Smoke ring at base of neck

[thekubiaks]

I have a reloading issue I can't quite figure out. On both my benchrest 7mmSTW and factory 7mmRM I am seeing a smoke ring on fired cases at the base of the neck where the neck and shoulder meet. The picture shows what I am talking about. There are no powder stains on the neck of the 7mmRM but there is on the 7mm STW. Quickload velocity predictions are usually real close but my actual velocities are about 75 fps less than predicted. It is almost as if the neck is not expanding enough to seal the chamber and allow all of the pressure to push the bullet.

I turn the neck to .115" on the 7mmRM which is just enough to clean it up. The SAAMI chamber is .315" and the loaded round is .307" The bullet sits .020" off of the lands. Maybe the .008" gap is too great?? and is where the flame/burnt powder is getting thru??

As for the 7mmSTW (that is getting smoke at the base of the neck and on the neck). The neck is .310" and the loaded round is also .307". I am pushing the bullet .010" into the lands and have a neck tension of .002". I am seeing some primer flattening even though my velocities are on the low side. According to my ballistics programs, I am not pushing the max pressures at all. I know pushing the bullet into the lands will raise pressure as well as the GM215M magnum primers. My load works out to around 54,000psi, which is ~5,000 short of max. I thought about pushing the powder up a little to see if I could get the neck to "seal" but decided that wasn't a good idea since the primers are starting to show signs of flattening.

By the way, both guns are shooting great and very consistant with respect to velocity but I am concerned by the "blowback" and lack of velocity on both guns. Anyone have any comments/suggestions. Thanks.

 

[dmoran65]

That smoke ring is you "seal point". If your not getting much smoke on the rest of the necks, that tells me the necks are doing a good job of sealing as well. Sounds normal to good in my opinion -- FWIW

How are you coming up with the 54,000-psi?
By internal ballistics, or do you have strain gauges on your barrels?

Happy Shooting
Donovan Moran

 

[thekubiaks]

That smoke ring is you "seal point". If your not getting much smoke on the rest of the necks, that tells me the necks are doing a good job of sealing as well. Sounds normal to good in my opinion -- FWIW

How are you coming up with the 54,000-psi?
By internal ballistics, or do you have strain gauges on your barrels?

Happy Shooting
Donovan Moran

Thanks for the replies. I am using Quickload v 3.2. It has been really good at predicting velocites and exterior ballistics as long as I got all of the data points entered correctly (case capacity, OAL, neck tension estimate, etc).
Quickload estimated 54,000 psi for the bullet, seating depth, powder, and case capacity I loaded (I wish I had a strain gauge).

I wonder if my loads are on the light side. Sometimes when people on other forums mention their loads and velocities, I punch them into quickload to see what kind of pressures they are theoretically getting. And in at least half of the cases, Quickload shows the estimated pressures to be in the red zone. I like to just barely get into the the "yellow", but the flattening primers are concerning me....

 

[dmoran65]

thekubiaks -- for what ever all reasons, I always see smoke rings on "turned necks" at the point where the cutting stops (as in your picture). On non-turned brass, the ring is not as obvious.
Hot loads, mild loads, etc... have little relevance, I see the ring to all. Just some are more visible.

Happy Shooting
Donovan Moran