Burn Percentage

[waldo1979]

im working a load with a .308WIN 116gr custom bullets (reserving the manufactures name for the time being). I don't have much data on the bullet so I'm going by best guess and the manufacture recommendation of 48gr of Varget @2.8" COAL. The closest match I can find is a 125gr or 110gr Berger, or maybe a Hornady Vmax 110gr.

Anyway, no matter how I look at it my burn percentage with Varget is going to be below 90%. I've never had such a low burn percentage before so im not sure what that means? Im guessing more carbon build up in the bore.

The best match powder for what I have on hand is VV N135 or maybe Benchmark. Both have a good burn percentage but the Benchmark pressure numbers are a little higher than I would like. I have 5 more matches in my season and I don't think I have enough N135 so it's looking like I'm going to be using Varget.

 

[LHSmith]

Define "Burn Percentage"?

 

[dcali]

Burn percentage means the amount of the powder that gets burned before the bullet leaves the muzzle. A low percentage means you'll be spitting fire and smoke out of the barrel in the form of still burning powder. Conventional wisdom says this is not a good thing - it's inefficient and possibly less consistent - you want something close to 100%.

I'm assuming you're using QuickLoad. I haven't found that their numbers are perfect on this. I had a 6XC that I got horrible smoking and was obviously not burning all the powder with a load that QuickLoad insisted had a 100% burn. It also shot poorly, for what it's worth.

Given the low bullet weight for the cartridge, it's not super surprising that Varget isn't the best answer. All you can do is live with it or try something else.

 

[Dusty Stevens]

That tells me youre using the wrong powder. That is a very slow powder for that light of a bullet

 

[Webster]

im working a load with a .308WIN 116gr custom bullets (reserving the manufactures name for the time being). I don't have much data on the bullet so I'm going by best guess and the manufacture recommendation of 48gr of Varget @2.8" COAL. The closest match I can find is a 125gr or 110gr Berger, or maybe a Hornady Vmax 110gr.

Anyway, no matter how I look at it my burn percentage with Varget is going to be below 90%. I've never had such a low burn percentage before so im not sure what that means? Im guessing more carbon build up in the bore.

The best match powder for what I have on hand is VV N135 or maybe Benchmark. Both have a good burn percentage but the Benchmark pressure numbers are a little higher than I would like. I have 5 more matches in my season and I don't think I have enough N135 so it's looking like I'm going to be using Varget.

Does 48 gr of Varget reach near the bottom of the neck. 90% fill doesn't sound like a realistic number. Varget is a bulky powder I would expect low fill with the fine grain powders.

Check this out for powders people are using.
http://www.6mmbr.com/308Win.html

A 308 case body is 1.556" long. .9 x 1.556 = .16". 90% fill would be .16" below the neck.

In the Berger Reloading Manual it gives:
110 gr & 115 gr no Varget data
125 gr. bullet. 49 grains Varget = 101% fill
135 gr. bulet = 47.2 gr Varget = 101% fill
How can 47.2 and 49.0 both be 101% ? The bullets are too short to interfere with fill.

VIHT N130 44.0 gr max 99% fill Doesn't list N135
110 & 115 gr bullet doesn't list N135.
125 Gr bullet VIHT N135 48.8 gr max. 105% fill
135 gr bullet VIHT N135 46.5 max 105% fill

Where did you get the less than 90% fill from?
If it shoots good don't worry about the % fill.

The recommended twist for light 30 cal bullets is 19. A factory barrel is probably 14 for 150 gr bullets.

HAVE SOME GOOD SHOOTING

 

[dedogs]

90% fill doesn't sound like a realistic number.

Webster, If you read the OP's question carefully you will see that his info infers a 90% BURN RATE not a 90% fill ratio. dedogs

 

[waldo1979]

Does 48 gr of Varget reach near the bottom of the neck. 90% fill doesn't sound like a realistic number. Varget is a bulky powder I would expect low fill with the fine grain powders.
...

