BARREL BURNING THEORY

[TonyR]

cam. You probaably need a different example. According to QL, 28gr of Varget with the 107SMK gives about 50000psi and 95% case fill in the 6mmBR but 75000psi and 114% case fill in the 6PPC which strikes me as unlikely just for the case fill. I routinely run 29.5gr of Varget in my 6mmBR with the 107SMK and the other bullets in that weight class but I doubt that many are jamming that much powder into a PPC case, at least according to QL.

 

[camac]

Tony, Can you try with the ADI 2208 powder instead. The ADI website and Hodgdon have 27.7 as max load (compressed). and 50,000 CUP (around 60,000PSI). They list up to 29 gr varget in lighter pills. I only know one guy who made an 8 twist PPC here and he told me he got up to 28 grains (rang him for the load). I have heard a few guys suggest to try the ADI data for 2208 instead of varget.
thanks

 

[TonyR]

Maybe the shank seating depth is the issue bit I come up with 110% fill which is the practical max I believe and about 69,000 psi for the ADI2208. Someone might actually be doing that (NOT ME!!)

 

[camac]

Thanks Tony, Yes but some of those PPC guys run some extreme pressures and the brass seems to like it better than the BR stuff. Anyway that was what I was after. A high pressure PPC case vs low pressure BR with same load. Cheers.
Using Mikes formula, 2349 rounds to burn out for the PPC and 3242 for the BR with same powder charge at 60 second shot interval. I certainly can vouch for the BR figure. Like most guys I use 29-30 grains and generally get over 2500 rounds so 3242 with a lighter load sounds about right. I don't know about the PPC as I have no experience and I doubt we will find too many guys who have shot out a barrel with that load. Maybe Mike has some similar examples from real life data?? I will ask John here again but don't think he has shot out his 8 twist PPC barrel yet and it is unlikely he would wait 60 seconds between shots plus I also think he went back to shooting 80 Grainers.

 

[camac]

Perhaps a better example that will get more feedback and have a better data set is 29 Gr of BenchMark behind a 70 gr bullet. or something similar. I know this is a very mild load for BR and will get below 3000 fps out of 24 inch barrel (3100 out of my 26 inch) and you should expect over 3000 rounds for this load too. But this would be a fairly hot load for the PPC but more efficient getting around 3150 fps from 24 inch.

Which would win in slow fire I wonder??

 

[TonyR]

Have you looked at the loads on the 6mmBR Cartridge Guides for some examples? Lots of"real world" stuff on there. There are seperate guides for the 6BR, 6BR Improved, and 6PPC there.

 

[TonyR]

cam. did you see this?
http://bulletin.accurateshooter.com/2010/11/how-to-wear-out-a-barrel-in-one-afternoon/

 

[mikecr]

I started this recently to validate something else:
http://benchrest.com/showthread.php?71525-Barrel-life-of-6PPC&p=596023&highlight=#post596023

The 6PPC is commonly run at very high pressures(competitive pressures). There are of course prices to pay for this, similar to top fuel drag racing..

 

[camac]

cam. did you see this?
http://bulletin.accurateshooter.com/2010/11/how-to-wear-out-a-barrel-in-one-afternoon/

Yeah I did, Maybe I could give them a couple of loads and see if they want to do it again.????
Cheers.

 

[camac]

I started this recently to validate something else:
http://benchrest.com/showthread.php?71525-Barrel-life-of-6PPC&p=596023&highlight=#post596023

The 6PPC is commonly run at very high pressures(competitive pressures). There are of course prices to pay for this, similar to top fuel drag racing..

Mike thanks - I actually watched that thread go through with great interest. The trouble I see at the moment is distinguishing shot timing from pressure and powder charge from pressure. Is there any benchrest data on PPC where high pressure but slow shot timing was taken?? I don't know anyone at the bench that would take 40 sec to 1 minute between shots like we do in F class. You might know some one who does? Or anyone want to chime in? Perhaps there are a few BR shooters in Benchrest that only push there BR's at same velocity as PPC guys?? Perhaps we could ask some more pointed questions at the BR site?? Essentially though I think we all agree shot timing seems to play a bigger role and the BenchRest data might be too "confused" due to the slight difference in shot timing (say 20-30 seconds) that makes a big difference in barrel life.

What we really need is some data on small case vs large case in slow fire situations. This would give a better baseline. Different pressures and different powder charges for same result. I think that was the basic question that was being asked in that previous thread that you correctly challenged. It is probably better comparing a high pressure 260/creedmore/6.5*47L round to a low 6.5*284 but pushing same speed. The second has a lot more waste energy, the first more pressure- I think that question has still to be answered and may come out too close to call in the relativity of the accuracy of barrel life figures. But I also have some first hand experience on this with the 6.5*284 and several barrels and there seems to be more and more people pushing the smaller 6.5's so I think we will start to get a good picture over time.

What I can tell you from a smlall sample size is that I, and several others over here have noticed there was not a great deal of difference in barrel life in loading back the 6.5*284 from 2950- 2850 fps. Perhaps only 100 rounds or so at the most. I tried for a season in doing this for weekend shoots then bumping up for bigger matches. Barrel still died around 1200 rounds and was completely shot. I did however jump up from 800 (first barrel) to 1200+ (2nd barrels onwards) by slowing my firing rate and regular good cleaning routine.

There are plenty of guys pushing the 6.5*47L, Creedmore, 260 and 6.5*55's at these type of speeds but they seem to be getting far greater barrel life with higher pressure but significantly less powder. Admittedly the extreme pressure of the PPC is much rarer though but starting to come through with people pushing the newer cases (creedmore and 47L especially) at some very high speeds and I am sure we will start to get more and more feedback on it - it is a very popular calibre et the moment.

Cam.

