Powder burn rate?

[750k2]

How does burn rate relate to burn temp?
My logic tells me slower would burn cooler?
If not what powders are easiest on bbl's in the
.243 class cartridges?

 

[flatlander]

QuickLoad gives burn rate & burn temp for a wide range of powders. It's a good tool for evaluating prospective powders, quite possibly the best resource available for the purpose.

 

[750k2]

I don't have that - would pressure figures be a good indicator
for heat range?
Pressure is a good heat indicator in other applications.

 

[BoydAllen]

Powders vary in their composition. Single base are of nitrocellulose and burn rate is varied by particle size, shape and deterrent coating. Double base powders usually have an added amount of nitroglycerin. These can burn hotter but may have advantages in performance. If you are looking for barrel life, you might also consider moly coated bullets. I understand that there is some controversy to this, but Norma did a wear test, and in it they extended barrel life. The only caution that I would add is that non- stainless barrels should probably have their bores oiled between shooting sessions if moly bullets are used. A friend has loaded for a 7mm mag. using bullets that were treated with a spray and bake moly treatment. He believes that one of the advantages of this is less barrel heat for a given amount of shots. Another issue related to barrel wear is rate of fire. Not giving a barrel time to cool off can be expensive.

 

[Laurie]

In modern powders, most of any change in burn rate comes from the coatings - you can see this by many ranges having most powders listed as having identical diameter and length grains, although the central hole could conceivably vary in stick powders. Therefore, all will produce the same amount of energy per grain weight of powder - again you see that where the manufacturer quotes this figure. All of the older IMR powders were listed as having identical BThU (British Thermal Units) per lb of powder; most Vihtavuori powders have similar values in J/gm (Joules per gram weight), the N500 double-base series obviously having more than the N100 single-base products though.

Deterrents therefore affect the burn's behaviour not the energy, slower burners taking longer to get into their full stride allowing larger case capacities and charge weights behind smaller calibres, or the use of heavier bullets in any particular calibre. A heavy bullet has greater inertia than a light one, so achieving maximum pressures has to be delayed time-wise to let the bullet get moving and increase the combustion chamber volume (case capacity + that of the empty bore behind the moving bullet) to match the increasing volume of the gas produced by combustion.

Heavy bullets + suitable powders generally increase throat wear if comparing two powders with identical specific energy levels because high pressures and temperatures are applied to the throat surfaces for a longer period than applies to a light bullet and faster burning powder. This can be significant in cartridges like .223R - you'll get noticeably faster throat erosion from shooting 80s than 50s, assuming they produce equivalent muzzle energies.

Some powders may wear throats faster than others, but manufacturers use additives to reduce this. Any effect from using modern double-base powders is probably marginal, but such is their reputation that many won't. This goes back to late 19th / early 20th double-base types such as British cordite in the .303 that had a 60% nitro-glycerine content and no flame temperature reducing additives. Barrels had an accuracy life of only 1,000 rounds despite modest peak pressures by today's standards, and it seems shooters have a very long collective memory.

Bullet weight and loading cartridges right up, plus the basic cartridge design is what mostly determines barrel life, plus maybe rate of fire / barrel throat temperature (even this is probably overrated in well-balanced cartridges massively over bore capacityh magnums aside, the much quoted military work based on automatic weapons trials, especially machineguns, that produce barrel temperatures that no civilian rifleman would ever come across). So, shoot a .22 Hornet loaded to 35,000 psi and your barrel lasts forever. Shoot a .224 Middlested or even .22-250 or .22BR with a fast twist barrel, heavy bullets, and 65,000 psi loads and you need to buy shares in a good barrelmaker! Try .30-378 Weatherby Magnum and you'll likely wear the barrel out before you find a load that shoots well.

Laurie,
York, England

 

[necchi]

750k2,
Your kinda mixing two different physics together
Powder burn rates and pressures,,
Physical transfer of heat,,

The longer heat is in contact (slow burn), the more heat can be transfered.

splash some ethal alchohol on metal an light it, it burns off fast,,
splash some gas on it !! It's gonna lay there and burn longer and make the metal hotter.

 

[BoydAllen]

"you can see this by many ranges having most powders listed as having identical diameter and length grains,"

I disagree. That is not what I see when I look a the different powders that I own. For instance, 133,322, Benchmark,and 748 all have different grain sizes, even though they are not far from each other in burn rate, and may all be used in the same cartridge, behind the same weight bullet.

