Thread: Projectile vs barrel length

Those velocitys seem to ring true. I get 2790 fps with my 123 A-Max out of a 20" with DPT can.

Originally Posted by chainsaw

your observation of grey deposit at crown - are you running a suppressor or brake by any chance ?
either one, but especially suppressor, can cause excessive carbon build up, most easily detected at the crown or muzzle but the gunk will be thru out the barrel. Your cleaning regime needs to take this into account. From my experience I would not expect a lot of difference between ADI powders like 2208 & 2209 in carbon build up, but could be better/worse if you changed brand of powders.

No brake or suppressor used. It took quite a lot of effort to get the barrel clean again. Thanks for the reply

Originally Posted by PERRISCICABA

Maybe a good read regards barrel length and velocities.

6.5 Creedmoor- Effect of Barrel Length on Velocity: Cutting up a Creedmoor! | Rifleshooter.com

Yes i read that a few times prior to load development (bloody good read) but didn't really highlight the issue I've experienced. Thanks for the on going help!

Originally Posted by sneeze

Considering only velocity, the best powder burn rate is governed by the projectile and the chamber not barrel length. The "faster powder for shorter barrels" is mostly myth.
There may be other advantages in reduced muzzel pressure etc with a quicker burn rate though.

I disagree. It absolutely 100% is NO myth. The end user explosion when you pull the trigger is not the burn rate. That rate is a constant (it is a quantified number in quickload). Have a play with various combinations using that program and you'll see its no joke. If i try a huge charge of slow burning magnum powder down a short barrel with a light projectile, quickload will show you the pressure curve, and tell you that the projectile left the muzzle before the propellant had finished burning in your specified barrel length.
My old powder that matched the std barrel (2209 for a 24" barrel) would not be the best for my new 29" barrel for instance. I'm using 2213sc as it produces a safer pressure curve which can actually go higher than 2209. Choosing the projectile is the last thing I do. (But that's just me)

Also, when I reccomended 2209, that was an abbreviated reply as I'd run just about every combination for you in QL using all the better projectiles and powders. Same goes for the pill.

Originally Posted by Dead is better

I disagree. It absolutely 100% is NO myth. The end user explosion when you pull the trigger is not the burn rate. That rate is a constant (it is a quantified number in quickload). Have a play with various combinations using that program and you'll see its no joke. If i try a huge charge of slow burning magnum powder down a short barrel with a light projectile, quickload will show you the pressure curve, and tell you that the projectile left the muzzle before the propellant had finished burning in your specified barrel length.
My old powder that matched the std barrel (2209 for a 24" barrel) would not be the best for my new 29" barrel for instance. I'm using 2213sc as it produces a safer pressure curve which can actually go higher than 2209. Choosing the projectile is the last thing I do. (But that's just me)

Iv got an ok understanding of burn rate and Iv had QL for quite a few years. My reference to reduced muzzle pressure with a faster burn rate was an example of why a faster burn rate might be desirable over best velocity. Probably not that relevant .

If I understand it correctly? you are saying that 2209 will give better velocity in your 24" than barrel than 2213 because it has a higher percentage of propellant burnt?

So, I will try to explain in a different way, all the figure I will put here is fictional to a 308 caliber and you just "transfer your imagination to other calibers.

Imagine a drag race track, it is what I will call "the barrel", then you have the cars and I will call it "projectiles" and now you have the engine that I wil call "the powder".

You have a race track as long 260 meters(26" barrel) and a light little car (120grains projectile), you will load it with a "fast explosive engine) that will push this little car very fast thruout the 260 meters race track, why? Because it is a light car and the extreme velocity will take a short time to "burn" and take it all the way to the destination and still have enough "horse power" to take it further if necessary. The "down turn" of it is the track is too long so the explosive start and will only last and be effective for the first 200-220 meters (20-22") of the track but hold the speed further than that.

Then, you have the same track with a heavier car (190 grains) and need a more powerful engine to push it for the length of the hole track, so you get an engine (powder) with slower start but it will "push" the car with extreme power for a longer distance optimising the length of the track and the weight of the car.

Moral of the story: if you use the fast powder in a long barrel it will "work" for Just a percentage of the barrel, if you use a slower powder it will work for the hole length of a long. Artel but it won't be effective for a shorter barrel because, as the bullet already exit the muzzle the powder will still be burning the excess.

I will clarify my idea when I get home if necessary.

Cheers

Mac

But thats not how internal ballistics perform and the "engine driving the car to the end of the track" is the myth. With even the slowest powder the effect the burn has on the projectile is dropping rapidly after just a few inches of projectile travel down the barrel. The push the projectile has received has it accelerating to the end of the barrel but the rate of acceleration is decreasing.
The best velocity will come from the flattest pressure curve which will be from the slowest burning powder that is suitable for the particular bullet weight, irrespective of barrel length. Any powder still burning after the first few inches of projectile travel will not be enough to effect the rapidly dropping chamber pressure and have no real influence on muzzle velocity. Think of it as if the chamber was a balloon, the powder ignites and inflates the balloon which sends the projectile accelerating down the barrel. A fast powder will inflate the the balloon to its maximum( say 60.000 psi) but the burn is done and dusted so the balloon deflates rapidly. A slower powder will inflate the balloon to max but keep burning and hold the balloon at max pressure for a little longer and exposing the projectile to max presure for longer giving better acceleration
The key here is all of this takes place in the first part of the projectiles journey down the barrel so by the time its traveled a few inches its rates of acceleration are fixed.

