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Post by geraldbergeron on Jan 4, 2006 19:39:30 GMT -5
First time I hear about "Secondary Pressures" in internal ballistic... It seems that a second "bang" can happen inside the barrel... www.shootingsoftware.com/barrel.htm WOW... "In every instance when secondary pressures are detected they can be eliminated by using a faster power, heavier bullet or a bullet with more bore contact area. Normal "tweaking" of loads may change the peak of secondary pressures but will not eliminate the problem. Below is the list of factors we now know can cause secondary pressures.
Powder burn rate too slow for the bullet.
Bullet weight too light for the powder's burn rate.
Bullet bore contact area less then normal for the bullet weight
Barrel longer then normal
Bore severely worn or incorrectly lapped (loose/worn toward the muzzle)
Moly in bore or moly coated bullets that reduce bore friction " Question: Have you heard of secondary pression inside a rifle barrel ? Is it a true phenomenon or a theoretical thing ? Is it possible inside a sm10-II ?? ($100,000.00 Can Question...) May be just one individual... lived that ?? What do you think ? ..........................................................Gerald............../ |
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Post by bwaddy on Jan 4, 2006 21:59:22 GMT -5
It can happen, and has happened to me in my comp'd AR. More of a slight up-down-back up. BUT..... I've never seen a spike like that! Maximum CUP for 223 is around 55K. Someone must have done something really stupid to get that spike. They had already achieved a 49K load quite quickly. That normally happens around 1 ms. My guess... Heavily fouled/bad barrel.
Bret
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Post by RBinAR on Jan 5, 2006 0:41:00 GMT -5
8-)The trace you list is of course one of the many posted on the RSI web site. Secondary pressures often occur with the items you mention but I'd add there might be other factors in a muzzleloader such as very low bullet inertial resistance with light weight bullets. You might take note of the following trace I shot with N110 it's a 44 grain charge behind a 300 grain SST.  N110 is not too slow for the 10 ML and the bullet is not too light so what causes the secondary peak? Jim Risling's comments on the subject are certainly worth reading. |
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Post by MountainMan on Jan 5, 2006 6:49:31 GMT -5
Where do we find Jim Risling's comments?
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Post by edge on Jan 5, 2006 9:16:24 GMT -5
RSI : www.shootingsoftware.com/index.htmHere is a trace that I had using 2400.  I believe that it was just a barrel harmonic since the bullet appears to have exited at about 1.15 ms I never tried that load again so I don't know if it was reproducible or not. edge. |
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KS
Six pointer
Posts: 93
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Post by KS on Jan 5, 2006 20:02:10 GMT -5
Is it posible that alot of these secondary hits are just barrel harmonics? Has any one actually tried to get a time reading of the bullet exiting the muzzle? I have seen photo of bullets exiting, so it seems likely that there is equipment to time this. If it could be proven that the bullet did leave before the 2nd hit, then is it really a problem, or could it just be something that pressure trace equipment can not explain? If you have not guessed by now I do not know a lot about pressure trace, other than people say that the second hit is a bad thing, and it is best to find a way to reduce it. Last question. How accurate have the double hits been? ks
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Post by geraldbergeron on Jan 5, 2006 20:42:08 GMT -5
One theory from RSI (http://www.shootingsoftware.com/barrel.htm) "The "Catch Up Theory"
We do not know if the above load suffered from an accelerated burn rate (problematic with some ball powders), but agree with ballistic engineers about the probable cause.
The area under the pressure curve directly relates to the energy imparted to the bullet. The rise to peak pressure engraves the bullet into the rifling and establishes it's initial acceleration down the barrel. The highest rate of acceleration occurs just past the point of maximum pressure. As the bullet travels toward the muzzle, lower pressure coupled with bore friction allows the rate of acceleration (not speed) to fall.
If there is insufficient gas produced by the powder (burn rate too slow), pressure behind the bullet will drop excessively. Then, as the bullet's rate of acceleration falls due to bore friction, gases may "catch up" to the bullet before it exits the barrel and produce a secondary pressure event. In the above load we believe the heat generated from initial ignition coupled with a secondary pressure event increased the burn rate of residual ball powder to near detonation." |
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Post by smokeeter on Jan 5, 2006 21:03:43 GMT -5
could this be an explanation for some of the barrel rings or bulges that was so commonly explained as a barrel obstruction. Where some movement of the bullet/sabot occurs before complete combustion of the powder.
RB any thoughts on this?
