Velocity-Pressure...When to Stop?

[Supercat]

Thanks to the kindness of Dr.Mike here, I am working up a load for my 7mm Rem Mag,175gr ABLR, 26” 1:8 barrel, with RL 33.

So far I have worked up to 76.0gr and although at 2,845fps it is still 193fps slower than the QL data, it shows no signs whatsoever of excessive pressure. According to the QL I am at the threshold of 61,000psi which is the max pressure for the 7mm but since I am not seeing pressure signs I am wondering on how far I can/should push it.

I didn’t shoot for accuracy yet, since I want to get in the ballpark velocity wise and then go from there.

What do you guys think?

 

[fightthenoise]

I’d keep pushing it. You won’t get enough powder in the case to really damage anything in one shot. You’ll most likely just get a stiff bolt lift and then you’ll know you’re there. The speed is the only thing you can measure, so use that as your proxy for pressure. If the speed is still low, pressure likely is as well. If you’re worried, just go in 0.2 grain increments. Only issue with that is it might take more rounds and the onset of pressure signs will be more gradual so you have to pay more attention to notice them.


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[Supercat]

Thanks for the response and that’s what I’m thinking too.

Besides the stiff bolt lift what else would you think would be me first sign on the case?

I’m thinking go to the limit, back off till sign disappears, then play with charge-seating for accuracy

 

[fightthenoise]

Are you doing the 10 shot load development method? If not, google that and watch the video by 6.5 guys. It kinda sounds like that’s what you’re doing but just making sure. That way you’ll find your velocity node that is also likely to group well.

On the case, the first sign you’ll likely see is flattened primers. The round radius on the cup of the primer will get mashed against the bolt as the pressure pushes the primer back out of the pocket and this flattens that radius out. There are lots of example images of flattened primers on the web if you want to see what you’re looking for.


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[Supercat]

I saw that video but I am actually just working up in 1/2 grain increments...I will look for a node though

I will also google flattened primers too

 

[BretN]

You will also see ejector marks on the case head, if you are shooting a bolt gun with ejector button in the bolt face (most push feeds like M700).

 

[preacher]

I've never had a problem with going until I see pressure signs, then back off some & tweak COAL, etc. I think each rifle is different, same with the accuracy desired/needed/acceptable to the shooter. A good chrono is a good indicator because pressure = speed. Velocity/pressure are "inseparable", so watch it close, then tweak. I never used a magnum case more than 4-5 firings and I liked to hunt with loads set up for once fired cases. I have had some rifles with some brands of cases/loads that I could trust with new brass, but I always partial size them. Rarely have I ever ben able to just load new brass straight from the box w/o any prep. RWS, Lapua, Norma, yeah, but never WW/Remington/Hornady.
My last 7mm Rem Mag also loved R33/175gr. I think you are doing it right going 1/2 grain at a time. I have used 1 grain at a time until I felt I was close to my goal, then went 1/2...in magnums. In smaller cases, I have gone as small as 2-3 tenths at a time. Depending on the rifle, for example. Hope this helps...

 

[Dwh7271]

An ejector mark is just going to be a little shinier place on the case head.
Flat primers as the others mentioned.
Loose primer pockets showing up when you reload them is another indicator that you’re pushing the limit also.

 

[Supercat]

Fellas I made it up to 78.0gr at 2,940fps and I saw some cratering so I stopped.

Do you guys think that I should back off or is this still OK?

 

[fightthenoise]

Did you ever notice any stiff bolt lift? If the cratering is all you noticed you probably have some room left. The primer still has a good radius, and there’s no ejector mark (assuming you’re shooting a push feed). Another thing you can look for is loose primer pockets by putting a primer on the bench and trying to seat a primer by hand just pushing the case head down into it. Or if they just feel loose when you seat them using your normal method. Are you running out of room in the case? RL33 is a slowwww powder so you may never actually see any obvious pressure signs before you run out of room in the case.


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[Supercat]

Did you ever notice any stiff bolt lift? If the cratering is all you noticed you probably have some room left. The primer still has a good radius, and there’s no ejector mark (assuming you’re shooting a push feed). Another thing you can look for is loose primer pockets by putting a primer on the bench and trying to seat a primer by hand just pushing the case head down into it. Or if they just feel loose when you seat them using your normal method. Are you running out of room in the case? RL33 is a slowwww powder so you may never actually see any obvious pressure signs before you run out of room in the case.


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The bolt lifted normally and there is still room in the case too, and it is a push feed M700

 

[fightthenoise]

Yeah dude let it ride. Also if you’re using quickload you can tune it now to get a better estimate of your pressure. Edit the overall length field, the case capacity (measure 5 cases w water fill and get an average), then adjust the Ba factor on the powder until it matches your speeds with your given charge weight. With all those fields tuned to what you’re working with exactly, you’ll get much more accurate pressure predictions.


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[Supercat]

You guys are incredible thanks!

 

[Alderman]

No expert here, but pay attention to temperature. What works in cool temps may be a bit too much when it gets hot outside.


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[truck driver]

You also can measure the case diameter at the web and compare it to cases that were fired with lighter loads or Saami specs.

 

[jimbires]

double post

 

[jimbires]

Fellas I made it up to 78.0gr at 2,940fps and I saw some cratering so I stopped.

Do you guys think that I should back off or is this still OK?

I have a rifle that does this with starting loads . it doesn't seem to get any worse as I work up to max loads . it's caused from the firing pin hole being a little to big for the pin . I would not use this as an absolute max pressure sign . the fix is to have the hole machined and a bushing installed , but this is not necessary . you'll notice stiff bolt lift when you get to max pressure . don't shoot anything you have loaded hotter than that . back off a little from your stiff bolt load .

 

[SJB358]

Just my take on it, I see a little scuffing on the case head from the bolt and 2940 with a 175 Bullet is trucking in a 7 Rem Mag. I know I’d be looking for accuracy at this point myself with that combo. I’d probably find where the bullet wants to shoot in regards to seating depth before I tried getting more speed.

 

[Supercat]

Just my take on it, I see a little scuffing on the case head from the bolt and 2940 with a 175 Bullet is trucking in a 7 Rem Mag. I know I’d be looking for accuracy at this point myself with that combo. I’d probably find where the bullet wants to shoot in regards to seating depth before I tried getting more speed.

SJB, are you referring to the mark below-between the 7 and the H?

Do you think that it's a pressure mark or just scuffing on the case from something else?

 

[SJB358]

I think it’s a sign Supercat. Not standing there to see or look it’s a scuff which means something is growing and planting itself against the bolt face. Lightly for sure, but pressure is certainly building for the next steps of ejector marks and such.

I’m nowhere near saying it’s unsafe and I’m sure I’ve got some loads that do the same thing but that’s probably close to safe operating pressure. And heck, you’re getting 2950’ish with a sleek 175, another 50 FPS won’t change anything for you. I STILL find myself looking for more at times but punching the numbers into a calc calms me down.