Powder burn rate question

[bobinpa]

This may sound dumb but........ When people say "that powder might be too fast for that cartridge" OR "that powder might be too slow for that cartridge" what do they mean and how do they know? I assume the powder might burn too fast causing undo pressure or too slow causing an incomplete and inefficient burn, but how do they know? Is it just experience?

 

[ShootDots]

Experience is a BIG teacher however, only in powders pretty close to the "ideal" burn rate for that particular cartridge.
The best way to answer many questions is with examples: Example#1: Varget is in the "middle burn rate" of a the "chart". However, if you tried to use it in a .221 Fireball with 40gr bullet it would be on the "slow-side".. Conversely, if you used Varget in a .260A.I. with 140 gr bullets, it would be on the "fast-side".. The burn rate has not changed, however, the USE of it determines whether it might be too fast or too slow. Example#2: If you took a .300 WSM shooting 230 gr Hybrids for F-Open, you could use H4350, a powder in the slow lane, BUT on the faster side of the slow lane. H4350 will work and may work well, however, you would be much better served with either H4831SC or something like VV N165. The H4350 might give you exceptional accuracy but you would build pressure before you reached the upper limits of velocity, where H4831SC or N165 could get you there, sans the pressure. Additionally, if you run "faster" powders for your application, premature barrel wear can and usually does set in. Example#3: Take a .260A.I. using 130 grain bullets. You could run H1000 and probably get some decent accuracy. However, H1000 is a VERY slow powder and you would be better served with H4350. You PROBABLY could not get enough H1000 in the case to bring the pressures up to a point where you would get the 3000 F.P.S. you would be looking for. So in this instance, H1000 is too slow. On the other hand, a .300 R.U.M. shooting 230 grain pills would be better served with RL-33 or Retumbo rather than H1000. The H1000 would most certainly work, however, it definitely would be on the fast side of the powders needed to make that cartridge work best, not just work.. I hope this helps..

 

[CJ6]

I like my cartridges to be 95-100+ (up in the neck) % full without undo compression. If I use a powder (N-133 eg.)that gives me 85% fill @ max pressure (I) feel it's too fast for that combo and look for one that's a bit slower in burn speed (4064 eg.) but it may fill the case TOO full (full to top of neck) and low pressure results and proper seating can't be accomplished so I end up with a powder in between those burn rates (8208 XBR) in this case maximizing pressure AND case fill.

 

[tenring]

I think the OP would benefit from just a very mundane explanation. IN GENERAL, large capacity cases pushing heavy bullets need slower burning powders to keep pressures within safe limits. Faster powders are for cases of lesser capacity, moving smaller bullets. This does not apply specifically to every cartridge, there are exceptions.

 

[Zero333]

Powder burn rate charts are everywhere, google it

Here is a relatively simple explanation of why you might want a slower or faster powder for certain applications.

I posted this explanation before so this time I just copied and pasted it here with the odd modification...

Blow air through a very thin straw and then through a very fat (say 3" in diameter) straw. You will never be able to create very much pressure inside your mouth when blowing through the extremely fat straw. But with the thin straw you can pop your eyes out with the pressure you create. Think of the cartridge case just like your mouth blowing air through a straw (straw being the case neck). If you try to blow really fast and hard through the thin straw you will pop your ears and eyes out, so you moderate the speed at which you create and release the air pressure in your mouth. Just as a slow burning powder does when trying to push all that gas through a small opening. Some cartridges use faster powder for lighter projectiles and slower powder for heavy projectiles for the same reason as stated above.

 

[ShootDots]

Powder burn rate charts are everywhere, google it

Here is a relatively simple explanation of why you might want a slower or faster powder for certain applications.

I posted this explanation before so this time I just copied and pasted it here with the odd modification...

Blow air through a very thin straw and then through a very fat (say 3" in diameter) straw. You will never be able to create very much pressure inside your mouth when blowing through the extremely fat straw. But with the thin straw you can pop your eyes out with the pressure you create. Think of the cartridge case just like your mouth blowing air through a straw (straw being the case neck). If you try to blow really fast and hard through the thin straw you will pop your ears and eyes out, so you moderate the speed at which you create and release the air pressure in your mouth. Just as a slow burning powder does when trying to push all that gas through a small opening. Some cartridges use faster powder for lighter projectiles and slower powder for heavy projectiles for the same reason as stated above.

What you are trying to explain, and did it adequately, is the concept of "the expansion ratio" of a cartridge. I never thought of it thru the straw idea>>>but it works... Good job!

 

[bobinpa]

Thanks guys. I understand the concepts explained above, but to help me understand better I'll give you an example:

In a 260 Running 123gr bullets I can use a max charge of 50 gr of H4831 or a max charge of 46.5 gr of H4350. Which one would you guys expect to give higher velocity and why?

 

[ShootDots]

Thanks guys. I understand the concepts explained above, but to help me understand better I'll give you an example:

In a 260 Running 123gr bullets I can use a max charge of 50 gr of H4831 or a max charge of 46.5 gr of H4350. Which one would you guys expect to give higher velocity and why?

