Accurate, subsonic loading for 300 AAC Blackout

[New Camper]

I've been trying a multitude of different angles to get my Remington 700 (1 in 7" rifling twist) to print accurate groups. Accuracy, or rather lack of, to date is at best around 1.5-2" at 100yards. I only care to bother with 220gr or heavier bullets and I have a few hundred Hornady 225 BTHP in the larder. I've been using H110 (and W296), IMR 4227 and H4198. I have the tools, and have determined free-bore of my rifle and have tried different seating depths in relation to the lands. About the only thing thus far that has shown a noticeable accuracy improvement was neck crimping. I've never seen this amount of difficulty in making an accurate load for a rifle: When I can make rounds for other calibers with extreme velocity spreads of only 10fps (happened to be a 30-06sprg) it makes me wonder if the 300blackout is never destined to be accurate?

Anyone else experience the same? Any suggestions using heavy bullets only? I've theorized that if I can't achieve an acceptable amount of accuracy (<1moa to be useful out to 300 yards on various small animals and targets) it's not a useful round to me and I'd be better suited making my own 338 wildcat on 300savage brass for subsonic loads using slower powders.

I've also theorized that slower powders would be better (if they could fit in the small case), as these would develop consistent velocity over the length of the 16.5" barrel where the powders listed (some, not all) in loading manuals are more appropriate with shorter barrels in 0.308" bores. Such powders were developed for magnum pistol, and small bore rifle.

 

[c1a1]

Try 'Lil Gun. I find it is the most accurate powder in my Ruger bolt gun. Have loaded bullets from 120gr, to 220gr., never crimped. Have you tried a smaller diameter resizing ball, instead of crimpimg? All brass used is reformed LC-12. Only problem is that the wife tried it, said "I like it", another rifle gone.

 

[tvanember]

A friend and I have come to call this round the 300 Black Cloud. I have gone through everything you have with I'm assuming is the same rifle? Remington 700 with AAC 300blk barrel? I've tried H110, Unique, and 4227 for subs, and supers. One day it would shoot sub MOA, then the next day it would open up to 2 MOA. Even tried using pistol primers to see if that would help. It's the most ignorant pain in the but rifle I've ever tried to develop a load for.lol. My only reasoning for this is the quality of the barrel. I recently had a 223AI built with a Shillen match barrel on a mossberg mvp, and load development for it was a dream. I've mentally given up on the 300blk rem 700. When funds are available, I'm going to re barrel it in 223AI for my wife to shoot

 

[Suputin]

1.5 to 2 MOA is actually quite good for subsonics.

There is no real good reason to use heavy bullets. They don't add anything extra downrange and they drop faster and produce more recoil.

30 cal subsonic is really not good for small game. The bullet has no chance of expanding and will simply zip through the target like a high speed knitting needle.

I haven't used any crimp but that may be a good idea to try.

 

[New Camper]

Thanks for the suggestions and sharing of experiences.

c1a1 - I'll try finding some Lil'gun. I used a Redding neck sizing die. I might give the Lee collet neck die a go.

tvanember - Yes, it's the same gun you had the same difficulty with. I hope the barrel is fine, but it has crossed my mind that this could be the problem. I've never found a Remington 700 that has been manufactured to the tightest tolerances... sometimes the result of mass production is what I see right now. I've considered a match barrel for the rifle, but if it's a cartridge based limitation (as Suputin appears to be suggesting), then it would be cash poured down the drain. Move on and let those who enjoy this sort of thing have the fun with it.

Suputin - I like the heavy bullets for a few reasons: I have them; being subsonic means less noise; a hole in the head or chest of a groundhog or coyote, particularly a 308 match bullet will stop them - I just need the tools to deliver such shots. I get what you say though: The B.0., theoretically could be useful for whitetail under 200yards. I relish the antiquated challenge of accurately "lobbing" bullets long distance. I have tried some factory supersonic loads in the rifle... with accuracy as bad to worse than my subsonic handloads.

I'll keep on trying different things and hopefully find that factor which will simply click. On the list is cutting down and forming some Federal 223rem brass in hopes that a thicker neck will improve things. I might experiment with Reloader 10x or another slower powder... maybe even the other way just to turn that rock over... hs-7.

 

[porpoise]

I would not go too slow on powder even with heavy bullets you will be able to fill the case pretty much with 4198 or rl 7. slower powder will just lower the pressure to less optimum level. I use n120 . 15 grains behind 168 bthp. works nice and the same charge behind missouri 245gr 300 blackout cast coated bullet also works fine and in my 700 prints about 2 inches directly below the 168 at 100 metres believe it or not. Note that for the heavy subs load data goes back to include light charges in the faster powder ie. n110 where it had dropped that powder in supers 150 gr. and up showing they think it isa good idea to maintain pressure even with the sub if you want it to shoot well. The reason i like these bullets is they both feed well in my 700 unlike everything else i tried and the missouri is cheap. they shoot fine for my purpose. if you want moa accuracy to 300 metres with a cartridge thats going to drop that much like every 10 yards by the time it gets there you are going to need some fancy math and a range finder or maybe a different cartridge

 

[cr5]

Try A1680 under those heavy pills. I use it under the 208 Hornady bullets, best groups were around 1-1.5moa but I haven't done a lot of testing with them in my bolt action 300BLK. I've found that pushing a 155gr Amax supersonic with LilGun or A1680 will produce around 0.8moa from my 16" AAC-SD so that mostly what I run now.

