BARREL PRESSURE MANAGER

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  • Last Post 23 March 2019
joeb33050 posted this 14 February 2019

Since I found that CBA shooters haven't made any substantial improvement in rifle accuracy in over 20 years, I've been experimenting and reading about jacketed bullet and rimfire shooting, looking for a secret.

My experience with a chronograph and both jacketed and cast bullets suggests that MV variation does NOT correspond to accuracy variation, at least at 100 yards.

The rimfire community DOES seem to agree that MV variation DOES correspond to accuracy variation at 100 yards; and take actions to reduce that variation by, for example, weighing/sorting cartridges.

It occurred to me that MV variation could be reduced with an adjustable, spring-loaded, pressure relief valve; a barrel pressure manager.

A hole drilled in front of the chamber and threaded, a needle valve, and a spring loaded adjustable force arrangement are easily imagined and easily constructed.

Perhaps MV / pressure variation by the shooter is A way to improve cast bullet accuracy.

I have a Savage .22 barrel as the test bed, who will volunteer to do the machine work?  

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Ed Harris posted this 14 February 2019

Why vent at the breech where pressure is much higher? 

How would you mitigate adiabatic expansion which occurs after the bullet passing the gas port?

Isn't it muzzle exit pressure which most affects dynamic stability the bullet?

How about some variation of the M1 Garand gas system with vented gas cylinder plug?

Before embarking on a costly machining exercise, how about fitting a strain gages at the breech, and also at midpoint and behind the muzzle of the barrel. Then determine which faster burning powders produce the best accuracy and attempt to determine IF grouping actually correlates with low muzzle pressure.  The strain gage will not register below about 10,000 psi, about the port pressure is on an M14 or M16 rifle having its gas port at the barrel mid-point, whereas for the Garand port pressure behind the muzzle is in the neighborhood of 6500-7000 psi.  Having low enough muzzle pressure so as not to activate a strain gage at the muzzle location might provide useful info.

Extensive testing was done at LC and NWSC Crane, IN in 7.62mm match ammunition, in which the different characteristics of the M1 Garand and M14 gas systems were compared.  As a result of these tests Federal 168-grain #308M ammunition produced for Army contracts to be fired in the M14 rifle was loaded with IMR3031, whereas that loaded for the Navy used IMR4064.  The Marines went their own way and developed their own S9 handload, which I won't elaborate on because it was loaded to excessively high pressure, was hard on guns and was dangerous, in my opinion.

It is well established that slower burning powders such as 4350, when used in the Garand, produce higher port pressures which bend the operating rod. Medium burning rate powders such as 4895, RL15 or Varget are reccommended.  I think exploring within the parameters of what is known to work provides a clue?

 

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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joeb33050 posted this 14 February 2019

Once again, I've failed to explain well. An adjustable relief valve would reduce the variation in pressure, hence MV. Imagine pressure varying from 8,000 to 12,000 psi, with sigma = 666 psi. Adjusting the relief valve to 10,000 psi means that the upper psi limit is now 10,000 psi, excess gassy stuff is vented, so all them >10,000 psi pressures are reduced to 10,000 psi, the pressure variation is halved, as is the MV variation. AND, we don't have to say "adiabatic"! And, this reduction in MV might reduce group size. Yowza!

"I think exploring within the parameters of what is known to work provides a clue?"

I think that's called "thinking within the box".

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Ed Harris posted this 14 February 2019

It's your money.  I look forward to the report.  Larry Gibson may have some helpful experience on the Oehler 43 system that might help you if you decide to go that way to measure the Delta-P

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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frnkeore posted this 14 February 2019

I like the idea and think that it has some merit!

This is where the CBA could do some research and invest in a project to do it scientifically. Possible the first test, ever in this area.

I could see the old H. P. White lab, doing something like this.

Frank

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Ken Campbell Iowa posted this 14 February 2019

ok, here's an idea ::   just run a gas tube from an inch ahead of the chamber to about 8 inches ahead of the chamber .

then if you have more pressure behind the bullet, it will quickly put more pressure in front of the bullet ...  faster bullets would be slowed more than slower bullets ... 

self-regulating, low parts count.

