100% powder burn in barrel - Desirable?

[Deleted member 46119]

I searched and there was a little discussion on this.

My sort of educated guess is that 100% burn is preferred at somewhere around 95% of barrel length.

Do I have this concept understood or is there something I don't know?

 

[westcliffe01]

How would one measure this ? A high speed video and "quantify" muzzle flash ?

Typically if you need to run compressed loads AND the bore is black after each shot, the powder you are using might be a bit slow. It need not be a problem unless you let the rifle get too dirty. My 6.5x284 with H4350 seems to be sootier than anything else I have loaded, but good accuracy so far and I'm only part way through load development.

Too much snowmelt and slush to either shoot at the range or on the farm right now. I don't like icy mud baths....

 

[Deleted member 46119]

I ask from the 'educated' position that QuickLoad provides.

Some of my accurate loads are estimated to be %100 burn in barrel and some not.

The easier to develop loads were estimated closer to %100 percent burn.

Trying to get more data and discuss.

 

[kcebcj]

I searched and there was a little discussion on this.

My sort of educated guess is that 100% burn is preferred at somewhere around 95% of barrel length.

Do I have this concept understood or is there something I don't know?

I ask from the 'educated' position that QuickLoad provides.

Some of my accurate loads are estimated to be %100 burn in barrel and some not.

The easier to develop loads were estimated closer to %100 percent burn.

Trying to get more data and discuss.

I think your thinking is right on. I'm no expert but I try to get 100% burn in the barrel finishing just before the bullet leaves the barrel. That generally is not an easy task but is achievable depending on powder choice.

Quick Load gives an estimate and I have always gone by that. At the moment I'm working on a load for a 300 WM that is being built using IMR 7828 and 215gr Berger's. What I will probably work up to is 102% fill and 99.91% burn in a 27 inch barrel according to Quick Load and see what I have. If I bump the barrel to 28 inches it gets worse and the same if I drop back to a 26 inch....go figure. Things could change as I'm still knocking things around waiting for the barrel.

I also usually get the best results when the powder burns 100% within the barrel but also the fill needs to be close to 100% or slightly compressed. Just my armature take on it.

I see you are from the Central Coast...what part? I grew up in Arroyo Grande.

 

[Mikecr]

Three reasons to design for higher burn percentage:
1. It represents a pressure curve that is more consistent
2. Lower muzzle pressures means less slap to bullet bases, at various angles
3. Less powder adding to traveling bullet mass means less recoil

There is a lot more to this than simple barrel length.

 

[Greyfox]

I voted yes ,but only because a "no vote" might suggest it was undesirable. A complete powder burn has never been a priority in my load development. I agree with the benefits that have been stated in the prior posts but I wouldn't trade them off against my criteria of accuracy, low ES, and desired terminal ballistics(on target energy/retained velocity) I'm not sure I have always had a complete burn with my loads, but then again, I tend to follow established load recommendations. iMO.

 

[davkrat]

I see you are from the Central Coast...what part? I grew up in Arroyo Grande.

I was in Arroyo Grande 3 days ago. Had some clam chowder at the Splash Cafe in Pismo then an ice cream at Doc Burnstein's (used to be Burnardos). Growing up in NorCal and my grandparents living in SoCal we used to meet half way every year and celebrate Thanksgiving at Lopez Lake. Love that area of the state but it sure isn't anything like it used to be.

I don't have QuickLoad. Could someone tell me what the burn percentage would be for a .308 Win with a 20" vs 24" tube using 44.5 grains of Varget under a 150 or 168 grain bullet? Sooner or later I'm just going to chop the barrel down just want all the facts before I do. I'd hate to cut it and then be mad at myself for buying 8lbs. of Varget that might not be ideal for a 20" tube. Wondering if perhaps the lighter powder charges associated with a heavier bullet might be better suited for shorter tubes? In other words 42 grains under a 180 vs 45 under a 150 might have a better chance of full burn in the shorter tube.

Thanks

 

[kcebcj]

I was in Arroyo Grande 3 days ago. Had some clam chowder at the Splash Cafe in Pismo then an ice cream at Doc Burnstein's (used to be Burnardos). Growing up in NorCal and my grandparents living in SoCal we used to meet half way every year and celebrate Thanksgiving at Lopez Lake. Love that area of the state but it sure isn't anything like it used to be.

