308 sub sonic

[Miseryguts]

Hi, Am trying to develop a reasonably accurate (to 100-150 yards) sub sonic load for my 308.

Before someone jumps in and says WHY??. The answer is "because I can" ( and I like the thought of a silent 308 round around the barns)

So, trying small quantities of fast pistol powders with 150gn RN bullets as used in the good old USofA. All going well, nic(ish) groups, whisper quiet(with a Mod) at 1040 ish fps, till I looked at some spent cases.

Picture below. Does that look like over pressure?

The 2 case at left and centre are sub sonic (1050fps) rounds with 8gn Green Dot under a 150gn Bullet

The case at bottom right is a standard velocity (2750 fps) round with 44gn N540 under a 155gn bullet

[Mattnall]

From those pics I would say no, not over pressured, the primer is still rounded at the corners and there is no cratering at the pin dent and no bolt face marks.

Compare to the bottom right (full pressure?); the primer fills the pocket more and the pin dent is shallower as the pressure is greater and there is some slight scraping by the N where it looks to have scraped on the bolt face.

Others may no more or better but this is just my opinion based on the evidence presented.

[One on top of two]

I use a 200 grn bullet and the powder you really want is trail boss 

 

[Miseryguts]

3 hours ago, Mattnall said:

From those pics I would say no, not over pressured, the primer is still rounded at the corners and there is no cratering at the pin dent and no bolt face marks.

Compare to the bottom right (full pressure?); the primer fills the pocket more and the pin dent is shallower as the pressure is greater and there is some slight scraping by the N where it looks to have scraped on the bolt face.

Others may no more or better but this is just my opinion based on the evidence presented.

Hi, thanks for that, if I had looked at some of my other calibre cases, then I would have seen that! DOH!

All my cases end up with scrape marks on them due to tight ejector pins, I have to clean the brass off the bolt face after every shooting session, no matter what the loads

1 hour ago, One on top of two said:

I use a 200 grn bullet and the powder you really want is trail boss 

 

Trail Boss unavailable, Green Dot and Unique in my cupboard. Both are as fast as Trail boss, but are denser i.e 8gn of trail boss nearly fills the case, 8gn of Green dot is about 1cc, 8gn of Unique is about 0.8 cc - hence green dot! The 150gn RN were a really good price(FREE)

Thanks for the feedback

M (feeling better, basking in the sun in Monmouthshire)

[Popsbengo]

7 minutes ago, Miseryguts said:

Hi, thanks for that, if I had looked at some of my other calibre cases, then I would have seen that! DOH!

All my cases end up with scrape marks on them due to tight ejector pins, I have to clean the brass off the bolt face after every shooting session, no matter what the loads

Trail Boss unavailable, Green Dot and Unique in my cupboard. Both are as fast as Trail boss, but are denser i.e 8gn of trail boss nearly fills the case, 8gn of Green dot is about 1cc, 8gn of Unique is about 0.8 cc - hence green dot! The 150gn RN were a really good price(FREE)

Thanks for the feedback

M (feeling better, basking in the sun in Monmouthshire)

Trailboss will fill the case better and therefor improve consistent burn rates - part of the problem of under-filled cases is the possibility of flash over - this is where the powder ignites across the surface thereby giving a pressure spike that can overpressure your action/chamber, which is not good.  Another method is to pack out the powder with inert material like kapok (traditionally) which just disperses on firing.

[BlueBoy69]

Some info I sent some friends from the local rifle club about making low-velocity ammo now that the import of IMR's Trail Boss is banned due to the European REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulation coming into force.

I'm starting to use Vihtavuori's N32C 'Tin Star' as a substitute for Trail Boss.

The bulk (load) density of Trail Boss in a 100% filled case, non-compacted/compressed, is 0.310 g/cm³ (grams per centimetre cubed). Tin Star is about 0.459 g/cm³, Unique 0.593 g/cm³. So quite low density, but not as low as Trail Boss. For note, ball powders are commonly around 0.910g/cm³ and stick (single perforation) around 0.840 g/cm³.

Trail Boss also has a relatively low energy density of 3,090 kJ/kg (kilojoules per kilogram), with Tin Star at 3,040 kJ/kg, so slightly lower. For note double base flake powder Unique is around 4,550 kJ/kg and Bullseye is 5,158 kJ/kg.

So as you can't get Trail Boss any more (I've still got two tubs), try Vihtavuori's N32C 'Tin Star'.