If they are both listed as MAX charges with the 123's, then they should produce similar velocities>>>not the same of course, just similar.. Which one would be higher>>>that could depend on barrel length, what 123 bullet. The Scenar has a considerably longer bearing surface than the Sierra>>>so the possibility exists that H4831 might get you the higher velocity.

 

[CJ6]

On the 4831 is that max pressure or max FILL or Max fill AND max pressure?

 

[bobinpa]

On the 4831 is that max pressure or max FILL or Max fill AND max pressure?

On the 4831, that is max fill.

 

[CJ6]

Then use a faster powder. 4350 in your case. BUT there are other powders between the 2 you mentioned and if available to you it would be worth trying them..Hybrid 100 V, RL 17,N-550, RL 19 etc. can help tune the load further.

 

[savagedasher]

I like my cartridges to be 95-100+ (up in the neck) % full without undo compression. If I use a powder (N-133 eg.)that gives me 85% fill @ max pressure (I) feel it's too fast for that combo and look for one that's a bit slower in burn speed (4064 eg.) but it may fill the case TOO full (full to top of neck) and low pressure results and proper seating can't be accomplished so I end up with a powder in between those burn rates (8208 XBR) in this case maximizing pressure AND case fill.

I like loading any case 95 percent plus full and pick a powder off of QL that gives me that.
But a burn rate needs to be 98 plus percent in the barrel .
Short barrels some time are hard to find a powder to give a 98 percent burn and 95 percent fill. Larry

 

[CJ6]

I like loading any case 95 percent plus full and pick a powder off of QL that gives me that.
But a burn rate needs to be 98 plus percent in the barrel .
Short barrels some time are hard to find a powder to give a 98 percent burn and 95 percent fill. Larry

And I think that this is where cartridge choice comes into play. Take the 260 vs 6.5x47 L. when looking at usable case capacity (in standard magazines)/powder burn rates used for each, barrel lengths needed IMHO the 6.5 L wins. when using longer than standard mags and longer barrels then the 260 wins.

 

[savagedasher]

And I think that this is where cartridge choice comes into play. Take the 260 vs 6.5x47 L. when looking at usable case capacity (in standard magazines)/powder burn rates used for each, barrel lengths needed IMHO the 6.5 L wins. when using longer than standard mags and longer barrels then the 260 wins.

I didn't say anything about what wins
But I was referring to any case fill ratio is one thing. Burn rate of powder is how fast a powder burns.
QL gives a reference of both.
Yes mabey a 6.5 -47 L could be a better choice but that can change with bullet weight and barrel length. Larry

 

[Geno C]

H4350 would give to a higher velocity in your example. Rl17 or even varget would be a better choice. I keep my powder stored in order of burn rate. If the powder I want to use is filling the case completely but I'm not able to max out on pressure or get the velocity I'm after, then I go one or two steps faster and that usually does the trick.

 

[BoydAllen]

In general, full cases produce more consistent velocities, and shooters would like to have all of the velocity that they can get that is consistent with safe pressure and good accuracy, therefore a powder that produces maximum safe pressure and fills the case is ideal. If a slower powder is used, it is likely that a full case will not produce as high of a velocity, and if a faster powder is used, the case will not be full, causing variations in velocity that become important at longer ranges. Additionally, a safe pressure limit may be reached at a lower velocity than an ideal powder would produce. These are just general considerations, they will not always identify the most accurate powder, particularly when testing is done at relatively short ranges.

 

[CaptainMal]

Getting good answers.

I look at it as pushing a bowling ball and a soccer ball. One is obviously heavier/massive, more than the other. One you can slap or punch and it goes. The other you could try that if you don't mind a smashed hand. You have to push that bowling ball slowly to get it started and then more and more and...

Look at the mass of the projectile. Look at how much time (barrel length) you have to do the pushing. Find the happy medium and don't "hurt your hand".

 

[CJ6]

I didn't say anything about what wins
But I was referring to any case fill ratio is one thing. Burn rate of powder is how fast a powder burns.
QL gives a reference of both.
Yes maybe a 6.5 -47 L could be a better choice but that can change with bullet weight and barrel length. Larry

"Wins" was a bad choice of words there, "Fits" better maybe. And I think we're saying the same thing here....It's Fill ratio,Burn rates, Bullet weights,Case size and Barrel lengths that ALL go together to make things work.

 

[savagedasher]

"Wins" was a bad choice of words there, "Fits" better maybe. And I think we're saying the same thing here....It's Fill ratio,Burn rates, Bullet weights,Case size and Barrel lengths that ALL go together to make things work.

You nailed it .

 

[Brians356]

FWIW Hodgdon published data (24-in barrel, MAX for 125-gr bullet - close enough to 123 for the purpose):

H4831: 48.0C 2862 fps
H4350: 44.3 2867 fps

Are you sure you can crunch 50 gr of H4831 under that bullet? And would you want to?
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