6.5x47 Lapua Pressure Signs

[Spin Drift]

I recently purchased a used rifle in 6.5x47 Lapua
Savage Action
28" Kreiger 1:8

130 VLD
Varget
CCI BR-4
0.010" into lands
Virgin Lapua Brass

I found nice accuracy right around 36.6 grains, no pressure signs and getting about 2866 fps. On that same day I tested up to 38.0 grains and didn't notice any pressure.

I returned a couple days later and started seeing the faintest, barely visible signs of ejector marks on some cases with this same 36.6 load. This didn't happen on all cases just some of them. The temperature was similar both days (~3f) It was snowing a little bit the 2nd day and I do know that I had allowed a few flakes of snow to make tiny water droplets on a few of the cases. Could that have caused the pressure signs?

Do I need to back down my load?

 

[CatShooter]

I returned a couple days later and started seeing the faintest, barely visible signs of ejector marks on some cases with this same 36.6 load. This didn't happen on all cases just some of them. The temperature was similar both days (~3f) It was snowing a little bit the 2nd day and I do know that I had allowed a few flakes of snow to make tiny water droplets on a few of the cases. Could that have caused the pressure signs?

Do I need to back down my load?

It is unlikely that a snow flake cased your pressure signs.

But if you are getting pressure signs (or even close) at 3° F, then you really need to back off.

 

[wwbrown]

If a snowflake landing on the case while being loaded staying on the case while it was chambered, the pressure could have spiked like a rain drop on a case often does.

wade

 

[nosualc]

If a snowflake landing on the case while being loaded staying on the case while it was chambered, the pressure could have spiked like a rain drop on a case often does.

wade

Water (whatever the source) in the chamber or on the case will cause pressure signs. I've had this happen during matches, and it really wreaks havoc.

I always thought it was because the case doesn't "stick" to the chamber walls on firing which increases bolt thrust.

-nosualc

 

[Spin Drift]

Thanks for the input folks.

I will retest when it warms up (currently -27f with the windchill).

I've plugged my data into Quickload and it says my load is very close to high pressure so I will have to keep a very close eye on this. I have calibrated the program to match my velocity. I did not measure the case volume of the virgin brass but I did measure once fired and that is about 49.85 Grains. When using virgin brass and Quickload, if I plug in the fire formed volume will that be inaccurate for the real pressures with virgin brass? It says I am at 60,331 psi with the formed brass volume and I am using a Burn Rate Factor of 0.650 to match my velocity. Should I tweak the shot start pressure instead because I am about 0.010" into the lands? At the range I also tested with 5 rounds loaded at 0.005" into the lands and the velocity dropped 14 fps.

So many variables...

 

[CatShooter]

If a snowflake landing on the case while being loaded staying on the case while it was chambered, the pressure could have spiked like a rain drop on a case often does.

wade

Water (whatever the source) in the chamber or on the case will cause pressure signs. I've had this happen during matches, and it really wreaks havoc.

I always thought it was because the case doesn't "stick" to the chamber walls on firing which increases bolt thrust.

-nosualc

This is a "Sticky" (pun) subject.

First, bolts don't have thrust - they are passive devices - cases have thrust, bolts restrain that thrust.

And in firearms, pressures cannot "Spike" (which means exactly what it says) electricity can have spikes (brief, transient increases that immediately drop down to the original value - this is a "Spike" _____­­­/\____).

Firearms can have increases in pressure caused by more powder, or bore/bullet problems, but they cannot have spikes. Spikes mean it goes up and immediately comes down... in a firearm there is no place for the gas to leave so it can come down.

That being said, why would a snow flake cause high pressure - properly sized and fitted cases have their head against (or within 0.001" of) the bolt face, so there is nothing for the body to "grab" and protect.

So none of this makes any sense.

I have had rain on my cases while in the field, with no effects whatsoever.

And, of course, think of all the military folks that shoot in God awful rain and snow - they have no problems with it.

So I am not buying the snow flake theory.

 

[Spin Drift]

This is a "Sticky" (pun) subject.

First, bolts don't have thrust - they are passive devices - cases have thrust, bolts restrain that thrust.

And in firearms, pressures cannot "Spike" (which means exactly what it says) electricity can have spikes (brief, transient increases that immediately drop down to the original value - this is a "Spike" _____­­­/\____).

Firearms can have increases in pressure caused by more powder, or bore/bullet problems, but they cannot have spikes. Spikes mean it goes up and immediately comes down... in a firearm there is no place for the gas to leave so it can come down.

That being said, why would a snow flake cause high pressure - properly sized and fitted cases have their head against (or within 0.001" of) the bolt face, so there is nothing for the body to "grab" and protect.

So none of this makes any sense.

I have had rain on my cases while in the field, with no effects whatsoever.

And, of course, think of all the military folks that shoot in God awful rain and snow - they have no problems with it.

So I am not buying the snow flake theory.

I am not necessarily arguing for or against the 'snow flake theory' but I do remember that David Tubb spoke about the grip that your brass needs to have in the chamber during his High Powered Rifle Reloading Videos. The context of his discussion was in regards to over polishing your cases making them too slippery having an effect because it can't grip the chamber which he said it needs to. I would have to go back and watch it again but I think he said this could cause pressure signs. I've also heard of this effect from not cleaning sizing lube off your cases but I don't remember if that was his video or another source. Ya, I know my info is anecdotal at best but I will dig around and see if I can find the sources.

As for the soldiers in the rain etc. is it likely that they aren't on the razor's edge of high pressure with their military loads as I may be with mine? I could see this making a difference.

