New Pressure trace discussion.......

[Richard]

I think I am starting to feel a little more comfortable with the instrument after my second trip to the range and some playing around since last week.
So, after shooting that muzzle bore guide off, we went down range to look for it..................Low and behold, I found it about 60 yards away ................But no, it was not the one I just shot, but rather the one I shot off about 4 months ago . I know it because I built both of them and this was definitely the old one Maybe in a few more months I will find the other one
Since the bullet fits thru the hole, no damage occurs and it barely disrupted the path of the bullet. Velocity was good and pressure did not spike
Richard

[edge]

I guess bore guides don't group well

Thank you for the traces and data.
These traces look great and consistent.

I still don't understand how you achieve your velocities at such low pressures! Strange....perhaps Samuel Clemens aka Mark Twain, was right about the three kinds of lies.."Lies, D@mn Lies, and Statistics" ;D

edge.

[Richard]

If I had acces to your CNC lathes, I would have a dozen or so made up so I always had one on hand ;D
Richard

[redpep]

Richard / Admins-
Thank you for your all work with this project, would it be wise to label the posted info as PT graphs and discussions on the PT's as- session #1, session #2, ect....
As these are viewded and commented on it might help.

Thanks again for all you are doing,

Longtime reader shorttime poster

[edge]

The posts with the actual traces are locked and can be found in the LOAD INFO section.

dougsmessageboards.proboards.com/index.cgi?board=loads&action=display&thread=6925

I will add a link in those posts to each "Discussion" thread.

edge.

[spaniel]

Just a suggestion...should the sessions be dated or numbered? Down the road when someone wants to read through this and there are multiple threads of traces and multiple discussion threads they may get confusing. I know one could figure it out from the date of the first post but just an idea to make any searching more straightforward.

[edge]

If you follow the link that I posted I think that it does what you want.

edge.

[jeremylong]

Couple things stick out... Check out the old reliable N110 with an ES of 11. Gotta like that.
The other is man, those secondary spikes just bother me. I cant understand what that is, but check out how different they are with the different loads. Notice like T-3 vs T-7.

[edge]

Since the bullet has exited by that time I suspect the spikes are some barrel vibrations and not true pressure.

edge.

[rossman40]

I tried to tell everyone on the secondary spikes but it seems everyone chose to ignore it. I'll just wait till someone bulges a barrel 2-4" from the muzzle....

[edge]

Dec 22, 2010 13:04:53 GMT -5 rossman40 said:

I tried to tell everyone on the secondary spikes but it seems everyone chose to ignore it. I'll just wait till someone bulges a barrel 2-4" from the muzzle....

1) Are you suggesting that the bullet is still in the muzzle for those spikes?

2) If not then how can you have high pressure?

3) If the bullet is still in the bore, why would 20kpsi cause a bulge?

edge.

[jeremylong]

Discusion of the secondary spikes. www.shootingsoftware.com/barrel.htm

Supposively Sisk blew the end off two barrels to prove it is real. IDK but hope not to find out.

[edge]

Dec 22, 2010 14:53:37 GMT -5 jeremylong said:

Discusion of the secondary spikes. www.shootingsoftware.com/barrel.htm

Supposively Sisk blew the end off two barrels to prove it is real. IDK but hope not to find out.

The spikes shown in the RSI article are High Pressure spikes and also when the bullet was in the bore!

The spikes in Richards traces are low pressure and most likely after the bullet has exited...hence my belief that they are vibrations and not pressure readings.

edge.

[rossman40]

You have to remember the pressure wave has to come back to the sensor at the chamber. Also the bullet exits before the wave gets back to the sensor so what you see could be greater at the point where it happens. I even found a tech article over on RSI's website that even covers this,

www.shootingsoftware.com/barrel.htm

In Richard's traces you see no secondary spike with the faster N110 in T-1 and then in T-3 with the heavier 230gr bullet and 60grs of 4198 but yet with the 200gr bullet and the same charge it looked like the secondary spikes were back. You could live with secondary spikes as long as they are not extreme but IMO it shows that your not efficient/consistant in the powder burn and it looks like the worse the secondary spikes the higher the ES.

When I went thru Aberdeen there was a case study back in the 50s with a lot of antitank rounds that would blow the barrel only in cold temps. The conclusion was the powder was temp sensitive and at colder temps the burn rate was too low/slow. The initiation charge was enough to send the projectile and the main charge down the bore and then when the main charge did ignite with a pressure spike in the thinner part of the barrel the barrel ruptured.

