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Post by ET on Jul 31, 2011 21:46:06 GMT -5
A little while ago a comment was made questioning if bore smoothness was a possible factor contributing to Secondary Pressure Spikes?
While it’s still hot in my location with temps reaching 90F during the day I have been trying to do a little more research about PT testing and causes for anomalies.
One area of interest even though I have yet to experience is the cause of Secondary Spikes. One suggested cause is insufficient bore friction.
Now I don’t think anyone would dispute the difference of bore friction between a rough bore and smooth bore so this would lead me to believe there is validity here.
Having said that I also know there are other causes not related to bore friction that trigger Secondary Spikes seen on a trace. For an example, while my PT unit was setup ready to record a shot I tapped the cable for the strain gauge near the PT module and it triggered a pressure spike reading. So a False Secondary Reading could be triggered mechanically from vibrations to the cable contact to the PT Module. Now I have taken precautions for this condition to eliminate a possible false reading.
So my questions here are for saboted loads.
Is having a bore polished extra smooth an advantage or disadvantage?
Would a regular lapped bore compared to a polished lapped bore be more instrumental in reducing or eliminating secondary spikes?
What say ye of the ML fraternity?
Ed
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Post by Deleted on Jul 31, 2011 22:47:10 GMT -5
ET, From what I've been reading here or FWIBRH,lol. Some guns like it clean some like it dirty,second spike relationship,no clue,but I would think there would have to be a good sabot/bore seal to produce such  I don't know. IIRC Richard Cleans shot to shot ,so the lands will engage agressively. But even with super match lapping i've heard they do like it dirty. Just my two cents bud. |
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Post by Richard on Aug 1, 2011 20:21:03 GMT -5
OK, so here comes Richrd's opinionated opinion ;D Clean vs. not clean..........Also, tight vs. loose barrels? I have listened to tales here where shooters claim they need X number of shots (maybe 5 or 6) before their barrel starts to shoot. Then I hear that they clean after maybe 25 or 30 shots? What I want to know is: "What is happening between shots 6 and 30? Is not crud and plastic accumulating? Does the barrel shoot accurate for those maybe 24 shots and then on shot #29 or 30 just stop shooting accurately? I would like to know? So then they clean and allegedly have to shoot another 6 shots in order for the barrel to again be shooting accurately? It seems to me that fouling is a cumulative thing. Accuracy does not just stop after a certain number of shots, it degrades the heavier the fouling becomes. In my opinion  it is more logical to keep fouling at a minimum by doing a minimal bore treatment (as SW turned me on to) each shot which keeps my barrel more consistent from shot to shot!  And yes, my barrel is "super match" lapped! I believe a waste of $20.00 since my bore scope can tell no difference in either treatment. Possibly in a match type CF bench rifle it may help or possibly with sabot less shooting. Visually, barrels match lapped and those not, look the same. Another thing I hear all the time: My barrel is tight.............My barrel is loose? P-N barrels are held to .0002" end to end. I doubt anyone can really tell the difference in tightness with a saboted bullet. The same goes for stock Savage barrels. Unless you actually have two barrels side by side.........both perfectly clean and you put two identical bullet/sabots down both, would you know if one is looser or tighter than the other. Even Savage has to have some manufacturing tolerances which I would guess are probably under .0005". And since most .50 are being shot with sabots, its pretty hard to tell tight from loose .........again, unless two or more barrels are "tested" at the same time. How would I know if my barrel is loose as compared to someone in Ohio? My lot of sabots might be from a different lot than the other guys? My barrel might be cleaner than his? So, how does all this relate to ET's secondary spike's? In a stock Savage barrel, they are all rough as a cob. With a PN, they are smooth as a babby's butt. Yet both barrels have experienced these secondary spikes? I can hardly see where bore condition will be an influencing factor in that spike. It is probably more related to a particular powder/bullet combo or a "bug-a-boo" with the PT instrument. Richard |
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Post by Dave W on Aug 1, 2011 21:06:17 GMT -5
There may be tolerances end to end but that is end to end, not ID. There are Pacs out there that a .452 bullet falls through, SW has one and I know there is at least a couple more from past posts.
I would say my .50 is tight since a .5 bullet is engraved by the lands sabotless. The others I have worked with are not as tight since a .5 bullet falls through the barrel with no pushing. Tight is a perception of the shooter since we are all of different builds and strength, no arguing that, but there are differences in barrel ID's also.
If one looks at the traces with the .50 that RB did in the Tips section, there are no secondary spikes like we have seen in the .45 with the exception of a few of TG's traces. The spikes are more the norm than the exception it seems for the most part in the .45. Is it due to equipment, poorly constructed loads, barrel condition-dunno but I would like to.
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Post by Deleted on Aug 1, 2011 21:13:46 GMT -5
This is only speculation but i believe there is little to no relationship in the secondary pressure spike and a rough or fouled bore. when you are talking 60 lbs of pressure to seat a bullet and the amount when fired I just cant see that kind of spike caused by a rough bore, If the bore had a very tight spot, maybe..
well I can only speak for one pacnor barrel and that one is on the boat anchor. It most definately is not at its best when clean. I have tried this several times on a clean barrel,( five shot groups that is), and there is a considerable difference between clean and dirty when it comes to group size. again that is only on one barrel but mine has not been cleaned in almost two years (breech plug yes, barrel, no)...I can tell no difference in the amount of fouling left in the bore related to bullet seating pressure from shot 7 to shot 150.