 

*******************

of course, to be sure this is a worthy goal, first we could also check out some chronograph testing where each shot placement on the target was correlated with the muzzle velocity  ...  i assume that each shot with the same muzzle velocity went into a smaller group ?? ...

that would be common sense, unless there are other variables ...  maybe we should contact some 600 and 1000 yard shooters, i bet they have done this, at least with mj .

ken

 

 

 

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joeb33050 posted this 14 February 2019

So, who's volunteering to do the easy machine work?

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Bud Hyett posted this 15 February 2019

This will be an opportunity for a parallel experiment. Put temperature gauges on the barrel and record group size to pressure to temperature.

When I was back seeing Ed Doonan after I moved to California, he was experimenting with barrel temperature and accuracy. He was measuring the outside barrel temperature at the chamber and getting the best repeat-ability when the barrel was 124 degrees. The greatest challenge was maintaining that temperature because this phenomenon had a +/- one degree variance.

I did not follow up with him and regret that inaction now. 

 

Farm boy from Illinois, living in the magical Pacific Northwest

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Brodie posted this 15 February 2019

In other words what you are all saying is: "PV=nrT".  or Pressure x Volume= nr Temperature.  THe  n and r are constants and if I could find my old chemistry book I would be happy to give you the values.

B.E.Brickey

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M3 Mitch posted this 15 February 2019

Just to clarify the idea - the thought is that a calibrated vent valve would open to reduce higher-pressure firing events, dropping pressure to be consistent with lower pressure firing events - or in any case to drop all various pressure firing events to a single lower number - right? 

That valve would have to move really fast.  From an engineering standpoint I am not sure this can be done.

Perhaps a simpler test would be to see if identical ammo fired in an M-1A, and in another '06 that has a manual action, if the M-1A gives statistically significant reductions in muzzle velocity variation, I'm assuming here that the M-1A bleeds more gas off the "hotter" rounds, so would be a half-step in the direction you are contemplating.

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Ken Campbell Iowa posted this 16 February 2019

... at first, i was thinking about this project as a test to see if bullets with a constant acceleration and muzzle velocity would give better groups.

but i think artillery tables would tell us that they would indeed do that.  at least at 16 miles ...

so now it is an engineering challenge....  gulp...  

i think this is actually possible ... somewhere between a electronic clipper circuit and a turbocharger pressure blow-off .  although things would have to act fast, good old A = F/M still holds true for gadgets.    just think, a 150 grain bullet hits 2000 fps in about 0.003 seconds ...  a " valve " that weighs only 1/10 that should take only 1/10 the time to open.   

in concept, a tapered needle valve comes to mind ... or a stack of needle valves that open at a range of pressures.  or a row of suicide valves that blow open at different pressures.   

or a spring preloaded sliding valve that as under pressure it slides and exposes a widening opening or more/bigger holes..   a simple tapered slot uncovered as the piston slides .    a straight slot would be easier to machine ...

just a start on the math ... but say our loads vary by 50 fps .... the gadget would have to be located on the barrel to reduce gas pressure enough to cause a 50 fps drop in muzzle velocity ( reduce all velocities to lowest performing load ... might name it the * Bernie * regulator )   ...  how far down the barrel is that ?? 

kinda interesting, hey, gunpowder was invented by some kids trying to build a stink bomb ... look how that turned out !! ...

ken

 

 

 

 

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joeb33050 posted this 16 February 2019

I'm thinking of

a hole in the barrel

an item that looks like a needle valve, the v to fit the hole

the item attached to a flat spring that looks like a feeler gauge

the spring held with force DOWN by a clamp, clamped to the barrel (hose clamp)

the force DOWN adjustable with a screw through the spring, pushing down on the barrel, reducing DOWN force

if only I could draw

 

 

 

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GP Idaho posted this 16 February 2019

Joe, I'm no machinist so I can't help out there but I do like the idea. Pressure regulation seems to be a big thing accuracy wise in the high end PCP air guns. Best. Gp

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joeb33050 posted this 16 February 2019

Just to clarify the idea - the thought is that a calibrated vent valve would open to reduce higher-pressure firing events, dropping pressure to be consistent with lower pressure firing events - or in any case to drop all various pressure firing events to a single lower number - right? 

