7mm-08 – accuracy load development results…where are my pressure signs?

[RonR]

7mm-08 – accuracy load development results…where are my pressure signs?

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1. I need help interpreting…I can’t derive any pressure signs. Am I missing anything?

I was at the range this afternoon with my son. I have results indicating that there may be some nodes at the top end of book value and I aim to push further.
Before too many of us jump at what may be the obvious signs, (what seems to be the most common signs of pressure i.e. extreme primer flattening, primer firing pin cratering, heavy bolt lift, case swipe marks) are all things I’ve been looking for. I don’t have evidence (as far as I can tell) that I’m over reaching pressures (so far) with this rifle.

Givens
- 7mm-08 bolt, belly button over the counter hunting rifle
- Recipe’s as per pictures below
- Objective is to develop longer range load for myself (300 plus yards) loads SMK 150 the bullet of choice at the moment
- Right now performing ladder tests to eventually use a form of OCW close to Mystic’s version. (Jerry’s methods have worked great for me in the past developing hunting loads)
- I’ve been reloading for about 4 years. Neck turning, annealing, chrono etc. Not too proud to state that I don’t know everything and I never will about this stuff. I’ll admit to chasing my tail with this craft as well.
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From left to right, unfired, the last fired W760, then the last fired V540.




Am I missing something? The reason I am asking is this…

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2. I believe there are nodes at the top end of book value and rifle responds at those charges like it’s got a bit of jump. Like a turbo or nitrous for a car. Yet on paper its looking promising as far as I can tell.


Here are the results. I have a couple more powders loaded to try, but tested this afternoon was W760, V540 and Varget. W760 produced good results but for myself the V540 is the most interesting. Varget results are not posted because the W760 and V540 more conclusive.

For myself, further testing and evaluation (for a future modified OCW) will be pursued provided vertical dispersion is at minimum. If there was nothing promising, that powder would not be considered further.

W760 is more condensed but V540 is really interesting. It has distinct breaks in the “groups”. I’ve never seen results like this V540 before. My reading of posts here and other materials suggests that each barrel would likely only have 2 nodes, possibly three. Am I interpreting that there may be more opportunity for more sweet spots in this case using V540? (Please keep in mind that the graduations between rounds is coarse. .4 gr or .3gr)




Regards
Ronr

 

[Hitzy]

What's your chronographed velocity? No way of knowing where pressure is at without knowing the velocity.

 

[Kelly Timoffee]

Mornin ,

For starters , your W760 ladder looks like a more compatible powder than your V540 , I have found that the more a rifle likes the components the tighter your over all ladder typically looks.

How is your bolt lift on your stronger charges?

Those primers don't look bad and are not a definitive sign but somewhat of a guide , remember Federal are the softest of the primers.

What distance are you currently testing at?

From what I see I'd load 3 shots each 45.8, 46.1 ,46.4 ,46.7 and see what happens, obvious stop if the bolt lift is getting stiff.

I am guessing that your velocities are going to be around 2700+ in those top loads and that is totally within reasonable parameters for A 7/08.

I also like how your group is moving(W760) , very consistently.

Accuracy in 7/08 in my experience with 150's is from 2625 to 2750ish and I think you are very close to being in there.

This is at 2674 ft/sec , 5 shots , 100 yards. 150Gr SMK,

 

[RonR]

What's your chronographed velocity? No way of knowing where pressure is at without knowing the velocity.

I didn't chrony these ladders. I've got a magnetospeed and didn't want to have any influence regarding POI.

However I have some results from fire forming. I realize different ambient conditions however...some reference

2017-08-03 - W760 44.0 gr, CCI 250, SMK 150, 2648 fps <<< book value fps here says 2640 ES 48 SD 18.6
2017-06-08 - W760 44.0 gr, F210, SMK 150, 2708 fps <<< book value fps here says 2640 ES 27, SD 11.2
2017-06-08 - W760 44.0 gr, CCI 250, SMK 150, 2705 fps <<< book value fps here says 2640 ES 24, SD 9.7

2017-08-03 - V540 37.7 gr, CCI 200, SMK 150, 2509 fps <<< book value fps here says 2500 ES 42 SD 18.0
2017-08-03 - V540 37.7 gr, CCI 250, SMK 150, 2509 fps <<< book value fps here says 2500 ES 42 SD 15.3 (double checked the SD yes 15.3)
2017-08-03 - V540 37.7 gr, F210, SMK 150, 2512 fps <<< book value fps here says 2500 ES 13 SD 5.0

Regards
Ronr

 

[jethunter]

W760 might be too slow burning to be optimum in that combination. I haven't actually used W760 in 7mm08 with anything but 175gr loads but even with that heavier bullet there some faster burning powders worked better.

