AIAX chamber oversized? (Bumping shoulder w/ Redding FL S die)

[Trek]

Rookie question... 1x fired Lapua brass (308) BartleiN/TAC stock barrel. Using a Co-ax press and a Redding FL S die its the button removed and a 0.335 bushing... I’m chasing my target 0.0015 should bump. Brass on the right is with the die screwed down and backed of an 1/8th - neck “sees” the full bushing constriction - bump is 0.0035; middle brass is with the die backed out (0.0025 bump); and brass on the right is where I am today (100 pieces prepped)... die is backed out to achieve 0.0015 bump, and a seating pressure of 30... yet the bushing constriction is only 2mm.

1) Concerned about concentricity / alignment vs the “full resizing) - right brass?
2) If the Redding die screwed down is bumping 0.0035 from fired - could the chamber specs be slightly larger than SAMMI (sp)... resulting in a larger variance?
3) Redding die out of spec?
4) Or, 0.0035 bump - consistently applied will be fine.... and AMP annealing every firing will help compensate for working the brass (0.0035 vs. 0.0015)?

Thanks for the guidance!

 

[whatsupdoc]

First how are you measuring the shoulder bump?
What tool do you have that has a resolution of .0001.

Looking at you cases something is not correct. For instance the 2 cases on the right, no bushing die will bump the shoulder with the bushing that high on the neck.

Is the bushing all the way in? There is something wrong with your die adjustment.

 

[spife7980]

Agreed. I have no idea what you are talking about that gives you those results.

 

[Trek]

The center/right the die is not all the way in… I’ve had to back it out to reduce the bump adjustment. This is creating the problem that the bushing die doesn’t have enough connection with the neck.

Screwed down, the die provides .0035 adjustment… So I can live with .0035, or I can get a different die... For those shooting the OEM barrel from AI it would be curious to see how they’re getting a .002 bump?

As far as equipment... I’m using the bump gauge from the Shooting Shed and a Mituroyo caliper. Thanks!

 

[Steel head]

Don’t worry about ten thousandths.
Calipers are only guessing at that point.
.001-.002 is fine.
Set your dies to bump that much from fired brass and go shooting.
You need to figure out your situation with the bushings though.
They’re never gonna reach all the way to the shoulder anyway but usually they get closer than your pics.

 

[whatsupdoc]

Ok first stop with the fourth decimal, your caliper CANNOT resolve that, it is accurate to .001 so that last digit is useless.

Take a couple of fired pieces of brass with the primer removed and measure the base to shoulder. What is that number?

 

[Trek]

Ok first stop with the fourth decimal, your caliper CANNOT resolve that, it is accurate to .001 so that last digit is useless.

Take a couple of fired pieces of brass with the primer removed and measure the base to shoulder. What is that number?

I measured 10 pieces (deprimred) CB to shoulder with the bump gauge = 1.620
Resized in a Redding 77355 308 Win Small Base die... the dimension got “larger” at 1.623 (2 pieces)... confusing... I was expecting to push the shoulders “back” (I.e. 1.618) but the longer dimension after sizing suggests I’ve bumped “out” the shoulders and the gauge is riding higher).

I did a “plunk” test on a spare barrel and they drop right in... and I’m seeing .26” impression of the .335 bushing.... thoughts?

 

[whatsupdoc]

Ok so you need to screw the die in further to push the shoulder back, the case getting longer is normal as you are squeezing the case and the brass need to go somewhere so the case grows longer. You will reach a point where the die shoulder starts to form "push" the brass shoulder back.

Make a mark on the die and another on the nut so you have a reference on how much you turn the die.

 

[whatsupdoc]

Forgot, for a preliminary adjustment start with the coax press handle down and shell plate up, now adjust the die so it makes contact with the shell plate.
Good solid contact. Start there and screw the die towards the shell plate "closer" in small increments until you get a .002 bump.

 

[Trek]

Forgot, for a preliminary adjustment start with the coax press handle down and shell plate up, now adjust the die so it makes contact with the shell plate.
Good solid contact. Start there and screw the die towards the shell plate "closer" in small increments until you get a .002 bump.

What’s up doc... brilliant- that was the advice I needed - thank you! I was elevating the die versus dialing down... a little trial and error... but I’m there. Lessons are important... I now have a 100 pieces of brass trimmed to 2.005 that when I size properly are going to be a wee short... now marked as “foulers”.

Thanks again for stepping in and assisting, much appreciate it!

 

[whatsupdoc]

No problem, you in the UK? never heard of shooting shed.

 

[Trek]

Michigan, but there is a really nice couple and a great gunsmith at “Shooting Shed”... “UK based” ... looking to support independents over factory, They supplied my comparator tools and a carbon bag rider for my AX but... nice folks! ?