 

[New Camper]

Thank you. I'll bear in mind these suggestions and experiences when I spend some more time loading for the rifle. Maybe I just need to get a falling block 45-70 to satisfy the heavy and slow aspect of accurate shooting from bygone years.

Further to Suputin's post: I did some more reading on subsonic accuracy and yes, 1.5-2" is on the better side in the world of subsonic. It puzzles me why that is... more reading for another time.

 

[Ganderite]

I have used 2400 for heavy subsonic bullets in 308. It works well at low pressure loads.

 

[Suputin]

There is a widely held opinion that heavier subsonics are required to improve downrange energy. The problem with this idea is that subsonics don't expand and a result they tend to wildly overpenetrate. I've done a bunch of terminal tests and have never failed to be impressed with how much penetration a subsonic can achieve.

What this means for the big picture is that extra weight for a subsonic just results in more penetration which means all that extra energy gets wasted when the bullet flies out the opposite side of the target.

Heavy subsonics have a number of downsides. They are harder to stabilize and unlike supersonics, flight stability can decay with distance on a marginally stable bullet. Heavy subsonics drop faster as well which means the rainbow like trajectory is even worse.

In a bolt gun it is possible to produce subsonic velocities with bullets as light as 110gr. Personally I use a lot of subsonic 150gr because the bullets are a lot less spendy. Probably the best single subsonic bullet available is the Lapua 200gr subsonic which has been specifically designed for accuracy and flight stability. If you are looking for max subsonic accuracy that's the bullet I'd go with.

 

[New Camper]

Thank you Ganderite, 2400 is a burn speed range I need to try.

There is a widely held opinion that heavier subsonics are required to improve downrange energy. The problem with this idea is that subsonics don't expand and a result they tend to wildly overpenetrate. I've done a bunch of terminal tests and have never failed to be impressed with how much penetration a subsonic can achieve.

What this means for the big picture is that extra weight for a subsonic just results in more penetration which means all that extra energy gets wasted when the bullet flies out the opposite side of the target.

Heavy subsonics have a number of downsides. They are harder to stabilize and unlike supersonics, flight stability can decay with distance on a marginally stable bullet. Heavy subsonics drop faster as well which means the rainbow like trajectory is even worse.

In a bolt gun it is possible to produce subsonic velocities with bullets as light as 110gr. Personally I use a lot of subsonic 150gr because the bullets are a lot less spendy. Probably the best single subsonic bullet available is the Lapua 200gr subsonic which has been specifically designed for accuracy and flight stability. If you are looking for max subsonic accuracy that's the bullet I'd go with.

Some of what you said I have yet to observe, but I know that subsonic bullets lose velocity much less than supersonic. It seems peculiar the amount of penetration that they can also achieve, and it seems rather backward but it's true. I don't believe the 1 in 7" twist of my barrel is adequate but I have several different bullet weights of 30 cal that I intend to test. Unfortunately I don't have any 200gr Lapua bullets you mentioned. I'll spend some time with the ballistics computer comparing trajectory etc. of different bullet masses.

In this frustration, there is an opportunity...

 

[Suputin]

You are going to have to actually measure and then calculate the BC for the subsonic bullets you intend to use. The published BC will be useless because it does not cover the subsonic velocity range. What you are going to find is that subsonic 30 cal spitzers have a very high BC.

 

[New Camper]

You are going to have to actually measure and then calculate the BC for the subsonic bullets you intend to use. The published BC will be useless because it does not cover the subsonic velocity range. What you are going to find is that subsonic 30 cal spitzers have a very high BC.

I never considered that there might be a difference in BC in subsonic as everything is done with supersonic in mind. I remember reading about the 458X1.5"(500gr): An experimental subsonic round used for sniping in the jungles during the Vietnam war. The bullet wasn't meant for long distance so that might have influenced the design: It was a round nose bullet with I think a flat base.

 

[Juster]

I never considered that there might be a difference in BC in subsonic

The difference is huge, and a wild ride in the transonic range:

If your muzzle velocity is an average 1050, there will be a fair bit of randomness.

 

[New Camper]

Thanks, I've been using powder charges straight off the Chargemaster. While this doesn't detract from the accuracy of the machine (last chrono reading on my 30-06 with charges off it measured an extreme spread of 10fps), in the subsonic range area I'm shooting is where the spike (referencing graph) occurs and every .001gr of powder will mean all the difference. I expect this would mostly increase vertical stringing, but with the variable BC, wind drift as a result will be influenced... it might be minimal, but every 1/4MOA adds up to that inch I want gone. This variable is easily controlled by using the balance beam to reduce powder charge variance further.