6.5x55mm using Barnes ttsx 120gr - good development with Viht N540

[Ronin]

VO is only one part of the solution to ballistic problem

Magnetospeed are pretty accurate - next to my oehler 35 I get the same VO

Zero range data must be absolutely accurate to ascertain reliable drop data to “confirm “ VO

Altitude
Humidity
Atmospheric pressure
Scope height above bore
Accurate BC of bullet - not suggested one from manufacturer

All factors which make ascertaining VO downrange quite an exercise

Borbal by the way is a trusted source of information - suggest you look up PMax software which in my opinion is as good as quick load in certain powder applications

 

[zambezi]

Borbal by the way is a trusted source of information

Noted. And apologies if I sounded dismissive of his perspective.

I can only speak of my own methods and diligence. I fully expect to make some errors. Recursive checks have yet to reveal any glaring errors.

So, I humbly submit that the drop data test I have planned will be a useful cross-check.

For the record, Strelok suggests that 14 clicks on my Z6i scope separate a 100m zero from a 300m zero. I will publish data once drop tests are complete.

 

[malmick]

Per Erik Cortina's tutorial last month, there are three snugness states a chambered round can enjoy: "jump", "just-touching" and "jam"........... etc.

Thanks for your response, I need to go back and do some reading. The loads I'm developing for .223 and 6.5CM start out at 20 to 35 thou off the lands but I've not done any variation on those starting points yet. Might save myself some bother. Having said that the best of last weeks 6.5CM groups and todays .223 groups were well under 1/2 moa at 100m, so there might be no point in messing around until I'm able to extend the range a bit.

 

[Ronin]

It wasn’t a dig at you , I didn’t know if you knew of Borbals provenance

Good luck with the drop testing

I’ve found that shoot at 100 , withdraw to 200 shoot same point of aim no scope ajustment and so on back as far as on earth can go to be a very good method of checking actual data

Provided one has a tall enough target ,,,

 

[zambezi]

I’ve found that shoot at 100 , withdraw to 200 shoot same point of aim no scope ajustment and so on back as far as on earth can go to be a very good method of checking actual data

Provided one has a tall enough target ,,,

That sounds like a good way to eliminate any click variance in the optic.

My max range available is 300m. Per Strelok, the drop will be sub 50cm at 300m. So setting up a 1m high target at 300m should make your approach do-able. Cheers.

 

[borbal]

My max range available is 300m.

The 120 grain TSX 6.5 projectile has a quoted G1 BC of 0.412.

The difference in drop at 300m is 2.5 inches (63mm in new money) between a muzzle velocity of 2650 ft/sec and a muzzle velocity of 2800 ft/sec

Given that you seem to be grouping to about 1 MOA (according to the target you posted), your group size at 300m will be about 3.5 inches.

I respectfully suggest that in these circumstances, 300m is not far enough for you to check the accuracy of your MV.

 

[borbal]

The other thing I should mention is that the BC of 0.412 which Barnes quotes for that projectile is almost certainly wrong. I ran that shape through my drag program Bullet Design form and the G1 BC at around Mach 1.5 is about 0.46. So, if you working back to MV from the drop, that is something else to keep in mind.

 

[zambezi]

More N540 testing today. Sadly some of the data is worthless: one load showed a group that started to grow. Urgh. The mod had worked loose. Irritating. Only my 6.5x55mm mod does that. Need to make a note to self to check after every shot.

But I do have some encouragement. Today's range work is at 100m. This load is giving an MV close to the Sako factory load. Still a little shy of the 2800fps I sought, but reliably accurate loads exist above and below this charge weight so I have probably found a node upon which I will settle.

Next step will be to make up 10 of these and collect meaningful SD, ES and group data.