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Thanks RD. I appreciate it. I looked at the weights/velocities of the BLK bullets and with a different twist than the barrel I'm using, I do really think it's possible to replicate it's subsonic performance. Don't know for sure though. Yet. I may ask HTR if I can come visit and try her out. Good thing is there are plenty of folks out there with suppressors that will work with this. I also believe its SBR performance will be quite efficient.
An interesting project.

As far as subsonic performance however I do not think this bullet will be able to match the Blackouts performance. The issue with subsonic usage is one of velocity. If all rounds are limited to velocities in the subsonic range then by default the larger bullets will almost always come out on top. Let's face it a .22 cal bullet traveling at 1000 fps will never equal a .308 or even larger slug traveling at 1000 fps. This is simple physics. About the only way a .277 subsonic bullet will gain a performance advantage over a 308 subsonic bullet is in the expansion envelope. But now we're talking bullet design which of course can work in both directions equally from the manufacturers. Right now the premier Blackout subsonic bullet(not taking into account the special made frangible one), the Sierra 220 gr, does not open at subsonic velocities.

Now however in the supersonic velocity ranges.....all bet's are off.
 
Discussion starter · #43 ·
An interesting project.

As far as subsonic performance however I do not think this bullet will be able to match the Blackouts performance. The issue with subsonic usage is one of velocity. If all rounds are limited to velocities in the subsonic range then by default the larger bullets will almost always come out on top. Let's face it a .22 cal bullet traveling at 1000 fps will never equal a .308 or even larger slug traveling at 1000 fps. This is simple physics. About the only way a .277 subsonic bullet will gain a performance advantage over a 308 subsonic bullet is in the expansion envelope. But now we're talking bullet design which of course can work in both directions equally from the manufacturers. Right now the premier Blackout subsonic bullet(not taking into account the special made frangible one), the Sierra 220 gr, does not open at subsonic velocities.

Now however in the supersonic velocity ranges.....all bet's are off.
That's a great point, thank you. I guess I should have rather said something like "I believe shooting this cartridge in the subsonic range will be as effective proportionately"... As in yes, you might be able to take a 150 or larger bullet and slow it down to run suppressed effectively. I am ego-in-check enough to say I am not experienced in sub's, as I have not had the pleasure of indulging because of where I live nor have I researched it thoroughly yet. Thanks for chiming in to put some perspective on it.
 
That's a great point, thank you. I guess I should have rather said something like "I believe shooting this cartridge in the subsonic range will be as effective proportionately"... As in yes, you might be able to take a 150 or larger bullet and slow it down to run suppressed effectively. I am ego-in-check enough to say I am not experienced in sub's, as I have not had the pleasure of indulging because of where I live nor have I researched it thoroughly yet. Thanks for chiming in to put some perspective on it.
I am in no way an expert either. But I wanted a Blackout so built one(an SBR) but am basically only going to shoot it suppressed subsonic. Only heavy bullets. So for me I was only interested in subsonic performance. Everyone was shooting the 220 gr subsonic. Then tests finally showed it was not fragmenting at all in ballistic gel tests. DUH! Sure it will do damage but........! That's why in some cases even a .45 acp SBR might be just as bad or badder at short ranges. If you're speed limited due to the subsonic category a larger caliber is better.

The other side of this equation is when using the larger(longer) bullets a completely different twist rate is often required. That in itself might limit users to one or the other barrel. For instance to shoot the Blackout optimized for subsonic heavy bullets requires a different twist rate vs the supersonic loads. And with the 6.8 shooting subsonic suppressed loads is great but with much faster twist rates than the normal 1:11 we see in most barrels now. So with your newly being developed round a subsonic twist rate might be 1:8 or 1:9 but supersonic might be more in the 1:11 range. So unless a good twist rate can be determined that will work with both subs and supers people who choose this round will have to either choose a barrel twist rate that works best with the one they will be shooting.

Of course this only applies to shooting subsonic ammo. One can always shoot suppressed in the supersonic speed range and still get some suppression.
 
Discussion starter · #47 ·
Less Filling !!! Shoots Straight !!!
Clever! I like it...

Been thinking about rebarreling my mini 14. Might wait and see where this goes.
Soon!

