.223 Subsonic 'problem'

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WhisperFan
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.223 Subsonic 'problem'

Post by WhisperFan »

I'm working on load development and I have noticed something very unusual going on with a .223 subsonic round I am working up

First, my method: I weigh the charge using a RCBS 750 electronic scale. I have found that my scale doesn't like to hold its zero, so I pour my charge into another powder pan, zero the scale and weigh it again.
Then I pour it into a RCBS 1010 beam scale to double check it.

I don't use this method for regular reloading, but when I am making 5 or 10 of one charge, then 5 or 10 of another, I take extra care to ensure that the charges were as identical as I can make them.

The powder is all from the same 8lb keg I have been working from for a couple years now. This powder yields very stable results from my 300/221 (300 Whisper)

The firearm is an AR-15 SBR with a 11.5" barrel 1:9 twist. No modifications have been made to the gas system. It is a D.I. with a carbine length gas system. The subsonic rounds do not cycle the action, making this into a 'straight pull' bolt gun. The firearm is suppressed with my Form 1 can.

I shoot one shot across the chronograph, record the speed, pull the charging handle, ensure I am not pointing at the face of chronograph, and pull the trigger. From one shot to the next is perhaps 15 to 20 seconds ... I load the magazine for the next load and start over. The time in between finishing one group of the same powder charge and starting the next was perhaps a minute or two (if that matters)

The components are: Hornady V-Max 55gr Moly Coated, Primers are CCI Small rifle, Powder is IMR TrailBoss. The cases are Winchester .223

What I find is that the first shot is the fastest, and typically each shot is slower, and slower (with an occasional exception) This is what I am seeing (just the powder weight is listed) I am just getting an idea of where I am, so 5 of each:
4.7 grains
1029 fps
986 fps
895 fps
869 fps
874 fps

4.9 grains
1068 fps
986 fps
992 fps
976 fps
957 fps

5.1 grains
1102 fps
1010 fps
997 fps
1006 fps
995 fps

5.3 grains
1128 fps
1080 fps
1071 fps
1064 fps
1067 fps

5.5 grains
1156 fps
1139 fps
1109 fps
1096 fps
1096 fps

I'm thinking that 5.2 grains of TrailBoss might be the load I go with for an likely average velocity of somewhere around 1050 fps

I don't have a bolt gun to check the results and see if the dropping velocity is something unique to a semi-auto with a gas system, or what ....

Has anyone else seen something similar?
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Garrett
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Re: .223 Subsonic 'problem'

Post by Garrett »

I have only played a little with subsonic .223. It seems like I've experienced the first-round-faster thing you're talking about. But not with .223 subs.

Shooting a 50 gr. Nosler Ballistic Tip from a 23" T/C Contender, I got the following with 4.0 gr. Trailboss (listed in the order shot):
1107 1109 1109 1107 1073 1090 1090 1064 1072 1054

And dropping to 3.7 gr:
1078 1093 1091 1065 1078 1081 1071 1061 1041 1056
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WhisperFan
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Re: .223 Subsonic 'problem'

Post by WhisperFan »

WOW ... what a difference a short barrel seems to make!
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markm
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Re: .223 Subsonic 'problem'

Post by markm »

Have you thought about a 69 grain SMK for this mission?

I might have to try some of my Trailboss for this... we do .308 loads which dazzle people. :D

I might try 3.6 grains with a 69 grain bullet for the heck of it.
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markm
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Re: .223 Subsonic 'problem'

Post by markm »

3.6 grains with a 69smk worked good.

I also tried 4.0 grains with a 55 gr Soft Point, and that worked good too. Hard to use SMKs for sub sonic fartin around.

I didn't chrono either to see what the velocity was, but they were sub.
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Re: .223 Subsonic 'problem'

Post by arrowshot »

A little bit off the subject but you mentioned your RCBS electronic scales fail to hold zero. I have a Lyman and they advised not to use it in the prescence of UV lights or wireless devices (to include cell phones). My wife can start using the phone upstairs (not her cell phone, just a wireless phone) and I will see the readings start changing on my Lyman. Also got rid of all UV lights in my garage.
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Re: .223 Subsonic 'problem'

Post by r »

i think you have the same problem that goes on in larger 30 cal calibers when downloading for subsonic. When you get down to a certain point you have a small amount of powder laying randomly in the bottom (actually along the side since the case is parallel to the gound) of the case. You have not reached the point of SEE (detonation) but you have reached the point where upon ignition your powder burns irratically from round to round and you get variations to measured speed between identical weight loads. I studied and read all I cound find. Finally I read a few articles about case fillers. The info indicated that if fillers are used (especially on these types of marginal loads) then all the powder is contained in the rear of the case against the primer and that a much more consistent string of shots could be produced as a direct result. These articles indicated that in general a 20-30ft/sec increase would be seen. I broke down a tried, taking a single sheet of of TP, cutting it into 1/4s with sissors then placing one in each case packing all powder to the bottom of the case. My speeds increased within the 20-30ft/sec range and IMMEDIATELY all my chrono speeds became extremely consistent. The only drawback is about every 3-4th rd I see what looks like a small puff of snow out my suppressor. My loads are hand weighted with a trickler and an Ohaus M-5 scale. IMR SR4759 is a nice bulky powder that lends itself to subsonic loads. TB might not be the best for 223 in subsonic. Once you get your powder measuring down look around the net for loads using fillers and check it out for yourself.
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Re: .223 Subsonic 'problem'