 

[RonR]

Mornin ,

For starters , your W760 ladder looks like a more compatible powder than your V540 , I have found that the more a rifle likes the components the tighter your over all ladder typically looks.

That's what I was thinking right off the hop. This rifle just sings with this stuff. I had some great chrono results for V540, so I didn't want to ignore those results either. I have 4064 and 4166 loaded to try. Want to give those a shot to remain objective.

How is your bolt lift on your stronger charges?

To be honest, I can't really tell the difference. It's not definitively harder. I shot factory Hornady Superformance in this rifle and the factory loads were sooo hot...not only was bolt lift a considerable effort but on one, the primer disintegrated and gases escaped on the port on the right of the chamber. Cleaned my shorts and took it into a gunsmith after that episode. I'll send you pictures sometime.

Those primers don't look bad and are not a definitive sign but somewhat of a guide , remember Federal are the softest of the primers.

Thanks for the reminder. From my limited testing...F210 good matches with Varget, W760 and V540.

What distance are you currently testing at?

100m for these ladders. Will be moving to 200m when I've landed on two powder options. Incorporate some OCW.

From what I see I'd load 3 shots each 45.8, 46.1 ,46.4 ,46.7 and see what happens, obvious stop if the bolt lift is getting stiff.

Good...I'm seeing the same thing. Are the first and second shots worth investigating? 44.0 and 44.3? It would be nice to have a hot weather load...

I am guessing that your velocities are going to be around 2700+ in those top loads and that is totally within reasonable parameters for A 7/08.

Yeah, based on the previous post with chrono results, I believe these loads are starting off there.

I also like how your group is moving(W760) , very consistently.

This was the response I was hoping for Kelly. For myself I was having a hard time believing chrono results being above book value in terms of speed with 760. It was unusual enough to question if I was missing something.

Regards and Happy Thanksgiving to those following along.

Ronr

Accuracy in 7/08 in my experience with 150's is from 2625 to 2750ish and I think you are very close to being in there.

This is at 2674 ft/sec , 5 shots , 100 yards. 150Gr SMK,

Ahhh...nice Kelly. I'm chasing that like my lab on a porcupine. Once the load's been figured out, I'll post the chrony results.

 

[RonR]

W760 might be too slow burning to be optimum in that combination. I haven't actually used W760 in 7mm08 with anything but 175gr loads but even with that heavier bullet there some faster burning powders worked better.

Noted. Did you ever try 748?

Regards
Ronr

 

[Hitzy]

I didn't chrony these ladders. I've got a magnetospeed and didn't want to have any influence regarding POI.

However I have some results from fire forming. I realize different ambient conditions however...some reference

2017-08-03 - W760 44.0 gr, CCI 250, SMK 150, 2648 fps <<< book value fps here says 2640 ES 48 SD 18.6
2017-06-08 - W760 44.0 gr, F210, SMK 150, 2708 fps <<< book value fps here says 2640 ES 27, SD 11.2
2017-06-08 - W760 44.0 gr, CCI 250, SMK 150, 2705 fps <<< book value fps here says 2640 ES 24, SD 9.7

2017-08-03 - V540 37.7 gr, CCI 200, SMK 150, 2509 fps <<< book value fps here says 2500 ES 42 SD 18.0
2017-08-03 - V540 37.7 gr, CCI 250, SMK 150, 2509 fps <<< book value fps here says 2500 ES 42 SD 15.3 (double checked the SD yes 15.3)
2017-08-03 - V540 37.7 gr, F210, SMK 150, 2512 fps <<< book value fps here says 2500 ES 13 SD 5.0

Regards
Ronr

46.5gr~2776 is Hodgdon max for 760. Since you are likely hitting that velocity before hitting that power charged based on your data above, you are overpressure. Maybe not a lot, but without the velocity of the 46.5 charge we don't know.

Just read your Hornady factory ammo issues, and with that I'd say your bore/chamber are on the tight side so you will hit max pressure before any book max load. The Hornady stuff is hot, but not enough to cause pressure signs like that.

 

[Kelly Timoffee]

Only things I will comment on now is .....

1)Why change up powder when you and I both know it works.I've burnt much 760 in the 08 for myself and many others.Mind you my accuracy load is with H4350, W760 just behind slight behind.

2)The distance of 100 is tough to get the subtleties on paper until the differences can be noted at further distance, HOWEVER , if you have three loads within 1/2" to 5/8" of an inch at 100 , I feel you have a good start with those charges.

P.S. - Don't be afraid to shorten the COAL when fine tuning those SMK later on once you settle on a charge weight.

 

[RonR]

46.5gr~2776 is Hodgdon max for 760. Since you are likely hitting that velocity before hitting that power charged based on your data above, you are overpressure. Maybe not a lot, but without the velocity of the 46.5 charge we don't know.

