Help me get my mind around this.

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Fire306

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I just came back from the range, trying out a few loads for my 260 Remington using 95gr Hornady V-max bullets.

The thing I have found, and this has happened to me working up loads in other rifles as well. Specifically my 280 Remington also a Sako.

I had 4 loads, 5 of each, using Varget. 1st one - 42gr, 2nd - 43gr, 3rd-43.5gr, and 4th - 44gr.

I fired them in strings, 5 at a time, pausing maybe 15-20 seconds between shots. Then pausing 3-4 minutes between loads to let the barrel cool. (Use this method for testing most loads)

Here's my question, the 42 gr load was showing pressure signs (flat primers, very slight stiff bolt, nothing serious), Then I fired the 43gr load, which increased velocity, but had less signs of pressure. 43.5 gr, same, more velocity less pressure signs. 44 gr again, more velocity, but no pressure signs at all. I expect the added velocity, but why do the "heavier" loads show less pressure signs.

This isn't the first time I have come across this but it just doesn't make sense to me.

Thanks in advance.
 
Was your chamber oil free? If you cleaned your rifle the last time out, and didn't dry out your chamber before firing that could explain it. The brass couldn't grip the walls of the chamber and put more force on the bolt face. After a few rounds the oil cooked off. Just an idea.
 
iceman2 said:
Was your chamber oil free? If you cleaned your rifle the last time out, and didn't dry out your chamber before firing that could explain it. The brass couldn't grip the walls of the chamber and put more force on the bolt face. After a few rounds the oil cooked off. Just an idea.
Click to expand...

Probably exactly what happened.
 
I don't think there was any oil on it. Chamber hasn't been cleaned recently. And these loads weren't the first loads I fired today either. So, I don't this that was it. That would make sense though.
 
If the chamber was dry, then maybe there was still some resizing lube on those particular rounds. Just guessing since I wasn't there and didn't reload them.
 
i dont know a bean about 270 .... but play with 22-250 alot. from what i understand too light of a load can be just as bad .. or worse ... than a heavy load. just curiuos, do you notice accuracy/consistancy difference between the varoius loads....
 
There wasn't any lube on the cases. Shouldn't have been any in the chamber.
The loads are above listed maximums. I believe 42gr of Varget is the max in Hodgdon's guides. That's where I started and went up.
To answer explorin2, the 44gr load had the best group.
It's just strange to me, that hotter loads show less pressure evidence. I was wondering if someone would have an explanation for it. I wondered if the lesser load/more air space had something to do with it.

The cases were brand new Lapua, no case lube was put on them, but maybe there is some kind of coating on them for shipping/corrosion protection?
I never wiped them off with alcohol or anything. Maybe that's it. If that was it though, it shouldn't lessen the effect with more rounds fired, because it would be equal on all cases.

I know using new unfired cases isn't ideal for testing loads. I was just looking for a decent coyote load, not a paper punching perfect grouping load. This time, not so fussy.
 
I don't pretend to know how more powder could mean less pressure, but a guess is that if the bullet got to the lands at considerably higher velocity, it would take less pressure to move it the first few inches down the barrel.. I know that I shoot a few loads of slow powder that are over book maximum, and I know that it is not predictable what a small change in charge will do to velocity.
 
Since they were above max that may explain why loading manuals suggest stopping at first signs of pressure. It could be that the cases are really sticking to the chamber walls not letting the brass expand rearward thus no primer indications. Since new brass they may be more elastic so no stiff bolt lift. How much higher than max velocity were you? Personally I think you are walking a fine line here and disaster could be close. Just my opinion and worth what you paid for it.
 
Velocity average at the maximum load I tried was 3145fps. The 42gr load produced and average of 2965 fps. Maybe it is a lubrication issue, that I haven`t found.
I will neck size and retest. Like I said in the original post, I have run into this with my 280 as well. The flattened primers are not completely mashed or anything like that, there is not cratering around the firing pin hit. I don`t think I am near any dangerous pressure levels. I have pushed loads in the past to showing higher signs of pressure than this. The weird part is that the pressure signs were diminishing as the load increased.
It seems the only logical explanation we can come up with is lubrication of some description.

I will clean the rifle, and thoroughly clean the cases before a re-test
 
If IRC I saw this somewhere once before. I believe it had to do with the less filled case getting better combustion of the powder thus higher velocities.
 
I've seen this before when working up a load where the lighter loads were not quite a compressed load and as the charge was increased the load gradually became a compressed load.

Once the compressed load was reached, pressure signs dropped off and then returned with further increases in charge weight.

Do you know if you were in this 'zone'? That may explain it.

Do you have velocities on these different loads?
 
Fire306 said:
There wasn't any lube on the cases. Shouldn't have been any in the chamber.
The loads are above listed maximums. I believe 42gr of Varget is the max in Hodgdon's guides. That's where I started and went up.
To answer explorin2, the 44gr load had the best group.
It's just strange to me, that hotter loads show less pressure evidence. I was wondering if someone would have an explanation for it. I wondered if the lesser load/more air space had something to do with it.

The cases were brand new Lapua, no case lube was put on them, but maybe there is some kind of coating on them for shipping/corrosion protection?
I never wiped them off with alcohol or anything. Maybe that's it. If that was it though, it shouldn't lessen the effect with more rounds fired, because it would be equal on all cases.

I know using new unfired cases isn't ideal for testing loads. I was just looking for a decent coyote load, not a paper punching perfect grouping load. This time, not so fussy.
Click to expand...

You started at maximum and worked up, and in full grain increments to boot? Then continued on up when the first load gave pressure signs?

What part of start at minimum and work up, stop if you see pressure signs did you miss in your reloading manuals?

While maximums are max in the gun being used for the test, and that's why they tell us to not start there, so it is possible your guns may be ok with over a max book load, you do not seem to have a good enough grasp of this to be going over max.

When I get a sticky bolt I stop, even if I'm 3 grains under maximum, I don't add another grain and try again. That is a good way to make it onto a demotivational poster.
 
Pressure

I'm thinking the lower loads were not indicating pressure at all but another phenomenum. Did you get any brass flow into the ejector cut in bolt face? I've never had stiff bolt lift even a little stiff, with out visable flow into the ejector cut. How's the headspace of your brand new brass, I've had "pressure" indicators with a rifle/case combo with headspace problems and minimal pressure in reality.
I'm not sure if this could change with increases in pressure (indicate less).
I would load your fired and cleaned cases again with the same loads and retry, I don't believe for a second it's pressure.

Just a thought, check your brass.
 
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