Longer barrel, slower powder?

[Texis]

Hi to all, first post.
I am about to start working up some loads for 7mm-08. I will be using 140-150gr hunting rounds (Berger, Barnes. Etc). I am not new to reloading, but do have a question.
The rifle has a 26" varmint profile Shilen 1:9 twist. All load data tables I've seen are based on 24" barrels. So, with 2" more barrel, would I gain any speed using a slower powder than is listed on the various load tables? What powders will take advantage of the longer barrel?
I need to stay with a temp stable, extreme type extruded powder, as I live on the Texas Gulf coast and hunt deer and hogs in the Texis panhandle. which means I work up my loads for long range (500-900yd hog rounds) in 85 degrees and may hunt in 20 degrees. Btw.. I won't poke at a good deer past 400 .. the wind is always howling in the panhandle, hogs are a different story lol.
Any inputs are appreciated, thanks.

 

[MagnumManiac]

The adage of longer barrel equals a slower burn, or a shorter barrel equals a faster burn simply isn't true….to a point in the extremes of either.
So, for example, you have your 7-08 with a 26" barrel and your buddy has a 20" or even a 18" barrel. The powders in the reloading book that give the highest velocity in the test barrel length, will also give your barrel and the shorter barrel the highest velocities per grain of powder.
If you stick with those top 3 powders listed in most manuals, you should be good to go.
In the wife's 7-08, we use either H4350 or 760 at this point, very early on in load development and the bullet she likes is 120g thus far due to recoil of the heavier bullets.

Cheers.

 

[Orange Dust]

The adage of longer barrel equals a slower burn, or a shorter barrel equals a faster burn simply isn't true….to a point in the extremes of either.
So, for example, you have your 7-08 with a 26" barrel and your buddy has a 20" or even a 18" barrel. The powders in the reloading book that give the highest velocity in the test barrel length, will also give your barrel and the shorter barrel the highest velocities per grain of powder.
If you stick with those top 3 powders listed in most manuals, you should be good to go.
In the wife's 7-08, we use either H4350 or 760 at this point, very early on in load development and the bullet she likes is 120g thus far due to recoil of the heavier bullets.

Cheers.

Exactly, burn rate equates to case capacity, not barrel length. Personally, I've had the best results with a 7-08 and 140's with 760 and a mag primer. Yes a Mag primer. Your mileage may vary and you should test both.

 

[Texis]

Thanks, I've used mag primers in 308 before. Not new to doing that, they are harder to find these days!
Correct me if I'm wrong, I didn't think 760 was particularly temp stable?
Q: if powder burn is all case capacity related, why do 16" barrels throw a huge ball of fire. Aren't they still burning powder past the barrel length?

 

[Texis]

I currently have Varget, CFE223 and H4895 on hand to try, of those frequently listed. I love CFE223 in my 308 and it looks a lot faster on paper in 7/08, but unfortunately not temp stable.

 

[MagnumManiac]

Huge muzzle flash is normally not powder burning but plasma igniting in the atmosphere.
If you look up videos of rail guns, no powder is used, but the plasma igniting is spectacular to say the least.
760 is not a temp stable powder, but I have never seen huge swings with it.
I don't hunt in temps above 80°F(33°C) normally, so don't see an issue using it.

Cheers.

 

[Orange Dust]

Thanks, I've used mag primers in 308 before. Not new to doing that, they are harder to find these days!
Correct me if I'm wrong, I didn't think 760 was particularly temp stable?
Q: if powder burn is all case capacity related, why do 16" barrels throw a huge ball of fire. Aren't they still burning powder past the barrel length?

