300blk sizing issue (forster die problem?)

What your photo shows is a difference in the shoulders and that indicates a difference in HOW the sizers were set up rather than a difference in the dies themselves. Sizer dies are occasionally slightly off in some dimension but that's really rare. It's really not rare for the user to fail to set a sizer correctly tho; I wonder what method of die set up you follow? This is the second sizer in sequence you've tried?

The primed AAC factory brass may need to be fire formed. Do both fit into the chamber of the firearm?

My 300 Blk cases look similar to the photo except the difference in shoulder position is not noticeable to the naked eye with my cases.

The unfired factory case has a rounded shoulder much like the factory case in the photo, the fired and resized case's shoulder is more pronounced as in the photo.

Measuring with my Sinclair Bump Gauge, the factory shoulder position is 0.005" to 0.008" shorter than the fired/resized case. I do not have a 300 Blk insert for the Sinclair gauge, it is one for 30-06 family of cases, so with the slightly different shoulder shapes with my 300 Blk cases, the contact point in the gauge may add to the variance.

The actual measurement number is not relevant to any other similar measurement or design number due to the nature of the gauge. The gauge is meant to measure differences, or comparisons.

My current sizing die is a Redding but I also have a Hornady. I did not see any difference in sizing between the two but I never measured the shoulder position with the Hornady resized cases. My die is set to contact the shell holder.

As already mentioned, maybe the Forester die is not set correctly. Or, if the die was properly set-up, maybe the chamber is out of spec.

I do not have any un-resized fired cases at present to see if my chamber is long. I will have to check that next time I get the 300 Blackout.

Control how much you bump the shoulder when sizing. In other words, back out the Lee FL die. I had a 7mmTCU die set that would crush the shoulder if set that the FL die contacted the shell holder. Factory new dies made by T/C. When you form the case, the die must push the shoulder back more than a standard FL die. This is because of spring back of the brass. Instead of buying/needing 2 dies, a form die & FL die, a die is made that will do both. But turning the die down into the press to much will bump the shoulder to much. The Lee die was a special run made for Midwayusa, Lee does not stock the die, last time i looked.

SAAMI set a standard in 1-17-11 for the 300 AAC Blackout. When it was a wildcat, different measurement?? Just a guess. SAAMI Drawings- http://www.saami.org/PubResources/CC_Drawings/Rifle/300%20AAC%20Blackout.pdf Light loads may not expand the brass fully on firing. May take 3 firings or more to blow the shoulder forward???

If the empty brass on the left, sized in the Forster die will not chamber = bad die. This would be with no expander used to size, because the neck may have to be outside neck turned.

Looks like you need either a shorter die or thinner shell holder - either could correct the error ...

I would expect that Forster would make it right. Have you sent them a copy of that picture?

Nick

Walkalong said:

My .300 Blackout barrel and my Hornady dies arrived today.

Click to expand...

Have fun with the new gear.

243winxb said:

...because the neck may have to be outside neck turned.

Click to expand...

Not required with 300 Blackout cases made from 223 Remington.

Attached is a photo of some of my 300 Blackout cases at various stages.

From left to right

New R-P 300 Blackout case, unfired.
Reformed R-P 223 Remington case, fired and resized
Reformed R-P 223 Reminton case, fired, but not resized
R-P 300 Blackout case, fired, but not resized.

Resizing die is a Redding set to touch the shell holder.

The necks are nominally the same length unlike the OP's original photo

Something's bad wrong with the OP's brass. Looks like the Forester die is out-of-spec???

Walkalong said:

I put everything together today. I shot 5 rounds of RP 115 Gr FMJ and 5 rounds of PNW Arms 147 Gr FMJ. The recoil was similar but the recoil impulse with the 47 Gr stuff was much shorter. I fired both with no muzzle devise, since it came in after I went to the range. The RP Averaged 2285 FPS & the PNW Averaged 1981 FPS. The ES for the RP was 47 and the ES for the PNW was 27. It was 98 Degrees with 34% humidity. (Hot) It is over gassed for both these loads, but OK. It is an AR Stoner Ultra-Lite barrel. About like a pencil barrel .223. Maybe a bit heavier.

Click to expand...

Nice upper. What sights will you be using?

Foster problem as well

I just received the Forster bench rest set and on the first case, which had been previously sized in a Lee 300 AAC die, jammed. Contacting Forster as I tore the die up trying to get the case out. It seems as if the case mouth is jamming on the die where the shoulder is created. Once i got the expander out, I couldn't t even press a sized case into the die? Not sure if its me or the die. Never had this type of problem with Lee or RCBS dies.