300 blackout recommendations

The question to you is how low (Or light in this case do you want to go?)
Also is this new pistol build based on an AR frame design, or as a single shot Thompson Contender version based design…?

The reason that I ask is that the AR based pistol design needs a bit more oomph in the loads to properly cycle the action. (Unless you don’t mind cycling the action by hand after each round…

I have been playing around with different 300 AAC Blackout loads for around a year now.
That’s with using 300 AAC brass brass, & making up my own brass from once fired 223 and 5.56 cartridge cases… which once tended to only litter the range bays…

With NOE Bullet moulds only… as a reference base line… that basically includes the 311-152, the 311-179, the 311-199, the 311-206, the 311-214, & the 311-222 RN cast bullets…

I have helped an individual or two with some subsonic heavy weight loads that they seemed happy with…

I’ll let them chime in on that if they so choose… down the line…

The twist on the barrel that you choose for the barrel on your 300 Blackout pistol build on an AR framework will determine how heavy you can go…
Whether that particular as of yet unknown short barrel length, and TBD twist will do optimal justice to the as of yet unchosen lighter cast bullet weights will remain to be seen.

A 1×7 Twist should theoretically stabilize the heaviest 30 caliber cast bullet weights. The issue on that end of the spectrum will be adhering to the maximum COAL for the cartridge and how deeply one must seat the cast bullets once one gets to a certain cast bullet weight to function through an AR action…
Please see the attached barrel twist vs bullet weight recommended guidelines for the 30 caliber barrels – cast bullets.
The remaining question that cannot be answered will be whether that particular short 30 caliber pistol barrel of as yet undetermined length… will like being fed a diet of the lighter cast bullets with that particular barrel twist. Only putting the components together and running a beta accuracy test with the lighter cast bullet weights will tell that tale. 
As you did not include any of the other projected details the proposed pistol barrel length, nor the barrel manufacturer, or the actual chamber reamer version to be used, (there are several versions of chamber and freebore length) on this new SAAMI cartridge. Unfortunately no more can be predicted at this early junction in time at this early point in the game… with the very minimal data provided…
Take Care & Stay Safe…

So what is the lighter cast bullet weight that you are thinking of for plinking purposes?
Also which 300 Blackout, AAC Blackout, or 300 Whisper chambering alternatives are you considering?
The Load Data website has a quite extensive set of cast load combinations listed on their website… for their members use…
It is too large an attachment to list here on the forum, or print out as a forum attachment & there is no intel on the powder types that you tend to favor for loading said as of yet unknown lighter cast bullet weights…
Finally if you live in an area that does allow suppressors, the choice of powders may be somewhat limited unless you consider purchasing a more expensive suppressor that can be disassembled for regular cleaning.
Otherwise you will end up filling up the sealed suppressor body & baffles with unburnt powder & gunk down the line…
I understand that it apparently takes at least a year to get permission to purchase a single suppressor that you must pay for in advance before applying for federal permission to own a suppressor.
It is also my understanding that a replacement suppressor if somehow damaged by subsequent round and or through a dirty suppressor… is basically the start of that permission process all over again…
That will mean using a set of bullet and powder load combinations that are basically 100% burning in that short 10.5 in barrel length… for both the heavy end of the load spectrum, & the lighter end of the load spectrum…
I’m not trying to sound like I am trying to talk you out of any of this.
I’m just trying to make you aware of the potential pitfalls… so that you go into the pistol build with your eyes open… to avoid the potential pitfalls.

A 300 AAC Blackout with a 1×7 twist is currently predicted that it will best stabilize the heavy end of that bullet spectrum… Circa 220 + grains in weight.

The corollary to that is that it also has been basically proven that one can over stabilize a much lighter bullet and thus lose accuracy with a super fast twist.

Therefore no one barrel twist will be optimal for all cast bullet weights especially in the 30 caliber diameter weight division offerings. from on average 90 to 220 gr ++.

