Extreme Blackout, What are the limits and how do we explore them safely. update 7/1/18

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dellet
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Re: Extreme Blackout, What are the limits and how do we explore them safely.

Post by dellet » Mon Nov 02, 2015 12:26 pm

Dr.Phil wrote:
Dolomite_Supafly wrote:The single most important thing I do to brass for consistency sake is uniform, chamfer and deburr the flash holes of cases. I now consider it part of the process of making brass.
I second this...
Through years of load develpment, I have discovered that this is the single best ROI when it comes to brass prep.
I will add to that. For me the eye opener was using a piece of .080 drill rod ti pick media out of flash holes. It was very surprising how often that the rod passed through the hole at about a 60 degree angle on brass with punched flash holes.
300 Blackout, not just for sub-sonics.

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Re: Extreme Blackout, What are the limits and how do we explore them safely.

Post by dellet » Mon Nov 02, 2015 1:03 pm

kroeker wrote:I'm also trying to test the limits on the blackout. Once I get I get a chronograph I'm going to try a load for long range. Flat line bullets claim they're 155 gr palma bullet will run 125 gr speeds and has a BC of .533 so if my figuring is right that supersonic to 1000 yrds.

Lil gun or 1680 looks like a winner for speed and lapua now making brass means should be able to get good es numbers. Will be an expensive round at $1.25 a bullet but if I could keep sub moa out to 800 yrds it could be worth it.
The hardest part of going long like that with 300 Blackout is bullet choice. In a hand fed platform it is easier because you don't worry about mag length. I have watched the Flatline Bullets a little bit, so far the reviews are mixed that I have seen. The BC seems to be reasonably correct, the velocity gain does not. There are also some questions about stability at lower velocities.

There is a about a six piece juggling act going on at all times squeezing out speed for this cartridge.

A lot of the VLD bullets like a jump into the lands, so you need to be far enough off the lands, without being too deep into the case, where you lose powder for much needed velocity.

To get the highest velocities with the lowest chamber pressures, you can be pretty certain you will be compressing a load and that means you will likely either want to crimp, or reduce the size of your expander for better neck tension. Consistency of compression can be a challenge.

Then there is barrel length, above 20" the gain from velocity is minimal, but the accuracy gain from changing the harmonics and exit timing of the bullet makes it desirable.

I won't say that I have given up on a bullet that will stay super sonic out to 1000, because I think it is possible, but right now I am looking at bullets that stay more stable in the transition. It seems that the bullets with the highest BC's are affected by this more. Twist rates will probably come into play to help solve that. This is done by loading to 1200-1300 fps and shooting at 200 yards or so, where they have to drop though that transition.

The other solution is to only shoot the 1000 yard matches in Alaska during winter when the transition to subsonic is at a much lower velocity :lol:

I think in the long run I think you will have better luck with 1680 than Lil'gun. The harder you push Lil'gun the more erratic it seem to become.
300 Blackout, not just for sub-sonics.

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Re: Extreme Blackout, What are the limits and how do we explore them safely.

Post by dellet » Thu Nov 05, 2015 12:33 am

Sierra 175 SMK,or 178 Amax. Which is the most "versatile" bullet?

I have a lot of fun with bullets in the 175 grain weight range. They do equally well at 1000 fps as they do at 2000 fps. For me the Amax seems to be slightly more accurate than the Match King, but the Match King is a little easier to fit in a magazine, so you can get a little better velocity and or have more room to adjust over all length for accuracy and manipulating pressures.

In a properly set up carbine gas system, it is possible to shoot either bullet as a sub-sonic round and then in that same setup, send it out at over 1900 fps. In a bolt action it goes a little faster yet.

My go to powders for these loads, is either 1680 or Norma 200. For me it has worked out to close to a 1 grain to 100 fps ratio using 1680. 10.8 grains is very close to 1050 fps, and 19.5 grains averages out to 1950 fps. The velocities in between have been reasonably true to that form.

For this exercise I'll talk about 1680 and 175 SMK bullets because they are both very popular. The principles will be universal, but I think it's rare to be able to have this extreme velocity spread with one powder/bullet combination, in an AR platform.

The specs for the rifle when I started this project was 18" carbine gas barrel .096 gas port, carbine spring and buffer, S/A carrier. When I wanted max velocity I made some changes explained later.

