Overpressure Signs ?

[Kennibear]

Clark

All true. All of little consequence. If I were measuring from a never been done before cartridge your statement is absolutely true. It would require a plug in the barrel and measured application of hydraulic pressure to establish the ratio of strain to pressure. I don't do that. Neither does SAAMI. But what does work is to fire the test setup with a known quantity and use an offset. That's why SAAMI members baseline their test barrels with SAAMI approved Reference Ammo.

Not being a SAAMI member I use factory ammo to reference my gauge, for example, Hornady DG 270gr RP Interlock 375 Ruger for that rifle. Since Hornady is about it for 375 Ruger ammo there is not much else. Referencing my shooting tests over the chronograph of many factory loads from many makers Hornady's Superformance and upscale series ammo deliver the highest velocities by far of all the makers. Their ammo is always the fastest in a cartridge/ bullet weight category. Since velocity=pressure I assume Hornady runs their's pretty hot. By shooting a known quantity it is like a story pole to a carpenter, I don't need a tape measure if I have a stick with marks in the right places. Reference ammo is my story pole.

The real stickler is the strain gauge install. It is easy but requires diligence and a quality bond. The gauge MUST be aligned perpendicular to the bore and exactly half way from the receiver front shoulder and the start of the cartridge/chamber shoulder in the barrel. Then carefully measure the barrel, case wall thickness etc. Not impossible but very necessary. But it beats the heck out of staring at the brass and primer!

I did it the old way for 40+ years. But I am older now and old dogs sometimes learn new tricks....

None of the above remarks are meant to disparage or criticize anyone.

KB

 

[seidersjoden]

Clark

All true. All of little consequence. If I were measuring from a never been done before cartridge your statement is absolutely true. It would require a plug in the barrel and measured application of hydraulic pressure to establish the ratio of strain to pressure. I don't do that. Neither does SAAMI. But what does work is to fire the test setup with a known quantity and use an offset. That's why SAAMI members baseline their test barrels with SAAMI approved Reference Ammo.

Not being a SAAMI member I use factory ammo to reference my gauge, for example, Hornady DG 270gr RP Interlock 375 Ruger for that rifle. Since Hornady is about it for 375 Ruger ammo there is not much else. Referencing my shooting tests over the chronograph of many factory loads from many makers Hornady's Superformance and upscale series ammo deliver the highest velocities by far of all the makers. Their ammo is always the fastest in a cartridge/ bullet weight category. Since velocity=pressure I assume Hornady runs their's pretty hot. By shooting a known quantity it is like a story pole to a carpenter, I don't need a tape measure if I have a stick with marks in the right places. Reference ammo is my story pole.

The real stickler is the strain gauge install. It is easy but requires diligence and a quality bond. The gauge MUST be aligned perpendicular to the bore and exactly half way from the receiver front shoulder and the start of the cartridge/chamber shoulder in the barrel. Then carefully measure the barrel, case wall thickness etc. Not impossible but very necessary. But it beats the heck out of staring at the brass and primer!

I did it the old way for 40+ years. But I am older now and old dogs sometimes learn new tricks....

None of the above remarks are meant to disparage or criticize anyone.

KB

Could you send a picture of your pressure guage?

thanks
Joden

 

[thekyrifleman]

Seider,

That would be 2.0 grains not 0.2 grains. That is if you have determined that 98 grains are indeed max.

 

[seidersjoden]

Seider,

That would be 2.0 grains not 0.2 grains. That is if you have determined that 98 grains are indeed max.

Thank you

Joden

 

[Kennibear]

seidersjoden

Click on the pictures for an enlarged view.




This is a dual strain gauge on a Savage. The front (green wires) SG is over the bullet throat per CIP standards. The back (black wires) SG is over the middle section of the chamber half way between the cartridge/chamber shoulder and the barrel nut on the Savage as per SAAMI standards. Short action Savages can only use the front/CIP location. Note the strain relief for the wires, white paper laminate on the green wires and red paper laminate on the black wires. The recoil is severe enough to shear the wires and SG loose so they must be secured against the recoil. I use Henkel/Loctite Plastic epoxy Component IDH# 1393761 to secure the wires and strain relief as it really grips the plastic insulation. Regular epoxy does not. The SG's and wires are final coated with Varnish.



This is where the SG is on a Ruger #3 under the forstock between the action/forstock tang and the barrel. The tweezers are holding a SG to give some idea of how small they are. Notice the tiny darts at top center and bottom center of the SG. These are used to align the SG to the setting mark on the barrel. They are dead center of the grid of the SG. This picture is before the leads are soldered to the SG. The green wire is 26ga and the black wire is 24ga. Most assembled SG tabs use 28ga leads.



This is a SG on a Rem 700 with the connector. The connector is assembled and epoxied with the same plastic epoxy and while in the gel phase shrink tubing is applied (two layers with the shorter inside the longer piece) and the epoxy squeeze out cleaned up with citric solvent while still in the gel phase. It is important to clean the contacts thoroughly. This makes a molded end that can take some rough handling. On the Remmy I used the cyanoacrylic gel that attaches the SG's to coat the SG instead of varnish. Won't do it again.

Hope this is informative.

KB

 

[semtex]

Yes, that is one thing overlooked is the type brass one is using some brands are soft others are hard and to me that would make a big difference in trying to reason with pressure signs gauging with primers and case head expansion. Also the chamber of the gun. But we have to hold it within those all round spec's.

Good points!!

 

[Demon061]

I've gone through most all of the pressure sign reading. It's pretty much witchcraft.....to me.

I've settled, if I want long case life, which I don't care about any more, I increase powder to the point where the Remington bolt "clicks" on the up lift. Pressure is getting there. Two clicks, the second when arriving at full bolt lift, the pressure is getting really up there.

Finally if I have to hammer the bolt back with my hand, pressure has increased a bit more. If I have to use any sort of "tool" to get the bolt back, I'm in territory that I shouldn't be treading.

All of this is with an alcohol cleaned chamber and brass.

I also use an RSI pressure system which is pretty nifty once calibrated. Which, in my case, from the above descriptions, has probably been a life saver.

Was pretty concerned with the brother's Model 70 in .300 because the bolt was sticking BAD after its first few shots. Thought the headspace might be off but the cartridges weren't swelling at the neck. Over time the problem mellowed out and now it cycles like a champ. Still pretty wary though