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Post by savagebrother on Jan 5, 2006 22:45:07 GMT -5
yes i believe this could be so, if the there was a loose barrel fit and incomplete ignition upon firing, the bullet moves partially down the barrel and then slows because of lack of constant pressure. then in a rare instance the powder has continued to burn inadvertantly and then catches up to the now dislodged sabot/bullet a.k.a a barrel obstruction. just my 2 cents with here.
sb
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Post by MountainMan on Jan 6, 2006 9:15:10 GMT -5
could this be an explanation for some of the barrel rings or bulges that was so commonly explained as a barrel obstruction. Where some movement of the bullet/sabot occurs before complete combustion of the powder. RB any thoughts on this? I seems to me that this could definitely be one of the causes of such bulges. However, you DEFINITELY want the bullet/sabot to have some or even significant movement before complete combustion of the powder. That's the whole reason for using a slower powder, isn't it? The fact that just about any load has some muzzleflash is an indication there is pretty much always some powder still burning at the time of bullet exit. Wouldn't the optimal curve (for velocity, not for reduction of muzzleblast) be one in which the powder could burn at such a rate that the pressure fell very little during the entire time of internal bullet travel? This would mean that a lot of the powder would be burning during the entire time of internal bullet travel. (Of course, it would also make for much more horrendous muzzleblast.) If all of the powder burned before the bullet started moving, you would either have (a) an absolutely ENORMOUS pressure spike, or (b) truly anemic velocity. As in, arrow-type speeds, I would think. Somebody tell me if I'm wrong, 'cause my entire understanding of internal ballistics is junk if this basic premise is incorrect somehow. |
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Post by edge on Jan 6, 2006 9:52:59 GMT -5
IMO, I think that there are 2 things that would not be helpful in your scenario. 1) Powder still burning as it exits the muzzle can cause inaccurate bullet stability, as will excessive pressure at exit; 2) the pressure of the burning powder needs "x" amount of time to "work" on the bullet, basically pressure and time. As always you got what you paid for  edge. |
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Post by MountainMan on Jan 6, 2006 10:10:13 GMT -5
I think those fit with what I postulated. Velocity must be balanced against muzzleblast and accuracy, and velocity equals pressure x time.
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Post by savagebrother on Jan 6, 2006 12:38:42 GMT -5
partially mountainman, we have always had to deal with bullet jump with the savage muzzleloader, or any muzzleloader for that fact. its just amplified by the use of smokeless powder. bullet movement prior to optimum pressure is a no-no, and causes erratic pressures.
thats why we use such large weights of slower powder. to allow for a continuous burn and an optimum pressure to be reached with a given powder and sabot/bullet combo at a given temperature.
sb
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Post by MountainMan on Jan 6, 2006 12:55:21 GMT -5
Exactly: a continuous burn while the projectile moves down the barrel. What you don't want to see is a acceleration followed by a decrease in acceleration prior to peak pressure being reached. So, I think we're all saying the same thing. That is, the powder usually, or at least often, continues to burn even after pressure has peaked and begun to fall.
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Post by geraldbergeron on Jan 6, 2006 15:35:54 GMT -5
" Jim Risling's comments on the subject are certainly worth reading " dixit RBinAR.
Hi RBinAR, I would be also very interestes to read that kind of comments OR any other that you would give us as references. Thank you |
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Post by savagebrother on Jan 6, 2006 15:51:51 GMT -5
yes as a generalization that is true, but if the bullet moves before optimum pressure is achieved your in trouble. cartridge guns have the case grip and a projectile thats the size of the groove. two things that hold it there until optimum pressure is achieved. we dont have that luxury with the savage. we have plasic and we have already graved it when we pushed it down the barrel. so there is a little more to it with a muzzleloader.
sb
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KS
Six pointer
Posts: 93
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Post by KS on Jan 6, 2006 17:02:54 GMT -5
So if I understand it correctly, we could cure this problem theoreticaly by increasing sabot friction? Now I know that would make it harder to load, but could enough friction be achieved and yet still be loaded by a human? If this leval of friction could be achieved, then would it make sense that we would use less powder, because we would have a more efficient burn? ks
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Post by savagebrother on Jan 6, 2006 18:48:47 GMT -5
yes you would, unfortunately i think we are just about at the level that the average guy can reliably load the savage. so we are stuck with using heavier loads of slower powder.
something to remeber here is the so called burn rate, what is really a conversion rate of a solid to a gas, the difference in that rate from the fastest burning to the slowest burning is about 2 milliseconds. that doesnt saound like much but considering we are going freom 14.2 psi at sea level to around 40,000 psi in about 1.5 milliseconds thats alot of difference. the real difference is how long the slower powders stay at peak pressure and how long it takes them to get there.
sb
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Post by MountainMan on Jan 7, 2006 23:51:34 GMT -5
I know this is way out there in left field, and I'm sure I'm not the first one to ponder this, but...