Correct!

 

That valve would have to move really fast.  From an engineering standpoint I am not sure this can be done.

But, from an engineering standpoint, or from a Knurlman standpoint, are you sure it can't be done?

 

Perhaps a simpler test would be to see if identical ammo fired in an M-1A, and in another '06 that has a manual action, if the M-1A gives statistically significant reductions in muzzle velocity variation, I'm assuming here that the M-1A bleeds more gas off the "hotter" rounds, so would be a half-step in the direction you are contemplating.

Let me know how it turns out.

 

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Ken Campbell Iowa posted this 16 February 2019

while we are chewing on this idea, we can think about the actuating system on the remington 1100 shotgun ... ( and a lot of similar ) .... the gas from the barrel hole blows back on the actuating rod piston ... the piston moving just a bit uncovers an escape hole and the excess gas is vented away ..

the idea is that you can now shoot different ... hotter and milder ...  loads without having to adjust the gas assembly.  it is self-adjusting.  self regulating.  to an acceptable extent that is, there will still be a variable acceleration before the exhaust port is reached .  

slower burning powders used in heavier loads might help in such a regulating system. hmmmm .

************

ken

 

 

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45 2.1 posted this 16 February 2019


Perhaps a simpler test would be to see if identical ammo fired in an M-1A, and in another '06 that has a manual action, if the M-1A gives statistically significant reductions in muzzle velocity variation, I'm assuming here that the M-1A bleeds more gas off the "hotter" rounds, so would be a half-step in the direction you are contemplating.

Let me know how it turns out.

 

M1A is a 7.62 Nato chamber, a ballistic match for an '06, but at a higher pressure..... therefore identical ammo and situation is a problem. It also has a bleeder hole so the piston travels a short distance before the gas is vented. Really, some advanced equipment is needed for this kind of testing.

 

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joeb33050 posted this 16 February 2019

A hacksaw blade would make a good spring. Hose clamp, shims, a screw with a point filed to a v, screw and nut to adjust pressure, and a hacksaw blade. Advanced equipment.

Must I contact MIT, or is there a machinist here willing to tackle this task?

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45 2.1 posted this 16 February 2019

Joe.... if it is as simple as you make out, then it would seem you have the capability of managing it yourself.... without the need of a machinist. We will all be waiting for your results.

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Brodie posted this 17 February 2019

When you get this whole thing assembled and working to suit you (assuming that it will) you won't have advanced cast bullet accuracy one iota.  You will only have made a cobbled together ad hoc pressure regulated gun.  Have Fun.

B.E.Brickey

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joeb33050 posted this 17 February 2019

Joe.... if it is as simple as you make out, then it would seem you have the capability of managing it yourself.... without the need of a machinist. We will all be waiting for your results.

Unfortunately, I can't do much of any manual work. How about you, Will you do it?

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M3 Mitch posted this 18 February 2019

Well, I don't have an M1-A, and I don't have a chronograph either.  Maybe someone who does will pick up the torch.

As to proving it can't be done - that proof is one of the few things that can't be done for sure.  All a guy ever knows, is that so far he has not come up with a way to do it.  "When you say it can't be done, be sure you are not interrupting the guy who has just done it"!

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joeb33050 posted this 18 February 2019

When you get this whole thing assembled and working to suit you (assuming that it will) you won't have advanced cast bullet accuracy one iota.  You will only have made a cobbled together ad hoc pressure regulated gun.  Have Fun.

HERE ARE 50 SHOTS, 200 METERS, MV AND ELEVATION

IF WE CAN MANAGE BARREL PRESSURE AND ELIMINATE THE 5 HIGHEST VELOCITY SHOTS, WE GET

 

AND MAYBE 5 GROUPS GET MUCH SMALLER.

IT WORKS FOR CAST, JACKETED, AND RIMFIRE.

Do you get it now?

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M3 Mitch posted this 19 February 2019

What round are you shooting, what load, what rifle?  Is this typical velocity variation? 