Start low and work up, or start high and work down? Yes

Are you shooting subs or supers? Yes.

What do the manuals say? Published material does not list many sub sonic loads that I can find for a 175 grain bullet, Lehigh has a load for their 174 grain bullet that is 10.7 grains 1050 fps. Accurate, Sierra, Hornady list max loads for supers of 19.3-19.7 grains and velocities in the range of 1800-1900 fps. Lows are 13 grains around 1300 fps. by those same sources.

You won't find to many load windows where you can double the charge weight, and velocity :shock:

Over all length in various load data is any where from 2.105-2.225. that's an 1/8 of an inch. So published data, that I am supposed to be able to trust says, I can load anywhere from basically 10 -20 grains and vary the seating depth as much as .120 and longer yet if I want to take advantage of the magazine. :roll:

Now the fun begins. I worked up these loads at the same time:
Subsonic
Brass, converted LC, trimmed to 1.355
1680, 10.8 grains
Bullet, 175 Sierra Match King
COL 2.250
AVG Velocity 1040 fps


Super sonic
Brass Converted LC, trimmed to 1.355
1680 19.8 grains
Bullet 175 Sierra 175
COL 2.250
AVG Velocity 2020 fps

In sharing loads we grind into the process, start low and work up for supers, star high and work down for subs. This is safe for me and my rifle, try at your own risk. That load's too high, that load is too low. That guy is irresponsible for posting that...................................

So how do you sort the wheat from the weeds? If developing loads is not safe, how do new cartridges get developed? Either Mikey steps up and tries it, or it just doesn't happen.

The powder/bullet combination above was a very good learning experience for me. I could safely explore the extremes, with a reasonable expectation of safety.

Let's go low. How low can we go? Well that depends.

A common question on the forum is "I need a load for this bullet to run subsonic". The common answer is " I use this powder at this charge at this length". The person runs that combination and guess what, it no worky. Now what? much of the time the answer is given, change the buffer, bore out the gas port, get a reduced spring, try a S/A carrier, get an adjustable gas block try a different powder, lube it more............

All good suggestions, but maybe it's just a different powder lot and the charge needs to be adjusted.

I hit a wall getting the 175 to cycle and stay subsonic. My gas port was smaller than most, my barrel was longer. So running less available gas, in a barrel that produces a higher velocity, using a lighter bullet, that will create less backpressure, and again move faster than the normal 200 grain bullets used by most. The most often suggested cure was open the port.

I posted a question, "How do you increase port pressure, without increasing velocity". Bad question. Not stupid, just bad. I explained what I was trying to accomplish, I need more pressure to operate the bolt, but I was already approaching max velocity so more powder was not the answer. Or was it?

Dolomite pointed out the obvious to me, I was not lacking pressure, I was lacking volume. So bore out the port. Wrong again.

More powder creates more gas, downside is that it also creates more pressure/velocity. So now I had a load that would cycle, but it was too fast. How do you drop pressure/velocity without losing gas volume? Increase the COL/decrease seating depth. You still have the same amount of powder creating same volume of gas, without the same increase of pressure causing increased velocity.

I found moving the bullet out .010 allowed me to add .10 grain of powder without increasing velocity. I increased gas volume available to the carrier without drilling out the port in the barrel. More work, certainly, but the knowledge gained allowed me to run a lighter than average bullet, in a longer than average barrel, with a smaller than average gas port. It also gave me a better understanding of how the platform worked and laid the ground work for the super sonic load.

Sierra 175 Matchking 2000fps +

This load is actually listed in the Faq section as a load that will meet Major power factor for competitive shoots. I took it a little farther.

The basics learned in the subsonic load were applied to a super load. More case volume, reduces chamber pressure. So how do we increase case volume. Two ways, move the bullet out or make the brass bigger. Moving the bullet out is easy, making the brass longer takes more thought.

If you form your own brass, it's easy, just don't bump the shoulder back so far. If you buy your brass, you need to shoot it as a super and size it as minimum as possible a couple of times to allow it to grow to it's maximum length at the shoulder. This will be somewhere around 1.070-.073 measured with a comparator. This will give you about .010 more body to the case and just a little more volume for powder or a significant drop in chamber pressure.

