Powder burning question

[Ranger188]

I'll be working on a 22 creed in a couple weeks. I see most are using a "slower" powder (RL26, H4831)
I shot a 6.5 and 6 creed and always found RL16 or H4350 to be the perfect fit for those and with H4831
couldn't get the speed as with the others.
So why when using a lighter bullet in the 22 creed, 88g vs. 105-140 with probably less bearing surface is a slower powder
getting more speed than H4350? With everything else being equal. (barrel length, case capacity)
What am I missing?

 

[XLR308]

Your bore to case expansion ratio is what you are missing, they maybe the same parent case but by necking down to a smaller caliber you are changing the ratio and what burn rates of powder will be optimum.

 

[b6graham]

Your bore to case expansion ratio is what you are missing, they maybe the same parent case but by necking down to a smaller caliber you are changing the ratio and what burn rates of powder will be optimum.

yup

i just got my 22LRV from WTO. shooting same H4350 that i did in 6XC before hand and hitting the velocity limit with ease with 95 SMKs. If i had a shorter barrel or wanted to push speed above 3200 I'd drop to H4831sc, but it's unnecessary for me to switch

no reason you can't try H4350/RL16 before you go buy a jug of something slower

 

[Milo 2.5]

Your bore to case expansion ratio is what you are missing, they maybe the same parent case but by necking down to a smaller caliber you are changing the ratio and what burn rates of powder will be optimum.

^^^ This a good answer. Parent case using smaller exit hole, use slower powder. Heavier bullet, use a slower powder. If case fill is not important to you, your H4350 will work, just less powder used.
A lot has transpired in the loading world as people have moved away from using loading manuals as gospel and are experimenting. A lot of it may be heavy for caliber bullets though, who would have thought there'd be a 95gr 22 cal bullet.

 

[spife7980]

As the bullet moves down the barrel over time the volume behind the bullet containing the pressure increases, so the longer the time goes on the more volume you have. The larger the bullet the slower it is to accelerate which means that it takes more time to move a given distance and provide a certain volume for the gases. The smaller bore means that there is less volume per inch than a larger bore per inch of barrel. So those are the two variables you have to weigh against each other, bore size to bullet weight.

A 150 gr 30 cal will be a lighter for caliber bullet, in a smaller barrel a 90 gr 22 cal will be heavy for caliber bullet. So while yes, the 90 22 is is lighter than the 150 30, in proportion to the size of its bore it is a heavier bullet. Since it is heavier it is slower to accelerate which means that for a given amount of time (and length of barrel) it will provide less volume. If a powder burns fast for a heavy bullet that resists acceleration it can create more pressure sooner than the volume of barrel can accommodate. In order to provide enough volume for the amount of pressure created you need to slow down the amount of time it takes the powder to combust, spread it out over more length of barrel and coincidingly more volume . To do that you use a slower burning powder.

In your example, the h4350 is creating more pressure early before it can properly expand for best velocity, if you were to get to the ideal velocity you would be adding additional powder and going over pressure. Its powder burn rate is mismatched for the amount of volume in the chamber and created in the bore over time during ignition than the barrel can accommodate. The slower powder will spread that pressure out over time and end up with more acceleration over the entire length of the barrel rather than pressuring out prematurely.

You will notice that the slower a powder burns that the longer it stays in the barrel the longer it will be accelerated. So the longer the barrel the higher your end velocity, especially so in heavy for caliber situations.

Lighter weight bullets per caliber is just the inverse situation. They accelerate easily and so to fill the volume created sooner you need a faster burning powder.

 

[b6graham]

^^^ This a good answer. Parent case using smaller exit hole, use slower powder. Heavier bullet, use a slower powder. If case fill is not important to you, your H4350 will work, just less powder used.
A lot has transpired in the loading world as people have moved away from using loading manuals as gospel and are experimenting. A lot of it may be heavy for caliber bullets though, who would have thought there'd be a 95gr 22 cal bullet.

glad there is though. things are amazing so far

 

[Ranger188]

Thanks, it makes sense. Always knew the heavy for caliber bullets needed a little
slower powder, just didn't know about the bore ratio and combining the two together.
Learn something everyday.

 

[Steel head]

Good example to above explanations with IMR powders.
308 relatively fast powder like 8208xbr.
260 bit slower powder like IMR 4451.
243 fairly slow powder like 7828ssc.
Same basic case with three bores.

 

[Sheldon N]

An analogy I like to think of is moving a couch across a room. You wouldn’t want to punch it, you’d want a longer slower push. But a lightweight beach ball might better with a punch rather than a push.

Same with fast and slow powders and light/heavy projectiles.

 

[Deleted member 10043]

Use what is recommended, available, and accurate. Somebody else not posting here figured out the science on a different channel. Kind of like going to the library and reading a book on a topic of interest.