 

[Laurie]

Boyd,

that's not what I said. I was talking about shapes / forms within a manufacturer's range. So compare Winchester 748 and 760 say. If you take Vihtavuori, where the manufacturer lists kernel sizes within its range, many powders share dimensions - N130, N133, N135, N140 are all 1mm length and three of the four are 0.8mm dia. N150 through N165 are all 1.3mm X 1.0mm. Energy content varies from a low of 3,500 J/g to a high of 3,950 J/g across N110 to N170, most being 3,700 or 3,750 which are likely to be roundings. However, despite N165 being not a great deal different in size from N110 (1.3X1.0mm v 1.1X0.8mm), it has a relative burning rate of 43%, so it's obviously not shape that is the primary driver of the difference, rather the chemicals used.

When you compare products from different manufacturers, they may have got to a similar burning rate by very different routes, and also have different specific energy levels from each other, hence requiring different charge weights in a particular cartridge-bullet weight combination. Nevertheless, that doesn't alter the fact that burning rate and energy output aren't directly linked. The older IMR powders from 4198 through to 4831 in DuPont days were listed as having identical amounts of energy in each pound of powder, but very different burning rates.

It's the mixture of the amount of energy released and rate of burn that interests us and affects what happens inside the barrel and how it affects wear on the chamber end of the bore. Light low-inertia bullets, low effective expansion ratios, low pressures, and fast burners in combination produce less wear & tear, hence 80-100,000 rounds from a .22LR barrel to less than 10 in Mik Macpherson's joke .22 Loudenfartenboomer that put some huge case and slow burning charge behind a 0.224" bullet.

Laurie

 

[necchi]

Nevertheless, that doesn't alter the fact that burning rate and energy output aren't directly linked.

Exactly +1

It's the mixture of the amount of energy released and rate of burn that interests us and affects what happens inside the barrel

And again,,well stated.
It can be tuff to wrap your head around those ideas but thats it in a nutshell, it's why some new to loading can get in trouble when they begin to think they can mix-n-match some powders because they'er "close" in the charts. Energy levels can "spike" suddenly when getting close to max charges.

 

[RonAKA]

Here are my "just thinking out loud" thoughts.

The barrel throat area essentially burns due to time above a certain oxidation temperature. From this thinking, a long barrel has the bullet in the barrel longer, and the time temperature effect is increased. A heavy bullet exits the barrel at a lower velocity, so spends more time in the barrel, and increases the time temperature effect. So barrel length and bullet weight increases barrel burning.

But some cartridges are barrel burners, and some are not. Which ones? Obviously the ones with a large case volume compared to the bore area. These cartridges have lots of powder, and the highest velocities. So does velocity increase barrel burning? I would suggest no, and in fact the reverse. The barrel burns only at the throat, where velocity of the bullet is the lowest. And the high velocity means barrel time is lower. So the time temperature effect is lowered. So muzzle velocity is not a barrel killer in itself.

But back to the question. What about powder burn rate? I think this is a relative thing. There is the perfect burn rate for a cartridge, and of course a slower and faster. The perfect burn rate would instantly raise pressure to a safe level (50,000 or so), and keep it there until the split second the bullet exits the muzzle. A slow powder will likely develop pressure more slowly and still be burning when the bullet exits. A fast power will develop pressure early and have it decay as the bullet progresses down the barrel.

So which is better for barrel life. I would suggest the faster burning powder. As an earlier Laurie posted earlier the heat in each powder within a range is quite constant. However, when using a faster powder you get early pressure which limits the amount you can use for a given bullet weight. This limits the heat, and thus the time temperature. With perfect powder you may get the optimum MV and thus heat effect. And with slower powder, it burns right through the cycle and even after the bullet has left.

You my vote goes for simplicity. It is the powder weight that determines heat input and barrel burning for a given bullet weight.

As for lighter bullets and more powder, it become more complicated. Perhaps just look at muzzle energy. More energy, more power, more burning.

Simple answer? For a .243 and 80-85 grain bullets I would be tempted to try H4895, and back loads off some to preserve barrel life.

 

[Frankr]

Wow! you guys are really into this one and seem very knowledgeable about this powder stuff. All very good reading, let me ask ya this one. a particular powder was brought up the other night at a friends house(i wont mention brands) and the question to me was what do you think of that powder? (i shot it for about 2 years).Well the answer was it shoots great but maybe, just maybe its hard on throats. i cant swear that it is but it seemed that it was. That is the old wise tale that ball powders are hard on throats,or spherical powders are hard on throats. any thoughts on that one and have you ever heard that before?? My reply to my friend was i found a stick powder that works as well as this other powder i was shooting.Its funny i cant swear it blew out my throat but it seemed it might of.