as Rich said, I am of the opinion that the super match lapping is a waste of money(and mine is sm) but again just my 2 cents...Bill
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Post by tar12 on Aug 1, 2011 21:28:11 GMT -5
I have experienced first hand tight VS loose barrels as I have set up many .50s for board members and friends alike. The amount of fouling required would vary with each barrel. On avg. 2-4 shots with the exception of Harleys .50 which absolutley had to be out of tolerance yet they told him it was not. For several weeks I tried in vain to find a combo that was acceptable....in the end it required 15 plus shots before groups would tighten up and the only combo that would shoot MOA was the BO/Vit/BCR combo.In this case I believe this particular gun could go a very long time with out cleaning..for the "normal" or avg. .50 barrel the 2-4 shot fouling routine coupled with cleaning every 25-30 shots worked very nicely. I believe the rough bored .50 required fouling to fill the chatter marks and you could count on a particular level of accuracy for x-amount of shots before accuracy slowly eroded away. No magic number where POOF! the accuracy was gone..just a experienced number you could count on. It is a given the fouling accrues and at some point you had to clean. NOW the Pac .45 has been a entirely different animal as far as fouling goes to settle in... only one is needed. I have only set up 3 Pac .45s and noticed no difference in loading pressure using like componets and no need for the .50 routine. As a side note the orginal .50 ML-1 that I purchased in 2000-2001 had a barrel as smooth as a babies behind and did not require excessive fouling shots and was very accurate compared to later .50s...one of Savages great mysteries....
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Post by moto357 on Aug 1, 2011 22:45:32 GMT -5
doesn't relate so much to the question reguarding PT, but in a recent mag. article i was reading on barrel break in there's a sub-section the guy shows to proove a point. comparing two barrels, one being a savage which in the bore scope looks just like a washboard, the other barrel being smooth, yet both rifles shoot tight little groups.
i do agree with hillbill that a rough or even fouled bore would not add enough friction to cause a noticible spike. and if so i would imagine it would be throughout the barrel/trace, not just secondary(at end of barrel).
can't say i know enough about internal balistics or the PT itself to give anything further except opinion but i would imagine with the pressures we're shooting at any secondary spike might be false for one reason or another
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Post by ET on Aug 2, 2011 15:46:43 GMT -5
Richard
You obviously display a conclusion from your resulting response.
DW is right about never seeing a secondary spike in a 50PT provided by RB.
RB did a trace on using 84gr of H332 with a 250gr bullet in a 50. Now that is twice the amount of powder than N110 being used and not even an indication of a secondary response is seen. If there was a candidate in the 50 for seeing a secondary response you would think this one would be it.
Would you care to share your opinion on this?
Ed
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Post by deadeye on Aug 2, 2011 21:19:01 GMT -5
OK, so here comes Richrd's opinionated opinion ;D Clean vs. not clean..........Also, tight vs. loose barrels? I have listened to tales here where shooters claim they need X number of shots (maybe 5 or 6) before their barrel starts to shoot. Then I hear that they clean after maybe 25 or 30 shots? What I want to know is: "What is happening between shots 6 and 30? Is not crud and plastic accumulating? Does the barrel shoot accurate for those maybe 24 shots and then on shot #29 or 30 just stop shooting accurately? I would like to know? So then they clean and allegedly have to shoot another 6 shots in order for the barrel to again be shooting accurately? It seems to me that fouling is a cumulative thing. Accuracy does not just stop after a certain number of shots, it degrades the heavier the fouling becomes. In my opinion it is more logical to keep fouling at a minimum by doing a minimal bore treatment (as SW turned me on to) each shot which keeps my barrel more consistent from shot to shot! And yes, my barrel is "super match" lapped! I believe a waste of $20.00 since my bore scope can tell no difference in either treatment. Possibly in a match type CF bench rifle it may help or possibly with sabot less shooting. Visually, barrels match lapped and those not, look the same. Another thing I hear all the time: My barrel is tight.............My barrel is loose? P-N barrels are held to .0002" end to end. I doubt anyone can really tell the difference in tightness with a saboted bullet. The same goes for stock Savage barrels. Unless you actually have two barrels side by side.........both perfectly clean and you put two identical bullet/sabots down both, would you know if one is looser or tighter than the other. Even Savage has to have some manufacturing tolerances which I would guess are probably under .0005". And since most .50 are being shot with sabots, its pretty hard to tell tight from loose .........again, unless two or more barrels are "tested" at the same time. How would I know if my barrel is loose as compared to someone in Ohio? My lot of sabots might be from a different lot than the other guys? My barrel might be cleaner than his? So, how does all this relate to ET's secondary spike's? In a stock Savage barrel, they are all rough as a cob. With a PN, they are smooth as a babby's butt. Yet both barrels have experienced these secondary spikes? I can hardly see where bore condition will be an influencing factor in that spike. It is probably more related to a particular powder/bullet combo or a "bug-a-boo" with the PT instrument. Richard facts are facts not opinions- if you were to have a adjustable "swinglock die" shooting sabotless you will see in a hurray there are difference's in bore's even from pac-nor etc. no plastic to absorb the true bullet to bore fit. now for the so-called" tale"-please explain in this experiment dirty vs. clean in my case only-did i suddenly forget how to shoot??? ;D ;D or was there something going on which i have observed over & over * over & over>>>>>>>>>maybe like groups here observed as tar stated are usually much better in cold-weather,huh-the bore was much different than a ambient temp w/ a cooling rod in a certain situation dougsmessageboards.proboards.com/index.cgi?board=smokeless&action=display&thread=4211 |
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I don't know. 
it is more logical to keep fouling at a minimum by doing a minimal bore treatment (as SW turned me on to) each shot which keeps my barrel more consistent from shot to shot! 
