Please help me solve 6 Creedmoor Velocity drop. UPDATE

[Unknown Marksman]

ADVICE WANTED. UPDATED

Sorry for the delayed update, and a big thanks to all who responded.

I sent the barrel back to the manufacturer, they tested it 3 times and said everything checked out.

When I got the barrel back, it worked flawlessly, velocity was slightly higher then before the issue started. I have no idea what changed from when I sent it in and got it bad, but it’s shooting great. ‍

I am a fairly experienced reloader with great equipment. I’m new to reloading for the 6 creedmoor.

I have an issue and looking to see if anyone has advice how to solve.

I fire form 125 pieces of brass and didn’t chronograph. On second firing I chronographed all shots. 3rd firing on ALL brass I dropped 300 or more FPS for any given charge.

Details.

22” 1-7.5 TW barrel (round count is currently 275) 105 hybrid, .070 jump, H4350, Peterson brass, bumped .0015-.0020, SAC die, .2415 mandrel, primer CCI BR-4

Anneal every time with AMP. Henderson Gen ii power trim, load +/- .02 with SuperTrickler.
Chronograph with Andiscan A2 (verified to be within 4 fps of a Labradar or Magneeto)

On third firing of brass with 39.3 grain H4350 Velocity drops from 2900 to 2550. And there is carbon from the neck all the way to the end of the shoulder. Obviously I’m not getting a seal and loosing pressure.

Have tried , fed sm rifle primer, more neck tension, less tension, higher charge, turned shoulders to remove slight donut, turned necks (from .014 to .013).

Nothing brings velocity back except new brass.

Any suggestions or thoughts????

 

[NZ_Fclass]

Seems odd. The load looks a little light to me, being .3g over Hodgdon's minimum, but that doesn't account for the loss of velocity, but may account for the carbon marks on the case. I'm interested what others say on this one. Worth trying another powder? R16 or StaBall ?

 

[Benchrest Braxton]

That makes zero sense…..im stumped.

even if you weren’t getting a great neck seal, i don’t see that causing your issue……

 

[big5ifty]

Is there any chance that on the 3rd round of reloading, the autotrickler was accidentally setup a couple grains low ?

 

[piie]

If everything else are guaranteed to be equal, then something went wrong with your powder measurement, or powder itself (got wet/damp), or you accidentally swapped powders between the 2nd and 3rd reloading, or huge environmental difference between 2nd and 3rd firings?

You don't mention how long it was between the 2nd and 3rd firings or whether you perhaps used a new batch of H4350 (or primers?).

 

[Beiruty]

Replace powder and/or bullet

 

[6.5 forever]

Verify your powder charge on a beam scale?

 

[6Creed73]

I've seen velocity drop for fired brass before due to volume change. Larger case volume means less pressure and less velocity. But I would not expect that much of a drop. I'd be interested to know the case volume difference between the new and fired brass though.

This one is a head scratcher

 

[DirtySteve]

just throwing this out there.. Did you change lots of powder? Or do you empty your powder hopper after each use? Leave powder in the hopper will change the moisture content and change the burning characteristics.. More moisture=slower burn..

 

[SeabeeKen]

I've seen velocity drop for fired brass before due to volume change. Larger case volume means less pressure and less velocity. But I would not expect that much of a drop. I'd be interested to know the case volume difference between the new and fired brass though.

This one is a head scratcher

^^^^
This
I think the problem may be 2 things.
1, case capacity increased after forming
2, your load was light to begin with and was made worse by increasing case volume without increasing powder charge.
Try redeveloping the load with fireformed brass or just simply increasing powder charge to get the case to seal and get speed back up. JMO

 

[Beiruty]

^^^^
This
I think the problem may be 2 things.
1, case capacity increased after forming
2, your load was light to begin with and was made worse by increasing case volume without increasing powder charge.
Try redeveloping the load with fireformed brass or just simply increasing powder charge to get the case to seal and get speed back up. JMO

Case volume would drop MV by some 40 fps max.

 

[Beiruty]

1) You are either shooting an undersized bullet
2) You are using a powder with a lot of moisture.

 

[ShtrRdy]

That is bizarre. I would like to follow along.

 

[Benchrest Braxton]

^^^^
This
I think the problem may be 2 things.
1, case capacity increased after forming
2, your load was light to begin with and was made worse by increasing case volume without increasing powder charge.
Try redeveloping the load with fireformed brass or just simply increasing powder charge to get the case to seal and get speed back up. JMO

if case volume from fireforming was the issue he would have seen the difference between loading 1 and 2, not 2 and 3.

 

[SeabeeKen]

I stand corrected

 

[HandgunHTR]

Based on your comments @Pudgy, it seems that you have been able to repeat this issue a couple of times. If that is the case, I would say that the issue may be your annealing process. If you are still getting good velocity on the 2nd firing and are losing it on the 3rd and this is repeatable, with nothing else changing, then my guess is that you are underannealing.

 

[Dimner]

Just a shot in the dark suggestion. Try a magnum primer.

 

[Straightshooter1]

I'd be sure to verify if I'm getting the right powder weight measurement and measure even measure the moisture content of the powder, if for no other reason than to eliminate that as an issue, as that powder residue down so low on the neck does indeed strongly suggest very low pressure.

 

[ebb]

Sounds to me like a crono problem. But Dimner has a good idea.

 

[Webster]

just throwing this out there.. Did you change lots of powder? Or do you empty your powder hopper after each use? Leave powder in the hopper will change the moisture content and change the burning characteristics.. More moisture=slower burn..

More moisture. Your weighing water and powder. 300 fps doesn't make sense.