My reloading book uses a 26" barrel when generating the data for the 7mm-08. My model 7 7mm-08 has a 20" barrel.

Does this mean that my gun will be more more efficient with a faster powder? I have read though that the powder is usually fully combusted within an inch or so of the chamber...then what about muzzle flash?

I have also read that slower powders are louder and have more blast..is this true?

My reloading and powder experience is very limited, only IMR4350 for a 30-06 and H380 for a .22-250

A bit open ended but please share your thoughts, especially if you have experince with this gun and caliber.

Thanks!

Use the book data and powders. You will realize slightly less velocity because the bullet will have a bit less time to accelerate in a shorter barrel, and you will have a bit more blast because the gas will be at a higher pressure at bullet exit, but the best powder for a long barrel will almost always be the best powder for a shorter barrel, also.

It's a myth that shorter barrels require faster powders in a given cartridge. Faster powders will reach their pressure peak faster, but also subside faster, giving less overall bullet acceleration than a powder that delivers a smooth, long pressure curve.

It's also a myth that muzzle flash is caused by powder that is still burning (or that re-ignites) after bullet exit. Muzzle flash is caused by the spontaneous ignition of unburnt flammable gases that are released by the previous combustion of the powder. There isn't enough oxygen released by the powder to burn all the fuel that is also released. The excess fuel gas ignites when it mixes with oxygen in the air.

Not all the powder always burns in the barrel, due to a variety of factors; but what doesn't burn is either ejected unburnt or left behind. It almost never burns afterwards.

That is all a bit oversimplified, but the basics are true: The best powder for a cartridge is independent of barrel length (within reason); and, muzzle blast/flash is not related to unburnt powder kernels.

Use the book data and powders. You will realize slightly less velocity because the bullet will have a bit less time to accelerate in a shorter barrel, and you will have a bit more blast because the gas will be at a higher pressure at bullet exit, but the best powder for a long barrel will almost always be the best powder for a shorter barrel, also.

It's a myth that shorter barrels require faster powders in a given cartridge. Faster powders will reach their pressure peak faster, but also subside faster, giving less overall bullet acceleration than a powder that delivers a smooth, long pressure curve.

It's also a myth that muzzle flash is caused by powder that is still burning (or that re-ignites) after bullet exit. Muzzle flash is caused by the spontaneous ignition of unburnt flammable gases that are released by the previous combustion of the powder. There isn't enough oxygen released by the powder to burn all the fuel that is also released. The excess fuel gas ignites when it mixes with oxygen in the air.

Not all the powder always burns in the barrel, due to a variety of factors; but what doesn't burn is either ejected unburnt or left behind. It almost never burns afterwards.

That is all a bit oversimplified, but the basics are true: The best powder for a cartridge is independent of barrel length (within reason); and, muzzle blast/flash is not related to unburnt powder kernels.

Hrm. Didn't know this. Thanks Rocky.

There can be better powders if there's a really major difference in barrel length, I've found. Like, a 4" barrel vs a 16" barrel. I've had a .40 S&W load that was, in a carbine and at a max load, slower than the expected velocity of the minimum load. I believe we tested it in a Glock 22 as well and it was running at about expected velocity.

Rocky covered the technical side pretty well. Efficiency? A sharp stick uses less powder, think about it..... we are in the field to get an animal, efficiency be darned.

All centerfire rifles are loud enough to damage your hearing. Yes the shorter barrel will be a tad louder, but the difference isn't going to protect your hearing. Use hearing protection when you can.

KO's example is why I qualified my "best powder for a cartridge is independent of barrel length" summary statement with the words "within reason." A 400% change in barrel length rather changes the equation, no question about it. But in MOST situations, the statement holds.

Thanks..

Now a question about bullet preference. Will a 139 gr Hornady Interbond give me the needed expansion from this gun or should I stick to standard cup and core due to the lower velocity? Rig is meant for mixed terrain whitetails at 250yds or less.

Ko,

The key is Rocky's parenthetical "within reason". I have a reference to a 1954 publication in which rifle ammunition fired in a very short barrel was shown to bulge the bullet base, ruining accuracy. In other words, peak pressure is so great the muzzle blast can actually deform a bullet base if it runs out of barrel near that peak.


Grapenuts,

To answer your original question a little more completely, no, the powder does not all burn in that first few inches. Peak pressure is reached then, however. That is due to pretty much all of the powder having started burning and being actively contributing gas to the pressure at that distance. Many powders that are slow enough will still have a few percent trying to finish burning when the bullet exits.

Going to a faster powder accomplishes several things. You will increase ballistic efficiency, the percent of the energy stored in the powder that is converted to kinetic energy in the bullet. In connection with that, you can't put as much stored powder energy into a case with a fast powder because it would create too great a peak pressure, so you generally end up using less powder by weight and save money. You reduce the pressure at the muzzle, which has several benefits: it reduces muzzle blast, it reduces recoil, and it reduces the amount of blast-propelling on the base of the bullet that can exaggerate errors due to bullet base or muzzle asymmetry and any bullet out-of-balance condition.