 

[camac]

Mike I also might point out I don't mind being proven wrong - the aim is to try and get to the truth whichever way it lies as you pointed out earlier. I would prefer to understand it and be proven wrong than be left wondering. At this stage I am definately still wondering???? ...... but nonetheless I have a theory. I might just pose this exact 6.5 question above as you did in BR central and see if anyone has burnt out a barrel doing this yet in F class shooting style and can they give us some results?? We have plenty of burned out 6.5*284 barrels and quite a lot of 6.5*55.

 

[RDavies]

How about properties of the barrel steel? I have seen a few times that with very similar loads to previous barrrels, some of mine have a very very short life. These have usualy been my most accurate though. Is the barrel steel softer, or for some reason, do some barrel surfaces soak up more heat?

 

[camac]

As far as I am aware there seems to be a significant difference in barrel steel "hardness" and indeed some do seem to wear out quicker. Some stainless steels are very poor conductors of heat. This actually makes them worse for wear as the heat cannot dissipate into the steel and away to the outside of the barrel. The surface temperature of rifling and inside of the bore remains very high for longer.

 

[mikecr]

The spreadsheet I posted will predict both the 6.5x284 and the 6.5mighty mouses.
There really is no basis to support predictions of the delusional here.
When a 6.5x47/CM is run to compete with heavier bullets than the cartridge was intended, it's expected barrel life will fall hard.

You know the 6.5mighty mouse shooters are really trying to do the same as a 6PPC, in 26cal. The ratios hold, and when shot the same the results will be close.
Nothing is free..

 

[camac]

Mike,
Don't get me wrong, I have a foot in both camps and am not sure but this makes soime sense to me without any practical data to really back it up but I suppose the data will start to come as these guys shoot out barrels in F class. but based on my heat theory (and it is still definately only a theory) Here is my prediction based on waste energy alone.
If you plug in 800 rounds for 6.5*284 (ie you shoot them at a reasonably fast rate for F class - say 30 second shots, I would predict an equivalent around 2000 rounds for smaller 6.5's at pressure. If you go slower and shoot around 50 sec to 1 minute and clean out the carbon regularly I predict you will get 1100-1200 out of 6.5*284 and an equivalent of 2200-2500 from the smaller cases. The 55 swede is in the middle.
Cam

 

[mikecr]

While your table reflects limited feedback gathered, if you look at it carefully it really doesn't support a notion that 6.5mighty mouses gain barrel life over a 6.5x284.
And that's fine, but no conclusions can be drawn yet.
The qualifier you imbedded was bullet weight.

Set bullet weights and velocities the same(with loads adjusted) so that it's apples to apples, and we'll see what's happening.

 

[johara1]

Cam,Just to add a little info. to your list, I just pulled my 6.5 x47 barrel after 2200 rds.scoped it and found very slight fire cracking, slight throat advancement. It had varget and RL15 and RL17 powders used in it with 130-140 gr.bullets. The best loads used were;42 gr. rl 17 and 140 berger @ 2968 41 gr. rl 17 and 130 jlk @2950 this shot in the low2's when i pulled it.
This barrel never saw a brush! the crown was perfect,maybe the way we clean has a little to do with it. Rod guides,cleaners, brushes,rods all have an effect on the barrel life. .......jim

 

[camac]

Thanks Jim, Yes totally agree - You can do a lot to extend your barrel life. I am proposing you can use this rule of thumb to compare barrels in the way you shoot, clean, load etc. Roughly by squaring the difference in waste heat energy. ie plug in a rifle you know for yourself in the way you used it and then compare different ones.

Mike, I also agree once again with you the data is thin so very hard to fit. Plugging in Jim's load above on the spreadsheet in both our formulas gave 1500 on yours (at 60 seconds) and 1384 (COMPARED TO 800 IN 6.5*284 AS BASE) to 2083 (COMPARED TO 1200 IN 6.5*284 AS BASE) on mine. I would assume 1200 for base with Jim is probably an underestimate as I am sure he looks after his barrel well enough to get at least this out of a 6.5*284 cartridge and it works. PLUS he has shot some of the barrel life at a light charge so should be between the two figures in the chart somewhere. I also think yours works and is a very good fit. I would love to see if you could fit your formula with an input energy (you basically have this in powder and charge weight) vs output energy instead of powder input energy and pressure.

 

[camac]

Added the 800 round base spreadsheet for clarity.

The big thing I notice is I don't get much xtra barrel life by backing the charge down a little on the 6.5*284. I noticed this when I tried with my last barrel and talked to a few others who have tried as well. I ran my last barrel at 2850 for most shoots and only pumped it up to 2950 (or 3100 for 123) for big shoots. I still only got 1200 rounds out of it. I take my time betweeen shots and regularly clean to remove carbon. I got approx. 1200 out of previous barrel without loading back but had same shot timing and cleaning routine.

 

[camac]

Mike -The essence of what I am saying still leaves a strong correlation between pressure and barrel life but I am arguing that it may not be pressure that is doing it..... For instance, as you pump up the charge within a given cartridge barrel life goes down disproportionately to charge increase. So fitting a curve to pressure * charge is effectively the same as a waste energy squared fit. As you increase the charge within a given cartridge, you increase the waste energy almost linearly. but the effect on barrel life seems exponential (or squared as a rule of thumb). It fits pretty closely to a pressure and charge theory when you plot both.
I can get my head around why heat could have an exponential effect on barrel life. I can't get my head around why pressure would have as big an effect.

Either way, I agree. Running the "mighty mouses" at higher charge and higher pressure will see an exponential decrease in barrel life (as you have well noted) BUT my catch - I don't think they will ever catch a 6.5*284. I think at the heart of this is the more efficient the case (and the less waste heat energy) the better. Pumping up the load will have detrimental effects on barrel life any way you look at it.