 

[Laurie]

FJIM,

it's more likely overall load combinations, that of bullet weight, peak pressure, and cartridge design that determines whether they're hard on the throat or otherwise. Powder A v Powder B less so for any particular bullet weight at the same peak pressure.

Ultimately, there is no free lunch, or only rarely anyway. Already, some people are worrying about the new Reloder 17 with its throughout-the-kernel infused deterrents (as opposed to purely surface coated) and barrel life. Probably rightly - if you up top MVs from say 2,900 fps with your previous powder to 3,100 fps with your new one, something has to pay for at least part of this extra performance. (Re17 works by extending the period of controlled burn which is a good thing, but at the cost of spreading it over a longer period of bullet travel, hence a longer section of the barrel. That may or may not be worse than concentrating it on a short section just ahead of the chamber - time will tell. I suspect that when a barrel used with hot Re17 loads loses performance it will be really done for - no setting back by an inch and rechambering, but that may not happen any earlier than with a conventional double-base powder.)

Then there is case design. The big issue is case to bore capacity ratio - 30BR has a small amount of powder (and light bullets too usually); .300 Win Mag or Remy Ultra-Mag a lot of powder (and heavy bullets usually). Both put their very different sized amounts of gas down the same size hole onto the same area of barrel throat and walls.

But ..... many people also say shoulder angle allied to neck length affect barrel life for any given case capacity / charge size to bore. This is down to the Turbulence Point (TP) factor. The theory goes that the charge doesn't necessarily all stay inside the case during combustion. As the bullet moves, it's partially followed by a swirling mass or ball of super-hot burning gasses with powder grains mixed up which not only attacks the barrel throat at the molecular level (chemical type action) but is very erosive through friction from powder and fouling particles. If you have a shallow case shoulder angle and short neck, the TP will be ahead of the case-mouth and inside the barrel throat. If you have a steep shoulder angle and long neck, it remains inside the case and the barrel is spared its effects. So, the theory goes anyway, and there is some evidence that something happens here, although nobody can prove or disprove the TP theory. As evidence, 6mm Remington is often quoted by its supporters as giving longer barrel life than the slightly smaller capacity and lower performance .243 Winchester. If you want to play with TP theory, photocopy cartridge drawings from loads manuals or elsewhere, put a rule on each shoulder line, and extend the line forward with a pencil. Where the lines cross is the supposed TP point - if inside the case (as in 6BR) good, if well outside (as in .300 H&H Magnum) bad. Many cartridges like those based on the .308W case have the lines intersect on the case mouth or just outside.

You can see something in all this. A good example is .222 Rem v .223 Rem with same weight bullets, say 50-55gn. The older cartridge has about 10% less case capacity, is rated at 53,664 psi PMax v 62,366 psi (CIP body using Piezo transducer) and has a much longer neck so the TP is inside it. Double the barrel life with the Triple Two if loaded right up using the same powders?

Right Powder A v B, especially ball v stick? Now you're asking a hard one! Here are a few facts. Stick powders are mostly single-base (nitrocellulose only) - All ADI manufactured Hodgdon stick powders; all IMR; Vihtavuori N100 series; AA stick powders (I think). A smaller number are double-base (nitroglycerine added, nowadays mostly in the 10-15% of overall weight range in rifle powders) - all Alliant Reloder series; Vihtavuori N500 series. ALL ball powders are double-base irrespective of brand name - it goes with the manufacturing method which is completely different from stick powders.

The relatively small amount of nitroglycerine in DB powders worries some shooters - burns hot, wears barrels out. It maybe did at one time, but that's much less of an issue today. If you use a DB powder to get a fair bit more velocity out of a heavy bullet, you will shorten the barrel life ..... fact. (We're back to Reloder 17 and whether it breaks the mould, or whether that extra 100 or 200 fps in 6XC or a WSM is really going to cost you!) I run heavy bullets with Viht N540 or N550 in both .223R and .308W in F/TR. I reckon 2,000 rounds is the likely barrel accuracy life as a result (for F-Class with half-MOA V bull, 1-MOA Bull, and each score ring only another half-MOA out, except at 500/600yd, we use even smaller targets).

