Pressure signs...

[Gnzrme]

I loaded some 6.5 Creedmoor with VV160 43.6gr. I lengthened out the seating depth about 30k, still well away from the lands.. I was having heavy pressure signs compared to the same load but 30k shorter... Would increasing the OAL but still away from the lands increase pressure? I would think that it would decrease not increase. ..

 

[Sako man]

What do you consider heavy pressure signs? A posted picture would really help. There are many false pressure signs. But in general the closer you're to the lands the higher the pressure. So many variables.

 

[AIdog]

Closer to the lands will always increase the pressure... Bad idea working towards lands without dropping the charge first.

 

[farmer7]

What do you consider heavy pressure signs? A posted picture would really help. There are many false pressure signs. But in general the closer you're to the lands the higher the pressure. So many variables.

Closer to the lands will always increase the pressure... Bad idea working towards lands without dropping the charge first.

Closer to the lands will actually decrease pressure, until you make contact with them. Quickload suggests adding 7200psi if you're seated to touch the lands.

 

[Sako man]

Closer to the lands will actually decrease pressure, until you make contact with them. Quickload suggests adding 7200psi if you're seated to touch the lands.

Please provide something that states that. By your comment it makes no sense to add PSI if your at the lands.

I would not advise the OP to add any powder. He needs to post images so someone can make an accurate assessment of what he is talking about.

 

[AIdog]

Yes some more info on this subject would be much appreciated...

 

[gewehr]

here is one way of looking at it, by seating further out the bullet occupies less volume in the case which will reduce pressure for the same charge, also peak pressure doesn't occur well until after the bullet is fully engraved by the rifling. However giving the bullet more room can decrease pressure under the right circumstances as well as long as its not contacting he rifling

 

[farmer7]

Please provide something that states that. By your comment it makes no sense to add PSI if your at the lands.

I would not advise the OP to add any powder. He needs to post images so someone can make an accurate assessment of what he is talking about.

What I meant, all other things being equal, i.e. powder charge, increasing the o.a.l. of the cartridge will decrease pressure as long as the bullet isn't jammed in the lands, when its jammed pressure increases, a lot. How much exactly I don't know but QuickLoad suggests adding 7200 psi to your existing pressure.

A load using 168gr VLD's out of my .308 loaded 0.1" longer showed a 35fps drop in velocity over the chronograph.

The way I read it the OP wasn't about to load more powder, he was asking about pressure vs c.o.a.l.

This is what Bryan Litz says on the matter:

"The primary effect of loading a cartridge long is that it leaves more internal volume inside the cartridge. This extra internal volume has a well known effect;for a given powder charge, there will be less pressure and less velocity produced because of the extra empty space. Another way to look at this is you have to use more powder to achieve the same pressure and velocity when the bullet is seated out long. In fact, the extra powder you can add to a cartridge with the bullet seated long will allow you to achieve greater velocity at the same pressure than a cartridge with a bullet seated short.

When you think about it, it makes good sense. After all, when you seat the bullet out longer and leave more internal case volume for powder, you’re effectively making the cartridge into a bigger cartridge by increasing the size of the combustion chamber. "

Full version here:

http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-1/

 

[Sako man]

What I meant, all other things being equal, i.e. powder charge, increasing the o.a.l. of the cartridge will decrease pressure as long as the bullet isn't jammed in the lands, when its jammed pressure increases, a lot. How much exactly I don't know but QuickLoad suggests adding 7200 psi to your existing pressure.

A load using 168gr VLD's out of my .308 loaded 0.1" longer showed a 35fps drop in velocity over the chronograph.

The way I read it the OP wasn't about to load more powder, he was asking about pressure vs c.o.a.l.

This is what Bryan Litz says on the matter:

"The primary effect of loading a cartridge long is that it leaves more internal volume inside the cartridge. This extra internal volume has a well known effect;for a given powder charge, there will be less pressure and less velocity produced because of the extra empty space. Another way to look at this is you have to use more powder to achieve the same pressure and velocity when the bullet is seated out long. In fact, the extra powder you can add to a cartridge with the bullet seated long will allow you to achieve greater velocity at the same pressure than a cartridge with a bullet seated short.

When you think about it, it makes good sense. After all, when you seat the bullet out longer and leave more internal case volume for powder, you’re effectively making the cartridge into a bigger cartridge by increasing the size of the combustion chamber. "

Full version here:

http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-1/

I see.

In either event the OP needs to give us more info if he wants an answer.

