Bto. Beating dead horse

[Bc'z]

And that makes complete sense.
Man the things I've learned here, you just cant put a price on.

 

[Bc'z]

Guff, Guff, Guffey.....
I couldn't resist... He it's your gun, you ammo. Shoot as many or as few in a group as you want... When someone else pays for your stuff they can tell you how many to shoot..

I just got it!!!

 

[Texas10]

Maybe on a different thread, but I'd really appreciate a thoughtful discussion on the whole neck tension aspect of load tuning. Some recent high speed camera recordings seem to be shedding new light on what happens in the micro seconds following primer detonation. Bullet is driven fully into lands by the primer, which seems to explain why primer selection is important in load tuning. But where is neck tension in that scenario?

Crap, I think I just brained my damage.

 

[Mad_Charlie]

Do you have a link to these recordings?

 

[Dgd6mm]

And that makes complete sense.
Man the things I've learned here, you just cant put a price on.

As I was reading this thread, this was my thought exactly, more than once. Excellent information you guys, thanks.

 

[ballisticxlr]

Came for some TCB references but no such luck so,

My method during load development is to go touch, -.010, -.040, -.080, -.120 and see how things roll. I've not had to fiddle around with increments much smaller than that but my requirements are for ~.5MOA for 5 shots and <.75MOA for 10 shots so it's not nearly as demanding of a performance standard as some other's. I don't even sort my bullets. Just haven't had to. I think a lot of people get into the weeds here. Benchrest guys and I'd even say serious F-class guys might justifiably get this anally retentive but I just don't have the need.

 

[Peebles24]

Ok but I dont want to hear any guff about not being 5 shot groups.View attachment 1103427 funny how shortly after my response earlier my friend/ gunsmith called saying how he was amazed at how .005 in seating depth made such a change.
He shot this target with his 6bra this afternoon. View attachment 1103428
This was 5 shots at 100

I was always told.... um well you know the story. Sorry had to bc

 

[dcali]

Maybe on a different thread, but I'd really appreciate a thoughtful discussion on the whole neck tension aspect of load tuning. Some recent high speed camera recordings seem to be shedding new light on what happens in the micro seconds following primer detonation. Bullet is driven fully into lands by the primer, which seems to explain why primer selection is important in load tuning. But where is neck tension in that scenario?

Crap, I think I just brained my damage.

My understanding is that neck tension is more about consistent ignition. You want the volume of the case to be the same for every round as the powder ignites. Inconsistent neck tension will allow this to vary slightly, as neck tension is one of the reasons the bullets stay put. This would also be consistent with why jammed bullets often show good accuracy - ignition is more consistent with the increased starting force. As with many of these issues, there is more than one way to skin a cat.

 

[Texas10]

Do you have a link to these recordings?

Here it is; http://forum.accurateshooter.com/attachments/arl-tr-7479-pdf.1092789/

And more light reading: https://apps.dtic.mil/dtic/tr/fulltext/u2/a341390.pdf

This link contains much discussion on related articles; http://forum.accurateshooter.com/threads/primer-output-pushes-bullets-into-rifling.3966017/

 

[Mad_Charlie]

Much appreciated!

 

[Texas10]

My understanding is that neck tension is more about consistent ignition. You want the volume of the case to be the same for every round as the powder ignites. Inconsistent neck tension will allow this to vary slightly, as neck tension is one of the reasons the bullets stay put. This would also be consistent with why jammed bullets often show good accuracy - ignition is more consistent with the increased starting force. As with many of these issues, there is more than one way to skin a cat.

I think you'll enjoy the second link I provided as it describes the M80 ball ammo research to determine what was causing a delayed ignition issue not exhibited by the M62 tracer that was loaded identically with the exception of the tracer bullet being loaded deeper into the case compared to the M80. (See conclusion on page 13 of the study.)

Testing determined that the cause of the ignition delays was the small extra free space volume under the bullet in the M80 compared to the M62. Seating the bullet deeper eliminated the ignition delays but proved to be a less than ideal solution due to the various weapons that used the M80 ammo.

The final recommendation was to change the propellant from WC846 to WC846FS (flash suppressed) which has a potassium sulphate coating, but of note was that in testing it as observed that WC846FS was identical in performance to WC749 used in M118 long range sniper round.

Once source I came across remarked that WC749 is the same as Winchester W748, although I was not able to confirm that.

 

[dcali]

Thanks for the links. I hadn’t seen those. I’ll give them a read when I get a moment. I’ve been doing a lot of reading up on internal ballistics lately and I’m beginning to wonder if seating depth and neck tension aren’t primarily explained by some sort of ignition optimization. Just a thought- I don’t know if any evidence that proves or refutes that. But it’s somethint I’ve been looking into.

 

[Metal God]

Ok. So I do get that. Its the .003 of extra bullet length is inside the case now. Which means increased pressure in that one cartridge, no?


No not really at all . We are talking rifle cartodges with slow powders . Reducing case volume by seating deeper which causes pressure spikes is more to do with small cases and fast powders . A good example would be the small 9mm case and a powder like Titegroup . That little case starts out with very little space to fill . Add a fast expanding gas like Titegroup produces and you need to take caution in what your doing with seating depth .

Now take a much larger case like a 6br , 308 , 30-06 with a MUCH slower power in comparison and seating deeper has much less of a effect .

In a rifle cartridge I’m much more concerned about pressure when I’m getting closer to the lands then I am seating deeper .