Science Fair Project Safety Assessment

[kingmt]

That is the point of reducing the case capacity is to get the pressure to spike faster. That is how you get by with less powder. Your reduced recoil will come from two things. First is easy to see. Less powder less gasses. Second is the lower volume gives you a quicker spike in pressure so the pressure is tapering of by the time the bullet leaves the barrel. That is why I suggested a longer barrel.

I don't know much about TB but see that it acts like Black. Black would be safe to do this so I figured TB would be also.

I wouldn't cut the case tho just shove it in deeper.

 

[manithree]

Second is the lower volume gives you a quicker spike in pressure so the pressure is tapering of by the time the bullet leaves the barrel.

Which is great for actually reducing perceived recoil. But I can't measure that, so it really doesn't help for a science project.

That is why I suggested a longer barrel.

As much as I would like to use this as an excuse to buy a GP100, that's not likely to pass the finance committee, especially since the gun is a control, so it doesn't help the science project, either.

 

[splattergun]

Go for it manithree. We still had a shooting range in the basement of my high school a long time ago. Then they downgraded to a 'safer' archery range. Now it's just used for ROTC drill and broken desks.
Let me suggest that your son doesn't have to measure recoil with a lighter projectile, it can be calculated. Very scientific.

 

[manithree]

Let me suggest that your son doesn't have to measure recoil with a lighter projectile, it can be calculated. Very scientific.

That's what we're doing (this year, too, actually). Just calculating F.R.E.

I wish I had a track on bearings so that I could securely attach a pistol to, then remotely pull the trigger (without moving the pistol) and measure the backward velocity over time with high resolution. Alas, I don't have the electronics or mechanical chops for that. We wanted another rig to measure muzzle flip, but that's even harder.

 

[Centaur 1]

Revolvers are tricky when you reduce the load too far. You can't reduce the load as far down as you can with a non-revolver. When the bullet sticks in the barrel you can hear the gas escape through thee cylinder gap. I also started worrying about lodging a bullet that's partly in the barrel and partly in the cylinder, locking up the gun. Lighter bullets are the way to go when reducing recoil. I use the Lee 105 grain swc loaded with Trail Boss and the recoil is way down.

 

[kingmt]

It isn't perceived it is real. It would be easy to build a rig to measure actual recoil & I'm one of the few trying to keep you with this but it doesn't sound like you want my help so good luck with the project.

 

[manithree]

I'm one of the few trying to keep you with this but it doesn't sound like you want my help

Sorry, I guess I wasn't clear enough in post #25. The consensus seems to be that reducing cartridge capacity to achieve lower velocity increases the risk of unsafe pressure. I'm not going to do that. So this particular project is on ice.

If you have ideas for a rig that will measure recoil, I would love to hear that. My son and I have batted that around for months and the only thing we have come up with is measuring velocity to calculate FRE.

 

[jmorris]

As much as I would like to use this as an excuse to buy a GP100, that's not likely to pass the finance committee, especially since the gun is a control, so it doesn't help the science project, either.

I get it now and have a solution for you. What you need is a 357 ruger blackhawk, with the 9mm conversion cylinder. That will give you 38spl and "reduced capacity" pre shortened cases in the form of 9mm brass. The last one I picked up cost $325 and the fellow had never even used the 9mm cylinder.

You need not worry about unsafe pressure spikes either as there is tons of load data for 9mm. If you can't find one or just don't want to spen the money, weigh the water volume of a 9mm case and trim down 357 brass to achieve the same volume. This will require to seat bullets at depth without a primer in place, and fill with a syringe and weigh inverted. I would pick 357 brass and only use a 357 for tests as unlike 38spl it runs higher pressures than 9mm.

 

[kingmt]

I agree a 357 would give you more insurance.

A powder like bulleye a 10th of the volume would be big difference while TB would be had to tell a difference. I wouldn't let the nay say people on here scare me but research it harder & find out the truth. Other ways could be used to reduce case volume then cutting the case. you could use filler like corn mill. That way you may be able to look at a different gun even bottle neck. Then take what you learn & related it to the smaller gun to see if you can repeat it.