Where did you get the less than 90% fill from?
...
HAVE SOME GOOD SHOOTING

I'm using Quickload and the Berger/Hornady/Sierra data. The 125gr Berger is pretty close but i think the B.C. on the bullet i'm using is a little better.

48.0gr ended up shooting at 3090fps with really low StdDev numbers. But overall i couldn't get them to shoot better than a 0.45" using Varget. I'm pretty sure the accuracy mode is around 47.8gr but i need to do more testing.

I am still fire forming my Lapua brass however they should be really close already. I ended up using a Lyman "M" die which i really like (although i crushed a couple brass).

Likely i'll be trying NN V135 next or maybe Benchmark. FYI, if you're looking at the Berger Manual M322 is really close in burn rate to Benchmark.

 

[Webster]

Where do you get % burn numbers from?

 

[357Mag]

Waldo -

Howdy !


A quote from ballistician Homer Powley's "Powley Papers ", as was printed in " Guns & Ammo 1974 Annual ".

" With normal loads only about 99 per cent of the powder burns inside the gun and the rest goes out the muzzle in the form of splinters; you can tell when you find them. All of the powder that is going to burn has done so at the place of peak pressure which is only a few inches in front of the chamber. "


With regards,
357Mag

 

[Webster]

Webster, If you read the OP's question carefully you will see that his info infers a 90% BURN RATE not a 90% fill ratio. dedogs

Sorry I must be getting senile.
In the Berger Reloading manual it list 13 powders for the 125 gr bullet. Only 4 give higher velocity than Varget. Isn't this an indication of efficiency?

 

[Nvreloader]

Waldo 1979

There are several items and functions that controls the burn rate, it is a combo of all these functions,
Case capacity,
Bullet weight,
Powder,
Bore size,
AND the biggest factor is your Barrel length.

Tia,
Don

 

[Nvreloader]

Webster,
QL give you the approximate burn rate of the load spec's you feed it.

Tia,
Don

Where do you get % burn numbers from?

 

[waldo1979]

Waldo 1979

There are several items and functions that controls the burn rate, it is a combo of all these functions,
Case capacity,
Bullet weight,
Powder,
Bore size,
AND the biggest factor is your Barrel length.

Tia,
Don

Yea I think the load I was given would be good for a longer barrel.

 

[Webster]

Yea I think the load I was given would be good for a longer barrel.

Can you explain how barrel length affects burn rate. If 99% of the powder is burned in a 22" barrel are you saying that a 24" barrel has a different burn rate. Doesn't make sense to me. Everything is the same for the first 22"?

 

[Nvreloader]

Webster
Using the load spec's that Waldo posted,
308= 116gr bullet, 48.0 Grs Varget, he does not give the bbl length??

QL gives the following info for Burn rate,
10" bbl length= 79.65%,
20" bbl length= 90.35%,
30" bbl length= 94.15%

The only spec that was changed was the bbl length.

Tia,
Don

Can you explain how barrel length affects burn rate. If 99% of the powder is burned in a 22" barrel are you saying that a 24" barrel has a different burn rate. Doesn't make sense to me. Everything is the same for the first 22"?

 

[Ned Ludd]

Not knowing much in the way of specifics about your setup, I played around with Quickload a bit using the 115 gr Berger from the pull down menu with some other generic inputs. Varget is simply a poor choice for the bullet you're using...there's no way around it. H4895 would be better, but still not where you want to be with that bullet. I would suggest H322 over Benchmark. H322 is an outstanding powder, very small grained like Benchmark, with low sensitivity to temperature, but I suspect you'll get much better velocity than with Benchmark. Its burn rate ought to be right in the range you need. In the crude predictions I ran, ~43.0 gr of H322 was predicted to give approximately the same pressure as your 48.0 gr Varget load, but would be about 50 fps faster. At ~91%, the fill ratio would be a little on the low side, but not too bad, and the burn percentage would be close to 99%.

