Alternative Measure Pressure?

[ballman6711]

I can only wonder how much pressure it takes to shear off the bolt lugs.

chris

 

[rfwobbly]

Years ago when my boys were Scouts, I took them to a nearby indoor range to practice .22 rifle. I guy came in with a high powdered rifle and took up the lane next to us. His reloads were so loud, that even with proper hearing protection, it was painful. We decided to leave. While we were packing, there was one last shot that was even louder.
Later in the showroom/lobby he was showing his rifle bolt to one of the range attendants and BOTH locking lugs were sheared off.

 

[N555]

One time I made the mistake of picking up brass after an action pistol match. At the next match some of my carefully crafted "Match" handloads wedged themselves solidly into the tapered chamber on my 9mm, thus ending that day's match for me. Later upon measuring these cases, it was discovered the case head had expanded just 0.002" at a position my dies couldn't reach. Those were the cases from the Open Class boys, and that's why they were left on the ground ! Lesson learned !!

So case head expansion is a real thing, but only in over-pressure scenarios. I agree with fxvr5. By the time you are expanding case heads, you are well into the Danger Zone... a place you shouldn't even be near. For the average shooter, "nothing good happens at Max Load". If you really want to know your chamber pressure, then buy a chronograph. For $100 you can get a very advanced chrono that will even send all the data to your phone.

Hope this helps.

I have loaded 9mm so hot 147gr bullets are super Sonic out of a 5 inch barrel and the cases didn't do that.

 

[Jim Watson]

Trivia Alert

An advertising point for the straight walled Improved and wildcat designs was that the brass would stick to a dry chamber wall briefly, reducing the bolt thrust by the force it took to stretch the case back through the head clearance to the bolt face, thereby allowing heavier loads than the standard tapered case that would "wedge" its way back. Somebody once measured the cross-sectional area of the brass in a case wall, multiplied by the tensile strength of cartridge brass, and came up with a rather low contribution toward containing chamber pressure.

Before DIY strain gauges, there was the Powley P-Max. It mounted to a rifle by the scope mounts and claimed to give a value for chamber pressure by the flattening of a lead crusher by a movable weight slamming forward in recoil.

I vaguely recall another pressure reading device that used a cartridge case with an insert of some responsive material set into the head. Load it up, shoot it, apply the readout instrument to the insert, get a number that could be translated to pressure.

That's all I have on those devices, refer to your Guns & Ammo collection of about 50 years ago for articles promoting them.

 

[jski]

Videos I am not sure about but I can provide a few images as they apply to rifle cases. Below are some 7mm-08 Remington cases I primed and fired in a 7-08 bolt gun. The cases were simply primed, no powder and no projectile means no real pressure to speak of. No cartridge head slamming into a bolt face, just a boring pop.

View attachment 1183963

Since there was not adequate pressure to violently slam the cartridge head into the breech face the primers are not flattened.

View attachment 1184076

Flat primers as a result of slamming back against the breech face.

Edit: The off center look of the second image is a result of poor camera angle.

Ron

Outside of some high-speed photography of the actual event, that paints a pretty good picture of what’s happening.

 

[kcofohio]

Are there videos of this?

I once took some primed (standard pistol primers) cases in 380 Auto with no bullet or powder. Loaded 6 into Bersa Thunder one at a time. Fired off 3 into the air. And the others I buried the muzzle into a pillow.
The 3 I fired into the air, the primers backed about half way out of the pocket. The 3 that I fired into the pillow, the primers were flush with the case head.
So, as long as there is back pressure (seated bullet) the primer will be pushed back into the primer pocket.

Edit, I wouldn't try the above in a revolver, as the cylinder may not swing out freely.

 

[.308 Norma]

Edit, I wouldn't try the above in a revolver, as the cylinder may not swing out freely.

It won't!