[One on top of two]

Blimey.

i didn’t know trial boss has gone to. I have around 4.5 tubs as I use it for my 44/40 sporting rifle as well 308 subs. 

Thank you blue boy for that info .

looks like it will be tin star for me too. I have tried it before and it’s not to shabby 

[Popsbengo]

1 hour ago, BlueBoy69 said:

Some info I sent some friends from the local rifle club about making low-velocity ammo now that the import of IMR's Trail Boss is banned due to the European REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) regulation coming into force.

I'm starting to use Vihtavuori's N32C 'Tin Star' as a substitute for Trail Boss.

The bulk (load) density of Trail Boss in a 100% filled case, non-compacted/compressed, is 0.310 g/cm³ (grams per centimetre cubed). Tin Star is about 0.459 g/cm³, Unique 0.593 g/cm³. So quite low density, but not as low as Trail Boss. For note, ball powders are commonly around 0.910g/cm³ and stick (single perforation) around 0.840 g/cm³.

 

Trail Boss also has a relatively low energy density of 3,090 kJ/kg (kilojoules per kilogram), with Tin Star at 3,040 kJ/kg, so slightly lower. For note double base flake powder Unique is around 4,550 kJ/kg and Bullseye is 5,158 kJ/kg.

So as you can't get Trail Boss any more (I've still got two tubs), try Vihtavuori's N32C 'Tin Star'.

excellent info thanks

[ubique]

19 hours ago, One on top of two said:

I use a 200 grn bullet and the powder you really want is trail boss 

 

Which 200grn bullet are you using, and are you getting expansion or are they still full shape, if you have ever retrieved one?

[One on top of two]

1 hour ago, ubique said:

Which 200grn bullet are you using, and are you getting expansion or are they still full shape, if you have ever retrieved one?

I use Lapua subsonic heads 

https://www.lapua.com/bullets/subsonic/

and no they don’t expand .

I have played with .308 subs on and off for longer than I care to remember 🤔

in my opinion... there no good for anything apart from steel targets  or at my local range @100 yards . They don’t expand as your only doing a fraction over 1 K 

rubbish on bunny’s. Waaaay to expensive and a 22 rimmy does a better job  ( you think a 22 Lr bounce about you’ve not seen nowt till you see 200 grns bouncing and skipping all over the place.  ) 

NOT legal/ Ethical  for deer 

and will just poke clean holes in a  fox at any range . 

And if your still not convinced with all of the above you have the most amazing trajectory ever witnessed by mankind to deal with 😂😂

however for sheer fun and something different there great . 

Just a word of warning though , if your not sure leave well alone , I know we as reloaders love to tinker but please keep in mind if you push your luck it WILL bite you .... case detonation is always a major factor during load development will this or similar loads mainly due to the cases having to high a capacity and too little powder , this is why I love the trail boss in the .308  like has been said it will nearly fill the case . 

there are much better .308s to do this with 300 black out or 7.62 x 39 i belive is another good one too . 

also take a rod with you as you may get bullets stuck halfway done the barrel . 

 

Enjoy 

[ubique]

Thanks for the reply, it was a curiosity question more so, we were playing with these back in the late 80's, and tried all sorts including soft lead bullets with and without gas checks, round nosed flat based and they worked well for plinking out to 200m, but trajectory was interesting! We then started using the factory Lapua with the same bullet that you mention, they were gratis so no more loading, happy days!

 

[One on top of two]

Yeah I have loads of stuff left over from a couple of years back when I bought a load of it cheap. Should see me out anyway. 

Like I said for something different they are good fun . And your get lots scratching there heads at your local range trying to work out why there as silent as there Rimmy’s 😂 

[BlueBoy69]

8 hours ago, One on top of two said:

Just a word of warning though , if your not sure leave well alone , I know we as reloaders love to tinker but please keep in mind if you push your luck it WILL bite you .... case detonation is always a major factor during load development will this or similar loads mainly due to the cases having to high a capacity and too little powder , this is why I love the trail boss in the .308  like has been said it will nearly fill the case .

I think this is one of those internet/shooting community fallacies or the phrase I like to use, it's one of those folkorical statements.

From a background of actual weapon testing as a contractor to the MoD measuring chamber pressures and many other things when a gun fires or a bomb goes bang, along with research into this, its highly unlikely detonation occurs. Firstly detonation is a shockwave driven decomposition event and what happens here is something different, a combination of extremely rapid burning (deflagration) due to the grain geometry (a flat bed, or towards one end or the other) and the effect of pressure wave formation on the propellant's burning rate.

