Trail Boss and 308 Subsonic Loading

[lonely_wolf]

I've been reading up on hand loading .308 win subsonic ammunition. Easy enough to check if a bullet is still lodged in the barrel, but SEE is a bit more intimidating...

My understanding is that SEE is caused by too little powder in the case (<30%) which causes improper ignition and disastrous effect. However, due to the bulkiness of Trail Boss it safely fills the 308 case even in low charges effectively eliminating the possibility of SEE.

Am I correct?

Also, I have found one comment stating that Trail boss is a filthy powder leaving significant carbon residue. What have been people's experiences? .
N320,Unique, and Tite Group were mentioned as cleaner alternatives. The majority of literature I have found has supported Trial boss as superior. I have never heard of N320.

 

[rjacobs]

Ive shot a ton of trail boss loaded 308 subsonics and never had an issue. Some people advocate magnum primers and opening up the flash hole and what not, but I dont do any of that and havent had any issues. 10.5g of trail boss looks like a 44g load of Varget.

 

[roggom]

I have been using Trailboss for reduced loads and shooting cast bullets for a few years. Red dot, Unique and all those other recipes will work, but it takes up so little space in the cartridge case.

All that cartridge case tapping, tilting the rifle back and other routines are not necessary to get a consistent burn with TB. Also less chance of double charging the case. TB is a much more forgiving powder.

 

[lonely_wolf]

[...]but it takes up so little space in the cartridge case.

All that cartridge case tapping, tilting the rifle back and other routines are not necessary to get a consistent burn with TB. [...]

...and eliminates the opportunity for SEE?

 

[roggom]

It helps mitigate SEE. One of the causes is that the powder can lay along the body of the case and the primer will ignite the whole surface of the powder vs back to front. If you are using a pistol powder and shooting from a bench you can gently tap the round on the bench to pack the powder against the flash hole then single feed them. Others recommend tilting the rifle up then down before firing to the same thing. It is just a pain in the ass ritual, but I always did it "just in case" as a matter of fact, I catch myself doing the tap with all ammo when I shoot from the bench, just a funky habit. Trailboss is so bulky, it takes up at least half of the case capacity (if not more) so you can load and shoot like any other. Just make sure your projectile has left the barrel if shooting from a long barreled rifle.

Just think of it this way. If you have ever seen one of those flaming shots at the bar, they are lit and burn on top of the glass. Now pour that on to the bar and light it.......wooof.

 

[lonely_wolf]

Roggom, that is the clearest explanation of SEE I have read. Thank you.

 

[7magsavage]

What is SEE anyway ?

 

[ksthomas]

SEE = Secondary Explosive Effect, aka, a pressure excursion. Bad news, not readily reproducible on a regular basis, but definitely well documented enough to avoid reduced charges of slow burning powders, especially in large capacity cases.

 

[7magsavage]

Thank you for the speedy reply Mr. Thomas.

Steve

 

[lonely_wolf]

What is SEE anyway ?

Sorry. The acronym was originally explained in the title, but I changed the title of the tread.

 

[7magsavage]

Sorry. The acronym was originally explained in the title, but I changed the title of the tread.

No problem. Just starting research on subsonic loads since I'm looking into a can within the next year. Not really expecting much as far as accuracy from a sub sonic load, just something to tinker with.
So, how is this SEE issue dangerous? Not sure I quite understand the secondary explosion thing. Is it like a delayed powder ignition or something? Or is it more dangerous than that?

 

[lonely_wolf]

7magsavage, two of the more quoted links on subsonics:

Develop Subsonic

Gunwriters' Handloading Subsonic Cartridges, Part 1


Some Trail Boss info:

http://www.imrpowder.com/PDF/Trail-Boss-data.pdf

 

[lonely_wolf]

Next question: Does a 308 subsonic loaded with Trail Boss have enough pressure to consistently expand the case properly? Or will shooting light loads repeatedly out of the same case eventually cause them to acquire excessive headspace?

 

[ksthomas]

7magsavage,

Yes, SEE can be extremely dangerous, but it's not really an issue with what you're doing here. SEE is a phenomenon that relates to reduced charges in large capacity cases, specifically charges of very slow burning powders. Using a powder like 4831 in a 300 Win Mag, and trying to develop very light loads would be where you're more likely to encounter this. And the results can be dramatic, acting like a gross overcharge and producing extremely high pressures (thus the "pressure excursion" notation) and leading to catastrophic failures' Blown bolts, shattered receivers, the whole deal. As I said, the situation isn't readily reproducible in a lab environment, but it's well documented enough that there's little question as to its existence. Light charges of faster burning powders, say, 4895 in the situation I mentioned above, don't seem to be subject to these excursions. There have been a few pieces done on this, but it's been a while since I've seen anything in print. Homer Powley, William Davis, and several of the old NRA tech staff had done some work in this field that was pretty much the standard today.

The reduced charge question in re subsonic rounds s a very different issue, and not one really subject to SEE. The real problems there relate to load density and powder positioning within the case. The major problem with these is the very different results that can be observed when the firer is shooting level, or aiming drastically up or downhill. The powder respositions itself within the case and can give drastically different velocities. Serious problem for those who use these rounds in the field. This is one reason the 300 Blk Out is so much better suited to this sort of role than the standard 308 Win, using greatly reduced charges. It's an interesting field, and one that has plenty of obstacles to overcome in creating reliable ammunition.

 

[7magsavage]

7magsavage, two of the more quoted links on subsonics:

Develop Subsonic

Gunwriters' Handloading Subsonic Cartridges, Part 1


Some Trail Boss info:

http://www.imrpowder.com/PDF/Trail-Boss-data.pdf

Thank you for the links sir.