HUGE velocity swings - WTF??

[ReaperDriver]

Today I finally got out to start development in my new 6CM Proof Research barrel for my AI-AT. I was very optimistic after I shot a few strings of factory Berger 109 and Hornady 108 ELDMs. Both of those shot half inch right out of the box.

So I loaded up a string of 5x 3 shot ladders of Superperformance with the 109 Berger LRHT bullets and another 5x ladder of 105 Berger Hybrids with IMR 4451. For both, consulted Hogden’s load site and started on the lower end of the Min/Max range. My goal was to try to match the factory velocities around 2960 ish.

At the start of this test, the barrel probably had a max of 20 rounds and was not cleaned since the factory round test the week prior. I shot another factory 3 shot group of the Berger 109 factory yellow box. They were almost dead on velocity from the previous session, maybe 15 FPS slower than the previous session as it was quite cooler. So I started with the 109s and Superperformance. Brass was virgin Lapua and Fed 205M primers. First string was a huge velocity split. 180 ES and an SD of 92.

The next 2 were slightly better ES in the 80s ans SD’s in the 40s.
#4

The last ladder was a spread of 80.

Accuracy was not terrible, maybe .75” or so. I was seriously thinking my Chargemaster 1500 was F’d. No way could I see these kinds of spreads.

So with dread, I began the next ladder with the 105 Bergers and IMR 4451 thinking either my powder thrower or LabRadar had sh*t the bed. The next five Strings were SD of 19, 14, 8, 3.5 and 5.1.

Any clue what would cause 200 foot spreads like that? All were virgin Lapua, match primers, neck mandreled, etc. WTF?

 

[nn8734]

I wouldn’t worry about it as 1) its only three shots and 2) mv figures from your other test groups with 4451 look “normal”

perhaps the barrel doesnt like superformance powder.

if you see spreads approaching that with 20 rounds of a given load using 4451 id be more concerned.

 

[FisherT&C]

If you didn't do a jump test ladder with the Superformance maybe that is the issue. Being too close to the lands can cause some erratic pressure contributing to erratic velocities, some of the time.

 

[nn8734]

If you didn't do a jump test ladder with the Superformance maybe that is the issue. Being too close to the lands can cause some erratic pressure contributing to erratic velocities, some of the time.

If that off the shelf superformance powder is the same used in some of hornady’s loadings I’m not surprised at those numbers. I’ve seen sizable velocity swings with my Mk12 running their 5.56 nato load. It’s known to be hot. Hammers out to 600m but is spikey in the MV dept.

 

[FisherT&C]

If that off the shelf superformance powder is the same used in some of hornady’s loadings I’m not surprised at those numbers. I’ve seen sizable velocity swings with my Mk12 running their 5.56 nato load. It’s known to be hot. Hammers out to 600m but is spikey in the MV dept.

Same here. I built a 7 Rem Mag years ago and about had a stroke when it shot 5 inch groups with Superformance ammo. I switched ammo and it went down to Sub-Half MOA, I chalked it up to the SF not being consistent. I never ran it over a chrono though.

 

[ReaperDriver]

I wouldn’t worry about it as 1) its only three shots and 2) mv figures from your other test groups with 4451 look “normal”

perhaps the barrel doesnt like superformance powder.

if you see spreads approaching that with 20 rounds of a given load using 4451 id be more concerned.

It was not just 3 shots. It's 5 ladders of 3 shots each (15 total) and all the ES and SD were off the scale, The Best spread was 69 fps with about a 44 SD. I did 5 ladders of 3 shots each from 40.6 to 42.2gr of SuperPerformance in .4 gr increments.

 

[ReaperDriver]

If you didn't do a jump test ladder with the Superformance maybe that is the issue. Being too close to the lands can cause some erratic pressure contributing to erratic velocities, some of the time.

This was the very first rounds of load development for the rifle. The barrel had about 20 total rounds down it when I started. I checked the distance to the lands and I'm nowhere close to it. I loaded these at 2.775 OAL to match the Berger factory loads. I figured that was a good place to start since the factory stuff shot really well.

 

[ReaperDriver]

If that off the shelf superformance powder is the same used in some of hornady’s loadings I’m not surprised at those numbers. I’ve seen sizable velocity swings with my Mk12 running their 5.56 nato load. It’s known to be hot. Hammers out to 600m but is spikey in the MV dept.

Yeah, no idea what Hornady uses - but this issue seems to be powder related. I've had powders that just dpn't shoot. But a 200 ES and and a 100+ seems out of the realm of possibility.

 

[nn8734]

Yeah, no idea what Hornady uses - but this issue seems to be powder related. I've had powders that just dpn't shoot. But a 200 ES and and a 100+ seems out of the realm of possibility.

Not outside the realm of possibility, ive seen that before at various times over the years, nothing to be worried about overall, esp if your other test samples w/other powders look fine, mv-wise.

