Interpreting Pressure Signs from Velocity (260 Remington load dev)

[1Moose]

Hello all,

Working up loads for 260 Remington. 24 inch Chanlynn barrel. Would appreciate any help interpreting if velocity for loads show any concerning pressure signs. First, no cases had any visible signs of pressure. Only the very slightest flattening on just a few primers across all loads, and not corresponding to the highest powder charge (still plenty of roundness to the edges). Not even the faintest extractor marks. No hint of stiff extraction.

Components: Lapua brass. H1000 powder. Rem 9.5 primers. Hornady 143 ELD-X bullets.
Labradar chronograph.

DECEMBER 26 (70*F). These are shots 40 thru 80 (roughly) in new barrel / rifle.
Load 1: 45.6 grains H1000. Jump = 0.050. Velocity avg = 2574.
Load 2: 46.1 grains H1000. Jump = 0.050. Velocity avg = 2596.
Load 4: 47.0 grains H1000. Jump = 0.047. Velocity avg = 2664.
Load 5: 47.8 grains H1000. Jump = 0.028. Velocity avg = 2677.

Load 6: 46.1 grains H1000. Jump = 0.156. Velocity avg = 2609.

JANUARY 20 (42*F). Tried three seating depths based off of 47.8 grains as that had tightest group earlier)
Load 7: 47.8 grains H1000. Jump = 0.010. Velocity avg = 2764.
Load 8: 47.8 grains H1000. Jump = 0.028. Velocity avg = 2759.
Load 9: 47.8 grains H1000. Jump = 0.033. Velocity avg = 2754.

Questions:
Q1) I've heard of velocity increases in first 150 rounds of barrel. First time I've had a chronograph to observe it myself. Even with lower temperatures in second outting, Load 8 is 82 fps higher than Load 5. <same load, a few more rounds down barrel, lower temp). Seem normal?

Q2) In Loads 7-9, I'm seeing approximately 150 fps higher than the Hornady manual's listed velocity. Again, no pressure signs. Maybe I have a faster than normal barrel? Have heard of +/- 100 fps not being uncommon. Granted, Hornady doesn't give many increments for powder and velocity for the 260 Remington, so I may not actually be that much higher than book if they showed more detail. (They show a lot more detail for Creedmoor for far more powders--likely given their affinity for their own cartridge). And I'm closer to lands and have longer overall cartridge length (2.820 vs 2.800) so less gas is escaping around the bullet I assume before it engages rifling.

Q3) Load 5 didn't show much velocity increase from Load 4, despite the powder increase. Should I assume this is a concerning sign? Max book load is 49.6 grains H1000 @ 2700 fps listed. Note that some load groups only recorded velocity for 2 shots given chrono position, so sample size isn't large.

Any thoughts could be useful as I haven't had benefit of chronometer for load development, so learning how to interpret things.

 

[MagnumManiac]

What you need to look for in regard to watching velocity is whether a single increase in powder tracks the same as the previous increase.
If say a 1gr increase from the start load increases velocity by 30fps, then subsequent loads do the same, then just as you hit max load, the velocity jumps 100fps, then max pressure has most LIKELY been exceeded. I have tested loads that would increase exponentially for 3gr then the next 3gr would be 100fps faster and track normally with a 30fps increase per charge weight.
Some say that if you exceed book velocity then you have exceeded max pressure, well, this is not what I have seen using a pressure trace. A loose bore will yield higher velocity at less pressure and vice versa.
You just need to know that a sudden sharp increase in velocity may be a cause of exceeding max pressure and, if you keep increasing the powder charge, it may actually stop increasing and actually decrease.
I find ejector marks are the first sign followed by flattened primers in SOME brands. Not all primer brands show up flattening until you are way past safe loads.

Cheers.

 

[desertcj]

BULLET WEIGHT140 GR. NOS PART
ManufacturerHodgdon
PowderH1000
Bullet Diameter.264"
C.O.L.2.780"
Starting Load
Grains48.0
Velocity (ft/s)2,619
Pressure51,200 PSI
Maximum Load
Grains50.5
Velocity (ft/s)2,730
Pressure57,000 PSI

In this case, I doubt you can stuff enough H1000 in the case to get yourself in trouble. Some loads are "max" just because the case can't fit anymore powder. The data above is from Hodgdon...

 

[scottishkat]

1Moose I will offer this along with above. The Nosler data indicates max of H1000 at 50 grains with Nosler brass the hornady data indicates a max of 49.6 with remington brass. Remington brass weight averages 161 grains per case. The nosler brass I have weights 166 grains per case. Lapua brass weights 173 grains per case.

All this can explain some of your velocity issues heavier brass can translate to lower case capacity and greater pressure during firing hence greater velocity. The best way to check is to prime a case and fill with water and measure it to see the difference in actual capacity.

The nosler data indicates 50 grains max and 2785 fps. You may have an anomaly with the chronograph or a faster barrel.

In any case as explained above I don't think you can fit enough H1000 in a case to go over pressure it's rather unique in that way.