This is where an accurate measurement of your chamber is needed. For an autoloader you will want to move the shoulder back .003-.005 from maximum for reliable feeding, this will vary with magazine and feed ramps, so it is not something that can be done without trial and error.

Having max case capacity, we need to have minimum seating depth, or if running an AR, no more than 2.260 COL. So remember the max published loads. I have increased the capacity of the brass a little more than .5 grains by water weight, and moved the bullet out .035-.150 depending on the data. This significantly reduced chamber pressure and volume, with only a small decrease in velocity.

Now that I have the lowest pressure combination available with my brass, bullet, powder combination, it is time to start working toward max safe velocity. I ended with the load above as my max, after pushing higher. I then changed my build.

Adjustable gas block to reduce carrier speed. LMT enhanced BCG to increase the amount of time the bolt would stay locked allowing the brass to shrink before being pulled from the chamber prolonging life and limiting case head expansion. JP captured spring to further slow bolt speed and dampen recoil impulse.

I can still run subs, the 178 amax works better for me than the 175 SMK and It no longer functions without a suppressor, but this build was all about supers. Subs is just a plus.

I will post more details about load work up in the hand loading thread, but the results here will put many 308 hunting bullets out to 200+yards at a velocity they were intended to work, 1800 fps.

A more in depth discussion of methods can be found here:

viewtopic.php?f=141&t=96465&p=928152#p928152
300 Blackout, not just for sub-sonics.

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Re: Extreme Blackout, What are the limits and how do we explore them safely. update #1 p4

Post by rebel » Thu Nov 12, 2015 10:32 am

The method dellet has used is explained very well in the 1st edition Berger reloading manual. While it contains no 300 Blk data, it certainly contains practices being discussed here. Natchez has them for 24.49. So for the " load police" crowd :P , this is a published method :mrgreen:
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Re: Extreme Blackout, What are the limits and how do we explore them safely. 125 sub AR load

Post by dellet » Mon Jan 11, 2016 11:20 am

125 SST subsonic SBR load

After working with heavy supers, light subs was the next logical step. The problem is light subs are way too easy in a bolt action or single shot to learn much. So how low can you go in an AR?

I was inspired by working with a new powder, Accurate LT 30. There were a few posts made about it but it never really caught on for some reason. It is always available on line, and I was able to find it local so I bought a pound. A while back this info was posted:

posting.php?mode=quote&f=141&p=899035
USBP379 wrote:This powder is WAY easier to find in stock and works better, in my very limited experience, than 5744.

Here's Accurate's data for LT-30 in the 300BLK. According to Don at Western Powders, LT-30 is only suitable in subsonic loads.

As always, YMMW. Use at your own risk and/or verify data with Western before trying.

Accurate LT-30

208 HDY BTHP

12.2gr MV: 1,059 25,610 pressure 2.245oal 112.1% compressed

210 SIERRA HPBT MK

12.4gr MV: 1,056 27,390 pressure 2.225oal 113.6% compressed

220 SIERRA HPBT MK

12.5gr MV: 1,055 28,870 pressure 2.220oal 116.1% compressed
I bought a pound and played with it. I ended up being able to have full function, cycling without a suppressor almost every bullet I loaded with it. Hornady 150 SST bullets in an 18" barrel with a carbine gassed system were no problem.

I had a gap in bullet weights with nothing between 150-125, I am sure the load would work for 140's. I was actually able to cycle 125's, down to 1175fps. Basically 11.5 grains ran every bullet I loaded over it, velocity varied according to weight. As the bullet weight got lighter, the firing became dirtier.

18" carbine gas, .110 gas port. carbine buffer.
150 SST
11.5 grains LT 30
2.170 COL
995 fps. avg.

That started the wheel turning. How low can you go in an SBR?

The longer the barrel, the harder it is to keep velocity low. A bullet at 1000 fps in a 8" barrel will quite possibly be super in a 16" barrel, easy to be 1150 fps with the exact same load. Using an SBR and a suppressor is a huge way to stack the odds in the favor of a light bullet. Just the same as working with the heavy supers, light subs is all about manipulating pressure with powder charge and seating depth.

