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Author Topic: 311-198 sp in 300 blackout  (Read 9103 times)

Odfairfaxsub

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311-198 sp in 300 blackout
« on: June 28, 2019, 07:52:55 PM »
Well I bought this mold a long time ago. It’s plain based and the idea was to use it as a blackout replacement for 308 Hornady 208 gr bullet

Loaded these awhile back for my bolt action that did close to half inch more like 3/4 inch at 50 yards off a book bag. I achieved those results using 9.2 gr h110 quite happy.

Sold the mold when I sold the gun figuring I’m out of the blackout game. Still had 20 of these shells loaded up gathering dust.

Well I built a 10.5 inch psa 300 blackout the other day and instantly regretted the fact that that mold might have been the potential one (you know that is right?). After putting the gun together I got sick and couldn’t spend anytime in the loading room making some sort of load development rounds for my new gun. Today Saturday I wanted to try it out and had only 20 rounds of this 9.2 gr h110 and this 311-198 sp loaded..... thinking to myself “ that’s pretty weak sauce for a new/non broken in gun....what choice do I have though”

20 rounds no fail to feeds shot one after another after another through a 2moa red dot trying just hard enough to be able to pay attention to my target and just enough to study this gun operating (basically my mind in two different places) and long behold a non broken in gun w a untested in developed load in this new gun I printed all 20 shots at 50 yards into a 2 inch cluster without giving the poor rifle any heat break.


I was so estatic when I saw the 30 cal sale and a 4 cavity plain based offering I scooped up on it. I’d suggest the same to you all if your a blackout dude

sgt.mike

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Re: 311-198 sp in 300 blackout
« Reply #1 on: August 05, 2020, 07:53:33 PM »
Have you reshot this Bullet in the new PSA?

 If so how was the results now considering that it should be broken in now
« Last Edit: August 05, 2020, 07:55:09 PM by sgt.mike »

Mike B.

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Re: 311-198 sp in 300 blackout
« Reply #2 on: August 06, 2020, 09:55:15 AM »
In order to do any meaningful prediction duplication on this new combination... on a 300 AAC Blackout with a 311-199 SP PB cast bullet one will need what the original COAL was & the final sized diameter. (incidentally all of PBs in that lot are currently sold out.)

https://noebulletmolds.com/site/product-category/308-311/311-199-sp-k5

As a very rough starting guesstimate... I used a 2.210 COAL which translates to a .423 seating depth with a .310 diameter for starters. The cast bullet OAL I used was 1.266.  In a 10.5 inch barrel that translates into about 13039 PSI & 962 FPS. if you used a different COAL like 2.260 (SAMMI Max) that will make a good bit of difference and a weaker max pressure and velocity than noted above.

As a separate side note ... The Forum does not send out a second notification to a reply if one additionally marks up an earlier one.
« Last Edit: August 06, 2020, 09:59:59 AM by Mike B. »

Mike B.

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Re: 311-198 sp in 300 blackout
« Reply #3 on: August 06, 2020, 12:31:30 PM »
A longer barrel length will increase the burn time and the velocity.

It will not affect the max pressure as that max pressure time occurred in about the first inch of the barrel.

Incidentally, if I remember correctly; a cast bullet needs about 1160 psi to get it going (if It is not jammed up against the rifling), while a jacketed bullet of the same weight needs about 3626 PSI.

Don’t quote me… if you want the exact calculation numbers I can reference that start pressure data and post it.

To help illustrate my point on the criticality of the seating depth let us take the SAAMI Min of 1.780 for the 300 AAC Blackout

Using the same 9.2 grains of H110 powder, & a seating depth of .839 which (also happens to translate to a 100% fill) in that cartridge - bullet combination.

The prediction now becomes ~36000 psi and 1200 FPS.

The seating depth difference between .839 (SAAMI MIN) & .423 (SAAMI MAX) = ~ .416 difference in seating depth. 

The max pressure difference goes from ~ 13000 PSI at max COAL to ~ 36000 PSI at min COAL.

(Both calculations I believe are valid within SAAMI specifications for the parameters utilized in the separate calculations).

I hope that this Intel helps.

Take Care & Stay Safe

« Last Edit: August 06, 2020, 12:37:25 PM by Mike B. »

rj5208

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Re: 311-198 sp in 300 blackout
« Reply #4 on: March 27, 2021, 12:48:13 PM »
A longer barrel length will increase the burn time and the velocity.

It will not affect the max pressure as that max pressure time occurred in about the first inch of the barrel.

Incidentally, if I remember correctly; a cast bullet needs about 1160 psi to get it going (if It is not jammed up against the rifling), while a jacketed bullet of the same weight needs about 3626 PSI.


Don’t quote me… if you want the exact calculation numbers I can reference that start pressure data and post it.

===================

Mike,

FWITW
My notes show that 1422 X the Brinnel Hardness Number (BHN) is the minimum Chamber Pressure Required to Obturate a cast bullet..

Thanks for pointing out the pressure differences based on COAL

Bob

« Last Edit: March 27, 2021, 12:52:21 PM by rj5208 »

 



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