Has anybody ever considered working up a tri-plex load? Say, a good booster powder in the N110 range, then a mid-range powder like H322/3031/N133/2015, then a fairly slow powder like 4350?
I know that it would take a LOT of 4350-type powder by itself to get adequate pressure and burn, and I don't think you ever would with 250-350 grain bullets, but that's what people said about H322/2015, etc., at one time. With a fast powder to get pressure quickly, followed by a mid-range powder to keep the pressure up there, and finally a fairly slow powder to keep a good burn/pressure going, would it be possible to get a 300 grain or 350 grain bullet up to 2800 fps with accuracy and safe pressures?
Of course, recoil would be pretty much unbearable, I'm sure. And perhaps it would just be to tricky to work up and keep consistency. It's a thought that's just kept niggling at me for a while now...
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Post by SW on Jan 8, 2006 7:50:26 GMT -5
Mountain Man,
I think we want the powder to complete it's burn enough prior to exiting the barrel that a triplex load would be difficult to acheive - especially in a 24" barrel filled with saboted bullet,possibly WW, a fair amt of powder and a long snouted breechplug. "Difficult" isn't "impossible" though.
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Post by RBinAR on Jan 8, 2006 9:50:11 GMT -5
I know this is way out there in left field, and I'm sure I'm not the first one to ponder this, but... Has anybody ever considered working up a tri-plex load? Say, a good booster powder in the N110 range, then a mid-range powder like H322/3031/N133/2015, then a fairly slow powder like 4350? I know that it would take a LOT of 4350-type powder by itself to get adequate pressure and burn, and I don't think you ever would with 250-350 grain bullets, but that's what people said about H322/2015, etc., at one time. With a fast powder to get pressure quickly, followed by a mid-range powder to keep the pressure up there, and finally a fairly slow powder to keep a good burn/pressure going, would it be possible to get a 300 grain or 350 grain bullet up to 2800 fps with accuracy and safe pressures? Of course, recoil would be pretty much unbearable, I'm sure. And perhaps it would just be to tricky to work up and keep consistency. It's a thought that's just kept niggling at me for a while now... If people will understand that I'm talking strickly theory and not advising this I could say a few things about maximum speed for a given bullet and the10-ML. I've often compared the 10ML to the 50-140 Sharps. The big 50 has a unique case able to hold ample powder but at a severe pressure limitation. Loads may have more than 100 grains of powder but the pressure cannot exceed 28,000CUP. With this combination the 140 shoots a 425 grain bullet to near 2300fps and a 515 grain slug to 2090fps. Such loads near the 5000fpe level. Could the 10ML equal that? Certainly it would. Sabots last to about 40,000CUP so the pressure limit is more than 33% higher in the 10ML. While it is certainly not necessary there is plenty of room (since there is no case) in the 10ML to equal the volume of the 140 in powder. How does that relate to a 300 grain bullet from the 10ML? 5000fpe would be about 2750fps. This could be reached with a single powder! Thats correct not a duplex, let alone a more complex load, only a single is required. So why have I not pushed for such a super load? Well you said it, "the recoil would be pretty much unbearable." |
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Post by wilmsmeyer on Jan 8, 2006 10:47:56 GMT -5
RB,
Even though you may not advise it, or recommend it, what is that load and how would you, theoretically, for conversations sake, assemble it?
