Barnes TSX & TR140 development

[redding]

Finally got the recipe right for Barnes TSX 130grn & TR140 powder

This is a .308 Sauer with an 18" barrel

50.7 grains of TR140 (no pressure signs)

Barnes TSX 130 seated 50 thou off the lands

Average muzzle velocity 2894 (quickload predicted 2884)

 

I did notice something strange, as I fired each batch with increased powder charges the point of impact dropped by about an inch from the lowest charge to the highest, anyone shed any light on why please. I would have thought it would have gone higher.

 

[redding]

Wow, over 3 months & 116 views and no-one has an answer to my question below. I guess it has never happened to anybody else or nobody knows why! He ho.

 

I did notice something strange, as I fired each batch with increased powder charges the point of impact dropped by about an inch from the lowest charge to the highest, anyone shed any light on why please. I would have thought it would have gone higher.

[gbal]

Wow, over 3 months & 116 views and no-one has an answer to my question below. I guess it has never happened to anybody else or nobody knows why! He ho.

 

I did notice something strange, as I fired each batch with increased powder charges the point of impact dropped by about an inch from the lowest charge to the highest, anyone shed any light on why please. I would have thought it would have gone higher.

OK...quick suggestion: increasing the powder will increase the velocity-maybe not much,but that should 'flatten the trajectory'-again not much especially over a short distance like 100y;about an inch would be in the ball park.If your initial low load POI was high,then it should 'come down' as the velocity increases,and trajectory reduces,toward your aiming mark....if it was initially low,you might expect it to come up..Individual barrel harmonics though might throw this either way-the barrel is actually vibrating as the bullet leaves,and just where it goes depends on just where the barrel is in it's vibration cycle.But being regular in effect,sounds more like the velocity.Or barrel heating,especially a light barrel...then shots can go walkies,usually up.Or all of these these,combined!

The three shot group is presumably stable(though it's not clear what it was aimed at...).

[Will0]

The barrel could be at a different point of its 'barrel whip' cycle?

[srvet]

Got to love the 130g TTSX, my load is 46g of H4895, works a treat.

[Laurie]

The barrel could be at a different point of its 'barrel whip' cycle?

 

 

That'll be the cause. Barrel and action harmonics see the muzzle at marginally different elevations under different chamber pressure / bullet 'barrel-time' combinations. Basically, your barrel bends after you fire and the muzzle passes through a range of elevations. Increasing the powder charge (i) increases the stresses on the metalwork so the 'bending' may become accentuated, and (ii), the main factor, the bullet travels faster, exits the muzzle quicker, and therefore leaves the rifle at a different point in the cycle - in this case lower. Some sporting rifles with thin whippy barrels and powerful cartridges can see large impact changes for a single grain charge weight change. I had an old BSA CF2 in .30-06 some years back that saw huge movements on the paper at 100 yards during working loads up. In this case, they shot higher if I remember right, but it can work in either direction depending on the action and barrel characteristics.

[redding]

Thanks for the replies, now I understand.

In the past the POI has risen as the powder charge increases.

 

It is only an 18" barrel so I thought most of the "whip" had gone, wrong I guess.

Regards

[redding]

Thanks for the replies, now I understand.

In the past the POI has risen as the powder charge increases.

 

It is only an 18" barrel so I thought most of the "whip" had gone, wrong I guess.

Regards

 

OK...quick suggestion: increasing the powder will increase the velocity-maybe not much,but that should 'flatten the trajectory'-again not much especially over a short distance like 100y;about an inch would be in the ball park.If your initial low load POI was high,then it should 'come down' as the velocity increases,and trajectory reduces,toward your aiming mark....if it was initially low,you might expect it to come up..Individual barrel harmonics though might throw this either way-the barrel is actually vibrating as the bullet leaves,and just where it goes depends on just where the barrel is in it's vibration cycle.But being regular in effect,sounds more like the velocity.Or barrel heating,especially a light barrel...then shots can go walkies,usually up.Or all of these these,combined!
The three shot group is presumably stable(though it's not clear what it was aimed at...).

Hi

The three shot group was aimed at the target disk in the picture, on the paper there were 4 other disks and the POI got lower as the charge increased, but now I understand.

[Laurie]

 

It is only an 18" barrel so I thought most of the "whip" had gone, wrong I guess.

 

 

 

Studies have shown that even .22LR smallbore match rifles see barrel harmonics inspired movements on firing. There's no such thing as a completely 'whip-free' gun barrel, well not until somebody invents a handheld laser cannon

[gbal]

As Laurie says,every barrel will have some harmonic displacement (vibration..."whip"..).

There may be more if the barrel length is increased,and less if the barrel is thicker. Rifles of course come to different compromises on this....and there is some controversy still about the trade offs-short very fat barrels were tried in bench rest,eg,but there we're into the .001 " group size differences,either way..(and complicated by velocity loss).And stalking rifles don't want undue weight,especially as very minor differences in performance hardly matter,so tend to the slender-first shot matters more,anyhow,and you have to carry it!

 

 

 

Gbal

 

PS the fun is quite general-"every object in the universe-be it palace ,plate ,pendulum or pancake,has a natural period of vibration"...that's why sopranos can break wine glasses by hitting the frequency the glass vibrates at! Beer glasses seem more resilient to those frequencies,so even excited post shoot discussions over a pint-unimaginable,I know- seldom end in spilled beer. :-)

 

The Beach Boys album "Pet Sounds" track "Good Vibrations" adds a human dimension.