Good bullet weight to use in 300blk subsonic and a .308 semi auto precision setup

[Len5E1]

Hello everyone.

I have been reloading the easy stuff for a while now (pistol calibers) but I am looking into getting into loading for my 8.5” supressed 300blk as well as my precision ar10 running a JP setup with 20” 1:11 twist barrel.

I have not loaded for either of these rifles yet but from what I can tell a lot of 300blk sub reloaders like to use 200-220 grain projectiles. I haven’t shot anything over 178 grain matchkings in my ar10 so I’m not sure what a good bullet would be that can double as a subsonic round in the 300 as well as a nice precision round for the ar10. Anyone know what the heaviest grain bullet that will work well in my ar10 setup without giving up performance and accuracy?

Thanks in advance! I realize most people might just say buy two different bullets but in these times it’s harder to find bullets and I think what I’m looking to do should be fairly reasonable to attempt.

 

[Snuby642]

Ah-no.

 

[Len5E1]

Ah-no.

I did meantion that I am new to reloading these calibers so please disregards any ignorance I may have here. I am posting looking for advice and suggestions and your reply was not very helpful...

 

[Snuby642]

I was just being a smart ass, my bad.

My favorite 300 blk load is round nose flat base 220g hornadys ran over 12.1 grains of cfeblk. That runs 1015fps on cold weather and does not go sonic on 95 degree days.
It has been more accurate than anything I have tried.

My 1/7 twist sbr and 16inch bolt gun like them.

That will not stabilize in a 1/10 twist 308 and not suitable for runnng fast as I understand.

Long pointy boat tail secant ogive type bullets dont like going slow and dont group well for me in a sub gun.

My shity original answer is still technically correct but this is probably more helpful.

 

[Len5E1]

Thanks snuby that was actually very helpful. I didn’t even think about the fact the subs wouldn’t like that pointy boat tail projectile so even if I found a weight that was good for both I probably wouldnt find a good profile. I appreciate your reply.

 

[Snuby642]

That load is published somewhere, not near my notes.
It was given to me by @spife7980 one of my favorite mentors.

It has beaten every purchased round and all I cooked up. It looks like an old buffalo gun round and I think I was paying about 36 cents a piece for them. If I get to my reloading room later today I,ll get coal and a book listing to confirm a (published) load.

I really dont think you can get a bullet to do two vastly different tasks.

Maybe someone will school us on that.

 

[jet_lagged]

As already mentioned, optimum in one is not going to be optimum in another.

But then what kind of range and accuracy do you really need out of the 8.5" Blackout?

For semi-auto .308, I would not really go heavier than 175/178 SMK/Nosler CC. They should also work in the Blackout, but naturally will have less energy than the 220 grain round nose. Load up a few and make sure they are stable and go from there.

 

[alamo5000]

In an AR it's a lot more complicated to try and get subsonic performance out of anything under 190 grains. Given we are talking about jacketed bullets here. There are a whole host of issues when you try to go lighter than 190. Even then 190's are harder to develop a load for because they are a bit more picky when it comes to using the right powder. You will basically cut back to the point that you get powder shift problems or cycling issues. Since you said you are kind of a newer reloader let me know if you understand what powder shift is.

You CAN use a powder like Reloader 7 to get subsonic loads for all types of light bullets but the characteristics of the powder make it really loud. Basically that powder and how it creates pressure is relatively slow, and with almost any slow powder, the bolt will open while everything is still under pressure and the port pop will be LOUD. It won't be hearing safe at the ear at all. I've tried several slow powders and it had the same result every time.

Pretty much unless you are shooting a bolt action rifle your bullets all need to be 190 grains or more to get reliable subsonic ammo. If you can figure out how to make quiet subsonic 180 grain or under ammo you will become famous because not many people have figured out how to do that (and it's not from a lack of trying).

Basically put the idea of running the same bullet in each rifle to bed. Odds are better than average that it won't happen that way.

 

[quietmike]

I've used a 90gr XTP bullet over trail boss.
Ridiculously quiet even w/o a can, and the bullets will still expand at sub velocities.

 

[Snuby642]

I've used a 90gr XTP bullet over trail boss.
Ridiculously quiet even w/o a can, and the bullets will still expand at sub velocities.

Interesting.

Could you provide more information please .

 

[Len5E1]

Thanks for the replies everyone. I didn't do extensive research before hand but the reason I even had the idea is because I've seen some manufacturers advertise 300blk bullets as subsonic even down to the 170 grain and below. Berry's has 180s they claim are for subsonic as well but since I don't see ANYONE loading subs that light I assume it's bs. Now that you guys have confirmed this I can start looking for the proper weights I need for each gun. Thanks

 

[quietmike]

Interesting.

Could you provide more information please .

I used 4.8 grains of Trailboss with a col of 1.85 with a slight crimp from a Lee crimp die*.
They aren't super accurate, but are minute of groundhog to reasonable distances.
Most rifles require it to be single loaded and it certainly won't cycle a semi, but for stupid quiet they're really good.

*Lawyeresque disclaimer: Never rely on internet loading data.

