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subsonic 308


remy17

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No joy so far, looked through back issues from 2001, 02, 03 and 05 (although not complete), it made me weep to look at the prices of PM Scopes and powder......

 

 

Although very amusing to read the "this product can do no wrong" school of journalism that was Shooting Sports... :lol:

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  • 3 months later...
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Sorry to drag this thread back up from the depths,

Has anybody had any success yet? If I recall correctly, the sako TRG has a 1 in 11" twist to allow it to stabilise the lap subsonics, so in hoping my sako will also do it with an 11" twist. I've a pot of trailboss on order and foxes to deal with where I need a quiet load, and I think a .22subsonic is inhumane at the distances they will come in (100+yds) but the area is amazingly hilly for this part of the country so backstops are ok for a change :)

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No joy so far, looked through back issues from 2001, 02, 03 and 05 (although not complete), it made me weep to look at the prices of PM Scopes and powder......

 

 

Although very amusing to read the "this product can do no wrong" school of journalism that was Shooting Sports... :lol:

 

 

Wait till you see some of the terrible truth coming soon.

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Federal cases are good as they have slightly less case volume than others, for projectiles try either the sierra or hornady 180 RN. You'll need to experiment on your load working down rather than up (without a can on in case of baffle strikes). Ive not done a whole lot of testing but watch out for cold bore shots - mine tended to be very low with the following shots then grouping consistently. This could cause a problem in the field! A 1:12 stabilised the 180's just fine.

 

Contrary to some advice I've seen loading a BTHP backwards produced awful results, for me anyway, I could actually see the bullet looping and swirling to the target - it held about a minute of barn door literally.

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The round 180's shot fine out of my 1-12", 20" barrel but spire points only worked up to 150gr. 180 noslers were fun as ypu cpuld watch them flap around like dolphins on their way to the target and i saw one strike it full in sideways making a neat sideways hole but if you dont try them, who knows? Trail boss is very easy to use and i settled at 9.3gr for spme 150 flat nose bullets for 3/4" accuracy at 100 yards buy 180 round nose sierras worked equally well.

 

Like i said, expansion is doubtfull and test 'bulk' targets tended to be cleanly holed but it was all just experimental fun. I imagine these want a very definate backstop as they will ricochet like a pebble but all i did was test them in front of a large sandtrap under a rockface so fairly definate no go beyond.

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Sorry to drag this thread back up from the depths,

Has anybody had any success yet? If I recall correctly, the sako TRG has a 1 in 11" twist to allow it to stabilise the lap subsonics, so in hoping my sako will also do it with an 11" twist. I've a pot of trailboss on order and foxes to deal with where I need a quiet load, and I think a .22subsonic is inhumane at the distances they will come in (100+yds) but the area is amazingly hilly for this part of the country so backstops are ok for a change :)

 

 

Yes, I have great success, my secret issuing something called a .300 Whisper

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  • 7 years later...
34 minutes ago, Dr. Strangelove said:

Gotcha, thanks! Can I ask what twist your barrel is? My .308 is 1:12 so am wondering whether it’ll stabilise heavier bullets 

1:11 @ 24” barrel 

and yes your be ok with a 1:12  ( just ) 

if it was me I would go with 168 grain .

 

 

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Hi, glad to see this thread resurrected, I have developed a subsonic load using Green  Dot, but would like to try the N32C as a pal of mine has a tub of it that he wants to split. So, if anyone has successful loads to share, I am interested.

My present load is:

1:11 twist, 24 in barrel

165gr H&N plated RN bullet, 6.8gn Green Dot COAL 2.645 PPU brass CCI 200 primer

Av MV 1058fps Sd 8fps

1.5 moa ES at 200 yd,  1 moa ES at 60 yd

Ear muffs not required

Miseryguts, slightly stir crazy in Monmouthshire

P.S. Green Dot is great in my 45-70 too, but always open to new ideas.

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  • 2 weeks later...