How is your accuracy at 47.8 gr you have an extreme spread of 10 fps and there is nothing wrong with that. Measure a few cases before firing and after firing above the case head and see how much expansion your are getting. This will be a better indicator than looking for pressure signs.

Noslers minimum data is 46 gr for 2596 and 48 gr for 2686 and above. Your load is about 70 fps over Nosler. I would increase as you have and see if ES improves. In all probability you will be able to increase until you get case deformation from powder compression this will generally happen at the shoulder but you can measure for this as well.

I hope this helps.

Good luck and shoot straight

Bob

 

[1Moose]

1Moose I will offer this along with above. The Nosler data indicates max of H1000 at 50 grains with Nosler brass the hornady data indicates a max of 49.6 with remington brass. Remington brass weight averages 161 grains per case. The nosler brass I have weights 166 grains per case. Lapua brass weights 173 grains per case.

All this can explain some of your velocity issues heavier brass can translate to lower case capacity and greater pressure during firing hence greater velocity. The best way to check is to prime a case and fill with water and measure it to see the difference in actual capacity.

The nosler data indicates 50 grains max and 2785 fps. You may have an anomaly with the chronograph or a faster barrel.

In any case as explained above I don't think you can fit enough H1000 in a case to go over pressure it's rather unique in that way.

How is your accuracy at 47.8 gr you have an extreme spread of 10 fps and there is nothing wrong with that. Measure a few cases before firing and after firing above the case head and see how much expansion your are getting. This will be a better indicator than looking for pressure signs.

Noslers minimum data is 46 gr for 2596 and 48 gr for 2686 and above. Your load is about 70 fps over Nosler. I would increase as you have and see if ES improves. In all probability you will be able to increase until you get case deformation from powder compression this will generally happen at the shoulder but you can measure for this as well.

I hope this helps.

Good luck and shoot straight

Bob

Bob,

Thank you for the detailed response on loads as well as how I might use web expansion to get some good info. I need to read up more on how to best measure the case web expansion. My early looks into that measurement had me confused (or maybe frustrated) for a couple of reasons. I need to dig in more and add it to my process. The frustrations that thwarted me originally, in case maybe I'm making this harder than I need to:
1) I read in places that I needed possibly a more accurate tool than my caliper which accurate to .001 (but shows measurements to the ten-thousandths, i.e., 0.0005)
2) It seemed I needed to get factory loads that used the same brass to use as a baseline (using unfired brass).

I do have another 100 Lapua cases (unfired), so I could mimic things, but I'd need to get a box of cartridges that use Lapua brass it seems, and possibly a better caliper?

To your question on extreme spread, I'd need to look that up at home. I recall the standard deviation to look pretty good (albeit from a small sample of shots for each Load).

Thanks again for your response. I appreciate the time you put into helping me out.

 

[bigedp51]

Measuring base expansion is only a indication of how much pressure that brand of brass can take.
The harder the brass and the thicker the flash hole web is controls base expansion.
There is nothing wrong with using base expansion because it lets you know if you are pushing the cases beyond there elastic limits. "But" as stated above you need to be able to measure in .0001 of an inch.

At Accurate shooter reloading forum many shooters increase the load until they get brass flow into the ejector and then back off 1 or 2 grains of powder.

Below this photo was posted at Accurate Shooter using the above method and then backing of the load.

Below you can see how much difference in brass hardness can effect base expansion. Along with the flash hole web thickness that adds radial strength to the base of the case.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com...r-brass-5-56-and-223-rem-base-hardness-tests/

Below the photo shows how the thickness of the flash hole web can effect base expansion. And also why some brands of brass have stretched out primer pockets much sooner than other cases.

 

[scottishkat]

No problem. I have been shooting and reloading for the 260 rem since about 2000. I really like the cartridge I've owned as many as 4 rifles chambered for it and 3 right now.

In that time for 140's I keep going back to H4831SC. H4350 is excellent for light bullets 120's RL15 or I4064 with 100's. I've tried a host of powders and have 100's of targets.

Stick with Remington 9.5's and Lapua brass IME it does not get better. 7828SSC shows promise as well.

If you're getting good accuracy and by good accuracy 1/2" 3 shots are common what you're running is pretty darn good.

Good luck and shoot straight

Bob

 

[1Moose]

Measuring base expansion is only a indication of how much pressure that brand of brass can take.
The harder the brass and the thicker the flash hole web is controls base expansion.
There is nothing wrong with using base expansion because it lets you know if you are pushing the cases beyond there elastic limits. "But" as stated above you need to be able to measure in .0001 of an inch.

At Accurate shooter reloading forum many shooters increase the load until they get brass flow into the ejector and then back off 1 or 2 grains of powder.

Below this photo was posted at Accurate Shooter using the above method and then backing of the load.

Below you can see how much difference in brass hardness can effect base expansion. Along with the flash hole web thickness that adds radial strength to the base of the case.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com...r-brass-5-56-and-223-rem-base-hardness-tests/

Below the photo shows how the thickness of the flash hole web can effect base expansion. And also why some brands of brass have stretched out primer pockets much sooner than other cases.