To measure recoil I'd put the handgun in a vise build your rig so that you can place a heavy spring 90^ from the back of the grip. Make sure the finish is protected. I'd use cheap caliper with the depth gauge inside the spring to measure how much the spring gets compressed. You could just get a $2 depth gauge then measure it with the caliper because the is a good chance that the recoil would destroy the caliper.

 

[rsrocket1]

The problem with measuring actual recoil means making something like a ballistic pendulum with a means to remotely pull the trigger without influencing the motion of the gun. Putting human hands in the test will throw and unknown variable into the mix.

That means something like a pair of plates or blocks to hold the gun which can screw together and allow the gun to move about so the recoil axis will be tangential to the arc of the swing. It can also be done with pressure transducers between the gun and blocks and a computer to log the data.

As a college experiment, it looks like something fun, but for a 6th grader, it reeks of too much parent involvement.

 

[jmorris]

Lots of ways to pull a trigger remotely. The syringe style "master/slave" cylinder style are really cheap and super simple.

 

[helotaxi]

There are those who disagree with that statement:
http://guns.connect.fi/gow/QA1.html
http://www.reloadammo.com/liteload.htm
http://www.thehighroad.org/archive/index.php/t-399439.html
http://africanxmag.com/secondary_explosion_effect.htm

But since there is no consensus on the cause, asking how to avoid it (which is only one of my questions), isn't very useful. But excess case capacity seems to be the common denominator, so that's why our plan would likely involve reducing case capacity.

If you look at all those, SEE (if it exists) relies on a very slow powder and a low charge density. Bullseye, Clays, Trailboss and powders like them burn so quickly that reducing the charge significantly only runs the risk of sticking a bullet. CAS shooters use extremely light loads of these powders with soft cast bullets to produce pop-gun loads in the 400fps range safely using .38spl or .357 brass. If you work down to ensure that the bullet leaves the bore, you are perfectly safe. Same concept as creating subsonic loads for rifles. Use the right powder that can be safely downloaded and work down to the results you're looking for.

 

[Edarnold]

Hmmm... Your aim is to reduce case capacity so as to ensure consistent combustion of a very light powder charge. The Old School answer to that was to to keep the case capacity the same, but fill the empty space with something that would hold the powder in place against the primer. The traditional filler was kapok fiber (used to be popular for cushion stuffing), an appropriate pinch of fiber pushed down on top of the powder to hold it in place. For your purpose the best powder should be Bullseye, ignites and burns better at low pressures than about anything else.

IMHO

 

[SSN Vet]

fill the empty space with something that would hold the powder in place against the primer. The traditional filler was kapok fiber

Over on the Cast Boolits forum, there's been discussion from time to time about using case fillers as a replacement for gas checks.

IIRC (which is a big if) oatmeal is a preferred filler mat'l.

Not sure if it's instant or old fashioned Quaker Oats though

 

[manithree]

but for a 6th grader, it reeks of too much parent involvement.

Even for a 7th grader, I agree. And some of them get expensive in a hurry. Add to that the fact that the building of the rig doesn't interest my son nearly as much as the re-loading and shooting, plus we're worried the FRE we were hoping to generate wouldn't even move a rig we could build, and I've got a really hard sell on my hands. We've discussed this before, and I brought it up again after these suggestions. I can see him glazing over with disinterest. Too bad these are so expensive and not available any more.

I hadn't thought of the transducers. That one was the one that he seemed most interested in. Anybody know where to get decent, fairly inexpensive transducers that would do this and work with Linux?

 

[jmorris]

I can see him glazing over with disinterest.

If the kid isn't fired up about it, it's going to be your project.

For light loads out of a revolver it would be pretty simple to make a simple sled that you could measure rearward travel. You would obviously have to come up with your own units of measure but could see relative differences.

 

[manithree]

If the kid isn't fired up about it, it's going to be your project.

He's intensely interested in the wildcatting/reloading/shooting part. It's the construction that loses his interest.

 

[jmorris]

Too bad, that is the fun part.