 

[Spin Drift]

I think what was meant by a pressure spike is when comparing max pressure from one shot to another, not when graphing the pressure curve of one single shot.

example:

Shot #1 60,000 psi
Shot #2 60,000 psi
Shot #3 60,000 psi
Shot #4 65,000 psi

In this example shot number 4 could be considered a pressure spike vs the other shots made. If you were to graph these 4 numbers you would see a spike.

If used in this context I think that the term 'pressure spike' would be very accurate.

 

[scott_at_vortex]

If a snowflake landing on the case while being loaded staying on the case while it was chambered, the pressure could have spiked like a rain drop on a case often does.

wade

Water (whatever the source) in the chamber or on the case will cause pressure signs. I've had this happen during matches, and it really wreaks havoc.

I always thought it was because the case doesn't "stick" to the chamber walls on firing which increases bolt thrust.

-nosualc

This is a "Sticky" (pun) subject.

First, bolts don't have thrust - they are passive devices - cases have thrust, bolts restrain that thrust.

And in firearms, pressures cannot "Spike" (which means exactly what it says) electricity can have spikes (brief, transient increases that immediately drop down to the original value - this is a "Spike" _____­­­/\____).

Firearms can have increases in pressure caused by more powder, or bore/bullet problems, but they cannot have spikes. Spikes mean it goes up and immediately comes down... in a firearm there is no place for the gas to leave so it can come down.

That being said, why would a snow flake cause high pressure - properly sized and fitted cases have their head against (or within 0.001" of) the bolt face, so there is nothing for the body to "grab" and protect.

So none of this makes any sense.

I have had rain on my cases while in the field, with no effects whatsoever.

And, of course, think of all the military folks that shoot in God awful rain and snow - they have no problems with it.

So I am not buying the snow flake theory.

If you have never had any problems from the rain it means that you are smart and are not running at the limits or above the limits of pressure in your loads. I have seen rain take many of guys out of match (stuck bolts,blowing primer after primer,broke triggers, extractors, stuck cases,etc..) Now I am not sure if anyone has ever proven what exactly causes this, but I am in the camp of the water not allowing the case to properly grab the chamber wall. Thus putting way more thrust on the bolt. However, there must also be a pressure increase from the water in the bore/on the bullet since primers are often blown and triggers broke.

On another note, even if you are running fairly mild loads you generally will get an occasional ejector mark on your case if your ammo gets wet enough.


This is just my real life experience.

Best Regards
Scott

 

[Patch700]

You can talk about it all you like but the bottom line is this , you wouldn't leave your chamber wet with any residue from cleaning would you?? I know I go to great lengths mopping out the chamber after cleaning and I know what happens when you don't.

One persons "A few wet flakes" could be another person's "Covered in droplets" ... In any event yes the original posters theory is very plausible.

 

[CatShooter]

You can talk about it all you like but the bottom line is this , you wouldn't leave your chamber wet with any residue from cleaning would you?? I know I go to great lengths mopping out the chamber after cleaning and I know what happens when you don't.

One persons "A few wet flakes" could be another person's "Covered in droplets" ... In any event yes the original posters theory is very plausible.

Actually, I oil my cases to prevent the walls from gripping the chamber - it keeps them from stretching - I do NOT shoot mild loads.

Give this some thought... if you load fired cases that have been "bumped" 0.001", and the bullet is loaded with 10 to 20 thou of Jam... then the head is already against the bolt face, so the case walls can grab the chamber all they want, it will do no good, cuz they can't restrain the case from pushing against the bolt.

So where is the increase of pressure or "case thrust" from, and how is it affecting anything that is already happening without a snow flake.

 

[Spin Drift]

Actually, I oil my cases to prevent the walls from gripping the chamber - it keeps them from stretching - I do NOT shoot mild loads.

Now that's a different way to go.

 

[Patch700]

You can talk about it all you like but the bottom line is this , you wouldn't leave your chamber wet with any residue from cleaning would you?? I know I go to great lengths mopping out the chamber after cleaning and I know what happens when you don't.

One persons "A few wet flakes" could be another person's "Covered in droplets" ... In any event yes the original posters theory is very plausible.

Actually, I oil my cases to prevent the walls from gripping the chamber - it keeps them from stretching - I do NOT shoot mild loads.

That is not the first time I've seen and heard of others doing such.... My experience with contaminants in the chamber or on my brass has been less than stellar... And by less than stellar I mean it's given me problems lol.

 

[Spin Drift]

If you have never had any problems from the rain it means that you are smart and are not running at the limits or above the limits of pressure in your loads. I have seen rain take many of guys out of match (stuck bolts,blowing primer after primer,broke triggers, extractors, stuck cases,etc..)

Good post.

I demand 100% reliability out of all of my firearm systems so I will treat your experiences with high regard. I don't always shoot in fair weather at a bench with a roof.

Wet ammo happens sometimes in the conditions I shoot in. I am pretty sure I have seen this phenomenon with another firearm at one point from rain water. I will look at my notes but I didn't take as detailed notes back then as I do now. If I recall it caused heavy bolt lift.

I plan to retest the 36.6 load but will also examine the next couple nodes down. The more I think about it the more it seems like a good idea to load down a bit.

 

[turbo54]

I have certainly experienced signs of high pressure (ejector marks) when shooting wet ammo while out in the rain. When this same ammo is clean and dry, no ejector marks whatsoever.

I subscribe to the theory that brass is not gripping the chamber as it should, and not a magic pressure increase.

If pressures were increased, you'd expect a corresponding increase in velocity - meaning you'd expect less drop at distance.

I've seen neither an increase in velocity, nor an upwards shift in POI at distance with wet ammo.