To bring things to modern times the Navy has been playing with the next generation of cannon propellants using LOVA (LOw Vulnerability Ammunition) technology. The stuff is hard to ignite and if not ignited/initiated properly causes big velocity swings plus secondary shockwaves that crushes the propellant grains and can actually shatter the crystalline structure of the propellant (in this case the use RDX explosive) resulting in dangerous pressure spikes.

[rossman40]

If they are vibrations you would see something more like this,

[Richard]

You will note in Trace 6 the red line "spike?" That came from just the firing pin striking the primer with no ignition? If a firing pin strike could cause that blip, I think Edge is more on the right track. And, if the end of my barrel was going to blow off, it would have occurred a long time ago with all the loads I have shot which exceeded those I tested
Spaniel..........If you look at the traces, my target and work sheet you can see the date imprinted from my camera
Each trace in the future will also have a letter after the trace number i.e. T-1a for next week..........T-1b the following week etc. So all traces for next week will be T-1a, T-2a etc.
Richard

[Jon]

Roseman. I injoy all the knowledge you have that I wish i had. But by your own admissions the bullet should be out of the barrel in no more than 1ms. So since we are not firing a cannon what does this mean?
Jon

[edge]

Richard, if you don't mind, when you have a load with a secondary spike could you go to the "View" and set it to 3 milliseconds.

That way everyone can see the trace for the entire capture.

Thanks.

edge.

[redpep]

could one of the math wizards calculate the distance of bullet travel in Richards barrel?
would we than be able to determine where the bullet is at?

[Richard]

OK, here is Trace 5 set at 3 miliseconds
Richard

[Richard]

Here are a few pictures of the Pressure Trace gages and how they look on my rifle. First of all, let me preface this by saying it does not look neat ;D If ET will post a picture of the gage he put on his rifle, you will see NEAT! Yes, I did have the scope off and the action out of the stock and held in my vise for ease of working. What I did not contemplate was the mess in doing the "super glue" thing! I should have had on rubber gloves but instead, my fingers started sticking to the gage and barrel and I had to use a paper towel to hold the gage while I got my fingers unstuck ......So, the gage does not look as neat as ET's! It is however properly/securely affixed to said barrel Now for the yellow masking tape? As you can see from the pictures, there are only those little yellow wires which are attached to that tiny white plug. Not much to work with. Fortunately, they give you a short "pig tail" extension wire so you have more to work with. Then you have the long..........maybe 3 or 4' grey wire which attaches to the pig tail and then to the instrument. According to Edge, this connection with the little plugs is a source of concern and too much movement can cause them to get damaged. So, I attached the pig tail and taped it at the connection to the yellow wires and then taped some more. PT gives you a Velcro strap to secure the grey wire to the stock or scope or barrel. This is more a problem with ML's since you are constantly removing the rifle to reload. Hence it looks a little cluttered.
Richard

[deadon]

Richard, you are filling the gap and that is a compliment. At this time you are the only one stepping up to the challenge. It is soooo far over my head that I cannot imagine what you are going thru but thank you and thank you to Jon for him helping you. I will have to wait til all this is interpreted in Idiot language for me to understand. Thank you both again , Rusty

[rossman40]

Jon, according to the sensor the bullet has exited the barrel but the sensor is at the chamber. If your secondary spike originates 20" down the bore you will have a delay when the sensor sees it because the shockwave has to travel back to the sensor to register. In the case of the antitank gun the casing and even gauges did not show high pressure. A possibility, if my theory is right, is the booster pushes most of the main charge and the sabot/bullet (projectile) down the bore. Pressure drops off and the projectile slows down then pressure comes back up as the rest of the main charge burns. This would explain the lower then predicted initial chamber pressure for the amount of velocity obtained. The shockwave would then have to travel from that point back to the sensor to register.

Now if we had a fancy-dancy ballistics lab and a government expense account we could rig a barrel with multiple sensors and have a doppler radar measure bullet travel/speed while still in the barrel and have everything time correlated.

I think Richard's data is still good and useful, we just have to figure what it is telling us. In the end I think it may show us the best powder to use specially for the lighter bullets. More insight on duplex loads in the .45 and show we are within the safety limits. Maybe in the future even if there is differences between vent diameters and regular and recessed vents on the burn/chamber pressure.

Most of my formal ballistics schooling came from working with artillery, working with big guns makes little things easier to see. We can shoot our bullets at 2700fps, they just weigh 97lbs (that's like 680,000grs) and are 6.1 caliber (155mm).

[ET]

As per Richards request here is a picture of my first strain gauge glued to my barrel today.