I am in no way an expert either. But I wanted a Blackout so built one(an SBR) but am basically only going to shoot it suppressed subsonic. Only heavy bullets. So for me I was only interested in subsonic performance. Everyone was shooting the 220 gr subsonic. Then tests finally showed it was not fragmenting at all in ballistic gel tests. DUH! Sure it will do damage but........! That's why in some cases even a .45 acp SBR might be just as bad or badder at short ranges. If you're speed limited due to the subsonic category a larger caliber is better.

The other side of this equation is when using the larger(longer) bullets a completely different twist rate is often required. That in itself might limit users to one or the other barrel. For instance to shoot the Blackout optimized for subsonic heavy bullets requires a different twist rate vs the supersonic loads. And with the 6.8 shooting subsonic suppressed loads is great but with much faster twist rates than the normal 1:11 we see in most barrels now. So with your newly being developed round a subsonic twist rate might be 1:8 or 1:9 but supersonic might be more in the 1:11 range. So unless a good twist rate can be determined that will work with both subs and supers people who choose this round will have to either choose a barrel twist rate that works best with the one they will be shooting.

Of course this only applies to shooting subsonic ammo. One can always shoot suppressed in the supersonic speed range and still get some suppression.
I think one would probably have to go with the 1:7 type barrels Bison offers and such for this... you're probably right, for sub's.
 
Discussion starter · #48 · (Edited)
After getting some QuickLoad numbers, and trying to figure out how to post a sheet here, I used Clint's spreadsheet (Thanks Clint) to put this up. Projected velocity with 95TTSX is 2550 fps, but pressures may make me kick it back to 2500 or 2450. So, I included 2600, 2550 and 2500. Good numbers. Either way she's good out to 300. The 100AB should be able to get to 2500 fps, but once again pressure might make me back it off to 2450 or 2400. I'm putting together 82 Raptor, 90TNT, 90HP and 90GD numbers (if they would ever offer it as a component), but it's interesting because I'm finding with their low BC's they lose energy faster than I expected... so although it may seem using the 80-90 grain bullets would make more sense, the 95-100 grain bullets seem to perform better (on paper). Time will tell. Going to run the 110 SPH's soon, too. These numbers are all theoretical for now, so who knows until I load them, test them and put them downrange. I'll start editing/adding to OP instead of adding replies that keep bumping this up as well.

 
6.8x40
1.555" -.030" case length
90TNT loaded to 2.17" COAL


Cartridge Comparison
5.56x45 - 6.8x40 - 7.62x35 - 6.8x43
 
What are you using for quickload assumptions?

I show a raw case capacity of ~27.5 gr H2O.

After getting some QuickLoad numbers, and trying to figure out how to post a sheet here, I used Clint's spreadsheet (Thanks Clint) to put this up. Projected velocity with 95TTSX is 2550 fps, but pressures may make me kick it back to 2500 or 2450. So, I included 2600, 2550 and 2500. Good numbers. Either way she's good out to 300. The 100AB should be able to get to 2500 fps, but once again pressure might make me back it off to 2450 or 2400. I'm putting together 82 Raptor, 90TNT, 90HP and 90GD numbers (if they would ever offer it as a component), but it's interesting because I'm finding with their low BC's they lose energy faster than I expected... so although it may seem using the 80-90 grain bullets would make more sense, the 95-100 grain bullets seem to perform better (on paper). Time will tell. Going to run the 110 SPH's soon, too. These numbers are all theoretical for now, so who knows until I load them, test them and put them downrange. I'll start editing/adding to OP instead of adding replies that keep bumping this up as well.
 
I am in no way an expert either. But I wanted a Blackout so built one(an SBR) but am basically only going to shoot it suppressed subsonic. Only heavy bullets. So for me I was only interested in subsonic performance. Everyone was shooting the 220 gr subsonic. Then tests finally showed it was not fragmenting at all in ballistic gel tests. DUH! Sure it will do damage but........! That's why in some cases even a .45 acp SBR might be just as bad or badder at short ranges. If you're speed limited due to the subsonic category a larger caliber is better.

The other side of this equation is when using the larger(longer) bullets a completely different twist rate is often required. That in itself might limit users to one or the other barrel. For instance to shoot the Blackout optimized for subsonic heavy bullets requires a different twist rate vs the supersonic loads. And with the 6.8 shooting subsonic suppressed loads is great but with much faster twist rates than the normal 1:11 we see in most barrels now. So with your newly being developed round a subsonic twist rate might be 1:8 or 1:9 but supersonic might be more in the 1:11 range. So unless a good twist rate can be determined that will work with both subs and supers people who choose this round will have to either choose a barrel twist rate that works best with the one they will be shooting.