As far as I can remember, what happens is when the case, or chamber for caseless guns, is mostly empty or partially full, the ignition phase of the propellant can result in dangerous pressure wave formation. These waves can reflect off the walls of the vessel without much attenuation as there's not much propellant there. If waves arrive at the right moment, they can add up, so increasing chamber pressure. Increasing the pressure increases the burning rate, which increases the pressure, which increases the burning rate, etc.. This oscillation occurs until the propellant burns away, the gun fails (the so-called detonation event), or for some reason, the phenomena stops.

Anyway, that's the basics of the more likely real reason for these blow-up with light charges of fast-burning powder in large cases. The other reason for this is probably double, or more loads of fast pistol powder by accident, something no one wants to own up to.

If you've actually seen the detonation of a high explosive within a chamber or the bore of a gun, the damage signature if very different to a high-pressure burst due to overpressure.

Anyway, for more info of pressure waves in guns, try the paper listed below.

Charge Design Considerations and Their Effect On Pressure Waves In Guns - ARBRL-TR-02277 (1990)

That or get the book titled 'Progress in Astronautics and Aeronautics: Vol 66 - Interior Ballistics of Guns'.

https://www.amazon.co.uk/Interior-Ballistics-Progress-Astronautics-Aeronautics/dp/0915928329

I have a copy, but due to its cost now, there's no way I'm lending it to anyone.

[Popsbengo]

BlueBoy, I'm not sure what you're telling us.  I was referring to flash-over burning - sudden rapid deflagration but not detonation as powder isn't a high explosive..  Ubique referred to detonation.   Please clarify which or both are wrong or mistaken.

Cheers

[ubique]

No detonation mentioned by me.

[One on top of two]

10 minutes ago, Popsbengo said:

BlueBoy, I'm not sure what you're telling us.  I was referring to flash-over burning - sudden rapid deflagration but not detonation as powder isn't a high explosive..  Ubique referred to detonation.   Please clarify which or both are wrong or mistaken.

Cheers

That’s what I’m talking about  flash over whatever you want to call it .

to be honest I mistakenly thought they where one of the same . 

Either way I think we can all agree neither would be welcome.

 

[Miseryguts]

11 hours ago, BlueBoy69 said:

I think this is one of those internet/shooting community fallacies or the phrase I like to use, it's one of those folkorical statements.

From a background of actual weapon testing as a contractor to the MoD measuring chamber pressures and many other things when a gun fires or a bomb goes bang, along with research into this, its highly unlikely detonation occurs. Firstly detonation is a shockwave driven decomposition event and what happens here is something different, a combination of extremely rapid burning (deflagration) due to the grain geometry (a flat bed, or towards one end or the other) and the effect of pressure wave formation on the propellant's burning rate.

As far as I can remember, what happens is when the case, or chamber for caseless guns, is mostly empty or partially full, the ignition phase of the propellant can result in dangerous pressure wave formation. These waves can reflect off the walls of the vessel without much attenuation as there's not much propellant there. If waves arrive at the right moment, they can add up, so increasing chamber pressure. Increasing the pressure increases the burning rate, which increases the pressure, which increases the burning rate, etc.. This oscillation occurs until the propellant burns away, the gun fails (the so-called detonation event), or for some reason, the phenomena stops.

Anyway, that's the basics of the more likely real reason for these blow-up with light charges of fast-burning powder in large cases. The other reason for this is probably double, or more loads of fast pistol powder by accident, something no one wants to own up to.

If you've actually seen the detonation of a high explosive within a chamber or the bore of a gun, the damage signature if very different to a high-pressure burst due to overpressure.

Anyway, for more info of pressure waves in guns, try the paper listed below.

Charge Design Considerations and Their Effect On Pressure Waves In Guns - ARBRL-TR-02277 (1990)

That or get the book titled 'Progress in Astronautics and Aeronautics: Vol 66 - Interior Ballistics of Guns'.

https://www.amazon.co.uk/Interior-Ballistics-Progress-Astronautics-Aeronautics/dp/0915928329

I have a copy, but due to its cost now, there's no way I'm lending it to anyone.

As above, go to:

https://www.thestalkingdirectory.co.uk/threads/subsonic-308-150g-or-220g.141266/

and scroll down to post 14. Written by some one quite familiar on this forum? 

