Barrel length question

[Mulligan]

While looking at the equipment list for the 1000 yd F-class nationals, it was obvious the .284 is king. I have always felt the 7-08 could do anything the .308 or .284 could do, only better (my personal opinion ). With that in mind I loaded up some 180 Berger's in front of IMR 4451 and others with H 4831 in a ladder test with .5 gr intervals. This is an trued 700 with a 22" factory barrel .......a hunting rifle. Both loads showed well and had velocities of 2505-2565 FPS at the upper end of my powder chargers. Without any pressure signs and still below the max listed on the Hodgon website, I have room for another trip to the range. I expect 2600-2625 is safely achievable in this rifle.
Now here's the Question; if I order a 32" barrel for my Panda F-class action, what velocity gain will I potentially see? I have read that 25 FPS is a good rule of thumb, any thoughts?
CW

 

[Dgd6mm]

200 more fps, guessing....

 

[Canadian bushman]

I think 10-15 fps/in would probably be a good educated guess.

 

[watercam]

I agree with approx. 200 fps gain. JBM shows a retained 1515 fps @ 1000 yds. and a drop of 27moa. Should work just fine if you do your part.

 

[savagedasher]

It is hard to say because the extra barrel length changes the powder that can be use. Short barrels use faster burning powders. Larry

 

[Sheldon N]

Ultimately with the 7mm-08 you're giving up 11 grains of case capacity to the 284, and it seems like most of those guys are running velocities in the mid 2800's. I think you'll have a hard time doing better than mid 2700's with the 180 hybrid even with a long barrel.

 

[Keith Glasscock]

Hmmm, Interesting...


How about a 7-08 AI throated for the 180 hybrid from a 30" tube propelled by H4350? According to my QL (tuned for my lot of H4350), it should just make 2720fps and hit the node and max pressure at the same time with a completely full case.

You would be giving up about 100 fps to the 284's that are running H4350 - more to the ones using slower powders

I wonder if it would be worth using small primer brass?

 

[XTR]

I think you will run out of case capacity. You cant get much more than 50 grains of H4350 in a 308 based case, using WW brass, and still seat a bullet, the powder is up to the bottom of the neck.

 

[Mulligan]

I believe with 4451 I could go up to 5 more grains and with 4831 maybe 3 grains, in capacity. If I get in the neighborhood of 2600-2650 safely then the 10" of additional barrel length my get me to 2800-2850. Having said that, will the Lapua 308 Palma brass be a benefit to accuracy with 50ish grains of powder? Is it a possibility that barrel life could be extended using 10% less powder then the .284?
I might have to order the reamer and find out.
CW

 

[Dshooter]

I'm with the majority...you could be competitive but still at a slight disadvantage no matter how you slice the apple. Give it a whirl though!!

 

[dmoran]

Throat it long, will enable you to achieve more speed at less pressure.
And consider a "bore rider" throat (aka: stepped throat) for even further potential.

My 2-Cents
Donovan

 

[savagedasher]

I think you ask about 7.08 speed difference I don't have a listing for the powder you ask replace it with H4350.
22'' 2402 24'' 2445 26''2484 28''2519 30''2550 32'' 34'' 2580 . Larry

 

[MrMajestic]

For fecal matters and light laughter try some H414. It is right there with 4350 on the burn rate and you will fit more into the case. I was pleasantly surprised with it in 308 Palma cases and heavy weights in 308 Win.

 

[Joe R]

Mulligan said:

While looking at the equipment list for the 1000 yd F-class nationals, it was obvious the .284 is king. I have always felt the 7-08 could do anything the .308 or .284 could do, only better (my personal opinion ). With that in mind I loaded up some 180 Berger's in front of IMR 4451 and others with H 4831 in a ladder test with .5 gr intervals. This is an trued 700 with a 22" factory barrel .......a hunting rifle. Both loads showed well and had velocities of 2505-2565 FPS at the upper end of my powder chargers. Without any pressure signs and still below the max listed on the Hodgon website, I have room for another trip to the range. I expect 2600-2625 is safely achievable in this rifle.
Now here's the Question; if I order a 32" barrel for my Panda F-class action, what velocity gain will I potentially see? I have read that 25 FPS is a good rule of thumb, any thoughts?
CW

Let me start by saying that I don't know anything about the 7.08, but I do know a few things about the .308, and given that they share the same case you may find this interesting.

