Home Forums Hunting & Shooting Ask The Gunwriters Powders for shorter barrels.

Forgive if this has been discussed ad nauseum, but, I would like something other than opinion on the subject of whether faster burn rate powders are better in short barrels. Our little groups gets into such discussions from time to time.

My personal experience has been that there is no need to use a faster powder in a short barrel. For example, I have two 243Wins, one with a 20" barrel, the other sporting a 26". My chronograph data suggests that the same powder (Reloder 19) gives the best velocities in both rifles when compared with some faster powders in the short barrel.

But, I am searching for the absolute Truth, a sign from the ballistic heavens. What is the gospel here and have I sinned?

I'm not a gunwriter but yor experience matches Mr. Sisk's when he did his test earlier.
You can probably look at his posts to see his findings.

In the meantime, I'd take a WA guess that there may be too many variables for anyone to make a blanket statement as to burning rates and bbl lengths. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />



In my own feeble experiences with my 20" barreled 8x57, wound up just using the same powder (IMR 4064), that works fine with that cartridge in the 24" bbls. Nothing faster worked as well, accuracy-wise.



Back when Sierra came out with their Single Shot Pistol bullets, had an urge to lop-off a 30-06 and try to build a handy short-barreled brush rifle that would still perform fairly well IF a longer task presented itself (primarily hunt deer in varied habitat and terrain). Then I did basically the same thing with an old M98 and the 125gr Hornady spire point and/or the 150gr Sierra spitzer. Works like a champ and is five for five on whitetails, including two at 100+yds in the open (with the Hornadys).



Oops, actually eight for eight, forgot about the three my son killed with it. <img src="/ubbthreads/images/graemlins/blush.gif" alt="" />

Hi Handloader,

I'm not a gunwriter, but I've got some evidence. My short barreled (~20") 308 performs
best with the same powders that work best in longer tubes. Also, my Hodgdon annual
manual shows 308 and 30-06 with 15" barrels in the pistol data section. In said data the
best performing powders are those that did well in the rifle data section.

Dave

Pressure in the case is what moves the bullet out the case. A case is designed to withstand only so much pressure. A certain length of barrel is required to burn the powder, not all is burned at the time of primer ignition. The bullet moves forward, contacts the lands and the pressure builds sufficently to start the bullet on it's journey. Bullet jump could enter into the equation, as in WBY, but we are still left with how much pressure is suitable for the system not how fast that pressure is made. With pistol cases, not short rifles, the case could not hold enough slow powder to build the pressure necessary to send the bullet at a reasonable velocity. If all we needed was a faster powder to use short barrels, our rifles wouldn't need the barrel length we commonly use to obtain our velocities. Barrel length allows the pressure to stay behind the bullet longer increasing the efficiency of the pressure created.

You use less of a faster burning powder to get the same pressure as more of a slower powder but you are dealing with the same amount of pressure. There is probably a barrel length where the faster burning powder might make a difference but it would be very short, think snub nose rifle.Rick.

The factors that determine the optimum "burning rate " (actually, the quickness) of the powder are all related to the specs of the cartridge as they are before the primer flash kicks the show onto the road � mainly, the net capacity of the case and the mass of the bullet. Less-than-optimum powders work after a fashion, but the optimum powders produce the highest velocities within the desired pressure limits with the case full (or nearly full) without having to be compressed.



The function of barrel length is to give the accelerating bullet the "run" space it needs to develop its eventual exit velocity. The "burning rate" of the powder is past history by this time.



Most charges of most powders (even the optimums) in most cartridges leave some kernels unburnt or incompletely burnt by the time the bullet exits the muzzle. The occurrence of unburnt or incompletely burnt kernels is not necessarily a matter of wasted powder. What count are the effects produced � the velocity and the pressure. Some of the best loads with available powders "waste" powder this way, if you insist that every kernel must burn completely.



There can be more than one "optimum" powder, because there are different categories of powder � single-base and double-base, to begin with. Also, the theoretically optimum powder for a given case and bullet may not exist � which may mean that more than one existing, available second-best powder may be the "best" as far as plain old country-boy practicality is concerned.

Handloader
I say the same as Mr Howell did, only I cant say it as well.... <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />......

But, I am searching for the absolute Truth, a sign from the ballistic heavens. What is the gospel here and have I sinned?

I am not one for blind faith, rather test it for myself and see....maybe we could do a test with an old take-off barrel and see........come down here with those other fellers and we'll try it and see... <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />
Charlie

Having played with 14" barreled contender hand-rifles, I concur that the correct burning rate powder for a given cartridge is irrelevant to barrel length.

Maybe this further note � looking at the matter from a slightly different angle � will make it a little clearer:

The desired quickness (popularly but erroneously called "burning rate," which technically is something entirely different) of powder for a given bullet in a given cartridge is determined by the bullet's resistance to movement � or, IOW, the containment it offers the burning powder.

Any given powder burns faster and more efficiently under tight containment, slower and less efficiently under looser containment. A heavier bullet in a given bore (or cartridge) resists movement more than a lighter bullet does, so it contains the powder better while the charge burns. The lighter bullet "flees" before the gas column more readily, so the powder behind it burns more slowly and less efficiently � which means that to burn efficiently, the powder must be quicker ("faster-burning," in loose popular terminology).

As the bullet moves forward, the space behind it increases � reducing or loosening the containment of the powder. A .458 bullet in a .45-70 increases the burn space faster than a .224 bullet does in a case of about the same net powder capacity, so the straight-walled .45-70 needs a quicker powder than the necked-down .22 center-fire needs for efficient burning.

In a given bore size, the mass or weight of the bullet determines how much the bullet resists movement � how fast its movement increases the burn space behind it. The less rapidly its movement reduces the containment of the powder, the more efficiently it allows a slower powder to burn efficiently. The faster its movement reduces the containment of the powder (by increasing the burn space), the more it calls for a quicker powder.

The slowest powder that will burn efficiently in a given bullet-and-cartridge combination is usually the best � it's less likely to build to its peak pressure too fast, more likely to produce the maximum ratio of velocity per grain.

All this is a matter of the bullet and cartridge, completely irrespective of the barrel length. Barrel length helps by giving the powder gas plenty of time to accelerate the bullet, of course, but it does not determine the desired quickness of the powder used in the charge.

Kudos to the patient and accessible Dr. Howell! Wrestling with some aspects and terminology of handloading is always made clearer when he responds and I know many on this list join me in saying "thanks!!".

Years ago I bought the Powley load and pressure calculators. These were made of durable cardboard and allowed someone to determine basic powder selection as well as the pressure and velocity such loads would likely yield. This was my basic introduction to terms like "expansion ratio", "ratio of charge to bullet weight", etc. After buying a chronograph, I began to appreciate just how accurate they were. The problem, today, is that the Powley system is based on IMR powders. I would like to see an update that incorporates other brands, but, perhaps, that is what some of the contemporary programs offer?