How much do you shoot THAT gun when it is hot? Temp stability is way overplayed on the internet. I don't care how stable a powder is, you have choices. Work up a summer load and a winter load for the rifle. Don't shoot it above 90deg. work up the load when it is above 90deg. Don't load to MAX. etc. Temp stability is a relatively new thing. Unless you are running fairly hot loads you will most likely not notice with a hunting rifle.
As for the barrel length, you are correct. Shorten the barrel and you get more blast, fireball, and concussion. However, if you put a chrono on it, The powder with the highest velocity in a longer barrel will usually also be fastest is a shorter one, although is will certainly be slower. In general, the powders in the faster range for the cartridge will work better with lighter bullets and slower powders are better with heavier ones. When choosing a powder I usually start with whichever one shows the highest velocity with above a 95% fill rate, or (lately) whatever I have onhand closest to that in burn / fill rate. Choosing the powder is not as critical as choosing the bullet. Hope this helps.

 

[Texis]

I shoot the gun a fair amount. It's was my range/hunting rifle in 308.. I'm swapping the barrel to 7-08, be the same scenario. Probably 600-800 rounds per year. A lot in 85-90 degree temps.
We don't walk or stalk where I hunt, too much ground to cover looking for critters, we ride 4 wheelers typically until we locate a suitable live target. Consequently I don't mind hunting with a 12+ lb rifle because the bike carriers it not me.
I have never had the opportunity to validate DOPE at 600+ with various powders in colder weather, so I'm a bit shy using non temp stable powders for hunting rounds., But you may well have a point about it being overrated. I don't know? My loads are never at max. I typically find a nice flat node in a ladder long before primers start popping out.
Thanks!

 

[Orange Dust]

Try working up to max pressure in your rifle with a Hornady 139gr SST, WW760 powder and a magnum primer. Chrono it and get back with me. You will be both surprised and enlightened. I once had a 24" one that liked 50grs. This is over max in the newer books, but was fine in that old gun. The surprise came when I was playing with it and the chrono. My FIL came out with a 7rem mag and some 140 grain bullets in green and yellow boxes. It chronoed 2950fps. My handloads in the 7-08 just broke 3k. He went straight to the store for dies.... I had a good laugh. Of course the mag will do 3300, but his wasn't..... Try that bullet/powder combo, and work it up in YOUR rifle. 7-08 is one of the best deer cartridges ever.

 

[Orange Dust]

I shoot the gun a fair amount. It's was my range/hunting rifle in 308.. I'm swapping the barrel to 7-08, be the same scenario. Probably 600-800 rounds per year. A lot in 85-90 degree temps.
We don't walk or stalk where I hunt, too much ground to cover looking for critters, we ride 4 wheelers typically until we locate a suitable live target. Consequently I don't mind hunting with a 12+ lb rifle because the bike carriers it not me.
I have never had the opportunity to validate DOPE at 600+ with various powders in colder weather, so I'm a bit shy using non temp stable powders for hunting rounds., But you may well have a point about it being overrated. I don't know? My loads are never at max. I typically find a nice flat node in a ladder long before primers start popping out.
Thanks!

Work up the load in high temps and forget about temp stability. You could work up a cold weather load and possibly get another grain in it, but WHY??? Unless your node is so narrow that a slight loss of velocity puts you out of it? Temp stability on the internet is very similar to a belt on a cartridge case on the internet. At 600yds it might make a difference shooting blackbirds, but not whitetails. 400Yds and it won't matter for either.

 

[Texis]

Great point about the node. I always look for a wide node. If I'm at the top of the node, should work in any condition temp I will find myself shooting.
CFE223 is looking pretty good, as I love it anyway.
Also, the altitude is 3200ft where I hunt, and 75ft at my range.. I always hoped the difference in altitude (flys better where I hunt) would offset the loss of speed from temp. It was being the optimist.

 

[Seabeeken]

Q: if powder burn is all case capacity related, why do 16" barrels throw a huge ball of fire. Aren't they still burning powder past the barrel length?

They sure are. I use GRT to balance my case capacity, barrel length, and powder burn rate to avoid waste and get the most efficiency

 

[Tiny Tim]

Powder burn rate is a complex subject, but for your question, within reason, the powder that produces the highest velocity will do so regardless of barrel length. Work up your load in heat and test in cooler temps. Then you'll know how much it truly affects your load.