Is Velocity a Good Indicator of Pressure?

[Woolsocks]

Noticing that the load data from nosler and my loading handbook differ by quite a lot (several grains). Both have exactly the same 3230fps velocity at max load, but the Lyman book shows achieving that velocity with 79 grains powder (their max load). Nosler shows that it takes 81 grains to get there(nosler’s max).

Question- im working up from the bottom and stopping if I get high pressure signs. In the abscence of high pressure signs (may not get any, cause I have good brass), would you consider a chrono reading at 3230 to be an indicator you’ve reached the high end of the safe range? I do have the same barrel length that the load data was based on.

 

[straightshooter1]

Noticing that the load data from nosler and my loading handbook differ by quite a lot (several grains). Both have exactly the same 3230fps velocity at max load, but the Lyman book shows achieving that velocity with 79 grains powder (their max load). Nosler shows that it takes 81 grains to get there(nosler’s max).

Question- im working up from the bottom and stopping if I get high pressure signs. In the abscence of high pressure signs (may not get any, cause I have good brass), would you consider a chrono reading at 3230 to be an indicator you’ve reached the high end of the safe range? I do have the same barrel length that the load data was based on.

The best indicators for the upper limits of pressure: stiff bolt lift; ejector swipe; flattened primers with some cratering. Chrono velocity can give you some idea when you might begin to see these things, but it's not really all that reliable as other things can be involved, like differences in what the length of a barrel will produce or how new or old the barrel is. It's best if you simply take the max loads from whatever loading handbook you have, back off ~10% and run a pressure test (like loading single rounds in .5 increments, like a ladder) so you know where your limit is. Then you know where your velocity max is and where you can run your load development.

 

[Doom]

Outside of overpressure signs ranging from primer signals to hard bolt lift the ONLY relative measure of pressure is velocity. But it is not a "perfect" correlation to pressure. Some barrels are faster than test and some are slower. Also you may not be at maximum pressure at a loading manuals maximum load. As I recall Lyman gives pressure for the load and in Nosler's case they do not. In the Hornady they test to determine maximum pressure, then shoot that load in a test rifle, then choose the maximum load based on the velocity of that load, rounded down. So to answer your question, you are wise to consider that your load for the published velocity is around the maximum load recommended. You also have to consider chamber differences, case capacity, seating depth, and barrel length.

 

[XLR308]

You can add case head expansion to all of the above but it to can be subjective depending on chamber specs, brass quality and type of firearm it's fire in. Calibrated Pressure transducer equipment would be best but I don't recall anyone here going to that extreme.
Also some cartridge designs and chamber specs do a really good job of masking pressure signs like the 6.5x47 lapua.

 

[spife7980]

Velocity can be a useful indicator but there is no conclusive indicator until something starts to give. Use all the indications you can.

Understanding Pressure :: Primal Rights, Inc

Reading pressure is a required skill that all shooters must have. Whether you are shooting factory ammunition or your own handloads, you absolutely must be able to detect and interpret pressure signs on your fired brass.

www.primalrights.com

 

[918v]

Noticing that the load data from nosler and my loading handbook differ by quite a lot (several grains). Both have exactly the same 3230fps velocity at max load, but the Lyman book shows achieving that velocity with 79 grains powder (their max load). Nosler shows that it takes 81 grains to get there(nosler’s max).

Question- im working up from the bottom and stopping if I get high pressure signs. In the abscence of high pressure signs (may not get any, cause I have good brass), would you consider a chrono reading at 3230 to be an indicator you’ve reached the high end of the safe range? I do have the same barrel length that the load data was based on.

If you’re using the exact same components loaded to the same coal in a saami spec chamber then you can reasonably assume that.

The problem is brass varies in thickness from brand to brand and even between different lots and times of manufacture of the same brand. Then there are chamber differences, coal differences, powder lot differences, etc.

I have found that you can get about 100 FPS more velocity than what the book says before you see pressure signs. But that’s because pressure signs usually don't manifest themselves until you’re way over max.

If you’re getting 3250 with no pressure signs and the accuracy is there then leave it alone. Don’t push your luck. If you need more speed then get a bigger round.

People who have to turn everything into a super magnum just so they can post on the forums to brag are stupid and they infect the reloading community with their unsafe ideology. The whole point of reloading is that you can reload the case over and over and over again. Pushing the limits goes against that idea.

 

[Woolsocks]

Welp, I went to the range today and put one round downrange. My lowest charge weight (77grs) had a flattened primer and was 3175 fps. So, guess I’m pulling all the loads I did above that. Time to work in the 74-76gr range.

Question. Would you re-size the neck after pulling bullets? Wondering if loading, pulling, then re-loading without re-sizing will mess with my neck tension.

 

[918v]

A flat primer in itself is not a pressure sign. Could be too much headspace.

 

[XLR308]

You might get better help if you include the cartridge, brass manufacturer, powder used, bullet make and weight and any other details that are non existent at this point.

 

[Woolsocks]

You might get better help if you include the cartridge, brass manufacturer, powder used, bullet make and weight and any other details that are non existent at this point.

Fair. 28 nos. Once fired Peterson brass pushed back 5 thou (long story). H1000, 160 grain accubonds, WLRM primers. Using a .314 bushing, loaded rounds have a .317 neck.

 

[straightshooter1]

Question. Would you re-size the neck after pulling bullets? Wondering if loading, pulling, then re-loading without re-sizing will mess with my neck tension.

I've often reseated bullets without re-sizing the necks and the results work out just fine, though my neck tension is ~.0015. Depending on the neck tension you started, like if it's .003 or more, there may be a significant difference due to the change in neck tension, which can show up on your target.

 

[918v]

Fair. 28 nos. Once fired Peterson brass pushed back 5 thou (long story). H1000, 160 grain accubonds, WLRM primers. Using a .314 bushing, loaded rounds have a .317 neck.

How much neck clearance do you have? Not enough (<.005”) will cause flat primers.

 

[Doom]

How much neck clearance do you have? Not enough (<.005”) will cause flat primers.

OP, to expand on this since it isn't obvious at first glance, insufficient next tension can allow the bullet to dislodge too soon before the pressure has built enough to ensure good combustion and the bullet doesn't have enough energy to engrave in the lands correctly. Then what happens is the bullet slows and the powder now sees a slower change in volume and the pressure goes high. More or less.

 

[secondofangle2]

Yes. If you’re over 3500fps