My apologies to the original poster for getting a little off course here.

I have family scattered along the coast from Santa Maria to Monterey. Left there in 1992 and now when I go to visit feel like a total stranger. It is certainly not the place I grew up in.

I don't have QuickLoad. Could someone tell me what the burn percentage would be for a .308 Win with a 20" vs 24" tube using 44.5 grains of Varget under a 150 or 168 grain bullet? Sooner or later I'm just going to chop the barrel down just want all the facts before I do. I'd hate to cut it and then be mad at myself for buying 8lbs. of Varget that might not be ideal for a 20" tube. Wondering if perhaps the lighter powder charges associated with a heavier bullet might be better suited for shorter tubes? In other words 42 grains under a 180 vs 45 under a 150 might have a better chance of full burn in the shorter tube.

Thanks

Just ran a couple quick comparisons in Quick Load for a 308 (SAAMI):


24 inch barrel
168gr Berger
44.5 Varget
Fill 105%...Burn 98.68%

20 inch barrel
Fill 105%...Burn 97.8%

24 inch barrel
185gr Berger
42gr Varget
Fill 103.5%....Burn 99.09%

20 inch barrel
Fill 103.5%...Burn 98.34%


This should give you an idea of what is going on.

 

[Deleted member 46119]

I voted yes ,but only because a "no vote" might suggest it was undesirable. A complete powder burn has never been a priority in my load development. I agree with the benefits that have been stated in the prior posts but I wouldn't trade them off against my criteria of accuracy, low ES, and desired terminal ballistics(on target energy/retained velocity) I'm not sure I have always had a complete burn with my loads, but then again, I tend to follow established load recommendations. iMO.

I would never trade %100 burn for accuracy. Accuracy is king.

 

[davkrat]

24 inch barrel
168gr Berger
44.5 Varget
Fill 105%...Burn 98.68%

20 inch barrel
Fill 105%...Burn 97.8%

24 inch barrel
185gr Berger
42gr Varget
Fill 103.5%....Burn 99.09%

20 inch barrel
Fill 103.5%...Burn 98.34%


This should give you an idea of what is going on.

Thanks you. That makes me feel much better. Was afraid I'd be dropping from 85% down to 70% or so. I think I can live with 97.8% and above!

 

[westcliffe01]

I'm curious:

What is the difference in pressure when the bullet reaches the muzzle between a 16", 20" and 26" 308 barrel running the 168gr bullet previously calculated ?

I have noticed a terrific muzzle blast on the 16" barrel carbines like the SCAR 17 or the short FAL rifles but don't have much experience with a 20" barrel. My 26" barrel is relatively mild by comparison...

Just ran a couple quick comparisons in Quick Load for a 308 (SAAMI):


24 inch barrel
168gr Berger
44.5 Varget
Fill 105%...Burn 98.68%

20 inch barrel
Fill 105%...Burn 97.8%

24 inch barrel
185gr Berger
42gr Varget
Fill 103.5%....Burn 99.09%

20 inch barrel
Fill 103.5%...Burn 98.34%


This should give you an idea of what is going on.

 

[kcebcj]

I'm curious:

What is the difference in pressure when the bullet reaches the muzzle between a 16", 20" and 26" 308 barrel running the 168gr bullet previously calculated ?

I have noticed a terrific muzzle blast on the 16" barrel carbines like the SCAR 17 or the short FAL rifles but don't have much experience with a 20" barrel. My 26" barrel is relatively mild by comparison...

westcliffe

308 (SAAMI)

168gr Berger Hunting VLD G7
44.5gr Varget

26 inch barrel
Pressure at the muzzle 7531psi
Vel 2763fps

20 inch barrel
Pressure at the muzzle 10,252psi
Vel 2622fps

16 inch barrel
Pressure at the muzzle 13,250psi
Vel 2490fps


Those short barrels blow your glasses off!

 

[Mikecr]

Those muzzle pressures are not 'good' for accuracy, or ES.

 

[westcliffe01]

That certainly explains why the short barrels are loud !