NAS3 5.56 Cases - Tikka 223 w/ 88 TMK

[B_Reynolds_AK]

Starting a new thread to address the issues I had with the NAS3 cases in my Tikka 223 with a 16", .100 fb, 1/7" twist bbl.

I loaded up 5 charge weights of N150 and 88 TMK's in the new NAS3 alloy cases, which Shell Shock indicates have
appx. 10% more powder capacity than standard brass.

The initial charge weight is what I've been using with ADI brass, 25.0 of N150. (2686 fps)

The first 3 loads ended up with "cookie cutter" holes in the Primers. I fired one more round and it did not go off.

On measuring the shoulders of ADI Brass and these, this is what I found.

ADI Resized: 1.361"
ADI Fired: 1.365

NAS Unfired: 1.351-1.355
NAS Fired: 1.359-1.362

What this is telling me is that the shoulder on the NAS cases are as much as .014" shorter than a fire formed case in my gun.
With what others have written in the 88 TMK thread, as well as from my research, this is causing an excessive chamber headspace issue.
Both the cookie cutter holes, from the primer slamming back into the firing pin hole, and the one misfire are both symptoms of this.

Velocites:
25.0 - 2704 fps
26.0 - 2764 fps
27.0 - 2840 fps



From Left to Right: 25.0, 26.0, 27.0. The ADI is a fired case with 25.0 and the 88 TMK.


I found two of the primer cutouts in my chamber.

 

[NWBLKTAIL]

Bummer this would have been pretty cool, but alas this is why things get tested.

Thanks for sharing I read your other post. I have had Peterson not form fully after first firing and shoulders varying in length. I can only imagine with harder alloy cases such as this the case hardly expands which probably also helps in aiding in the additional velocity via pressure.

Hopefully there comes a solution of some kind.

 

[Thegman]

The first 3 loads ended up with "cookie cutter" holes in the Primers. I fired one more round and it did not go off.

This last piece pretty much confirms the "too short case" hypothesis as the root of the problem.

 

[RockAndSage]

Separate from the case length problem, what primers are you using?

 

[B_Reynolds_AK]

Separate from the case length problem, what primers are you using?

Fed 205

To be clear, case length is fine. Shoulder to base length is the issue.