Chamber assessment help

[Chris Edmondson]

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:



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.

 

[WSnyder]

Possibly not too far off when considering a +.002" tolerance on all DIA.

 

[Coyotefurharvester]

What sizing issues are you having?
Does fired brass chamber correctly (before sizing)? Yes, than.
Does sized brass chamber properly? If no, than
Have you used a markered case in the rifle to determine where the contact is?
After this( your sizing is causing chambering issues) what equipment are you using?

 

[Chris Edmondson]

What sizing issues are you having?
Does fired brass chamber correctly (before sizing)? Yes, than.
Does sized brass chamber properly? If no, than
Have you used a markered case in the rifle to determine where the contact is?
After this( your sizing is causing chambering issues) what equipment are you using?

The only issue is FL sizing; requires more than the "usual" amount of press force with all the dies I've used in the past, and very difficult with a small-base die, regardless of lube. No issues with chambering or shooting.

 

[urbanrifleman]

Probably a go and no go gauge set would be where I suggest you start.

 

[Coyotefurharvester]

Is it a gas gun?

 

[Chris Edmondson]

Possibly not too far off when considering a +.002" tolerance on all DIA.View attachment 1639370

My SAAMI drawing indicates cartridge diameters are nominal to -.008

EDIT: You are correct chamber is +.002.

 

[Chris Edmondson]

Is it a gas gun?

Bolt action.

 

[WSnyder]

and very difficult with a small-base die

Why use a small base die when the chamber appears to be on the large side? Seems to be forcing the issue where it's not needed. Why not stay with a std die if you aren't having chambering issues with one? What does the brass measure after it is sized in a std die?

 

[Steve Donlon]

What brand of brass? The reason I ask is because I had some 6.5 Peterson Brass from years ago that was FAT BRASS they made to be neck turned and I did not know that's what i had. The neck was thicker as it moved to the shoulder and was hard to size and I was getting pressure signs, hard to extract ,when my other Peterson brass was fine. Took be awhile to figure out what was going on. If you measure the neck width before you seat a bullet and the sides are parallel then after seating the bullet they are not then the brass is thicker at the bottom if all the bearing surface is in the neck.

 

[DShortt]

Hard to guess what you have going on but as other's have mentioned, try some different brass before you get too far down a rabbit hole and while you say you've tried different lubes, try Imperial.

If it won't resize fairly easily with Imperial and you've tried 2 or 3 different batches of brass, then I'd do a Cerrosafe chamber cast and take a bunch of measurements because something must be really off.

That doesn't mean you can't work around it. But I'd suggest you identify the exact problem before you decide what to do next. Maybe your sizing die is off. No way to know without taking measurements.

And yeah, if your chamber is oversized then brass run through a standard die will chamber easily because it's well below chamber dimensions.

 

[Chris Edmondson]

Why use a small base die when the chamber appears to be on the large side? Seems to be forcing the issue where it's not needed. Why not stay with a std die if you aren't having chambering issues with one? What does the brass measure after it is sized in a std die?

I didn't know I had a large chamber until I tried a small base die, make sense?

 

[243winxb]

Brass is hard to size when to much powder is used.

High pressure does not allow brass to spring back after firing.

What are you loading?

 

[Coyotefurharvester]

No, a small base die takes brass to minimum size. For autos,pumps. Why would you need to size that far for a maximum size chamber?

 

[Doom]

The fired brass dimension is irrelevant to the SAAMI maximum unfired case dimension. As for the fired case versus the the chamber dimension the data is similar to what I see in my 308.

There is absolutely no reason to need a small base die for the cases shot in same rifle each time. Even an over pressure load that expands the base (0.200" dimension) should not be an issue in the same rifle unless the round is severely over pressure. Round would have been hard to extract.

Almost any production rifle is going to have a chamber larger than SAAMI minimum dimensions because the reams are built to the higher side tolerance because the reamers wear and that wear reduces the camber size that is cut.

 

[Alex Wheeler]

Its very hard to get an exact shoulder diameter measurement and usually you end up a little fat because your actually measuring back a little. Your .2" number is right on as most reamers run close to .0005" over the print numbers on diameters. Id say your chamber is pretty normal on the diameters.

 

[SeabeeKen]

I agree with the above. Shelf the SB die and use a standard. What is your load info?

 

[urbanrifleman]

If you are claiming the chamber is beyond spec for headspace, then it would seem that all of these other various reloading considerations are secondary to establishing if the headspace is within spec.

 

[dgeesaman]

I’d ditch the small base die, set your fl die to headspace to .002 less than your actual chamber, and see if the issues go away.

I personally prefer custom dies when my fired brass is being sized more than .002 on diameter near the shoulder but with saami specs and factory dies that’s all but guaranteed. Lots of shooters shoot great groups by focusing on headspace only and focusing on pressure signs in their loading.

 

[JFrank]

The only issue is FL sizing; requires more than the "usual" amount of press force with all the dies I've used in the past, and very difficult with a small-base die, regardless of lube. No issues with chambering or shooting.

If you were using Wilson FLD dies you could send the die along with a couple fired cases to the tech department for a slight bit of honing.