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joeb33050 posted this 19 February 2019

What round are you shooting, what load, what rifle?  Is this typical velocity variation? 

 

22-250, 7/Titegroup, Savage M12. The standard deviation for the 50 shots is 20.2 fps. The standard deviation for ~188 loads, 10 shots/test, is 19.6 fps. So, yes, the velocity variation is typical.

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joeb33050 posted this 20 February 2019

Well, I've moaned a guy at the gun club to the point where he has agreed to drill and tap a hole in my Savage M110 22-250 barrel, about 2 1/2" from the chamber end. However, he does not have a lathe, and refuses to buy one for this project.

Thus, I'm still searching for a lathe guy, to make this relief valve/pressure manager. Imagine a screw with a 2 diameter hole bored through it. Large and small diameters. Imagine a threaded cap to fit the screw. That's it. I'll be happy to pay, or accept charity. There's a good chance that your name will go down in history. Next to Pope, Roberts, Horace Warner and Edmund Fitzgerald. Who will respond?

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joeb33050 posted this 23 February 2019

The CR25 pressure relief valve, 0-100 psi micrometer adjustable, arrived yesterday. Now to see Mike. 

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joeb33050 posted this 24 February 2019

Picture

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Squid Boy posted this 24 February 2019

 This is an interesting discussion but I do think that if such a device were possible that it would have already been done. I know Mann tested barrel venting near the muzzle without finding any advantage. I think the issue is the pressures and times involved prevent anything mechanical from working as desired. My load program shows a 30-06, 180 grain cast bullet loaded in front of 53 grains of H-4895 reaching Pmax (57,120 psi) at just .6 milliseconds at a velocity of 1,008 fps when the bullet has traveled 1.95". This is a lot happening in a very short period of time and I don't know many mechanical devices that can react that quickly or accurately especially at the pressures and volumes we are discussing. I have been focusing on lowering the SD on my loads with careful powder selection and other techniques. I have a load for a cast bullet in the 32-20 that shows an average SD of only 1.6 fps. The real trick is finding the ideal velocity and still keeping the very low SD. This loading is quite accurate but I need to get a good scope on the rifle to really realize what it can really do. That's just my opinion for what it is worth. Thanks, Squid

"Squid Pro Quo"

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joeb33050 posted this 22 March 2019

Barrel hole; .050" through to bore, ~ 2.5" from bre3ech end. 10-32 threaded above.

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joeb33050 posted this 22 March 2019

Transition, hollow 10-32 rod one end, IPS (1/2?) other end

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joeb33050 posted this 22 March 2019

Assembled with pressure relief valve

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joeb33050 posted this 22 March 2019

On the barrel-barrel is on an action, ready to shoot tomorrow

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M3 Mitch posted this 22 March 2019

I would be wearing serious eye protection for sure.  I might want to do the old "tie it to an old tire" trick and fire the first shot with a string.  That thing may, possibly, come off the barrel on the first shot or it may take several shots.  Or it may work great.  But just don't get hurt!

Don't take that as me being negative about this, far from that.  It's just when you do something that has not been done before, at least IMHO one should take all reasonable precautions.

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muley posted this 23 March 2019

Joe , why have the guage on top of the barrel in line with the sights? it could be placed at 2 o,clock and still get the same pressures and still fit in the stock.

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mashburn posted this 23 March 2019

I'm going to stay out of this one. My pay grade is a way too low to respond to this. If you think; Since the invention of a firearms: nearly every patent for firearms is an improvement over something that already exists. I'll stick to making everything mechanical as perfect as I can make it, including ammunition and rifles. Someone mentioned that they thought  that varying pressure at the muzzle was detrimental to accuracy. I definitely agree with this. Being a old Hot Rodder  and knowing a valve will flow more air with a three angle seat I have crowned some muzzles with a 3 angle crown ending up with an 11 degree angle on the outside one and sometimes on the inside. They were all accurate but I never did do a experiment on the same rifles with different crowns. One of the attractions to me for shooting cast lead is the nostalgia.But of course I want to have all the accuracy that is possible Good luck and success with your  ideas.

Mashburn

David a. Cogburn

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