It was not just 3 shots. It's 5 ladders of 3 shots each (15 total) and all the ES and SD were off the scale, The Best spread was 69 fps with about a 44 SD. I did 5 ladders of 3 shots each from 40.6 to 42.2gr of SuperPerformance in .4 gr increments.

Lol, yea those numbers are brutal but it happens sometimes. Again, nothing to worry about. Superformance and your rifle just dont mix, that’s all.

 

[buddy.223]

I had similar issues with imr 4955 in a .284 win, it spiked before achieving usable velocity. Try another powder

 

[FisherT&C]

This was the very first rounds of load development for the rifle. The barrel had about 20 total rounds down it when I started. I checked the distance to the lands and I'm nowhere close to it. I loaded these at 2.775 OAL to match the Berger factory loads. I figured that was a good place to start since the factory stuff shot really well.

Sounds good. I'm sorry to here the SF isn't working out, it's probably too finicky to be worth trying different seating depths. I personally am using SF in my 6.5 CM with 142 SMK's and I'm very pleased with it. Sometimes a certain powder bullet combination does or does not get along with a barrel.

 

[ReaperDriver]

Not outside the realm of possibility, ive seen that before at various times over the years, nothing to be worried about overall, esp if your other test samples w/other powders look fine, mv-wise.


Lol, yea those numbers are brutal but it happens sometimes. Again, nothing to worry about. Superformance and your rifle just dont mix, that’s all.

Understood. After shooting the 4451 string, I was happy again and at least it ruled out most other things other than the powder. I guess I won't be using SP anymore for this cartridge. And I bought a brand new 8lb jug of it just for this caliber based on others saying they've had good luck with it. I'm just surprised that the swings in MV were that big.

Anyone want to buy a brand new, just opened yesterday, 8lb jug of SuperPerformance - minus 15 loads??

 

[ReaperDriver]

Sounds good. I'm sorry to here the SF isn't working out, it's probably too finicky to be worth trying different seating depths. I personally am using SF in my 6.5 CM with 142 SMK's and I'm very pleased with it. Sometimes a certain powder bullet combination does or does not get along with a barrel.

Yup, definitely not going to bother with SP at all. I've got plenty of 4451 (~20lbs), which it absolutely likes. And I've got an unopened 8lb'er of H4350.

Based on my results yesterday with the 4451, my load dev is done in 15 rounds. I found a node right at 3000 fps that shoots into a tiny cloverleaf with a 3.5 SD. I *might* do a seating test, but its shooting so well at factory OAL, that I'm not sure it's worth the components and barrel life. Next week, I'm going to take it out to 1000 and beyond and see how that load shoots. If it shoots as well as I think it will, I'm done.

 

[ReaperDriver]

Sounds good. I'm sorry to here the SF isn't working out, it's probably too finicky to be worth trying different seating depths. I personally am using SF in my 6.5 CM with 142 SMK's and I'm very pleased with it. Sometimes a certain powder bullet combination does or does not get along with a barrel.

I may give the SP a try in my 26" .260 Rem with Berger 140s or 144s. It's a pretty slow powder, so should be good with some heavier bullets, longer barrels.

 

[918v]

You should run the brass through a FL die. The neck needs to be sized down and then expanded back out. That’s the only way to have the necks exactly the same. Mandrelling a new neck is not enough.

 

[Doom]

My speculation is that the SP is having ignition/combustion issues. Looking at Sierra data SP is the slowest powder they recommend with the 107. If the bullet is releasing before enough pressure builds it can result in inconsistent peak pressure and velocities.

You may find that the spread improves at higher charges.

 

[ReaperDriver]

You should run the brass through a FL die. The neck needs to be sized down and then expanded back out. That’s the only way to have the necks exactly the same. Mandrelling a new neck is not enough.

I neck sized the virgins down to .270 and then ran them through the 6mm Wilson neck mandrel. It's my standard process now, so pretty sure inconsistent neck tension is not the cause of 200 ES and 107 SDs.

 

[ReaperDriver]

My speculation is that the SP is having ignition/combustion issues. Looking at Sierra data SP is the slowest powder they recommend with the 107. If the bullet is releasing before enough pressure builds it can result in inconsistent peak pressure and velocities.

You may find that the spread improves at higher charges.

Yep, that's pretty much what my shooting partner said as well. My top load that day was about 2 full gr short of max, so maybe as you said the higher end charges may work. Given that the 4451 shot so well, I'll probably just shelve any additional testing with other powders for now.

 

[918v]

I neck sized the virgins down to .270 and then ran them through the 6mm Wilson neck mandrel. It's my standard process now, so pretty sure inconsistent neck tension is not the cause of 200 ES and 107 SDs.

Inconsistent neck tension is a variable. Eliminating variables is what consistency is all about. Glad you’re prepping your brass correctly, tho.