Using Trail Boss and not N32C I worked a load up using the Hornady 220Grn RN bullets which was good enough for vermin shooting in the woods.

I recall reading that the powder volume density for N32C was slightly lower than Trail Boss, but there wasn't much in it.

The thread is here...

 

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16 minutes ago, cooter said:

I recall reading that the powder volume density for N32C was slightly lower than Trail Boss, but there wasn't much in it.

Hi Cooter,

It's the heat of explosion (energy content) of N32C Tin Star that is very slightly lower than Trail Boss. So 3,040 kJ/kg for N32C and 3,070 kJ/kg for Trail Boss.

The volumetric density of N32C is higher (it weighs more per unit volume) than Trail Boss. The volumetric density of N32C is 0.459 g/cm3 and 0.310 cm3 for Trail Boss.

So you can roughly load weight-for-weight, but not volume-for-volume.

For example, a 308 case loaded to COAL of 2.800" with the aforementioned Hornady 220 gr RN and a full case of Trail Boss (14.49 gr), according to QuickLOAD's estimation, gives a pressure of 34,511 PSI and an MV of 1,319 ft/s from a 20" barrel.

If you load volume-for-volume, the same case filled with N32C weighs 21.45 gr and gives a pressure of 62,514 PSI and an MV of 1,627 ft/s. That pressure of over the maximum average pressure allowed for the cartridge, so very high!

If you load weight-for-weight, 14.49 gr of N32C gives a pressure of 35,639 PSI and an MV of 1,319 ft/s. So identical velocity, and only slightly higher pressure.

The pressure is different as the two grain types and hence their burning characteristics are very different, with N32C being a hollow tube and Trail Boss a thin washer. There are obviously lots of other minor differences, such as coating, deterrents, etc., etc., but their morphology is the primary one.

So, as long as you load weight-for-weight, and start off at the lowest recommended fill weight of a Trail Boss load, you should be fine most modern cartridges.

Neil

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44 minutes ago, BlueBoy69 said:

Hi Cooter,

It's the heat of explosion (energy content) of N32C Tin Star that is very slightly lower than Trail Boss. So 3,040 kJ/kg for N32C and 3,070 kJ/kg for Trail Boss.

The volumetric density of N32C is higher (it weighs more per unit volume) than Trail Boss. The volumetric density of N32C is 0.459 g/cm3 and 0.310 cm3 for Trail Boss.

So you can roughly load weight-for-weight, but not volume-for-volume.

For example, a 308 case loaded to COAL of 2.800" with the aforementioned Hornady 220 gr RN and a full case of Trail Boss (14.49 gr), according to QuickLOAD's estimation, gives a pressure of 34,511 PSI and an MV of 1,319 ft/s from a 20" barrel.

If you load volume-for-volume, the same case filled with N32C weighs 21.45 gr and gives a pressure of 62,514 PSI and an MV of 1,627 ft/s. That pressure of over the maximum average pressure allowed for the cartridge, so very high!

If you load weight-for-weight, 14.49 gr of N32C gives a pressure of 35,639 PSI and an MV of 1,319 ft/s. So identical velocity, and only slightly higher pressure.

The pressure is different as the two grain types and hence their burning characteristics are very different, with N32C being a hollow tube and Trail Boss a thin washer. There are obviously lots of other minor differences, such as coating, deterrents, etc., etc., but their morphology is the primary one.

So, as long as you load weight-for-weight, and start off at the lowest recommended fill weight of a Trail Boss load, you should be fine most modern cartridges.

Neil

Neil,

It was your first point that I recalled, but thanks for expanding it. 👍

Just to add to your post.

Based on the above powder information it means that to use the same powder weight of N32C as could be used of Trail Boss the case will be only half full, and to get it down to sub sonic level (10 - 11 Grns) means it will be around the 50% fill level, which can mean an uneven burn, or using fillers.