Then there is kernel burning behaviour - Regressive through Neutral to Progressive. Very early powders were made by mixing the ingredients up until they formed a colloidal (plastic) mixture that was rolled flat before cutting into lots of little thin squares or rectangles, then the volatile parts of the mix drawn off. These powders were highly regressive - initial combustion had the largest surface area so produced gas at the highest rate. As the flake burned it got smaller and the rate of gas production slowed - the opposite of what you want in a firearm, as you want slow initial production that accelerates as the bullet moves down the barrel. So manufacturers developed stick powders that have a hole up the middle. The outside of the stick burns inwards and the surface area reduces, but the hole burns outwards and gets bigger increasing the combustion area and rate of gas production. The two cancel each other out, so they are called Neutral burners by engineers - and that's what most of our powders are. Big stuff (for large calibre military weapons - cannon and artillery) have multiple holes and are actually progressive, but you can't do that in our little cartridges.

Right? Now ................ think of a ball or sphere. No hole, so the burning area can only become smaller as the ball burns away - highly Regressive. Burning rate is partially controlled by sphere diameter (putting the grains through rollers often to change the shape to a partially or fully flattened ball or disk as in Hodgdon Titegroup pistol powder). To get around this problem, ball powders not only use clever deterrent coatings, but a lot of them. While a stick powder might have 1.5-2.5% of its overall weight made up of these coatings, a ball powder typically had twice as much. Since deterrents don't burn like the active components, ball powders left more residues, hence many got a reputation for being 'dirty'.

Diverting off the main topic for a minute, this was a big issue in the early days of the M16 rifle, especially in Vietnam. Stoner / Armalite / Colt / Remington developed the rifle and 5.56mm cartridge for a DuPont stick powder; the US Army changed the spec to an Olin ball number when they adopted the rifle and cartridge without telling the designer / manufacturer. Not only did the new powder change the combustion hence operating gas pressures so things like cyclic rate increased to levels that risked damaging the mechanism, but there were major issues over gas pipe and bolt carrier assembly fouling in a rifle that had been sold on being reliable with minimal cleaning. It took the M16 a long time to get over the bad reputation that this foul-up (no pun intended) gave it amongst US frontline troops.

Having a pretty high nitroglycerine content, they also got a repuation for being barrel burners amongst some.

So ................ stay well clear of ball powders seems to be the morale of this story? Probably not. This isn't the 1960s and there has been A LOT of development in coatings and powder technologies over the last 40, 50 years. The US military have used smallarms ammunition loaded exclusively with ball powders since the 7.62mm was adopted in 1952 and started replacing .30-06 (which in WW2 and later used both types depending on manufacturer). They are a litle bit dirtier burning (although Ramshot claims theirs are clean burning, but we don't see them in the UK, so I can't comment on this claim).

The military like ball powders for another couple of reasons. It stands up very well to long term storage especially in less than ideal conditions (this applies to all double-base powders to a greater or lesser extent) so ammunition has a longer shelf life and doesn't deteriorate as fast in humid jungle warfare conditions. It meters very well in large scale production, so variations in charge weights are small. (Same applies to many handloaders - a friend only uses ball powders in his .223R match rifle to cut down on handloading time.)

There are issues over temperature induced variations - a subject I've no views on either way until I see some proper research. There is an ongoing topic on this forum as to whether Re15 is badly affected by high temperatures. Some people say DB powders are worse than SB varieties. Some say the opposite ........... you pays your money and makes your choice! Let's put it this way though. Uncle Sam like ball powders. Uncle Sam says any cartridges he buys have to function within set parameters in an M16 or M60 and kill people whether in the Arctic at Minus 20, or at midday in mid summer in a Middle East desert at 100 degrees plus. That tells you something, I reckon. On the other hand ......... only ADI / Hodgdon SB stick powders are made as 'Extreme' varieties and aren't much temperature affected. No, I'm probably wrong there - the new 8208 XBR is an IMR brand (still Hodgdon) powder, and other IMR powders are made in Canada, but I don't know about this one. It appears to be the ultimate temperature-insensitive powder from what people are saying on this forum. It hasn't quite reached us in the UK yet, so again we've no experience of it over here.


So ................?? All powders on the market nowadays are good. They all work. They all have some upsides and downsides. I reckon that choice of (a) cartridge design, capacity and shape (b) bullet weight, and (c) the loads / pressures you run at have more effect than any individual powder type of model. Run something like .308W at 45,000 psi pressures and the barrel will last A LONG TIME. Personally, I prefer stick powders and don't bother whether they're SB or DB as I put the performance I need first - accuracy and velocity. It costs me - but so do club membership fees, range fees, fuel and mileage costs to get to the range, etc, etc. You only live once after all, so make the most of it!

