Does anyone know at what pressure sticky bolt lift occurs?

[Carey Farmer]

I read a lot of posts about folks inching their powder charges up until they start feeling sticky bolt lift, then backing down their charge a percent or two and calling that safe enough. Does anyone know what chamber pressures are usually associated with sticky bolt lift, for the various cartridge diameters?

Based on a simple hoop stress model for a pressurized cylinder, chamber pressure for sticky bolt lift should be different for different cartridge case diameters. For example in Remington-pattern 1.0625" tenon barrels, sticky bolt lift should take 35% more chamber pressure in a standard (0.471" diameter) chambering than in an "ultra-mag" (0.551" diameter) chambering. That suggests that going up to sticky bolt lift pressure with say, 30-06 Springfield or .280 Remington cartridges might involve pretty high pressures.

 

[WeiserBucks]

7 Million PSI

 

[Dmagna]

I think you are really overthinking the process, just shoot until you start to feel and see signs of pressure. Each rifle is different, that why everyone says work up slow. .2 or .3 of a grain at a time

 

[Mikecr]

There are a few other things to separate out & consider.
Are you talking about popping extraction, or difficult bolt turn? They are different animals.

Popping extraction can occur with either poor bolt timing, or insufficient breech support (leading to case-chamber interference).
More barrel steel around a given chamber, finer/shallower tenon threading, and coned breech help with the latter.

Difficult bolt turn means you have a case pressing hard against the bolt face. Negative headspace.
This is a pressure problem, but doesn't indicate the actual pressure.

I have never read/heard of anybody suggesting a certain pressure based on bolt lift.

 

[Koda_]

Ive never heard of any way to actually measure chamber pressure in production guns?

 

[Mikecr]

With a strain gage, and careful validation of the particular barrel steel as a standard, it's possible to get close on pressure.
But WE never really need that, as we can see when local pressure is a 'problem'. We all have different problems at different pressures.
This is normally well below a safety issue.

I use a chrono and QuickLoad, and I can see them follow each other.
If there is not a gun problem, or reloading/brass problem, I can see when I'm at or above SAAMI max, usually without a bolt lift issue. That's normal. This is .473 casehead cartridges at normal tenon diameters. For a WSSM cartridge I went with a magnum diameter tenon per BATs recommendation. And I believe that was a smart move (Savage also does this).

I also do testing which I coin as MyMax. This involves measure at new case web-lines as I go up in load.
I watch for growth that goes up, levels off, and then step changes upward. This indicates (to me) the point where FL sizing would be required to reuse a case (every cycle). I don't FL size.
So far this has correlated with just going past SAAMI max, per QuickLoad.
Thing is, I wouldn't get difficult bolt turn with this unless I kept going. Why would I keep going?

 

[Rich Coyle]

Thing is, I wouldn't get difficult bolt turn with this unless I kept going. Why would I keep going?

Because you want more?

 

[Mikecr]

More means bigger cartridge,, better planning next time.
To me, it doesn't makes sense to cause high brass turnover -for more velocity -from a hunting cartridge.

 

[Seabeeken]

Ive never heard of any way to actually measure chamber pressure in production guns?

Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace

Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.

www.shootingsoftware.com

according to grt, ejector marks in my rifle occurred at 74,000 psi

 

[Carey Farmer]

I think you are really overthinking the process, just shoot until you start to feel and see signs of pressure. Each rifle is different, that why everyone says work up slow. .2 or .3 of a grain at a time

Yeah. I used to work in hydrocarbon processing and I do tend to over-think pressure and what it can do.

 

[Carey Farmer]

There are a few other things to separate out & consider.
Are you talking about popping extraction, or difficult bolt turn? They are different animals.

Popping extraction can occur with either poor bolt timing, or insufficient breech support (leading to case-chamber interference).
More barrel steel around a given chamber, finer/shallower tenon threading, and coned breech help with the latter.

Difficult bolt turn means you have a case pressing hard against the bolt face. Negative headspace.
This is a pressure problem, but doesn't indicate the actual pressure.

I have never read/heard of anybody suggesting a certain pressure based on bolt lift.

I'm probably using the wrong terminology. I'm talking about difficult bolt turn. Only had that happen to me once - wasn't paying close enough attention, didn't have my reading glasses with me, and missed an ejector mark.

I now have safety glasses with built-in reading lenses along the bottom.

 

[Carey Farmer]

With a strain gage, and careful validation of the particular barrel steel as a standard, it's possible to get close on pressure.
But WE never really need that, as we can see when local pressure is a 'problem'. We all have different problems at different pressures.
This is normally well below a safety issue.

I use a chrono and QuickLoad, and I can see them follow each other.
If there is not a gun problem, or reloading/brass problem, I can see when I'm at or above SAAMI max, usually without a bolt lift issue. That's normal. This is .473 casehead cartridges at normal tenon diameters. For a WSSM cartridge I went with a magnum diameter tenon per BATs recommendation. And I believe that was a smart move (Savage also does this).

I also do testing which I coin as MyMax. This involves measure at new case web-lines as I go up in load.
I watch for growth that goes up, levels off, and then step changes upward. This indicates (to me) the point where FL sizing would be required to reuse a case (every cycle). I don't FL size.
So far this has correlated with just going past SAAMI max, per QuickLoad.
Thing is, I wouldn't get difficult bolt turn with this unless I kept going. Why would I keep going?

Thanks Mikecr. I use a chrono and Quickload also, and develop loads with soft case-head (Nosler or Norma) brass. Ejector imprint usually shows up on that brass when QuickLoad says chamber pressure is 68,000 to 70,000 psi. I just don't know if what Quickload is telling me is really close to reality. I've never loaded heavy enough to get ejector imprint on ADG or Peterson brass, I just rely on max load load data developed in Nosler or Norma brass (corrected for any variation in case capacity).

There's so much variability in case head hardness (from one brand to another) that I was looking for some other indicator of chamber pressure. Do you see much variation in QL pressures associated with case web diameter vs pressure from one manufacturer to another?

I also use actions threaded for oversize tenons (1.120" x 20 tpi), and extra-long (0.550") bolt head lugs, for ultra-magnum diameter cartridges.

Agreed on not going much past SAAMI max. Just chamber for a bigger case if you need more velocity. For hunting rifles in long action I shoot 28 Nosler and .264 Win Mag. In short action I shoot 6.5 SAUM.

 

[dogz]

IMO, follow the guidelines of the manuals and don't forget that "pressure equals speed and speed equals pressure"

 

[Carey Farmer]

Rifle Barrel Chamber Pressure Testing Hardware & Software | Pressure Trace

Measure ACTUAL rifle chamber pressure for each shot, barrel harmonics, rise time, time to muzzle exit and OBT barrel timing.

www.shootingsoftware.com

according to grt, ejector marks in my rifle occurred at 74,000 psi

Thank you Seabeekin. My experience (at work, with piping, pressure vessels, and structural members) is that external strain gauges need to be initially calibrated against measured pressure, load, or deflection ... or else absolute error can be significant.

If you don't mind saying ... what brand of case shows ejector marks at 74,000 psi?