 

[Burning sensation]

I have an old custom Remington 700 in 300 Blackout that never handled the heavies very well (2 moa best), but is very accurate using a 175 smk over Lil gun. I don’t remember the charge weight off hand, but I can look later if interested, though I doubt it would cycle an AR. I don’t think anything that light subsonic will.

 

[Grant77]

Thanks for the replies everyone. I didn't do extensive research before hand but the reason I even had the idea is because I've seen some manufacturers advertise 300blk bullets as subsonic even down to the 170 grain and below. Berry's has 180s they claim are for subsonic as well but since I don't see ANYONE loading subs that light I assume it's bs. Now that you guys have confirmed this I can start looking for the proper weights I need for each gun. Thanks

I’ve used Berry’s 200g with 11g Accurate 1680 to great effect; super accurate at 100yds (that’s my current range limit so can’t speak to the precipitous drop after that) and velocity range of 1090-1110 avg in my 50rd sample group.
I’ve also used a number of formulations and had consistent sub success with 190g Sub-X and 208g ELD with CFEBLK, Lil’ Gun & A 1680...so tons of options out there for 300blk

 

[Snuby642]

@Grant77
What kind of accuracy did you get with the Hornady subx?

Im using thier 220g fbrn interlock an good accuracy but no expansion.

 

[Grant77]

I’ve found accuracy to be quite good and with surprisingly good expansion; velocity avg 1105 with CFEBLK, don’t have my book handy to pull grain weight but will look it up when I get home and update.

 

[Grant77]

I’ve found accuracy to be quite good and with surprisingly good expansion; velocity avg 1105 with CFEBLK, don’t have my book handy to pull grain weight but will look it up when I get home and update.

Sorry for the delayed response.
The subsonic 300BLK load I've had success with using Sub-X bullets is 12g CFEBLK, 190g Hornady Sub-X, COL 2.038, seated so the bullet is sitting gently on the powder without compressing it (approximately). To determine my target seating depth I measured the powder height of 20 filled cases, took the average height of the powder level (which only varied by .002 and could easily have been user error), loaded 10 rounds each with COL of 2.036 & 2.038, benchrest fired the two groups for accuracy and velocity @100yds...found COL 2.038 to be both slightly more accurate as well as slightly more consistently stable velocity as well; when I say "slightly" I mean significantly less than a single standard deviation, so while it's pretty much a meaningless difference between the two and I definitely tend to nerd out over the data (clearly), I just went with my gut and followed where the data seemed to be heading. I'm sure that if I went to the trouble of doing a larger sample size comparison I'd have hard data...but wtf, it's not like we're using 300BLK for 1,000m precision shots where the difference could actually have an impact.

 

[Grant77]

Sorry for the delayed response.
The subsonic 300BLK load I've had success with using Sub-X bullets is 12g CFEBLK, 190g Hornady Sub-X, COL 2.038, seated so the bullet is sitting gently on the powder without compressing it (approximately). To determine my target seating depth I measured the powder height of 20 filled cases, took the average height of the powder level (which only varied by .002 and could easily have been user error), loaded 10 rounds each with COL of 2.036 & 2.038, benchrest fired the two groups for accuracy and velocity @100yds...found COL 2.038 to be both slightly more accurate as well as slightly more consistently stable velocity as well; when I say "slightly" I mean significantly less than a single standard deviation, so while it's pretty much a meaningless difference between the two and I definitely tend to nerd out over the data (clearly), I just went with my gut and followed where the data seemed to be heading. I'm sure that if I went to the trouble of doing a larger sample size comparison I'd have hard data...but wtf, it's not like we're using 300BLK for 1,000m precision shots where the difference could actually have an impact.

referencing my above post: I also hope it goes without saying, but I'd welcome thoughts from anyone out on here as to a alternative/better ways of approaching load development etc. I have gone deep on a couple of very specific things, but as a whole I've only been reloading for a couple years...so always more to learn and better ways to do things. thanks guys.

 

[Flightmurse]

It was already been covered that you will have trouble getting the same bullet to work with both. A 208 grain would be your best bet.

The most important thing with reloading subsonic .300 is getting a chronograph. Always work from the top down and get the velocity you want. I prefer to shoot at steel for this, but make sure you have a hole n the target for each shot. It’s easy to get a bullet stuck.

 

[Snuby642]

Well 3 years later I'm back trying to get the sub-x 190 flying. Lol

I went for about 2 years and could not get any sub-x 190's. They disappeared from retailers and only resellers had them at prices I was not going to support thier cocaine and whore habit.

Prices back to reality and vendors stocked. And hopefully the resellers I see tring to unload thier stash choke on them. That is the ones not dead of drugs and disease allready.

The family finds ourselves this fall in need of suppressed expanding rounds on a new location.

Hodgdon shows 190 sub-x over 12.3g of cfeblk at 2.050 coal.

This sounds right to me since my old load was 12.1 with 220g rnfb at 2.100 coal. I want it setting down lightly on top of the powder I think as a friend said my old load worked better slightly shorter.

Our sub guns are all 1/7 twist so do not expect problems.

Going to try my diminutive grandson on suppressed sbr since the stock collapsed all the way is about what fits.

 

[wvfarrier]

I use the Lehigh 176 grain Controlled Chaos in both 300blk and 308 Win. Ive killed several deer with it

 

[wvfarrier]