 

[BuzzBoss915]

I loaded some 6.5 Creedmoor with VV160 43.6gr. I lengthened out the seating depth about 30k, still well away from the lands.. I was having heavy pressure signs compared to the same load but 30k shorter... Would increasing the OAL but still away from the lands increase pressure? I would think that it would decrease not increase. ..

I'm going to take a wild stab at it:

All things being equal and not making contact with the lands; this should not increase internal pressure. If, on the other hand, the OP has misjudged things, and IS contacting the lands, then he WILL see higher pressures. So, what he is saying runs contrary to the law of physics, same exact load, different seating depth but higher pressure? Nope, something else is going on? We really need more information. Why does he think he has higher pressures? BB

 

[Fred_C_Dobbs]

Slightly OT but this thread has touched on precisely why TresMon, in his reloading tutorials stickied in this forum, is adamant that you should jam seat when determining your max load. That way, if you screw the pooch and accidentally load one long into the lands, you don't blow your rifle to hellen gone.

 

[Gnzrme]

I am not at a place that I can get a picture of a casehead, but I can see a bright spot on the casehead from the ejector and I actually split a case!!.. bolt lift was stiff..

 

[BuzzBoss915]

Hmm? Kinda useful information in post #12. BB

 

[chefcam864]

Please provide something that states that. By your comment it makes no sense to add PSI if your at the lands.

I would not advise the OP to add any powder. He needs to post images so someone can make an accurate assessment of what he is talking about.

I don't know anything that states it, but common sense certainly dictates it. Increasing oal increases available volume in the case. Loading closer to the lands decreases pressure, until contact is made with the lands, at which time, pressure increases.

 

[Gnzrme]

I guess the only thing that makes sense is that I AM in the lands...I have no bullet marks and my regular load of H4350 41.5gr shoots fine at the longer OAL...

 

[Gnzrme]

Anybody have quickload numbers for VV160 43.6gr, 139 Scenars and lets go with 2.830 length. I do not have water capacity for the cases but they are Hornady's

 

[Deadshot2]

What do you consider heavy pressure signs? A posted picture would really help. There are many false pressure signs . But in general the closer you're to the lands the higher the pressure. So many variables.

Yes!!! And the most often used for "pressure signs" are primers, both flattening and cratering, which are also the most common source of false signs.


Own a Remington? You'll see cratering on the primers, even at starting loads that don't have enough pressure to form a seal at the neck leaving soot down the case. Remington purposely chamfers the firing pin hole so you get a false crater.

Different primers have different consistency of metal. A Winchester primer can look like it was melted then poured into the primer pocket with again, light loads.

Use a CCI or Wolf Primer and you'll get heavy bolt lift before you flatten the edges on those, as a rule.

I just look for heavy bolt lift and ejector marks (the horseshoe mark) while working up my loads. Most of the combinations I've used so far yield a nice accurate, and fast enough, round that I don't have to go to any extremes. If working up a load just remember to stop when you hit "Accurate" rather than trying for "light speed".

 

[918v]

Primers often give false pressure signs. Case heads flowing into ejector tunnels are not false.

 

[Sako man]

I guess the only thing that makes sense is that I AM in the lands...I have no bullet marks and my regular load of H4350 41.5gr shoots fine at the longer OAL...

Well if your getting split cases then yeah your lucky you have not gotten some powder in the eyes. Ok, well you really need to back off obviously. Your chamber could be very tight, as well how many firings on the brass, and who makes the brass? Sounds like around the low 40s of H4350 is just fine.

In 6.5mm if your throwing a 139-142gr projectile past 2750, then your good for quite a ways (past 1200+). I know there are a lot of people that like to make them fly at 2900+ but it's not entirely necessary. 2700+ will get you way the heck out there with plenty of oomph and authority. So don't be so worried about getting them going at 2900, not necessary.

Deadshot is totally right. If your shooting a Remington then you can get cratering yet the loose tolerances of a R700 take pressure well, its a paradox.

 

[Kirkd]

Anybody have quickload numbers for VV160 43.6gr, 139 Scenars and lets go with 2.830 length. I do not have water capacity for the cases but they are Hornady's

Nope. Need h2o capacity and this site does not want us running and sharing quickload data.


Sent from my iPad using Tapatalk

 

[AIdog]

Thanks for the follow up on that... Seated longer makes larger case chamber with less bearing surface on the bullet... as long as it is NOT contacting the riflings ushould not see an increased pressure spike. If anything u should see a decrease of pressure.