The question that can only really be answered by your beta testing load data which will show what your barrel will like that answer will be how light can you actually go in cast bullet weight before the accuracy tends to go to heck in a hand basket.

Personally I tend to think that you can not necessarily go as light as a 130 gr cast bullet with that super fast twist, & get any kind of real accuracy…

But then to me real accuracy is putting 10 shots or so into a 1″ or less grouping… For this short range cartridge that is most probably 50 yards…

A super heavy cast bullet tends to take up a bunch of the cartridge cases internal capacity when seated to feed and function reliably through an AR action & magazine.

If you to look back into the forum discussions on the 300 Blackout you may possibly find my superimposed drawing of a super heavy cast bullet shown in a SAAMI spec cartridge dimensioned cartridge case to the max COAL to function in an AR based firearm.

I tend to believe at that time the cast bullet weight was in the neighborhood of 242 grains…

It memory serves me correctly to make COAL the bullet took up approximately 50% of the internal case capacity of the cartridge case…  thus not much room for any powder let alone a load that would burn clean (100%) in a very short barrel configuration.

To me a 130 grain cast bullet means at least two different uppers or firearms with different twist barrels that best accommodate the cast bullets weights chosen or nearest and dearest to ones heart… to be shot that day, & to change out as the cast bullet weight demands.

So may one ask : What is your individual particular definition of sufficient accuracy?
10 shots into a pie tin?
10 shots into a trash can lid?
Or 10 shots that can be covered with a quarter that just happens to be a few thousandths less than 1″ in diameter?

What is Heck in a Hand Basket accuracy to the individual shooter may be just fine for the next shooter in line…

At this early point in the game only the finished product can tell the truth…

Basically
You will also most probably also be less than ~1125 fps which is basically subsonic.

May one assume that you are talking about the TL310-225-RN & the HTC310-225-RN?
Hopefully you bought the PB versions as the GC version is only really needed if one is going to attempt shoot the cast bullet supersonic above 1600 FPS…

I have once again attached the drawing that I made up right after the fourth of July this year illustrating what I noted earlier about the remaining powder capacity combination of that particular bullet shape & the 300 Blackout cartridge case. Granted that data was originally based on a 16 inch barrel not a 10.5 inch one.
Take Care & Stay Safe…

I was going to recommend at this point that you go to the NOE forum webpages labeled Reading Our (NOE’s) Dimensional Diagrams pages, as those NOE Website pages now apparently have some preliminary CastData on them… in addition to the various NOE dimensional drawings for NOE product. Along with the cartridge types that the bullets are apparently compatible with dimensional wise…

However those two particular tacos do not seem to be listed as of yet on those pages, so you will need to post a request to NOE to include those two bullets dimensional drawings on the NOE forum pages for the possibility of getting some bit of CastData apparently generated by NOE. Or better yet phone and ask… for those details to be included on the forum pages…

If you want some LoadData you will have to PM me with your measured cast bullet intel including your actual cast bullet weight details depending on the alloy actually used to cast your two tacos of choice… and the measured diameter that you sized to that you plan to load into cartridge cases. Then one can feed that data into QuickLoad to generate an accurate prediction.

I do not any longer post in public… data generated from QuickLoad… as those files… even in a .jpg format are apparently still too large for the NOE forum to accept, & there are a number of specific variables that need to be strictly adhered to… if one is to also properly predict the ballistics down range with QuickTarget, & the load pressures accurately, and not cause problems due to non adherence to the QuickLoad details down the line.  Unfortunately even the NOE forum PM’s do not apparently allow any attachments… at all.
                I sincerely hope that you understand…                Sorry about the legal verbiage…

I also do not want to pay for an off website page for posting purposes as some have suggested on the forum … As that costs funds that could be better spent on Moulds & Sizing product, especially when the Internet ether for sending PM’s and emails… at this point in the time game is still free as long as the file size is less than 30 MBs per email. To make the Internet email WebServers’ happy

Take Care, & Stay Safe…