Post by 2bad4u2 »

r wrote:i think you have the same problem that goes on in larger 30 cal calibers when downloading for subsonic. When you get down to a certain point you have a small amount of powder laying randomly in the bottom (actually along the side since the case is parallel to the gound) of the case. You have not reached the point of SEE (detonation) but you have reached the point where upon ignition your powder burns irratically from round to round and you get variations to measured speed between identical weight loads. I studied and read all I cound find. Finally I read a few articles about case fillers. The info indicated that if fillers are used (especially on these types of marginal loads) then all the powder is contained in the rear of the case against the primer and that a much more consistent string of shots could be produced as a direct result. These articles indicated that in general a 20-30ft/sec increase would be seen. I broke down a tried, taking a single sheet of of TP, cutting it into 1/4s with sissors then placing one in each case packing all powder to the bottom of the case. My speeds increased within the 20-30ft/sec range and IMMEDIATELY all my chrono speeds became extremely consistent. The only drawback is about every 3-4th rd I see what looks like a small puff of snow out my suppressor. My loads are hand weighted with a trickler and an Ohaus M-5 scale. IMR SR4759 is a nice bulky powder that lends itself to subsonic loads. TB might not be the best for 223 in subsonic. Once you get your powder measuring down look around the net for loads using fillers and check it out for yourself.
The OP mentioned he was using TB for a powder. IMR notes that TB should not be compressed, so I would be careful with the use of any filler, TP included. I decided to use some TP 1/4 squares in my .308 Win using 10.5gr. TB with Hornady 110gr. RN-FMJ .30 Carbine bullets.

My (10) shot groups @ 100 yds. w/o TP filler are 2-3 moa. With the TP filler, my groups could be measured in feet. After shooting about (15) of the filler loads, I decided to stop and pull the remaining loads apart. I noticed some ejector swipes on some of my cases and decided this combination definitely wasn't the way to go and was potentially unsafe.

Why not experiment with primers to see if you can get better consistency? Although not normally necessary with fast powders like TB, it may very well improve the situation. Others have reportedly tried pistol primers with some success, though I'm reluctant to do so.
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Re: .223 Subsonic 'problem'

Post by AMProducts »

I know the problem you are talking about with the RCBS scales... the problem is the scale runs on 9v AC, and is very sensitive to changes in electrical supply (what cause me tons of problems was a dillon case feeder), the solution... put a power line conditioner or a ups on the line (UPS doesn't even need good batteries, just needs to be a good sine-wave generator with a bit of buffering).

Now, as far as your loads go, I can think of a few things that can cause these sorts of problems, I am guessing they are likely as a result of barrel heating, cartridge, powder and primer position.

What I think is happening (because I've noticed this also, but to varying degrees), subsonic ammo has a much smaller amount of energy in the cartridge, however it still has to do the basic things all cartridges do... it has to push the bullet down the barrel and out. However there are these historic jerks, Boyle, von Guericke, and Hooke that have made just doing something as simple as this really hard. So what's happening at least according to my hypothesis is on the first shot, the barrel heats up, however the barrel does not heat uniformly, which means that until the heat becomes uniform through the material, you will have the inside of the barrel being hotter than the outside, which will ever so slightly reduce the inside bore diameter. This means friction goes up, and the whole thermodynamic process gets thrown out of whack.

Now if you look at the hotter loads, you had significantly less variation, which tells me something else you were getting significantly better and more uniform ignition at this higher charge. All powders have a "sweet spot", they may have several, but for any cartridge and bullet combination, you will find a grain weight, at which your standard deviation will drop considerably (sometimes to single digits) and varying the charge up or down by even half a grain (for a full-size rifle charge) all that consistency goes out the window. I can't tell you exactly why this happens, but it does happen.

What I might suggest, go with the lower powder charge, and test again with a hotter primer, or take a little chunk of cotton ball, and after charging, push that cotton ball down on top of the powder to keep it in place.
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bts0irv
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Re: .223 Subsonic 'problem'

Post by bts0irv »

A little less precise, but fun and easy. I dip Unique with a .3 CC Lee dipper and dump it it into a case after impact pulling 55GR FMJ's. It will exit the muzzle on my 1/7 twist DD barrel. Very quiet and actually very accurate. I dont have a chrono, but it is subsonic and Hollywood quiet when coupled to the Yankee Hill suppressor. This method works with Wolf and PRVI Partizan ammunition.
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Re: .223 Subsonic 'problem'

Post by pdull »

Did you ever get a solution for the varying velocity after the first shot. I am having the same problem with 300 Blackout.
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Re: .223 Subsonic 'problem'

Post by cdhknives »

Old thread, but I'll throw this out: Powder position in low density loads. Assuming an autoloading rifle or pistol, but can happen for on any gun if you work the bolt briskly. If you are loading round 1 with the rifle in any position (usually vertical for typical gun handling esp. after inserting a mag) other than horizontal firing position, the powder will fall to bottom after chambering. You then fire round 1 with the powder probably against the flash hole. The second and later rounds are slammed home in a horizontal position and inertia allows the powder to flow to the bullet end of the cartridge creating a gap between the flash hole and the powder. With very low density loads this air gap in front of the flash hole CAN affect ignition and result in first round differences.
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Tackleberry47
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Re: .223 Subsonic 'problem'

Post by Tackleberry47 »

I tried the various recipes on the internet for subsonic 223. Trailboss, titegroup, bullseye. They all gave garbage results. Wide spreads in velocity, often 200fps. One might be fine, the next barely makes it out of the barrel. The trick I found was drilling the flash holes, not needed on 308 or 30-30, or other things I have messed with. But really made the difference in a 223, use solo1000, just have a bunch of it. Use a jewelry scale, can get them down to 10fps spreads. Use a 80gr NOE cast bullet, powder coated. Never could get decent results with jacketed.
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