 

[Webster]

Not knowing much in the way of specifics about your setup, I played around with Quickload a bit using the 115 gr Berger from the pull down menu with some other generic inputs. Varget is simply a poor choice for the bullet you're using...there's no way around it. H4895 would be better, but still not where you want to be with that bullet. I would suggest H322 over Benchmark. H322 is an outstanding powder, very small grained like Benchmark, with low sensitivity to temperature, but I suspect you'll get much better velocity than with Benchmark. Its burn rate ought to be right in the range you need. In the crude predictions I ran, ~43.0 gr of H322 was predicted to give approximately the same pressure as your 48.0 gr Varget load, but would be about 50 fps faster. At ~91%, the fill ratio would be a little on the low side, but not too bad, and the burn percentage would be close to 99%.

The powders that give the best velocity may not give the best % burn. The only criteria is accuracy. Why would you care what the burn % is if you get the accuracy and fps you want. Is there a correlation between % burn and accuracy, I doubt it. Do you really think the record holders even know what the % burn is in their loads? They know from experience and what others are using and burn rate charts how to pick powders. I understand that you need to operate within a certain burn rate of powders but the range can be wide. I wonder how accurate QL is at some of their calculations? 90% is is a pretty small number for burn. I would like to see the OP shoot at a piece of paper at about 5 feet and see if there are powder holes.

 

[Ned Ludd]

To start with, it's precision, not accuracy. Leaving 10% or more of your powder unburned is pretty ridiculous, no matter how good the precision. It means the load is grossly sub-optimal and will go hand in hand with other undesirable issues. Most people are going to find the best loads somewhere slightly below max pressure, where fill ratios, burn rates, and just about any other parameter you care to mention that is associated with combustion have been optimized.

That specifically means choosing the right powder for a specific barrel, bullet, and cartridge combination. Varget is a poor choice for the OPs bullet, it's that simple. On the other hand, H322 has been a winning BR powder for a very long time. It's capable of ridiculous precision in the hands of the right reloader, and IMO would be just about perfectly suited to the bullet the OP is using. The OP is certainly welcome to keep trying to shove a square peg in a round hole (i.e. use Varget), but he'd be well advised to use a powder better suited to what he's trying to accomplish, regardless of whether it's H322, Benchmark, or something else.

 

[waldo1979]

To start with, it's precision, not accuracy. Leaving 10% or more of your powder unburned is pretty ridiculous, no matter how good the precision. It means the load is grossly sub-optimal and will go hand in hand with other undesirable issues. Most people are going to find the best loads somewhere slightly below max pressure, where fill ratios, burn rates, and just about any other parameter you care to mention that is associated with combustion have been optimized.

That specifically means choosing the right powder for a specific barrel, bullet, and cartridge combination. Varget is a poor choice for the OPs bullet, it's that simple. On the other hand, H322 has been a winning BR powder for a very long time. It's capable of ridiculous precision in the hands of the right reloader, and IMO would be just about perfectly suited to the bullet the OP is using. The OP is certainly welcome to keep trying to shove a square peg in a round hole (i.e. use Varget), but he'd be well advised to use a powder better suited to what he's trying to accomplish, regardless of whether it's H322, Benchmark, or something else.

That's what i suspected. That 48.0 gr Varget recommendation would probably work for a much longer barrel. BTW, i was only able to get an average 0.6" group in my load testing. Best was 0.45" and worst was 1.06".

I'm going to step down to a N135 which has a burn percentage around 98% and good pressure numbers.

 

[Nvreloader]

Waldo1979

What is your bbl length?

This info will help in getting headed towards the best powder possible.

Tia,
Don

That's what i suspected. That 48.0 gr Varget recommendation would probably work for a much longer barrel. BTW, i was only able to get an average 0.6" group in my load testing. Best was 0.45" and worst was 1.06".

I'm going to step down to a N135 which has a burn percentage around 98% and good pressure numbers.