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Post by Harley on Mar 30, 2009 23:48:40 GMT -5
I really didn't know what to call this thread, so I'll just describe what happened.
After loading duplex charges I stuck a wad into the muzzle like I always do; this time, though, the wad canted a little. It was too deep to retrieve, so I seated it as usual. When I leaned on the ramrod to press the wad against the powder (like I always do) the rod felt "spongy". I next seated the bullet and noted that it felt a little looser than it should on the way down. The witness mark was where it should be.
When I fired the round, it recoiled more than usual. The chrony indicated 2582 fps. Normal average today over six shots was 2350 fps. That's a 232 fps increase. I might have thought the chrony returned a false reading except for the significantly heavier recoil and the bullet's impact five inches higher than the others in the group.
I now believe the "spongy" feeling was due to the wad's going down and seating sideways. Yes, I know it's not supposed to be possible, but I think it did. I also think I must have somehow flattened it out when I leaned on the ramrod, because the witness mark was okay.
I just don't understand that +232 fps increase in MV. I keep my two powder types in separate trays and I use a loading block for each load. Each component goes into a designated slot in the block so there is no possibility of a mistake. After shooting I invert the empty vials back into the trays. After shooting this round I double-checked and everything was where it should be. Also, don't forget the witness mark was correct.
Do I just shake my head over it or does someone have an idea?
Harley
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Post by wilmsmeyer on Mar 31, 2009 4:05:48 GMT -5
A agree. The chance is slim that it would not self correct. However, you may have had the "perfect" scenario where the wad went down at 90 degrees and rode the whole length of the barrel. When you seated it, it may have folded in half and favored one side of the base of the bullet. And you did note spongy-ness. From this point I do not know what could have caused the spike in speed other then the obvious spike in pressure. Caused by what? The wad slamming one side of the bullet harder then the other on ignition? Don't know. May be a mystery for you.
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Post by smokeeter on Mar 31, 2009 5:33:21 GMT -5
Depending on which wad you were using ( veggie or wool) . If the wool wad was used it would probably just conform under pressure, the veggie wad is stiffer and it might have buried itself in the powder and left an ever so slight gap between the powder and bullet ( even tho the witness mark was verified) that might explain what caused the raise in velocity. Check the barrel either way.
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Post by edge on Mar 31, 2009 6:00:16 GMT -5
Very strange indeed!
IMO, almost an scenario where the wad did not go flat would intuitively cause a reduction in pressure!
The only thing that seems remotely plausible would be a veggie wad going down at slightly less than 90 degrees to the bore.
When it hits the powder it rotates to its normal position. However in doing so it could also dig into the powder and scoop up the powder.
This powder would now be on top of the wad and a secondary load trapped between the wad and bullet, and burning in a delayed manner.
That would seem to be very unlikely...but plausible.
I think that you need Myth Busters to check it out..... but you do need to check out your barrel since an increase in velocity by that much may have had a very large increase in pressure.
In general, an increase of 5% velocity results in a 10% increase in pressure using the same components!
edge.
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Post by Harley on Mar 31, 2009 7:33:44 GMT -5
The wad was wool, not veggie.
Ok, you're scaring me; how do I check out the barrel? All my subsequent loads (14 of them) seated with a normal feel, with no felt reduction of seating pressure at any point. Do I just look through the barrel for some sort of "ring"?
Thanks.
Harley
P.S.: I agree that you'd think the pressure and MV would be less, especially since the bullet felt looser than normal when pushed by the ramrod.
P.P.S.: Another question: the observed 2582 fps MV, while much higher than expected, isn't, in an absolute sense, higher than other Savage shooters load, is it? So, why should my barrel be damaged by it? Is it because the pressure in this case may have risen too suddenly?
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Post by edge on Mar 31, 2009 7:58:38 GMT -5
To check the barrel just take out the breechplug and clean the bore. Then run a saboted bullet all the way through. You would normally feel an area of reduced resistance if there was a bulge.
With a bore nice and shiny and looking through it toward a light source you should see a shadow, which would be an area of different diameter near the breech.
edge.
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Post by Harley on Mar 31, 2009 8:05:36 GMT -5
Thank you, Edge; would you please answer the P.P.S. part of my last post?