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3 hours ago, cooter said:

Based on the above powder information it means that to use the same powder weight of N32C as could be used of Trail Boss the case will be only half full, and to get it down to sub sonic level (10 - 11 Grns) means it will be around the 50% fill level, which can mean an uneven burn, or using fillers.

N32C Tin Star seems fine with partial fills, and like many of Vihtavouri's propellants, it does not seem to be very position sensitive. Just peruse to Vihtavouri's cowboy action area, many start around 50% full.

I've used it in my 22 PPC (6.0 gr, 44.5% full), 300 AAC Blackout (4.8 gr, 44.2%), and 45-70 (10.5 gr, 40.9%). I use no fillers and the accuracy is good.

If you are concerned that the low fill may result in the potential for pressure oscillations (oft most likely incorrectly referred to as propellant detonations), it would be best to stick with Trail Boss until it runs out and then build-up loads that use a filler. Though using fillers with a suppressor is probably not a good idea though 😟

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Hi, Slightly off topic, but as Blueboy said sometime ago, these fast pistol powders do not suffer from the detonation effect. As I cannot travel to shoot, I have been using subsonic loads with a moderator on 22, 223, and 308 to shoot at home without drawing attention. Obviously the 22 is bought, but the 223 and 308 both use Green Dot (which is the same speed as N32C).  2.8gn with 55gn bullet gives 1090fps average in 223 with ES 31fps and Sd  11.3

6.8gn with 165gn bullet gives 1058 fps average in 308 with Sd 8

As an aside, I have developed a little Excel file which calculates the change in elevation required from your normal 100yd zero for a subsonic load at various ranges. You input the velocity of your normal 100yd zero load, the velocity of your subsonic load, and the range you are shooting at (in feet), and the file then returns the change in elevation in inches, mr, and moa. It is not exact, but with my rifles and loads it gets you on paper within 1/2 inch.

If anyone is interested, PM me and I can e mail the file to you.

M with too much time on his hands in Monmouthshire

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47 minutes ago, Miseryguts said:

Hi, Slightly off topic, but as Blueboy said sometime ago, these fast pistol powders do not suffer from the detonation effect. As I cannot travel to shoot, I have been using subsonic loads with a moderator on 22, 223, and 308 to shoot at home without drawing attention. Obviously the 22 is bought, but the 223 and 308 both use Green Dot (which is the same speed as N32C).  2.8gn with 55gn bullet gives 1090fps average in 223 with ES 31fps and Sd  11.3

6.8gn with 165gn bullet gives 1058 fps average in 308 with Sd 8

As an aside, I have developed a little Excel file which calculates the change in elevation required from your normal 100yd zero for a subsonic load at various ranges. You input the velocity of your normal 100yd zero load, the velocity of your subsonic load, and the range you are shooting at (in feet), and the file then returns the change in elevation in inches, mr, and moa. It is not exact, but with my rifles and loads it gets you on paper within 1/2 inch.

If anyone is interested, PM me and I can e mail the file to you.

M with too much time on his hands in Monmouthshire

I’m going to having a play with .223 subs And N32C ( got a a couple of lbs of it ) as I have a little job for them and I think there be fun too . I do Use my .308 now and then for close range foxing around my horse paddocks around the winter months as  the horses are Stabled at night . And found them to be very successful 👍 

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21 minutes ago, Miseryguts said:

these fast pistol powders do not suffer from the detonation effect.

It's unlikely to be a detonation, this is one of those folkloric myths bandied around the internet. It's to do with pressure wave oscillations. A large empty case (or chamber) and a small charge of propellant can result in a destructive pressure wave forming.

Essentially the propellant starts to burn and a pressure wave travels from the burning propellant charge, say at the back of the case, to the front of the case or chamber. The wave strikes the front of the case/chamber/base of the projectile and reflects back towards the burning charge. If the reflection coincides with the peak of another pressure wave, the pressure is increased. This reflection/reinforcement can oscillation backwards and forwards until the pressure exceeds the strength of the gun, blowing it up.