Of course this only applies to shooting subsonic ammo. One can always shoot suppressed in the supersonic speed range and still get some suppression.
Seems like I've been away too long and missed out on recent developments. LOL, boys and their toys and yet another round. Too danged funny you all are.

I selected this post to reply because of the bolded comment above. I did some fairly extensive testing with the 300 BLK and yes, I told people the 220g SMK just was not meant to do what they were asking. Some I shot through wet phone books looked almost good enough to load up and shoot again. I have pics somewhere. There are MUCH better choices for the 300 BLK, but trying to talk sense to some of those guys is like talking to wet paint. Nosler 210g Accubond was fantastic, expansion wise. I am certain I got them as over runs/seconds from Shooter's Pro Shop. Odd thing was/is, I don't see load data for them anywhere as the bullet itself isn't listed in any source I have. It is on Nosler's site Here. I just used 220g SMK subsonic loads I developed and it was fantastic.

OK, so OP, HS . . . yet another exciting development. I certainly thought about it. Great job on making it happen I may be able to test some subsonic ideas if you'd like some help. Very cool idea!
 
Discussion starter · #55 · (Edited)
What are you using for quickload assumptions?

I show a raw case capacity of ~27.5 gr H2O.
I got approx 28 grains H20. QuickLoad gave 2600 fps with 90TNT using Win296. H110, Lil' Gun all showed different numbers. I took bullet length and weight into account and tried to estimate what the heavier/longer bullets might produce.

I will in no way overstate the cartridge if errors are found. I'm hoping for what I'm estimating, but I'm not selling anyone anything.

Barrel gets here soon, but not soon enough. Same with dies. Powder, stocked up there with 7 or 8 different varieties to test them all out. I don't have the ability to pressure test yet, so will have to work off of pressure signs and behavior at the start.

If you and/or anyone else at any time see things differently, I want to know. This cartridge does not have "magic bullets that fart rainbows" and all the other jokes out there. Unfortunately, I'm still working in estimates because I haven't been able to run them through a Chrony yet. I value your input here!

If I can get a 95TTSX to even go 2400 out of a 16" barrel, I'll be very, very happy. Right now I see this as a CQB/Mid-Range cartridge, 0-300 yards, and don't expect it to take down Elk at 800 like some folks would proclaim. I won't do that; I'm just trying to figure it all out, make it work and produce something I'm happy with. If you have any advice, let it rip! My ego is way in check here.

ETA: I see my errors after reading back... Using words like "projected" and "should" are not right, I should have used "hoping for" and "frickin fingers crossed" LOL.
 
Discussion starter · #56 ·
Seems like I've been away too long and missed out on recent developments. LOL, boys and their toys and yet another round. Too danged funny you all are.

I selected this post to reply because of the bolded comment above. I did some fairly extensive testing with the 300 BLK and yes, I told people the 220g SMK just was not meant to do what they were asking. Some I shot through wet phone books looked almost good enough to load up and shoot again. I have pics somewhere. There are MUCH better choices for the 300 BLK, but trying to talk sense to some of those guys is like talking to wet paint. Nosler 210g Accubond was fantastic, expansion wise. I am certain I got them as over runs/seconds from Shooter's Pro Shop. Odd thing was/is, I don't see load data for them anywhere as the bullet itself isn't listed in any source I have. It is on Nosler's site Here. I just used 220g SMK subsonic loads I developed and it was fantastic.

OK, so OP, HS . . . yet another exciting development. I certainly thought about it. Great job on making it happen I may be able to test some subsonic ideas if you'd like some help. Very cool idea!
I am very interested... Even got a quote from the barrel maker today for a 10", 1:8 twist pistol gas barrel. Gonna wait until winter or after for that one, wanna try out the basics first. Like I said in last post, any and all suggestions and advice welcome here. My plan was to run some 150's through it... But I need to get the 16" 1:11 guy checked out first.
 
Honestly for subsonic use the 338 Spectre should be what you guys are looking for if you already have 6.8's...
 
Honestly for subsonic use the 338 Spectre should be what you guys are looking for if you already have 6.8's...
Have to agree with Adam. 300 grain bullet suppressed with a 9mm can. If you want a heavier sub it's hard to beat the 500 grain out of a 458 SOCOM.
 
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