Wilmsmeyer
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Post by RBinAR on Jan 8, 2006 12:56:09 GMT -5
RB, Even though you may not advise it, or recommend it, what is that load and how would you, theoretically, for conversations sake, assemble it? Wilmsmeyer Powders like H322 and Xmr-2015 can be shot with a 313 grain bullet (remember to count the weight of the sabot) to at least 85 grains and stay within the limits of a sabot. There speeds in the 2500fps range are possible. Moving to about 90 to 95 grains of the correct powder that would supply pressures in the 37,000 to 40,000psi range would seem to be ideal to reach 2700fps. The exact powder for that purpose is yet to be known but likely lies between the burning speed of the fastest powder used in the 50-140 (Varget) and the slowest powders currently used in the 10ML (H322 or 2015). That powder could be Benchark, N133, Imr-3031, or H4895. There is a lot of ground to cover to find a optimum place for consistency as well as energy. If anyone does decide to have broken shoulders for fun please do not attempt a load for yourself. E-mail me and let me shoot the load first, though I have no interest in such a load I would rather build it than find someone put a lot of powder in the rifle and found out it was the wrong option, powder, eerr move. |
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Post by wilmsmeyer on Jan 8, 2006 14:26:08 GMT -5
RB,
What about 3,000 fps 250 grain loads? Just for conversation purposes. Is it another scenario for broken shoulders or just not possible?
As I've told you before, I've shot 76 gr of H4198 with 245 grain Spitfires @ 2,704 fps. Accuarcy has been very good to great, recoil is stout, muzzle flash is dramatic, but broken shoulder syndrome is nowhere in sight IMO at least for me. I would love to try more if sabots could hold up and pressures could remain @ 40,000 or so. I also have access to just about any powder mentioned and may even have it downstairs!
Wilmsmeyer
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Post by RBinAR on Jan 8, 2006 15:50:40 GMT -5
RB, What about 3,000 fps 250 grain loads? Just for conversation purposes. Is it another scenario for broken shoulders or just not possible? Wilmsmeyer Sure we can do that, it's about the same level as in the 378 Weatherby. We can't get to that pressure but because the bore is so much larger the powder level won't be quite as much. I've known the power limit for the 10ML is enormous for a long time, I just didn't think an elephant gun was a popular choice for muzzleloading. |
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Post by edge on Jan 8, 2006 15:58:55 GMT -5
wilmsmeyer, 75 grains of H4198 gave me just over 2700 fps also. What we don't know is the pressure reached. RB traced 74 grains @ 35,000 psi but only timed it at 2485 fps! Based on his traces I would guess that our pressure will top 45,000 psi. Perhaps not too high, but certainly getting there When I tried to shoot the lighter bullets with 4198 I needed huge amounts and the velocity barely moved. I had to move to N110 to get the velocity I needed. I write this not to suggest N110, but to point out that powders and bullet weights go hand in glove with each other. I agree with RB that the energy out the barrel is doable, but that for each bullet/velocity, finding the powder that won't reach sabot blowing pressures may not be easy. IMO, I would not think about 3,000 fps with a 250 grainer without a Pressure Trace or similar strain measuring equipment attached! edge. |
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Post by wilmsmeyer on Jan 8, 2006 19:23:38 GMT -5
I looked for the thread that estimated the 76 gr of H4198 with a 245 gr bullet and can't find it offhand. I think someone estimated, using software, (RB maybe?) that it would only be around 39,800 or so.
Without a proper trace these program estimates are speculative so maybe the pressure would be as high as 45,000. I also have seen folks here talk about sabots generally having a limit of 40,000 before they become suspect. I've not blown one with this load to date and have probably sent 50-75 down the tube. Does this mean I have a really tough sabot or is my pressure probably around 40,000? I don't know.
Wilmsmeyer
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Post by edge on Jan 8, 2006 19:37:57 GMT -5
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Post by ma on Jan 8, 2006 23:05:16 GMT -5
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Post by RBinAR on Jan 8, 2006 23:07:16 GMT -5
wilmsmeyer, 75 grains of H4198 gave me just over 2700 fps also. What we don't know is the pressure reached. RB traced 74 grains @ 35,000 psi but only timed it at 2485 fps! Based on his traces I would guess that our pressure will top 45,000 psi. Perhaps not too high, but certainly getting there edge. LOL I hope that's not the way it works. Now let's see it shoots 35,000psi in my rifle but 45,000 in yours.... Na I don't think so. Before I reach that conclusion I'd have to check three or four new bullet timers to see if mine is off 150fps. The load may be slightly higher pressures in a tighter bore but more than 1500psi is not subjective. Think of what happens if your idea is correct. A powder or bullet company could shoot a load in a test rifle and list it as safe or even SAAMI compatable and the pressure in your rifle might be off as much as 23% different. How much could the pressure be if 60,000psi is the base load? 73,800psi... This is the maximum possible pressure for 75 grains of powder and this weight bullet at 2700fps. Pressure(CUP) 40935.548 Expansion Ratio (R) 12.492 W 91.015 F2 2.612 K1 20278753.822 K2 2.111 K3 1045.984 |
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