M

 

[BlueBoy69]

19 hours ago, One on top of two said:

That’s what I’m talking about  flash over whatever you want to call it .

to be honest I mistakenly thought they where one of the same . 

Either way I think we can all agree neither would be welcome.

 

No problem 'One on top of two'.

It's a common misconception that detonation and deflagration are one and the same. Ian McCollum from Forgotten Weapons is always making the same mistake. I did email a few times when I worked for Jane's, but he didn't bother to reply.

Deflagration is 'simply' burning, so a thermal conductively-driven process.

Detonation is a shockwave (shock pressure) driven event. The initial shock, from a detonator for instance, causes the decomposition of the explosive material. The decomposition components react together, releasing energy. This energy reinforces the shockwave which continues to propagate through the material until all of it is consumed.

You do have the process called 'deflagration to detonation transition', DDT for short. This is where the burning process progresses so rapidly that the pressure level reached is high enough so that it can transition to a shock pressure-driven event, aka detonation. Many detonators and other similar devices work in this way.

For note, nitrocellulose-based and many other similar smokeless propellants are in reality denatured high explosives.

Edited September 23, 2019 by BlueBoy69
Mixed the words up for DDT, oops :O

[One on top of two]

14 minutes ago, BlueBoy69 said:

No problem 'One on top of two'.

It's a common misconception that detonation and deflagration are one and the same. Ian McCollum from Forgotten Weapons is always making the same mistake. I did email a few times when I worked for Jane's, but he didn't bother to reply.

Deflagration is 'simply' burning, so a thermal conductively-driven process.

Detonation is a shockwave (shock pressure) driven event. The initial shock, from a detonator for instance, causes the decomposition of the explosive material. The decomposition components react together, releasing energy. This energy reinforces the shockwave which continues to propagate through the material until all of it is consumed.

You do have the process called 'detonation to deflagration transition', DDT for short. This is where the burning process progresses so rapidly that the pressure level reached is high enough so that it can transition to a shock pressure-driven event, aka detonation. Many detonators and other similar devices work in this way.

For note, nitrocellulose-based and many other similar smokeless propellants are in reality denatured high explosives.

👍👍

[Popsbengo]

44 minutes ago, BlueBoy69 said:

No problem 'One on top of two'.

It's a common misconception that detonation and deflagration are one and the same. Ian McCollum from Forgotten Weapons is always making the same mistake. I did email a few times when I worked for Jane's, but he didn't bother to reply.

Deflagration is 'simply' burning, so a thermal conductively-driven process.

Detonation is a shockwave (shock pressure) driven event. The initial shock, from a detonator for instance, causes the decomposition of the explosive material. The decomposition components react together, releasing energy. This energy reinforces the shockwave which continues to propagate through the material until all of it is consumed.

You do have the process called 'deflagration to detonation transition', DDT for short. This is where the burning process progresses so rapidly that the pressure level reached is high enough so that it can transition to a shock pressure-driven event, aka detonation. Many detonators and other similar devices work in this way.

For note, nitrocellulose-based and many other similar smokeless propellants are in reality denatured high explosives.

👍  Nice to know we have some expert resource on this forum!

[gruntus]

Ditto. Thanks for actually taking the time to explain BlueBoy, its a fascinating topic. Very helpful.

👍

[GunsZen]

I have had some very consistent results with Tin Star and the Lapua 200gn sub heads. I shoot them through a 1-9 twist barrel. They will tumble in a 1-12 at least they did in mine. The Tin Star fills the cases up quite nicely as voids tend to mean inconsistent velocity. Low, consistent velocity ES is vital to keep vertical groups from stringing. 

[Scotch_egg]

I used Tin Star and 175gr Sierra March Kings. I got very consistent velocities. That was through my 18” Blaser Barrel

[TC]

4 hours ago, GunsZen said:

I have had some very consistent results with Tin Star and the Lapua 200gn sub heads. I shoot them through a 1-9 twist barrel. They will tumble in a 1-12 at least they did in mine. The Tin Star fills the cases up quite nicely as voids tend to mean inconsistent velocity. Low, consistent velocity ES is vital to keep vertical groups from stringing. 

Can you share your load details please?

Powder weight, brass spec and primer.

cheers

 

[Scotch_egg]

Cast can leave larger deposits in the silencer which are unwanted