Chamber assessment help

[SKWERLZ]

I needed to address very difficult FL sizing with a new die recently, the fired brass from this 6.5 Creedmoor barrel has never been what I'd call easy to size but, in this instance it made me wonder what is going on.

Fired brass was assessed and a determination made that the chamber exceeds SAAMI specifications with respect to base and shoulder diameters, and length. Below is a marked-up SAAMI cartridge drawing showing the two body dimensions mentioned above for the fired brass as they relate to the specification:

View attachment 1639364

With respect to length, the fired brass indicates a headspace of GO +0.007".

Whatever the numbers say at this point, it's water under the bridge. What I'd like to know is if this level of apparent SAAMI non-compliance considered "normal", "just a bit off", "way off", or "WTH"?

Thank you.

Make of the dies?
I’ve had to polish dies a few times, the finish in my recent Hornandy 22arc set was tragically bad but easy to remedy with a bast difference in force needed to size brass.

 

[Chris Edmondson]

Thanks for the comments; I'm not going to use this SB die with this rifle any longer. As much I really like how the die handles neck sizing, it's just too tight for the fired brass body. The die is a SAC modular.

 

[AlNyhus]

Chris, it could be as simple as another die or having that one honed a bit. -Al

 

[243winxb]

The die is a SAC modular

https://www.midwayusa.com/product/1025513331?pid=944366
The Short Action Customs Modular Neck Sizer Die has a unique design where the cartridge’s body geometry is sized by the die body, the cartridge’s shoulder and neck geometry are sized by a “Neck/Shoulder Bushing” (sold separately). This allows one die body to be used for the whole cartridge family. Furthermore, the Modular Sizing Dies are precision machined with the main focus of properly sizing your fired brass. The modular resizing dies will size the base of the cartridge slightly more than the shoulder. This die is considered a full length sizing die.



After studying precision CNC machines and tooling, SAC designed the Modular Sizing Dies to utilize a series of shallow tapers, not threads to properly center and secure the Solid Decapping Pin. The tapered geometry offers unparalleled concentricity and repeatability. Last but not least, they designed the cartridge sizing geometry to size a little more at the base and a little less at the shoulder when compared to most resizing dies on the market. In properly sized rifle chambers, this helps eliminate extraction issues of fired brass. This shoulder sizing geometry helps minimize case runout and over working of the brass by not sizing the shoulder too much.



Interesting. I like my Redding type S fl bushing die in 6.5 CM. Perfect match for my Savage Axis chamber.

 

[Chris Edmondson]

Chris, it could be as simple as another die or having that one honed a bit. -Al

I agree, I could revert to my Redding for shoulder bump, Lee collet for neck, or Redding with a bushing and expander, or...

I'm not inclined to hone the SAC die, the barrel in question is closing in on end-of-life, not to say it isn't worth saving, it shoots very well, it just may not make financial sense to permanently alter the SAC die right before the funeral .

I have another thing I may try: size and shoulder bump only with the Redding die, size the neck with the SAC die adjusted for no bump. The Redding may reduce the case dimensions enough so the SAC doesn't have as far to go, if it works, it's an additional step which detracts from the SAC's ability to do it all in one step, but it's a way to get the best from the barrel at this stage.

 

[DanSavage]

Get a no go gauge,, if the bolt closes on it it’s got to be corrected or have custom dies made for it.

 

[Codyway]

I have a 308 chamber that's fat also.
I use a multi step sizing process rather than go the custom die route since I shoot multiple 308s.
1- Redding body die only enough to reduce the .200 line 0.002-0.0025, but don't bump the shoulder, i.e. leave it screwed out some to only get what you need
2-Forster bushing bump to set headspace and neck

 

[JFrank]

Get a no go gauge,, if the bolt closes on it it’s got to be corrected or have custom dies made for it.

A go gage won’t provide any information regauding radial dimensions, only length.

 

[DLT]

A go gage won’t provide any information regauding radial dimensions, only length.

That’s a very true statement

 

[DanSavage]

A go gage won’t provide any information regauding radial dimensions,

A go gage won’t provide any information regauding radial dimensions,

A go gage won’t provide any information regauding radial dimensions, only length.

he said length was out also