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You still cooking menudo , Atkinson ? Had a bowl of the really good stuff in Lamesa last week .

All I know about the current topic is what I done and what happened as a result :

I got a 300 ultra ,then a 338 Ultra in 700 Remmies as soon as they came out . I settled on RL 22 like most everybody else at that time . RL 25 wouldn't get close to the same velocity . These were both factory rifles with 26 in barrels .

Then I had a 7 Ultra made on a Ruger No. 1 leaving the barrel at 29 i/2 in. Believing the same stuff you and I read , I tried the RL 25 since I had a longer barrel to work with .

Sure enough , I got higher velocities with the RL 25 than with RL 22 . In fact I got much higher velocities than the books showed and more than would usually be attributed just to more barrel length .

That brings me to the question I came here to ask : If all the powder is burned , and the gas can't keep up with the bullet , how come longer barrels shoot faster ?

Just kidding . I know why .


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You have a major uncontrolled variable in your comparison of 22 or 25 working better in different length barrels: you changed the cartridge when you built the long barreled gun. Going to a smaller bore on the same size case is pretty much the recipe for needing a slower powder to get better velocity.


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Not to argue , but , 7828 works best in my 257 and 270 wby's. Then the 7 rem mag likes RL 22 which is faster .

And everybody knows the " double radiused shoulder " is just an advertising gimmick - Right ? grin


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I'm getting the impression we're not on the same page.

I'm not saying that two different cartridges, even of similar capacity and performance potential, can't like different powders best.

What I am saying is that a particular cartridge, 7mm Rem. magnum for example, that finds RL22 to be a clear winner in a 26" barrel isn't going to suddenly like 4064 the best if you have that same barrel cut and crowned to 20" for some reason.

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Sorry , I might shoulda ' 'splained that I was addressing the second sentence in your post .The three cartridges I mentioned are the same case with three different bore sizes .

Your statement is true when dropping from .284 to .277 . Not true from .277 down to .257 . At least in my rifles .

And , the 300 and 338 ultras like the same powder . Granted , those cases ain't exactly the same .

This just proves that when anybody posts a " truism " , some bonehead will try and point out an exception . grin


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You still aren't getting my point.

Your post read as if when you went from 26" to 29" barrels was when RL25 took over because the slower powder did better in the longer barrel. As if you could lengthen the barrel on the 300 or 338 and then 25 would take over from 22.

My contention is it was more likely that you reached the tipping point of needing a slower powder when you went from 300/338 to 7mm on the same class case. In the 7mm on that case 25 would be faster in a 29" or 26" or 23" for that matter.

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"As far as I've been able to determine (and I'll say it yet again), the end of effective burning is signalled by the pressure peak."

Is ALL of the powder that is going to burn burned at the at the pressure peak?

The reason I ask, as the bullet accelerates down the barrel,the bore volume is increasing, resulting in a corresponding drop in pressure.

If the bullet is out running the pressure build up of powder continuing to burn, would not that also result in the pressure drop.

I remember reading that for the M1 Garand, a powder in the burning rate range of IMR 4895 is recommended over a slower powder such as IMR 4350. The reason given is that the pressure, with IMR 4350, at the gas port opening, is too high and can cause damage to the gas operated mechanism, where the pressure from the smaller amount and faster burning rate of IMR 4895 has dropped low enough to prevent damage to the operating rod.

This would indicate to me that a larger amount of slower burning powder remains at a higher pressure, even after the peak has been reached, for the entire length of the barrel.

The peak would not necessarily be higher or last for a longer interval, but the drop in pressure on down the barrel would not decrease as much.

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No, all it means is that the volume of gas is greater with the larger charge of IMR4350, which cause pressure to be higher down the barrel, all the way to the muzzle.


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Volume can't be more. The volume of the bore stays the same regardless of powder used, although the volume increases as the bullet moves down the barrel.

At, for example, 55,000 PSI, the compression of the gas in the barrel would be the same with either powder, but since the larger amount of 4350 produced more gas (and is possibly still producing) the pressure on down the barrel does not decrease as rapidly as the volume increases as the bullet moves forward, increasing the bore volume as it travels.

However, this theory comes apart if you consider that the peak pressure of 55,000 PSI for either 4895 or 4350 remains at 55,000 for the same interval.

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1234567, there are two factors raising the pressure at the gas port. First, there is simply more gas due to the larger charge. Second, in order to avoid excessive pressures early on, this gas has to be created later in the bullet's travel. Since the total volume behind the bullet at the gas port stays the same, this means the gases in the bigger (slower) charge didn't have as much expansion. Less expansion means less energy transfer to the bullet, leaving more energy in the gases. In short, more units of gases with each unit of gas retaining more energy.

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I've checked over numerous reports available at army lab web sites. Unfortunately, the older papers most likely to answer whether all the propellant is burned by the peak pressure point aren't (yet) available digitally.

Recent reports show the army is actively trying to improve the modeling of small arms ammunition. The biggest inaccuracies come from primer ignition and bullet engraving, and work is being done on both these fronts. One abstract suggested the army isn't entirely satisified with the performance of the 5.56 NATO and wants to get more fps out of it. Frontal ignition is being studied again.

In conjunction, the army is working on full 3-D modeling of the flows inside both guns and small arms.

Reports from the 1980s summarize what could already be done using their lumped parameter modeling. Work in this field is still quite active with the army labs. Such models are extensions of those summarized by Corner in the late 1940s. QuickLoad is such a model, but it uses a different burning model. In these older reports, cannons were calculated to have burned as little as 30% of their charge when peak pressure was reached, and signficant burning was calculated as the muzzle was approached. Sadly, no small arms examples were included.

I'll keep looking for a definitive answer. I remain convinced a fair portion of the charge in a rifle burns after peak pressure.

Karl

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I'll be very interested in what you find.

By the way, your answer on the Garand 4895/4350 is correct as I understand it. The max charge with a 150-grain bullet is around 50 grains with a 150, while it's about 60 grains with 4350. This means 20% more gas in the same bore volume, which means the slower powder maintains higher pressure further down the bore..


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MD , In your illustration , is the speed of the bullet as it exits the muzzle the same with either the fast or slow powder ?


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Learned a lot reading this thread, hope there's some more research coming from 2525.

"I remain convinced a fair portion of the charge in a rifle burns after peak pressure."

I think I agree, but the point is academic. It is moot practically, ie: if peak pressure is around 3", even if powder finishes burning at 6"....

Or are you saying powder could still be burning at 16" ?

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Man Oh Man!

How can you guys have 6 pages of this conversation without mentioning the new Hodgdon Superformance powders?!

The whole proposition that Superformance is based on is that powder doesn't completely burn in the barrel!

If you read nothing else, read the first paragraph of this document:
Superformance Technology


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How can you guys have 6 pages of this conversation without mentioning the new Hodgdon Superformance powders?!


Easy, it wasn't out when this thread started. I do have some Leverevolution powder on the way though. Hope to shoot in the next few weeks.

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Originally Posted by prm
Easy, it wasn't out when this thread started. I do have some Leverevolution powder on the way though. Hope to shoot in the next few weeks.


LOL! I didn't notice that! Boy, this was dredged up from the bottom of the pile! laugh


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