Thread: .223 Subsonic

Originally Posted by No.3

You're right - the main issue with sub loads in anything is expansion. Effectively with .223 you are attempting to turn it into a .22 rimfire - this requires a bulky fast powder and one of the better options when it's back available is TrailBoss as everyone keeps pointing to. Issues with TB are it's a smokey powder and some have complained that it can leave a lot of crud not sure if that actually affects anything though - and the obvious issues with availability at the moment.

One of the next best options is Red Dot fast pistol and shotshell powder - I'm told it runs about the 70% density of TB range which means it will still be possible to double charge or overcharge a case with it. One of the issues with RD and other super fast powders is that they have an almost 'instant on' pressure curve (read it's near vertical on the graph) then dropping away as the bullet progresses down the barrel so the only thing limiting the amount of pressure in the gun on firing is the amount of powder you put in. Put to much in and you blow up your gun... On the other hand, don't put enough in and you risk the pill not exiting and you blow up your gun on the next firing with an obstructed barrel.

With Red Dot, it appears you can't load too light for ignition and firing pressure hazard purposes though - the only real risk at the low end appears to be insignificant pressure created to kick the bullet out of the barrel leading to an obstructed bore. RD burns so quickly that there doesn't seem to be much risk with the position in the case as used to happen with much slower powders, where the powder lying along the full length of the bottom of the case exposed a LOT more surface area to the primer flame than expected and resulted in a much quicker burn than usual which steepened the pressure curve to dangerous levels. With slower powders, a lot of the powder burn continues outside of the barrel where the increase in pressure just creates noise (muzzle blast) and flash. This is one reason why faster powders can be loaded to be a lot quieter - the lower volume of powder can be consumed in the barrel rather than out in the air.

With these faster powders and slower loads, the general procedure seems to start with finding a safe starting load for the combination of case, bullet, primer and powder which is within 10% or so of max and trying it out for performance. You start with the suppressor removed, checking for stability and velocity and then drop the powder charge slowly until you get to around 1050-1080fps or so. Much slower than that and I'd be concerned about a non-exit (check after each round), but your mileage might vary especially if you're running into large elevation and temperature variations in your shooting areas. Once you hit the velocity you want, it's reliable, and the bullet proves stable then chuck the suppressor back on and test that it functions correctly. Some people have reported that they found the pills went supersonic after rehanging the suppressor on, possibly the bullet was getting a little extra kick in the extra length of contained gas so they had to work the powder charge down a little (but better a bit of a crack than a big boom from a blocked barrel).

As far as the pill - a bit of a hard one as you need a reliable source of soft near-pure lead for expansion at subsonic speeds. A lot of lead like wheel weights has tin in it to improve the flow characteristics of the lead in the mold but that also makes the lead harder. This is where I think the commercial subs are a little lacking nowadays, they chuck tin etc into the brew to be able to cast or stamp the wire cores reliably without quality control issues and sending things back for rework. Ideally you want something will the biggest hole in the end of it you can get, that still fits in the magazine and loads and chambers OK. You don't need aerodynamic performance as subsonic rounds don't travel that far, blunt is good. If it opens to four times the surface area, more the better. Energy transfer is what you want, the ones I was using a while back (don't have the contact details of the guy who was making them unfortunately) were pretty bloody good, he was using a drink can disc as a gas check and loading into .22H cases. Don't know what the mold was either but a plain pill with gas check and hollowpoint. Roughly the junction of the thick post to the thinner wire below the crosshair was the 80m or so aiming mark with a bit of guesstimate at other ranges - surprisingly effective with the option of full house loads at anything longer. More effective than .22LR at any rate.

I am trying to get my head around the reason for using fast burning powders for subsonic and not just lowering the normal powder.

Hi Bob
i use the faster powder because of the short barrel [no flame @ night ]
and also because of a short burn [quick burn ] rate the push behind the pill is just a jab rather than a full power haymaker swing
if using a slow burn powder the push is over the longer length of a long barrel,
but becareful of using a fast burn powder on full loads as the pressure will spike real quick
cheers

Originally Posted by BOBINNZ

I am trying to get my head around the reason for using fast burning powders for subsonic and not just lowering the normal powder.

Lowering the load of a "normal powder" will not work for the following reasons
Smokeless powders burn rate depends on a few things grain size, the use of graphite or other retardent coating and most importantly PRESSURE and dwell time. The higher the pressure the faster the burn rate, retardents are used to control initial burn as is grain size. The idea being a steady increase in velocity and pressure. Shotguns and pistols use much faster burning powders as the requirements are different and a quick boot up the arse works best for them.
A reduced charge of normal powder behind a light bullet will result in inconsistent ignition and lots of unburnt powder in the bore both of which do nothing for accuracy.

Originally Posted by BOBINNZ

I am trying to get my head around the reason for using fast burning powders for subsonic and not just lowering the normal powder.

Reducing slower powders below the posted safe lower limit is dangerous, for two reasons:

One, the more powder available to be ignited by the primer flame the higher the pressure spike before the projectile leaves the muzzle. Slow powders are designed to be held against the base of the case for the powder burn timing to be as designed, which is basically a small surface area which acts as a delay for the burn of the powder column. If you put half the powder in and lay it along the bottom of the case the primer flame hits many, times the number of grains of powder which then all burn at once. It defeats the coatings on the powder designed to control the burn rate, and worst case is spiking the pressure high enough to pop a case or on certain actions even damage the breech. Fast powders all burn at once anyway, so aren't as sensitive to position in the case. The old skool way was to hold small amounts of slow powder against the bottom of the case with an inert filler that was just ejected from the rifle, but it's not an ideal solution.

Two, the powder granules can be ejected prior to being burnt and if they collect in the suppressor it can cause an overpressure of the can when they all decide to finally burn.