Consistent CBTO?

[mikecr]

It's not a big deal really. Your optimum CBTO, as identified with full seating testing, has a window.
You should have +/- a few thou & be okay.

I want mine exact, so I short seat as someone mentioned and dial in dead nutz for final seat.
That's with micrometer top seater dies, and an arbor press. There are mic-top threaded dies.
But you could set a threaded die a touch under desired CBTO, and slip feeler gauges between the case head and shell holder for final seating.
Measure every round.

 

[nwmnbowhunter]

What seating die are you using?

Are you having this problem only in one cartridge or multiple?

Make sure your measuring technique is consistent. If you measure the same round 10 times you should get same result.

 

[wkdickinson]

Some bullets will vary as much as .003 difference when going from one lot to the next. Some will vary as much within the same box.

I recently did a study of Berger 105gr Hybrids, the same lot - I was shocked! Here what I found:


And we wonder where flyers come form!

Wayne

 

[marchx]

Wayne, I did it with Hornady. Results were far more interesting.

 

[WIB3]

Neck tension is your culprit, especially when you have high neck tension. The seater in the die will create a ring around your bullets circumstance. The harder the neck tension the deeper the ring. Try to modify your neck tension to the lighter side. 0 to 15 psi should not impact your measurements. Try to find a supplier who will manufacture you a seating stem contoured to your specific bullet ogive. You can do this your self by putting Devcon in your punch and doing it yourself. Just remember to use lots of lube to the unaffected parts of your die.

 

[Skeptic123]

Marchx, you didn't say how much powder you are using. The reason I ask is if it is creating a compressed load, you will get very erratic cbto numbers and they will change once they've been loaded too.

 

[marchx]

No compressed loads. I ordered an arbor press.

 

[nwmnbowhunter]

No compressed loads. I ordered an arbor press.

What seater die are you using currently that's giving you issues?

 

[marchx]

Forster Benchrest die.

 

[ckaberna]

Forster Benchrest die.

Try a Wilson arbor seater. I never used the Forster but once I went to Wilson I sold my others.

 

[nwmnbowhunter]

Forster Benchrest die.

Someone may flame me but I've had the worst luck with forster seating dies.
- flared seating stem
-chamber of die was not wide enough for bullet to pass through.
- great idea... Redding mastered it.

Redding competition works much better.

Wilson chamber dies are also pretty awesome.

 

[JFrank]

Believe it or not I had great luck seating consistent ammo with a Hornday seater.
I can't remember what happened to it. Lost in the shuffle maybe.

 

[marchx]

Someone may flame me but I've had the worst luck with forster seating dies.
- flared seating stem
-chamber of die was not wide enough for bullet to pass through.
- great idea... Redding mastered it.

Redding competition works much better.

Wilson chamber dies are also pretty awesome.

I ordered a Wilson seating die. I had bad lack with Forster FL dies. The first case was Forster FL die in my PRS caliber. Their die was defective and I could not size my brass at all. The dealer reported the problem and Forster said I broke the die. The dealer however replaced the defective die with a new one. I have also a Forster FL die in 6BR and I encounter the following problem: after firing my brass has 1.162 headspace. I set up the Forster die according the manufacturer's instructions: I screw down the die until it touches the jaws, then I pull the handle up and screw it down even more (1/4 of a turn). With this set up if I FL size my fired brass I get 1.164 headspace (!) and moreover I get a sticky bolt while chambering a round (after FL sizing!). If I use another die I get 1.160-1.161 of headspace as it should be. It's one of life's mysteries why Forster is still in business while fucking up their products so frequently.

 

[JFrank]

You haven't set your die correctly..

 

[marchx]

You haven't set your die correctly..

I doubt that. I screw the die ridiculously deep down and still can't get a proper shoulder bump.

 

[wkdickinson]

Neck tension is your culprit, especially when you have high neck tension. The seater in the die will create a ring around your bullets circumstance. The harder the neck tension the deeper the ring. Try to modify your neck tension to the lighter side. 0 to 15 psi should not impact your measurements. Try to find a supplier who will manufacture you a seating stem contoured to your specific bullet ogive. You can do this your self by putting Devcon in your punch and doing it yourself. Just remember to use lots of lube to the unaffected parts of your die.

When I decided to try 140 gr SMK I got that ring (not a compressed load and only 0.0015 neck tension). I order the correct stem from Whidden and the problem was gone.

 

[Coyotefurharvester]

Since changing to a decapping die and a mandrel for I.D. neck sizing, using any standard(I have Redding,RCBS) seater, consistent cbto +,- .001 is easy. I do anneal, not every firing. I am making hunting ammo, but it nice having small, small groups. Scope zeroing and wind calls are easier.

 

[Skeptic123]

I doubt that. I screw the die ridiculously deep down and still can't get a proper shoulder bump.

I had the same issue...as a final resort I used Emory paper and took off some of the die so that it could close more and it would bump the shoulder what I wanted...could also have sanded the shell holder but it worked well for other processes...eventually I just got a Whidden click adjust die and now I can bump as little or as much as I want (1.148) 6br

 

[marchx]

When I decided to try 140 gr SMK I got that ring (not a compressed load and only 0.0015 neck tension). I order the correct stem from Whidden and the problem was gone.

It's easier if you live in the US. Especially considering Whidden lead times right now. Not every die maker ships overseas. And even if, It takes months. I ordered a trigger from a US company early June and I still don't have it.

 

[marchx]

Since changing to a decapping die and a mandrel for I.D. neck sizing, using any standard(I have Redding,RCBS) seater, consistent cbto +,- .001 is easy.

this thread proves the opposite. There are certain variables in this equation which yo have to take into account. If you miss even one of them, you can have a problem.