[/QUOTE

Great photos and graph. I guess that's exactly why sticking to similar brass when measuring web expansion for pressure is important. Per that graph, some brass is nearly twice as hard, and then from the photos there is often significantly more in one case than another. This sport / hobby is going to give me more gray hair.

In all my rifles I've only ever shown a very faint half-moon mark from the extractor. Never like your first image where there's a prominent dimple. I'll keep experimenting and looking at the signs available to me.

And maybe I can find a good .0001-capable caliper on sale. I'd be willing to spend $100-150 if there was a reliable (and reasonable durable) model out there. Thanks again.

 

[1Moose]

No problem. I have been shooting and reloading for the 260 rem since about 2000. I really like the cartridge I've owned as many as 4 rifles chambered for it and 3 right now.

In that time for 140's I keep going back to H4831SC. H4350 is excellent for light bullets 120's RL15 or I4064 with 100's. I've tried a host of powders and have 100's of targets.

Stick with Remington 9.5's and Lapua brass IME it does not get better. 7828SSC shows promise as well.

If you're getting good accuracy and by good accuracy 1/2" 3 shots are common what you're running is pretty darn good.

Good luck and shoot straight

Bob

Thank you Bob. I do have H4831SC. I'll have to give that a try (I have both H4831 and H4831SC).

 

[Pdvdh]

1) I read in places that I needed possibly a more accurate tool than my caliper which accurate to .001 (but shows measurements to the ten-thousandths, i.e., 0.0005).

You only need a tool designed to measure 0.0001" accuracy if you need to identify 0.0001" case web expansion.

0.0001" case web expansion is not a problem, therefore you won't need a tool that measures accurately to 0.0001".

I've been measuring case web expansion for 30 years now with 0.001" dial and vernier calipers. Never felt needy for additional measurement accuracy.

The rule of thumb is 0.0005" case web expansion on a single firing of a new casing is ~maximum pressure load. Has to be the initial firing on the cartridge case. You shouldn't be having any big problem identifying 0.0005" case web expansion using a 0.001" caliper. It's 1/2 the distance between the indicator marks on the dial caliper. Or 1/2 the way across the indicator marks on the vernier hash marks.

If you want to identify 0.00005" expansion, then better buy a 0.0001" tool. But it's completely NOT necessary.

 

[Pdvdh]

And I still have all my fingers, eye lids, eyebrows, eyesight, and functioning firearms.

 

[bigedp51]

Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/rel...-trick-monitoring-pressure-your-rifle-reloads

One of the first rules of handloading is to always follow the approved reload data. The cautious reloader gradually works up to approved maximum loads to ensure his particular gun does not show pressure signs. Generally this is visual observation of the fired shell case head and primer. There is another slick way to check for pressure signs if you are interested.

Using a blade micrometer that measures in ten thousandths (.0001"), new, unfired cases can be gauged before and after firing to determine reasonably accurate maximum loads. Micrometers measuring in thousandths (.001") are insufficiently accurate to perform these measurements, and should not be used. Previously fired cases cannot be used accurately due to various levels of brass hardening. Measurement is taken just ahead of the extractor groove on the case head and must be taken at the same place on the case before and after firing. By placing a small mark on the case head – entering the cartridge in the chamber with mark at 12 o'clock – a consistently accurate measurement can be taken with each firing.

Lower pressure rounds, like the .30-30 Winchester, usually yield maximum pressures at .0003"-.0004" expansion. Modern cartridges, like the .223 Remington, will show maximum pressure at .0004"-.0005", while .308 Winchester, .270 Winchester, etc., typically yield .0005"-.0006" expansion at max pressure. Magnums, like the .300 Winchester Magnum, show maximums at .0006"-.0007" expansion, and should be measured on the belt.

In conjunction with these measurements, case head signs of pressure should be monitored as well. These signs include very flat primers, slightly cratered primers, ejector marks on the case head, and stiff extraction. All these case head signs indicate high pressure, and loads should be reduced until these signs disappear.

As always, start with the beginning load listed, and cautiously work up to the maximum shown for that set of components, using the methods listed herein.

 

[Pdvdh]

Did I say I still have all digits and eyesight...
You want to believe 0.0001" is necessary, the you should also believe 0.0001" case web expansion poses a real overpressure risk. It doesn't.
Those that claim otherwise must be marketing 0.0001" measuring tools.

 

[Pdvdh]

Using a blade micrometer that measures in ten thousandths (.0001"), new, unfired cases can be gauged before and after firing to determine reasonably accurate maximum loads. Micrometers measuring in thousandths (.001") are insufficiently accurate to perform these measurements, and should not be used. Previously fired cases cannot be used accurately due to various levels of brass hardening. Measurement is taken just ahead of the extractor groove on the case head and must be taken at the same place on the case before and after firing.

First they say a 0.0001" measurement accuracy is required. Next they say no problems with 0.0003-0.0007" case web expansion.

So which is it? A guy can't ID 0.0005" movement using a 0.001" caliper needs an eye exam.