The wave can, of course, oscillate up and down too, like in a small arms cartridge case with a small amount of powder running along the bottom of the case. In small arms cases, both the up and down, and the forwards and backwards likely occur.

Anyway, it's not detonation of the charge, the failure of the gun is due to excessive pressure caused by pressure oscillations. Pressure oscillations and differentials are the bane of big gun designers.

Look up the US Army Ballistics Laboratory paper (ARBRL-TR-02277) from 1990 titled 'Charge Design Considerations and Their Effect On Pressure Waves In Guns'. This is also in the AIAA book I have titled 'The Interior Ballistics of Guns' with the same paper in. That book's rather expensive now (link), so just go for the paper.

Neil

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2 minutes ago, BlueBoy69 said:

It's unlikely to be a detonation, this is one of those folkloric myths bandied around the internet. It's to do with pressure wave oscillations. A large empty case (or chamber) and a small charge of propellant can result in a destructive pressure wave forming.

Essentially the propellant starts to burn and a pressure wave travels from the burning propellant charge, say at the back of the case, to the front of the case or chamber. The wave strikes the front of the case/chamber/base of the projectile and reflects back towards the burning charge. If the reflection coincides with the peak of another pressure wave, the pressure is increased. This reflection/reinforcement can oscillation backwards and forwards until the pressure exceeds the strength of the gun, blowing it up.

The wave can, of course, oscillate up and down too, like in a small arms cartridge case with a small amount of powder running along the bottom of the case. In small arms cases, both the up and down, and the forwards and backwards likely occur.

Anyway, it's not detonation of the charge, the failure of the gun is due to excessive pressure caused by pressure oscillations. Pressure oscillations and differentials are the bane of big gun designers.

Look up the US Army Ballistics Laboratory paper (ARBRL-TR-02277) from 1990 titled 'Charge Design Considerations and Their Effect On Pressure Waves In Guns'. This is also in the AIAA book I have titled 'The Interior Ballistics of Guns' with the same paper in. That book's rather expensive now (link), so just go for the paper.

Neil

I stand corrected! My apologies for my loose tongue

M going back to sleep in Monmouthshire

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36 minutes ago, Miseryguts said:

I stand corrected! My apologies for my loose tongue

No apology needed. It's just one of those myths you see all the time and I try my best to bust them.

It is possible that a DDT reaction, deflagration to detonation, may occur if the pressure gets high enough. I don't know offhand what pressure this occurs at, so would have to look it up.

For note, many single and double base propellant can be made to detonate as they are essentially denatured high explosives. It's a problem for ammo stored in vehicles if struct by very high-speed objects, such as shell, or amour (spall) fragments (these are not shrapnel, as that's another erroneous internet and media mistake to call frags shrapnel), or the jet from a shaped charge. The pressure from the impact of the frags or the jet tip can be high enough to detonate the propellant. As if it wasn't bad enough for them to burn within the confined space of a turret, or vehicle hull!

Anyway, enjoy your snooze 😴

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Afternoon, oomans.

We have a nice subsonic load for .308"

  • 240 gn cast lead bullet (NOE mould, 311-247 FN ,  gas checked, sized appropriately)
  • 10.6 grains of TrailBoss
  • CCI large rifle primer
  • GGG case

We find this gives us an average muzzle velocity from a 16", 1 in 8 twist, barrel of 1068 feet per second, with a standard deviation of 6.7

That gives us a 1.6 MoA group at 100 metres, which we finds quite adequate. We tend not to use it beyond 300m.

Problems experienced:

  1. Zealous RCOs insisting we wait 30 seconds afore opening the bolt on what they perceive to be a dud round (we use a DTA rifle and an ASE Utra moderator)
  2. Butts crew not spotting the impact as the rounds, at 300m range, drop in from high above like a mortar and so don't splash high up in  the sand where they are looking. 

Once our supplies of TrailBoss expire we'll move on to either Viht's N32C or Reload Swiss's RS30, both of which we have used successfully in other calibres for low power rounds.

 

 

 

 

 

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