cluster vertically. Inside of this you can also shoot groups. As an initial coarse discriminator, you can likely get by with 3 round groups.

To see the vertical clustering you likely need to shoot at a few hundred yards.