6.5x55 Case Dimensions After Firing out of a m96

[ojibweindian]

All

Need some input concerning fired Lapua cases out of an m96 that I own.

Once-fired Lapua case:

Case head diameter: 0.478"
Diameter at shoulder: 0.443"
Diameter at midpoint: 0.459"
Case length: 2.153"
​

For comparison, the dimensions for an unfired Lapua case are:

Case head diameter: 0.478"
Diameter at shoulder: 0.433"
Diameter at midpoint: 0.452"
Case length: 2.158"
​

The once-fired case was a load consisting of 44.7 grains of Reloader 19, a CCI 200, and a 140 grain Hornady Interlock.

My question is this: do these measurements on the once-fired case indicate a prudent load? Let me qualify my measurements above by stating that there was no sticky bolt, and recoil was just a bit more forceful than my m4 running 55 grain FMJ ammo.

Thanks!

 

[243winxb]

The fired case diameter measurements are close enough to the SAAMI chambers standard to be ok. https://saami.org/technical-information/cartridge-chamber-drawings/ But brass may not expand fully to the chamber with less then a maximum load. And may require 3 or more firings.

Your loading is maximum & for a commercial action. (Alliant)

The most important measurement is head to datum. Case stretch on firing. A comparator is used to measure it.

The M96 action has its own load data at Alliant.

 

[ojibweindian]

The fired case diameter measurements are close enough to the SAAMI chambers standard to be ok. https://saami.org/technical-information/cartridge-chamber-drawings/ But brass may not expand fully to the chamber with less then a maximum load. And may require 3 or more firings.

Your loading is maximum & for a commercial action. (Alliant)

The most important measurement is head to datum. Case stretch on firing. A comparator is used to measure it.

The M96 action has its own load data at Alliant.
View attachment 943121 View attachment 943122

I am aware that my load exceeds what Alliant lists as max for an m96. My reason for it is because at lower charge weights (within spec for military actions), the primer backs out. 44.7 grains of RL-19 is the lowest charge weight at which the primer doesn't back out.

Another question; based on the measurements of my once-fired case, it can be assumed that my m96 has a somewhat generous, yet still within spec, chamber?

 

[243winxb]

The C.I.P. independently standardized the cartridge. This may be different then SAAMI.

By SAAMI, it seems the diameters are on the larger side at the shoulder.

The chambers headspace is what matters most.

44.7 grains of RL-19 is the lowest charge weight at which the primer doesn't back out.

The primer may back out till the brass fire forms to the chamber. Less head clearance. New brass is almost always undersize, head to datum.

Learn how to bump the shoulder back correctly, when full length resizing. Lots of info online.

 

[ojibweindian]

The C.I.P. independently standardized the cartridge. This may be different then SAAMI.

By SAAMI, it seems the diameters are on the larger side at the shoulder.

The chambers headspace is what matters most.


The primer may back out till the brass fire forms to the chamber. Less head clearance. New brass is almost always undersize, head to datum.

Learn how to bump the shoulder back correctly, when full length resizing. Lots of info online.

I'm using a collet die now and bump the shoulder back with a FL die when closing the bolt on a case takes a bit of effort. I've not had issues with protruding primers in some time.

I will be picking up a comparator; was not aware of that and it seems a vital tool to have on hand.

 

[lonniemike]

Old like me, Hodgdon # 26 lists Reloader 19 start 44gn @2677 and max as 47gn @2773 in 28" barrels. You're ok and working up. Chrono and camber cast can be good things. Chrono first. Best

 

[ojibweindian]

Old like me, Hodgdon # 26 lists Reloader 19 start 44gn @2677 and max as 47gn @2773 in 28" barrels. You're ok and working up. Chrono and camber cast can be good things. Chrono first. Best

Does Hodgdon #26 state pressure values for min and max loads in either PSI or CUP?

 

[Rabble_Rouser]

Have you experienced the primer backing out on cases that were fired then reloaded? It sounds like a headspace issue. A headspace gauge is kind of invaluable for the old milsurps to measure the fired cases and then limit your resizing to just bumping the shoulder back .002 from there, regardless of spec.
Be careful pushing max pressures with the M96. I'll second the recommendation for a chrono.

 

[ojibweindian]

Have you experienced the primer backing out on cases that were fired then reloaded? It sounds like a headspace issue. A headspace gauge is kind of invaluable for the old milsurps to measure the fired cases and then limit your resizing to just bumping the shoulder back .002 from there, regardless of spec.
Be careful pushing max pressures with the M96. I'll second the recommendation for a chrono.

I did experience the primer backing out on fully resized fired cases. Once I started using a collet die, though, backed out primers were no longer an issue.

Today, while at Cabelas, I bought a case comparator, per advice of 243winxb. I'm pretty sure my m96 chamber is a bit generous in its dimensions, but not woefully screwed. I've never experienced an instance of a sticky bolt, excessive recoil, pierced primers, etc.

 

[243winxb]

Neck sizing and getting a crush fit when closing tne bolt will give an accurate reading of the fired case head to datum measurement.
This measurement is to compare fired to sized brass. The tool is not to measure the SAAMI chambers headspace.

There are go, no go & field gauges to measure the rifles chamber.

 

[ojibweindian]

Neck sizing and getting a crush fit when closing tne bolt will give an accurate reading of the fired case head to datum measurement.
This measurement is to compare fired to sized brass. The tool is not to measure the SAAMI chambers headspace.

There are go, no go & field gauges to measure the rifles chamber.

243winxb, using the comparator i bought today, I took the average of 4 unfired cases and 4 fired cases; the delta is 0.007". What can I infer from this?

 

[243winxb]

Not much stretching happening from new brass to fired.

Compare new to a crush fit case.

 

[lonniemike]

no pressures in hodgdon's book. Find borrow or buy a chrono. Find borrow or buy some Swede Prykette(139-144) ammo(getting hard to find). Shoot your reloads and mil ammo over the same chrono. I believe that you'll find your chamber is just fine with any further checking and that your reloaded velocitys are way slower than the mil ammo. The mil stuff should exceed 2600fps by a little. Norma made/makes a 140gr load exceeding 2800fps. Best