Just read your Hornady factory ammo issues, and with that I'd say your bore/chamber are on the tight side so you will hit max pressure before any book max load. The Hornady stuff is hot, but not enough to cause pressure signs like that.

Sage points. Thanks Hitzy.

Regards
Ronr

 

[RonR]

Only things I will comment on now is .....

1)Why change up powder when you and I both know it works.I've burnt much 760 in the 08 for myself and many others.Mind you my accuracy load is with H4350, W760 just behind slight behind.

2)The distance of 100 is tough to get the subtleties on paper until the differences can be noted at further distance, HOWEVER , if you have three loads within 1/2" to 5/8" of an inch at 100 , I feel you have a good start with those charges.

P.S. - Don't be afraid to shorten the COAL when fine tuning those SMK later on once you settle on a charge weight.

Yes to no. 1. No need to change. For some reason I want to get into the sticks (a little bit) and experience for comparison's sake what it's like to compare "given" powders to something that isn't as "go to". Seeing the difference supports why the go to powders are "go to"... I hope to learn from interpreting the differences and experience myself first hand why this is the case. I think it will help me troubleshoot better in the future.

Yes to no. 2. You understand what I'm doing. Maybe wouldn't do it that way lol...but can help chart the path a bit.

Shortening the COAL...never done that yet but can hardly wait!

Thanks Kelly and Hitzy for taking the time. It's sincerely appreciated and valued by myself.

Regards
Ronr

 

[350 Mag]

I found Ramshot Big Game to be an excellent powder for 7mm-08.....

 

[RonR]

I found Ramshot Big Game to be an excellent powder for 7mm-08.....

That's in the nosler manual I believe... One day I'll give it a go when I come across some at a good price. Got some stuff working for this load.

Nice to hear about other powders. Thanks for the tip!

Regards
Ronr

 

[hunters home]

I've had a 7/08 for over 30 yrs. In my experience with 140-150 gr bullets W760/H414, H380 are great powders. Max loads of 760 in mine with the 145 Speer SBT gets me 2898 ft/sec with under moa accuracy.

 

[bigedp51]

Besides looking at your primers you can measure base expansion, I thought .001 was the ball park figure but according to Hodgdon's its much less.

Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-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.


Measuring above the extractor groove tells you more about the strength and hardness of your brass. It does not tell you the pressure, it tells you the yield strength of the brass and how much pressure the case can take.

How Hard is Your Brass? 5.56 and .223 Rem Base Hardness Tests
http://bulletin.accurateshooter.com/2014/05/how-hard-is-your-brass-5-56-and-223-rem-base-hardness-tests/

 

[savagelh]

Interesting thread to me. I just picked up a 7mm08 but haven't shot it yet. My first load will be some combination of h4350 or cfe223 and 120 tsx or 140 nbt.

 

[350 Mag]

That's in the nosler manual I believe... One day I'll give it a go when I come across some at a good price. Got some stuff working for this load.

Nice to hear about other powders. Thanks for the tip!

Regards
Ronr

Ya pretty much follow data for 140gr AB, Nosler brass, Fed Match primer and max load of Big Game should produce desired result.

There is some debate about temperature stability of Big Game....but I try to do most load development in Fall when temps are just around zero.

 

[RonR]

I've had a 7/08 for over 30 yrs. In my experience with 140-150 gr bullets W760/H414, H380 are great powders. Max loads of 760 in mine with the 145 Speer SBT gets me 2898 ft/sec with under moa accuracy.

That makes 3. Thanks for sharing.

Regards
Ron

 

[RonR]

Besides looking at your primers you can measure base expansion, I thought .001 was the ball park figure but according to Hodgdon's its much less.

Simple Trick for Monitoring Pressure of Your Rifle Reloads
http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/simple-trick-monitoring-pressure-your-rifle-reloads

Thanks Ed. I'll have to study this a bit more. I think you understand where I am at.

Ron

 

[RonR]

Interesting thread to me. I just picked up a 7mm08 but haven't shot it yet. My first load will be some combination of h4350 or cfe223 and 120 tsx or 140 nbt.

FWIW, the hunting load for this rifle is nosler accubond 140gr. This is over Varget and this load is sub MOA at -5 and colder. (that was developed a couple of years ago and I'd like to revisit now that I have some more experience.)

I haven't tried H4350 because it's been a little tougher regarding availability and price in Saskatoon. However by all accounts this is supposed to be a great powder for this caliber as a few on here with lots of experience have stated. ( At the 140 gr bullet weights I've tried IMR 4064, IMR 4166, Re 15 and W760. All had interesting results, Varget being the most consistent so H4350 would be something I wouldn't hesitate to try)

Never tried 120gr bullets.

Regards
Ronr