Does anyone know at what pressure sticky bolt lift occurs?

[lancetkenyon]

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

Not always.

I had a 26" 6.5SS that would pressure up WAY before I got the speed it should have run at (tight spot in bore). I could nearly match the speed with my 20" 6.5SS. And once I swapped barrels, I can get an additional 155fps before seeing even a hint of pressure with the new 26" barrel.

 

[Carey Farmer]

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

Yep, good advice. I ran into problems with N570 & N565 (which I bought a couple years ago when nothing else was available). No-one, including VV, has N570 load data for .264 Win Mag, which is a primary chambering I shoot in long action. My short action chambering is 6.5 SAUM, which of course doesn't show up in anyone's load manual; and because I was loading with N565 there wasn't a lot of tribal knowledge on the shooting / reloading message boards.

I'm back to Retumbo and H1000 now, in part due to a little better availability, but also because I discovered that N570 and N565 burn up barrels way faster than Hodgdon's single-based powders. That was a pretty expensive lesson.

 

[Rosebud]

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?

Just about all of them. Most very high pressure rounds are going to show pressure at high sixty thousand PSI. Seventy four thousand is asking for serious issues, including blown primers, case rupture. Locked up bolt. Or worse, physical injury. Loss of eye sight. I think you get what I'm talking about.

 

[Carey Farmer]

Just about all of them. Most very high pressure rounds are going to show pressure at high sixty thousand PSI. Seventy four thousand is asking for serious issues, including blown primers, case rupture. Locked up bolt. Or worse, physical injury. Loss of eye sight. I think you get what I'm talking about.

Thank you Rosebud. I get ejector marks during pressure ladders on Nosler and Norma brass at 68,000 - 70,000 psi (per QuickLoad tuned via my normal practice). But I normally am able to find an accuracy load in my preferred 56,000 - 60,000 psi range.

I haven't been brave enough to get ejector marks on ADG or Peterson brass. They have pretty hard case heads, apparently.

 

[Seabeeken]

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?

You're right, the pressure trace system needs a proof load to calibrate it as I recall. A friend has the system and I recall him telling me about it. When I work on powder models for GRT, I send him the data and he runs them thru the PT2 system. When I worked on my 250AI, he didnt have a barrel for it so I was on my own. As for the brass, It was Lapua 22-250 formed into 250 AI and I was working up loads to fine the upper limit

 

[Carey Farmer]

You're right, the pressure trace system needs a proof load to calibrate it as I recall. A friend has the system and I recall him telling me about it. When I work on powder models for GRT, I send him the data and he runs them thru the PT2 system. When I worked on my 250AI, he didnt have a barrel for it so I was on my own. As for the brass, It was Lapua 22-250 formed into 250 AI and I was working up loads to fine the upper limit

That's good info Seabeeken. Yeah, Lapua brass has pretty hard case heads too.

Based on all the responses, I won't be taking loads up to heavy bolt lift as a calibration check for QuickLoad tuning.

 

[243winxb]

When brass no longer springs back. Your over maximum. Its a cartridge thing, not a set pressure thing.

Above 76,000 PSI all brass is toast.

Look up SAAMI Proof Loads, they are not all the same.

Just how i see it. Most likely wrong.

 

[Mike Matteson]

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?

I find that interesting that you only Neck size. I did that for years. From what I have read over the past few years. It pointed to FL sizing, but only bumping the shoulder back a few .002": or so. In the past year I have added new equipment for my reloading. Changing my ways to reload, greatly. The rifles I use I have already develop a hunting load for them. I don't change that load after that unless I can't get what I was using for it.
The one thing stumbled over, over 20 years ago. I have a 308 N.M rifle. The length to the shoulder is shorter than the 300 WM case. The neck is longer. It would have taken months to get a neck sizing die for the 308NM. So I used a 300WM neck sizing die. It didn't full length the neck. I use powder loads in the 75 gr area with 165gr bullets. Two thins happen then. 1. my groups tighten up some. 2. my case separation stopped. After that I would lose my case do to primer pockets in 10 to 12 firing. I can't remember having a problem with chambering the cases either after that.
So with my new 6mm/280AI rifle I will have to try both to see what's up. Back to the net to order a neck sizing die for that rifle. I am just about ready to go back to MT to do load development with that rifle and hopefully a 338WM rifle too.
Always enjoyed reading your comments.

 

[Lefty G-gear]

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.

I did the bolt-face truing cutter sequence.
The barrel has to be removed.
No more squeak n hard bolt lift.

 

[Lefty G-gear]

Bolt Face Truing Cutter - Carbide - Pacific Tool and Gauge

223 Bolt Face Truing Cutter - Carbide at Pacific Tool and Gauge

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Truing Blocks & Cutters - Pacific Tool and Gauge

Truing Blocks & Cutters at Pacific Tool and Gauge

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Find the right one for your rifle - if you need it.

 

[Carey Farmer]

I did the bolt-face truing cutter sequence.
The barrel has to be removed.
No more squeak n hard bolt lift.

Thank you Lefty. Most of my rifles have floating bolt heads. I had imagined that since the bolt head isn't held in a fixed attitude by the bolt, it's not really practical to square up the bolt face with a cutter, and probably not necessary anyway. Is that your understanding also?

The only time I've had a slightly stiff bolt lift on one of my rifles was when I didn't notice an ejector print during a pressure ladder, and shot the next (higher) powder charge round. Fixed that problem with safety glasses that have built-in reader / magnification lenses. along the bottom edge of the lens.

I used to work about 75 miles south of you. At Lost Cabin.

 

[Doom2]

Sticky bolts occur when the brass and chamber expand under pressure and when the pressure is removed the brass doesn't contract as much as the chamber due to differences in Young's modulus. The exact pressure depends on the barrel/receiver design but someone at LBL (Lawrence Berkley Labs if I remember correctly) estimated it to be around 70,000 PSI for a rifle cartridge.

 

[Carey Farmer]

Sticky bolts occur when the brass and chamber expand under pressure and when the pressure is removed the brass doesn't contract as much as the chamber due to differences in Young's modulus. The exact pressure depends on the barrel/receiver design but someone at LBL (Lawrence Berkley Labs if I remember correctly) estimated it to be around 70,000 PSI for a rifle cartridge.

Doom,

Sure appreciate the info!

 

[Mikecr]

'barrel/receiver design' and other conditions.
Number of firings on the brass. The case diameter, chamber clearance, brass thickness and alloy.
There is no possible way to put a rule of thumb to this.
It could only be tested locally, and you will still never know the actual pressure..