I started with a mix of bullets 125 SMK, 125 SST, 110 Black tips and 110 Barnes blue tips and LT 30. What I was looking for was the longest, lightest bullet possible. This would allow me to seat the bullet as deep as possible and keep the powder charge filling as much case as possible. This keeps velocity more consistent and lowers the chance of having a kaboom due to a low powder charge.

Surprisingly I was able to get all four bullets to cycle and lock back suppressed, while staying subsonic. The problem was due to a high charge and low firing pressure the percentage of powder burn was probably in the single digits. The rifle stopped functioning after a dozen shots.

Time to start looking for a new powder. I needed something that produces a lot of gas, and is somewhat bulky. Candidates in my mind were:
1680
5744
4227
4198
Norma 200.

Those were narrowed down to 4227 and 5744 by starting at 12 grains and working down until they quit cycling. I ended up with 4227 since it burned significantly cleaner than 5744. This was a visual judgment call based on carbon and unburned powder left behind on a white shooting table :shock:

The load work up was counter intuitive. I counted on a poor burn rate due to low firing pressure of a light bullet. As an example Hodgdon load data calls for 10.5 grains under a Sierra 220 for 1050 fps. I started at 12.5 grains of 4227 and worked down.

To keep from making a long story any longer, I will get to the point. from 11-11.5 grains of 4227 and a COL of 2.00 and 2.150 using a 125 SST I am able to have full function suppressed and subsonic. one of the things that is enjoyable with this load is to be able to shoot and stay on target, there is just about as close to zero recoil as you can get.

I had similar results with a a cast bullet and those results are here:
viewtopic.php?f=185&t=97185

Rifle is a 7" barrel, pistol gas with a .098 gas port.
Carbine buffer and spring or
JP silent captured spring with black or white spring
T2 buffer will cycle but not hold open on last round.

Load:
125sst
LC converted brass 1.355"
COL 2.10
11.1gr 4227
1050 fps avg.

Results:
Image
300 Blackout, not just for sub-sonics.

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Re: Extreme Blackout, What are the limits and how do we explore them safely. update 1/11/16

Post by rebel » Mon Jan 11, 2016 1:10 pm

Nice, consistant shooting dellet. I bet than one question marked one ticked you off a bit. I swear there exists a bullet gremlin that prevents mere mortals from shooting a perfect group :mrgreen: Nice write up.
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Re: Extreme Blackout, What are the limits and how do we explore them safely. update 1/11/16

Post by plant.one » Mon Jan 11, 2016 1:39 pm

ya thats awesome shooting.

but the real question is - will it blend?!?

Image
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Re: Extreme Blackout, What are the limits and how do we explore them safely. update 1/11/16

Post by rebel » Mon Jan 11, 2016 1:50 pm

I don't think his rifle will blend, but it slices, dices and pretty sure it could circumcise - if loaded with a double of #9 :mrgreen:
( we are even on the "....how many deer he killed with it........" comment :lol: )
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Re: Extreme Blackout, What are the limits and how do we explore them safely. update 1/11/16

Post by Dr.Phil » Mon Jan 11, 2016 2:06 pm

rebel wrote:I don't think his rifle will blend, but it slices, dices and pretty sure it could circumcise - if loaded with a double of #9 :mrgreen:
Now that is pretty funny!!!
It may be too soon though.
dellet is still trying to overcome the flinch it induced.

That is the likely source of his flyers. ;)
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don't tell them where they know the fish."
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Re: Extreme Blackout, What are the limits and how do we explore them safely. update 1/11/16

Post by dellet » Mon Jan 11, 2016 2:09 pm

rebel wrote:Nice, consistant shooting dellet. I bet than one question marked one ticked you off a bit. I swear there exists a bullet gremlin that prevents mere mortals from shooting a perfect group :mrgreen: Nice write up.
No bullet gremlin. I think that happened about the same time I reached around and patted my back seeing I had a reasonable group going :shock:
rebel wrote:I don't think his rifle will blend, but it slices, dices and pretty sure it could circumcise - if loaded with a double of #9 :mrgreen:
( we are even on the "....how many deer he killed with it........" comment :lol: )
Post Posted: Mon Jan 11, 2016 10:50 am
Somehow I knew that was going to come up and rightfully so. Notice one of the requirements for powder in this load was bulk. With most 125 bullets being short, filling space was needed.
300 Blackout, not just for sub-sonics.

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