It does drop but it's still there, adding velocity right till the last mm.
I agree that bullet weight / type is just as important and deffinately effects the pressure generated. He'll, I was surprised to see the 140 bergers have a higher mv than the 140 Amax. Still don't quite know why as the seating / powder etc was all the same.

Say you're right. Does this mean short barrel guys should start using magnum powders because they have flatter pressure curves?

Originally Posted by sneeze

But thats not how internal ballistics perform and the "engine driving the car to the end of the track" is the myth. With even the slowest powder the effect the burn has on the projectile is dropping rapidly after just a few inches of projectile travel down the barrel. The push the projectile has received has it accelerating to the end of the barrel but the rate of acceleration is decreasing.
The best velocity will come from the flattest pressure curve which will be from the slowest burning powder that is suitable for the particular bullet weight, irrespective of barrel length. Any powder still burning after the first few inches of projectile travel will not be enough to effect the rapidly dropping chamber pressure and have no real influence on muzzle velocity. Think of it as if the chamber was a balloon, the powder ignites and inflates the balloon which sends the projectile accelerating down the barrel. A fast powder will inflate the the balloon to its maximum( say 60.000 psi) but the burn is done and dusted so the balloon deflates rapidly. A slower powder will inflate the balloon to max but keep burning and hold the balloon at max pressure for a little longer and exposing the projectile to max presure for longer giving better acceleration
The key here is all of this takes place in the first part of the projectiles journey down the barrel so by the time its traveled a few inches its rates of acceleration are fixed.

Agree with you 95%, what you can help me to understand now is, in the case of those people shooting thruout short barrels why or when a slower powder "help" keep the pressure curve till the end of the barrel if the total length is not optimised to the for it?
I do acknowledge all the things "we" are talking here and "I" personally don't have a QL software to check all the possible data and variations the combinations will give "us". I am learning more and more here.

Cheers

Mac

Originally Posted by Dead is better

It does drop but it's still there, adding velocity right till the last mm.

Yes some pressure is available till exit which is why longer barrels give higher velocity but the amount of pressure available is determined early in the process. As the projectile travels down the barrel the internal volume available grows substantially and quickly becomes to great for any still burning powder to have any affect.

Originally Posted by Dead is better

Say you're right. Does this mean short barrel guys should start using magnum powders because they have flatter pressure curves?

It depends on the chamber and projectile. In simple terms for example if 2217 gives the best velocity for a particular 338 300gr combination in a 28 inch barrel it will give the best velocity in a 22 inch. There is no free lunch, you cant chop a barrel , throw in a faster powder and get velocity back without running higher peak pressure or dropping bullet weight. Be nice though eh, I could have a 15 in 7mm remag pushing162 amax with BM2

Originally Posted by PERRISCICABA

Agree with you 95%, what you can help me to understand now is, in the case of those people shooting thruout short barrels why or when a slower powder "help" keep the pressure curve till the end of the barrel if the total length is not optimised to the for it?
I do acknowledge all the things "we" are talking here and "I" personally don't have a QL software to check all the possible data and variations the combinations will give "us". I am learning more and more here.

Cheers

Mac

A slower powder will generally give a flatter curve and therefor more area under curve( it will provide peak pressure for a longer time) proving more initial push for want of a better term, better acceleration. How far away the muzzle is has no affect on how fast or hard the bullet can accelerate. You do have to be able to fit enough in the case though which is why we cant just use US 869 for everything, it has to match the chamber and projectile.

.308 Win Barrel Cut-Down Test: Velocity vs. Barrel Length « Daily Bulletin
If what you're saying was true, the above experiment would not have documented a 261fts drop in mv when they sawed off the barrel from 28" all the way down to 16". They average was a loss of 22.5fts loss per inch
So, the powder ain't burning past 3 or 4 inches but that really is semantics. The bullet is still accelerating all the way up so a shorter barrel does leak a crap load of wasted 'expanding gas' shall we call it.
Your post did make me go looking and a lot of guys find unburnt powder but that's due to the oxygen being depleted apparently and nothing to do with barrel length

The propelant creates its own oxygen as it burns.

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Originally Posted by Dead is better

.308 Win Barrel Cut-Down Test: Velocity vs. Barrel Length « Daily Bulletin
If what you're saying was true, the above experiment would not have documented a 261fts drop in mv when they sawed off the barrel from 28" all the way down to 16". They average was a loss of 22.5fts loss per inch
So, the powder ain't burning past 3 or 4 inches but that really is semantics. The bullet is still accelerating all the way up so a shorter barrel does leak a crap load of wasted 'expanding gas' shall we call it.
Your post did make me go looking and a lot of guys find unburnt powder but that's due to the oxygen being depleted apparently and nothing to do with barrel length

Yes if you chop a barrel you loose velocity. Iv said that already. Yes you may not be burning all of the powder because of the shorter barrel and there could well be some kernels that didn't ignite and yes there will be more gas wasted as you put it, (more muzzle blast). They are all symptoms of a shorter barrel.
None of which changes the fact that you can not win back velocity by switching to a faster burn rate. .

You have QL, while its not prefect it normally gives a good indication

6.5 creedmoore 140gr amax.

2213 46.88gr for 60184psi. in a 28inch barrell propelant burnt =98.27% for vel of 2958fps.
drop it to a 20 in barrel and we get propelant burnt =95.85% for vel of 2738.
Load and chamber pressure remain the same

If I use 2209 (slightly faster) 44.74gr for 60211 psi
20 inch barrell propellant burnt =97.39% for vel of 2713fps


So with 2209 in a 20 inch we have a higher percentage of propellant burnt slightly higher chamber pressure but LESS velocity.