Dimpled brass

[Okdeerman]

Anyone have an idea why this is happening. It shows no sign of excess pressure. I chrony every shot and this one was about 30 fps slower. This is a 6.5-06. The brass was made by sizing 270 brass down and trimming excess length.

 

[WAMBO]

Possibly pressure is too low.
Neck not sealing and letting pressure escape pushing that area of the shoulder in.

 

[Frog4aday]

As @WAMBO said, you are TOO LOW in pressure so case neck is not sealing, leading to gas blow-by causing the dimbles. Up your powder charge until dimples go away.

 

[eshell]

Agreed: Pressure too low or powder too slow.

 

[Okdeerman]

I am using 53.5 grains of iMR 4350. My velocity does not vary much. Running usually +or- 10 to 15 fps at 3210. The accuracy is real good. I might try 1/2 to 1 g higher. The higher the velocity the flatter the trajectory.

 

[Tiny Tim]

Possibly pressure is too low.
Neck not sealing and letting pressure escape pushing that area of the shoulder in.

If this were the case, wouldn't there be soot in/near the dimple?

 

[Okdeerman]

There is blackening on the neck. Thanks for your info guys, I will probably bring the charge up a grain and use the same powder since I have plenty of that powder.

 

[WAMBO]

If this were the case, wouldn't there be soot in/near the dimple?

I don't know, maybe, maybe not.

I'm curious as what bullet amd weight he was using?

 

[Okdeerman]

Hey Wambo, the bullet is a 123g Hornady SST. The barrel is a 26in McGowen Precision, 1in 8 twist. Recoil is easily manageable, I love it. This is my 3rd McGowen barrel and they have all been more than acceptable in accuracy.

 

[K.E.C. Darkside]

As mentioned above, this is a sign of Low
Pressure, and possibly lite neck tension.

 

[BK6x47L]

I also had this happen fireforming 25-06 AI brass trying to seat the bullet into the lands. The bullet left the neck early in the pressure curve. Are you by chance seating your bullets long with minimal bearing surface in the neck?

 

[Okdeerman]

Yes the bullet is .002 back of the lands which does make a minimal amount of bullet in the neck. I am glad you responded because that thought had crossed my mind. Should I seat the bullet a little deeper or try increasing the powder?

 

[BK6x47L]

I would seat deeper. You may not have much more room pressure-wise to add powder and would probably still have the same issue.

As long as you are not trying to fireform an ackley shoulder and are pushing the 270 shoulder back to the correct headspace dimension with the sizing die, I would seat the bullet into the neck so that the bearing surface of the bullet is just forward of the neck-shoulder junction(option 1).

At a minimum, I would seat the bullet with bearing surface halfway into the neck. (option 2)

It really depends on how the rifle shoots with the bullet seated deeper.

I prefer option 1, and usually have the freebore set for my bullet 0.020" off lands at this seating depth, if possible.

 

[Dave in WI]

Yes the bullet is .002 back of the lands which does make a minimal amount of bullet in the neck. I am glad you responded because that thought had crossed my mind. Should I seat the bullet a little deeper or try increasing the powder?

Either way, only change one thing at a time