The muzzle blast effects take some further explaining. The effect on accuracy happens because muzzle and bullet base symmetry ensure the blast acts uniformly on the bullet base as it exits. Without those, the blast will start to escape from one side of the bullet base before the other and the bullet will be slightly tipped by that, which the bullet has to recover from in flight. Additionally, if the bullet mass is at all eccentric, after leaving the muzzle, instead of continuing along a trajectory in line with the bore axis, it will start to spin about its center of mass instead. The shift from spinning on the bore axis to spinning around the center of mass is called bullet jump. That is because the bullet moves over slightly to find that new rotation axis. During and after the jump, the bullet is no longer quite centered over the muzzle blast, and so, again, it can be slightly blown off course or tipped by the asymmetrically applied pressure. It's one of those things that wouldn't matter if every bullet had same error and started out oriented so they jumped the same amount and in the same direction every time, but that isn't how it works.

The recoil difference is due to two things. Half or more of the powder gets blown down the tube with the bullet, plus the evolving gas has no less mass than the powder generating it (mass can neither be created or destroyed except in nuclear reactions), so the more powder you put in the case, the more recoil you have from accelerating its mass down the tube. The more significant effect, though, is rocket effect. That is the rearward propulsion of the gun due to the rapid acceleration of the mass of the gas in the barrel once the bullet exits. So this is a push that occurs after the bullet is clear of the muzzle. It can be responsible for up to 40% of total recoil. Venting muzzle pressure before the bullet clears the muzzle is how muzzle brakes reduce recoil even when their holes just vent sideways and equally in all directions. If you have a smaller charge of a faster powder that produces less gas mass and exhausts out the muzzle at a lower pressure, you can cut the rocket effect down. In another forum I once helped a fellow looking for a low recoil load for his kids reduce the recoil of his light load from 14 ft-lbs to 11 ft-lbs just by changing powders, but not giving up any bullet velocity.

The drawback to a smaller charge of a faster powder is it will usually leave more empty space in the case. That can reduce ignition consistency, so it isn't always the best thing to do. The fact you are lowering muzzle pressure also costs you some velocity. You end up having to decide what trade-offs are suitable in your gun?

Either the Interbond or the standard non-bonded version of the same bullet will be exemplary deer bullets, Grapenuts. You'd be hard-pressed to detect any forensic differences on two identical dead deer shot with either. If you already have one, there's no reason whatever to buy the other in its place.

Thanks Rocky, I get the feeling you didn't start playing with firearms just yesterday.

I have to ask though, in your response about the 139 bullets, did you allow for my decreased velocity? I may even load 150gr just to help me be certain of good penetration.

Stepping down from an '06 and am little shy about shooting smaller bullets at deer.

Yes, I did. The difference in velocity you might see (and there are no hard and fast rules in this) is roughly 25 fps per inch of barrel. Of course, it might be a bit more or a bit less. Nothing to lose sleep over.

Read some of the early stories about the 250 Savage. Back when, using bullets that were MUCH inferior to today's, that little .25-cal bullet weighing 100 grains and launching at 2800 fps knocked 'em deader than Pet Rocks. Compared to that, you're overgunned!

Actually, if those "early stories" were prior to 1932, they referred to the original 87 grain bullet at 3000 fps. Even though that load performed very well, some people insisted that a heavier bullet would surely be better just because it was heavier, so the 100 grain at 2800 fps was introduced in factory ammo in 1932. Some have claimed the heavier bullet sort of "took the luster off the 250/3000".

Thanks..

Now a question about bullet preference. Will a 139 gr Hornady Interbond give me the needed expansion from this gun or should I stick to standard cup and core due to the lower velocity? Rig is meant for mixed terrain whitetails at 250yds or less.

Under those conditions the 139gr Interlock is just about perfect in a 7mm-08, and so is the 154gr Interlock for that matter. I've used both in the 7mm-08, and 7mm RM for well over 20years, and have had excellent results with both from 20ft to 400yds on deer and antelope.

Interbonds are a response to market trends. The perception that megadollar bullets are a necessity for deer size game is a real stretch, to say the least. The 7-08 just isn't that hard on bullets.

Yes, I did. The difference in velocity you might see (and there are no hard and fast rules in this) is roughly 25 fps per inch of barrel. Of course, it might be a bit more or a bit less. Nothing to lose sleep over.

Read some of the early stories about the 250 Savage. Back when, using bullets that were MUCH inferior to today's, that little .25-cal bullet weighing 100 grains and launching at 2800 fps knocked 'em deader than Pet Rocks. Compared to that, you're overgunned!
Hey rock ButchB here, my very first rifle was a savage 99 with the rotary magazine in 250 savage, or 250-3000 as it was still called then. That win 100gr silvertipped bullet made alot of deer meat for my family. Put the little bullet where it belongs and the deer die. Big hole little hole it don't matter. I bang my head on the bed post every night for ever selling that rifle to this very day.:o