Laurie,
York, England

 

[Frankr]

laurie,Thanks for the reply. Yes i agree,you have to do what makes ya happy.

 

[BoydAllen]

Many years ago, I asked a prominent local high power shooter about what he and his friends had observed in the way of differences in barrel life that might have been attributed to different powders. At that time he told me that one particular brand that shot well in their magnum bolt rifles, seemed to burn out throats faster than another, that also shot well. They were both extruded powders, in the same burning range, loaded to a similar velocity, using the same bullets. I believe that the faster wearing powder was double base, which probably contributed to a higher peak temperature, and the other was single base. As far as the comment about ball powders burning out barrels faster, I believe that Winchester 748 has an excellent reputation as far as barrel wear goes. One other thing, no powder maintains the same pressure till the bullet leaves the barrel of a rifle. There is a pressure curve.

 

[Laurie]

I believe that Winchester 748 has an excellent reputation as far as barrel wear goes

I wouldn't be surprised. It comes from the same plant (the former Olin outfit in St. Marks, Florida that is now the St. Marks Powder Company and makes all Winchester and Hodgdon brand ball powders) as the powders the US forces use in 5.56 and 7.62mm cartridges. 748 is the same stuff, just from different production batches, as Hodgdon BLC(2) and isn't that different from that used on the military ammo. In my experience, governments are a tight-fisted lot (when it comes to screwing value out of private suppliers anyway, maybe not always in their own expenditure and practices) and Uncle Sam simply wouldn't use a powder in his cartridges if it gave a noticeably shorter barrel life than available alternatives. If it gives a longer life, so much the better!

These people in Florida know their stuff. They've been making ball powders since before the USA entered WW2 and put a huge amount of research into this type, no doubt some of that funded by the American taxpayer through the US Army. Incidentally, mentioning early WCC ball powders, I was asked to demill a large quantity of 1930-50s US military .30-06 ball ammo a few years back that had corroded cases and couldn't be sold. It ranged from pre-war M1 (173gn FMJBT) to late wartime / early post-war M2 152gn flat-base FMJ bullet stuff plus the odd Remy 220gn RNSP heavy deer/bear cartridge mixed in. The stick powder examples had deteriorated and the cases were rotting from the inside out thanks to the powder having turned to a form of corrosive slurry in the worst examples. 1943/44 dated WCC examples with ball powder looked and smelled perfect, no sign of powder breakdown at all - I was tempted to try the powder in a modern .30-06 handload, but decided that was taking a stupid risk. Some has gone in home-made fireworks. Anybody want a couple of pounds of apparently good 65 year old ball powder?

One other thing, no powder maintains the same pressure till the bullet leaves the barrel of a rifle. There is a pressure curve.

Yes absolutely Boyd - a good point, one that I should have made. Ultimate performance comes from the total area 'under the curve', not the initial spike representing peak pressure that largely determines the maximum charge that can be safely loaded. This appears to be where Re17 (and other grades using the same technology that we are promised will follow on behind it) is revolutionary in that obviously flattens the early part of the curve giving a longer period of peak but safe pressure, hence higher MV when the average pressure X time equation works through. To put it in regressive / progressive terms, it is a more 'progressive' type than Re15 or Re19 on either side, as well as having an intermediate burning speed.

In an ideal world we would have totally progressive powders that saw pressure in a load climb to 60,000 psi (say) and hold it there for the entire bullet trip down the barrel. No ......... actually, that's not ideal either now that I think about it. 60,000 psi muzzle pressure would deflect the bullet badly as it exits the barrel, not to mention deafening anybody within a half mile of the discharge!

Anyway, with the new Alliant Nitro-Chemie AG manufactured powder(s), the game obviously has still got a lot of play left in it. If we had a crystal ball, it'd be interesting to see what everybody will be using in 10 years time

Laurie

 

[BoydAllen]

Reloader 17?

 

[BoydAllen]

Laurie,
Going back to your comparison of N110 to n165, the surface to vloume ratio of n110 is approximately 21% greater for n110 than for N165 (using your numbers for particle size). If the total difference in relative burn rate is 43%, then one could postulate that almost half of that might be due to the difference in particle size. I realize that this makes a great leap that is unsubstanciated as to how the ration relates to speed, but we do know that if all else is equal, the relationship exists.