Yes it can be sloppy and need to avoid trapped air bubbles for best contact. The nice part of the clear plastic base you can watch for air bubbles.



Ed

[smokepole50]

This may be some what revel ant to this discussion.....

In a 6.5x55 Swedish Mauser it is advised that when using bullets weighing less that 140gr that a faster powder should be used. This is suggested because the long throat of the Swedish Mauser was originally meant for a 160gr bullet. When using shorter and lighter bullets like 100gr and 120gr there can be issues with the LR primer actually pushing the bullet out of the case and forming a bore obstruction at the forcing cone before slower burning powders can come up to pressure and force the bullet into the rifling. This momentary obstruction can cause pressures to spike and IIRC some Swedish Mauser have been blown up because of this problem.

If Rossman40 is correct, this same situation could be happening with the duplex loads, creating a higher then recommended pressure in a thinner part of the barrel. Maybe it would be a good idea to attach a second sensor 6-8 inches from the muzzle to see if the second pressure spike gets bigger.

Smokepole

[Richard]

Are you buying the second PT instrument and lap top for this second strain gage?..........I suppose if you have a load that consistently produces the same pattern, that you could put that second gage there and switch which one you use . But let me ask this.............How many barrel ends have been reported being blown off??? As one can see from the above graph, the pressure on those spikes are down below 20,000 psi and all pressures are only varying by 1,000 psi initially?
I just put a custom barrel on a persons Rem. 700 -- 300 Ultra Mag. The chamber area on this barrel was, I believe 1.125" like most Remington's. Then immediately tapered down and ended up around .650 at the muzzle! These Ultra-Mags I believe are SAAMI rated at 60 OR 65,000 psi! . Has anyone heard of one of them blowing off a barrel? Of course I have no idea of what a trace looks like for one of them...............It just seems that over all, we are not dealing with any type of excessive pressures........even with duplex or triplex loads........Even when we (yes, I include myself) DOUBLE charge these guns, at most, we might bulge (slightly) the barrel. I believe that because we are not dealing with a "forcing cone" or "leade" angle in which the bullet needs to engrave the rifling, that high pressures are not a major concern......At least to me...........MY OPINION!
If you saw the way I had to pound that 250 gr. bullet down with the leather mallet on Tuesday Yes, I was working up a sweat doing it, you would swear that gun would have to blow up!!!!! Like I said, our friend John actually left the building while I sat and shot it. And, it only produced 34,000 psi? These sabot less bullets are just baaaaaaaaaaarrrrrrrrrrrrrrrrrrrrrrely pressing against the lands. There is very little engraving when seating the bullet. I can go from a bullet being sized so it will slide down the bore with just the slightest feel of "scrubbing" the lands to a bullet a few ten thousandths larger that will not want to go down at all......except with a mallet.
Now, take a center fire rifle that a bullet got stuck in the barrel ( no powder - just a primer) and then fire a good round? Now you got trouble! Resistance in a ML is just so much lower.
Anyway, the PT is interesting
Richard

[edge]

rossman40, I may have been to quick to assume that the bullet had left the bore!

The second bump clearly starts less than one millisecond after ignition ( T-5) and a bullet most likely could not have exited in that short a time and at that MV.

edge.

[rossman40]

Having less resistance could be part of the problem. With a centerfire you have to have pressure to "break" the crimp and then engrave the bullet into the rifling. I was told it takes 5000psi just to accomplish this in a M16 shooting 5.56. With a muzzleloader your "pre-engraving" the bullet during the loading process and there is no case crimp to break. With a saboted bullet your riding on low friction plastic. We do have some bullet oburation if we have a good shockwave smacking the bullet in the rear and we have pressure working to force the cup of the sabot against the bore when shooting with a sabot. We have resistance increase as the bullets get heavier as they take more inertia to get them going.

With BP guns we have already seen where a hot 209 primer is not the best for performance. The primer forces the bullet down the bore before the main charge ignites fully.

Right now the secondary spikes may not be enough to bulge or rupture the barrel. But then again if you think of it like a water hammer in a plumbing system, a study diet can not be good. I think it at least shows some inefficiencies. So if you can do away with the secondary spikes then perhaps your ES will drop.

[jims]

Richard: If you did not have good scope clearance that could have presented some more difficulty in securing the same where you wanted it. I enjoy reading about the pressure trace but I am glad you are doing the experimenting and not me. I like testing with firearms but this almost seems like work. Thanks again to you and all and Jon.

[chuck41]

Yep, I was right. This is definitely gonna keep you off the streets and outa the bars for a while.