Pressure Trace II: First outing

[Blood Trail]

Finally got a chance to use my pressure testing unit. I traded a feller some reloading equipment for a used 835 barrel. I’m using that as a stand-alone test barrel. I started off by cutting the first section of the vent rib off to epoxy my strain gage over the chamber area:

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You have to measure the chamber ID (easy using cerrosafe) and the OD of the area of the barrel where you’re placing the strain gage. Those are values you have to add to the ballistic software system.

Next, you have to standardized your unit with a known pressure load. The developer recommends choosing a load from Lyman’s. I chose to use the pressure results I got back from Precision Reloading from Uncle D’s Fury slugs.

Theres a correction you can add to the software based on the reading you initially get with your previously tested load. In my case, the first three shots UNCORRECTED with Uncle D’s known pressure slugs where coming in around 6kpsi. They should of tested out 10.5kpsi.

Apply simple math, I added a correction of 3kpsi and tested 3 more of the same loads. Those read on the money and I was in business.


I started off testing a 3.5” 18 pellet buckshot load I’ve used in the past. I knew these where heavy loads. I’ve had slight signs of over pressure but never really had any absolute pressure values.

I shot three loads through my system and they came in around 17kpsi...... 3kpsi over SAAMI spec for 3.5” 12 ga.

I also tested a couple of factory 2.75” buckshot. Those avg around 11kpsi.

Factory slugs came in around the same.

All in all, I’m happy I purchased this unit. It’ll pay for itself after about 2-3 range outings.

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[Hogtamer]

Nice work BT!

[bikerbeans]

Leon,

Your system will great for load development. It save you a lot of time looking for the parts of a blown up scatter gun.:bigsmyl2:

BB

[sharps4590]

Outstanding sir!! I'm most grateful for your work and experience!

[Blood Trail]

Outstanding sir!! I'm most grateful for your work and experience!

I’ve learned a lot from the old timers on here.


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[tomme boy]

Won't that 835 barrel show less pressure than a standard barrel?

[megasupermagnum]

Won't that 835 barrel show less pressure than a standard barrel?

Why would you think that?

[Blood Trail]

Won't that 835 barrel show less pressure than a standard barrel?

There’s important dimensional data fields you must enter in the software for the barrel you’re using. Since the strain gage measures how much the barrel expands (in micro ohms), it needs to know the OD of the portion of the barrel where the strain gage is and in ID of the chamber in relation to the placement of the strain gage.

The data acquisition makes linear measurements so that’s why you have to standardize the unit with a known tested load prior to its use.


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[tomme boy]

Why would you think that?

I thought back bored barrels were made to reduce pressure.

[megasupermagnum]

I didn't realize it was back bored. That's a very good question, one I do not know the answer. Wow, a quick search shows an 835 uses a .775" 10 gauge barrel chambered for 12 gauge. That could certainly promote blow by. I also see it is not recommended to shoot slugs through them.

I've got mine set up on a Mossberg 500 12 gauge, Savage 506 16 gauge, and a Ithaca mag10 10 gauge. All three are standard bore size, and produced pretty dang close right out of the gate. I have a 500 psi correction the 10 gauge, but none on the 12 or 16.

[Blood Trail]

I don’t believe it makes a difference by it being backbored. The chamber isn’t overbored. I don’t believe overbored barrels affect pressure at all.

I know back bored barrel reduces barrel friction and you might see a decrease in pressure on down the barrel, but the strain gage is over the chamber.


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[megasupermagnum]

That's a good point, I've read that peak pressure happens before the shot, or slug, etc. has even left the shell. PTII only graphs pressure over time. I'm sure a good engineer could calculate how far the projectile has moved based on acceleration and muzzle velocity. I know PTII can calculate the point it leaves the barrel, but not earlier in the barrel.

[tomme boy]

I do know that you are not supposed to shoot any load that does not have a full plastic wad. No fiber wads. I know they stated that slugs were to never be shot out of the bird barrel. They COULD turn sideways and get stuck. I think Mossberg had it happen to them. Thats why they came out with a slug barrel about a year later with a normal barrel.

[Blood Trail]

I do know that you are not supposed to shoot any load that does not have a full plastic wad. No fiber wads. I know they stated that slugs were to never be shot out of the bird barrel. They COULD turn sideways and get stuck. I think Mossberg had it happen to them. Thats why they came out with a slug barrel about a year later with a normal barrel.

Yeah, I’ve heard the same thing. Don’t apply to slug in wad configurations as the wad obturates in the bore. My most accurate Lee Key Drive Slug is out of this barrel.

Would I run full bore slug through it? Sure. I ain’t skeered.

Hell, I ran a couple thousand through it before I found out it wasn’t recommended.

I have a couple more strain gages I’ll use on rifled barrels. My whole intent was using this barrel for buckshot shot pressure testing.


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