Harley
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Post by edge on Mar 31, 2009 9:13:46 GMT -5
The velocity increase of 232 fps was probably caused by an increase in peak pressure or an increase in average pressure. The pressure of your standard load is unknown, at least to me  If it is in the low 40 kpsi range then this increase may not cause a problem. BUT, on the other hand if your normal load is in the mid 50 kpsi range then it could have caused a problem pressure spike! What was the exact load? Perhaps we can get a reasonable approximation of pressure...assuming a standard pressure curve. edge. |
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Post by edge on Mar 31, 2009 9:59:14 GMT -5
I went back through your posts and it seems that you shoot 275+wad Parkers using 12/47 4759/2015 Since 4759 is bulky I will estimate that the powder column is 1.67 inches long in your barrel. My program would estimate a powder midway between 4198 and 3031 and would generate about 47,000 psi and result in a velocity of 2500 +-fps. Your "normal" 2350 would be around 41,000 psi and your 2582 would be into the low 50 kpsi range. While that might be higher than you may want, assuming that there was nothing funky, as in a super high pressure spike, then there is probably nothing to worry about.....but I would still inspect the barrel to be sure edge. |
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Post by Harley on Mar 31, 2009 10:35:17 GMT -5
I just gotta say it: I'm a competent shooter and an occasional innovator; but, here's an example of what overwhelms me. We've got a bunch of people on this Board who bring such a variety of complementary statistical, technical, engineering and machining backgrounds. It's really "ask and you will receive".
Edge, thanks in particular for doing the homework on this load. Your conclusions - along with my having just cleaned the barrel, then bore-lighted it for "shadows", then loaded a saboted bullet - all indicate I got away with something, even if I don't know what it was or how to protect myself from it in the future.
Harley
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Post by chuck41 on Mar 31, 2009 10:57:21 GMT -5
Those witness marks are a real salvation as long as they are used as you indicated. If everybody would consistently do as much I think the "bulged barrels" would become a thing of history.
Sure would be interesting to figure out exactly what happened here, but I suspect that may forever be a mystery. Best thing is there was no damage.
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Post by rexxer on Mar 31, 2009 11:20:06 GMT -5
Lloyd- Chrono verified the reason why you felt more kick. Without chrono you might have just wrote it off. Like you and Chuck have suggested-We all need to keep an eye on our witness mark! Sorry ,but I have no guesses on where the spike could come from. Glad the barrel is fine,would of been a real shame!
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Post by fishhawk on Mar 31, 2009 12:18:52 GMT -5
I agree with smokeeter that the bullet was a little higher off the powder column with the wad on edge causing a slight air gap resulting in a spike above normal pressures for that load.
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Post by boarhog on Mar 31, 2009 19:19:44 GMT -5
This board is wunnerful!
I have been going over, and over what could have caused a similar jump in recoil and chrono speed for me last Sunday. My load was 43 gr SR4759 behind a 246 gr cast, and black MMP. The MV jumped from an av of 2050 to 2450, and as I said in my earlier post about it, my first thought was that I had dbl charged. I carefully checked every possibility. It could not have been a dbl charge, as I had no missing powder charge. My other possibility was that I had mis-weighed a charge. I use an RCBC electronic scale, and was using a Lee dipper and a powder trickler to carefully weigh the charges. On top of that, I would think it should take a minimum of 4-5 gr of 4759 to boost the MV 300 fps.(if not more), and the little pill holder I was using would overflow if I tried that much powder.
I now wonder if I may have failed to seat the bullet/sabot firmly enough against the powder, or possibly had one of those theoretical double bangs where the primer pushes the load a bit up the barrel and then the powder ignites causing a pressure spike.
I didn't have a witness mark on the ramrod, but will before I ever fire another shot.
Boarhog
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lc
Forkhorn
Posts: 72
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Post by lc on Mar 31, 2009 20:11:39 GMT -5
What would happen if the 2015 was under the 4759 would that cause for a velocity increase?
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Post by rexxer on Mar 31, 2009 20:52:05 GMT -5
Interesting,never thought of that!!!
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Post by Dave W on Mar 31, 2009 20:54:08 GMT -5
I have mixed duplex but never reversed the booster and primary, I think it might be possibly slightly slower if he had mixed the loading order.
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Post by jims on Mar 31, 2009 20:58:59 GMT -5
I do not know this as a fact and do not try it but I thought I read here once where the duplex loads were purposely intermixed before being put in the barrel and it did not make a significant difference as long as the type and powder quantities was correct.
I hope someone jumps in here that can verify that or eliminate that.
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Post by Dave W on Mar 31, 2009 21:21:11 GMT -5
I do not know this as a fact and do not try it but I thought I read here once where the duplex loads were purposely intermixed before being put in the barrel and it did not make a significant difference as long as the type and powder quantities was correct. I hope someone jumps in here that can verify that or eliminate that. I believe SW said the pressure would be lower mixing instead of stacking the powders. At a 100yds, there was little difference in group size, mixing vs. stacked, at 200yds there was quite a difference. I'm confident RB and others would have thoroughly tested duplex and various loading procedures before releasing info to the public to make sure it was safe. |
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