I'm attaching a page from my shooting diary from July of 2014. I was using a 30" Krieger barrel, 1:11 twist, pushing a 180 grain JLK. As you can plainly see I pushed it to 2906 fps. Don't jump to conclusions about precision because at the time I was having horrendous neck tension problems and I didn't even know it.

In conclusion, IMO you can easily attain mid 2800s fps with a 7.08 and a 30"+ barrel.

Kindest regards,

Joe

PS I agree with Donovan that having a long freebore (around .180+) will be a great help.

 

[ShootDots]

I think that the 7mm-08 is a "viable" but "less than stellar" option. However, if you decide to go down that road, I would do a few things to "maximize", as much as can be, your potential..

1.) Go with a 7mm-08 A.I.

2.) Go with a .235 Freebore to get that 180 Hybrid "out there"..

3.) Use necked-down .308 Palma brass..

4.) Use a 6" drop tube to settle more powder in the case.

5.) With that freebore in the A.I. version, using Palma Brass, I believe you could safely go to "around" 50.0 grs of H4831SC..

If my assertion is correct (it won't be far off) you should get to 2700+ with a 30" barrel. Now will it shoot "up there"? There is only 1 way to find out. But 2700 or so F.P.S. with a 180 Hybrid would not be easily sneezed at..

I love to "tinker" with new things... I am in the process of "tinkering" with something right now! LOL!! That is half the fun of shooting>>>at least to me!

 

[Mulligan]

Thanks all for the info.
Joe, that is really useful, thanks for sharing.
CW

 

[Sheldon N]

Throat the gun as long as possible and you'd get an OAL cartrige length of around 3.05" (leaving around 1 caliber worth of bearing surface in the neck with a 180 Hybrid). If you put 50g of H4831 in there that would be a VERY compressed load and QL predicts 73k PSI and 2850 fps with a 30" barrel.... ie possible but not something I'd want to do. H4350 is less compressed but likely lower velocity at the same pressure levels.

If you stop at 65k PSI you're in the mid 2700's for velocity and it would still be a compressed load at around 110% fill capacity with 4831 SC.

Go to the 7mm-08 AI version throated long and you're right in the ballpark with 50g of H4831 getting you just over 2800fps at reasonable "hot load" pressures.


Of course now you can't mag feed in a short action. So you might as well go long action and shoot a 280AI.... 59.7g of H1000 over a 180 Hybrid get me 2810fps in a 26" barrel right in the accuracy node at around 55k PSI. Super easy on the brass, no issues with mag feeding and it's a pussycat to shoot.

I'm with Ben, this stuff is fun to tinker with and "what if" the options you could choose.

 

[jim_k]

The difference in wind drift for a 7mm bullet between 2650 and 2850 fps is about 1/2" per mph of direct crosswind at 1,000 yards. Do whatever you like. If the rifle is going to be a dedicated F/O rifle for 1,000 yards, go with the cartridge that gets the most velocity. Or else accept getting beat. If it's a sometimes 1,000 yard rifle that you want to do hunting with, I would get 24-26" barrel in a medium weight. That's a good compromise. I like stainless barrels, and there are a bunch of good ones out there. With the right bullet and cartridge, a 22" barrel can shoot 1,000 yards. I've done it with 185gr Bergers in a .308 Win using Lake City cases. But not if you want to campaign with it competitively.

 

[swd]

I like the 7-08 a lot and played with a bit at 1k. I never tried the 180s but did shoot a lot of 162 A Max's. I'm interested to hear how the 180s do but I think they're too heavy and the 162-168 is a better balance. RL17 always gave me the best speed and excellent accuracy but I never did try 4831. Throating it long is the way to go but don't throat is so long you can't go back to 162-168s if you have to.

 

[savagedasher]

Throated long and 30'' barrel with powder change from H4350 to Norma MRP you can expect 100 + FPS with the same pressure. OL gives 140 ' more speed. Larry