I am contemplating a 7mm-08AI light rifle. My action and stock will come in at 3.5lb. To keep the weight close to 6lb. I need a 20 inch number 2 contour barrel fluted. Can I expect 7mm-08 24 inch barrel velocity with a 20 inch AI, or close enough? Anyone have a similar rig, (AI or not) with real world velocity that is not primer popping hot? Thanks.
7mm-08AI?
- Thread starter Glenn Powell
- Start date
XTR
F-TR obssessed shooting junkie
A 308 is a pretty straight walled case to start with, I read somewhere that doing the AI thing gets you about 3% in volume. Personally I didn't see it as worth the trouble to have to fire form cases and I went with a standard 7-08 for my hunting rig, and I used a 24" barrel. I'm getting 2800 or so from a case full of H4350 with 140 Accubonds. I think you'd be reaching to get there with a 20.
From both your 140g bullet numbers there is a 200+ feet per second increase in velocity in 24" barrels. The Burger manual says with the standard 7mm-08 you loose 21 fps per inch of barrel. So in theory I should gain 100 fps or there abouts, with the AI in a 20" barrel compared to a 24" standard 7mm-08. Thanks for the info fellas, any other input is very welcome.
XTR
F-TR obssessed shooting junkie
You may want to find someone with quickload and see if they can give you some inputs. In order to get the velocity up and not pop primers the powders are necessarily a bit on the slow side. You may not be able to utilize the powder in a 20" tube. Just a thought, I've got no experience to say one way or the other.
I'm going to experiment with Varget this yr and see how it works too. I think the 4350 was a tad slow for the 140.
I'm going to experiment with Varget this yr and see how it works too. I think the 4350 was a tad slow for the 140.
Maybe someone with the software will chime in. Just getting close is good enough for me, I have yet to shoot a deer up here past 40 yards any way. Its going to be more of a caribou/goat/black bear rifle, though I havent done the boo, and can't find anyone nuts enough for a goat hunt :
speaking of different powders in the AI vs std 7-08
in my 5 different 7-08 standard chambers, all shot inthe 2800-2875 with 22-24 inch bbls using 4064, an simular speed powders.
in the AI if found two things - the powders of this burn rate peeked in pressure to fast to get a significant speed increase, the 40degree shoulder tends to "hold the pressure in" while the lesser angle lets it flo out, this may not make good sense but that is my explanation. the result is you need to go to a slightly slower powder so the pressure does not peek too fast and allows the bullet to gain velocity as the presure has a longer curve.
in my 24" Hart tube 9 twist, i began to get better velocity with 4007 and RL 17, these were producing in the mid to upper 2900's
Thus with the shorter bbl i would think their burn rate may be more desirable than the H414 and still get you into the 2900 range
Speaking of the heavier game, the nosler partition produce the same results as the 140 Sierra SBT with just a little less accurcy.
Bob
in my 5 different 7-08 standard chambers, all shot inthe 2800-2875 with 22-24 inch bbls using 4064, an simular speed powders.
in the AI if found two things - the powders of this burn rate peeked in pressure to fast to get a significant speed increase, the 40degree shoulder tends to "hold the pressure in" while the lesser angle lets it flo out, this may not make good sense but that is my explanation. the result is you need to go to a slightly slower powder so the pressure does not peek too fast and allows the bullet to gain velocity as the presure has a longer curve.
in my 24" Hart tube 9 twist, i began to get better velocity with 4007 and RL 17, these were producing in the mid to upper 2900's
Thus with the shorter bbl i would think their burn rate may be more desirable than the H414 and still get you into the 2900 range
Speaking of the heavier game, the nosler partition produce the same results as the 140 Sierra SBT with just a little less accurcy.
Bob
Clancy
Silver $$ Contributor
I don't think it's worth the trouble. I have a 20" 7-08 model 7 and I can send you a book of pictures of critters it has taken with a single shot.
Im not talking about coyotes and deer either. I've used it on elk bear aoudad sable .....
7-08 is a real deal sleeper round that doesn't need a 26" tube to impress.
The 21 fps per inch is almost spot on by the way, my friends gun is 24" and he gets about 90 fps more.
Im not talking about coyotes and deer either. I've used it on elk bear aoudad sable .....
7-08 is a real deal sleeper round that doesn't need a 26" tube to impress.
The 21 fps per inch is almost spot on by the way, my friends gun is 24" and he gets about 90 fps more.
Is it worth the trouble? Heavens no. I know the plane Jane 7mm-08 will do the job, and without a fuss. I don't mind the fuss though, and actually enjoy fire forming brass. It gives me time to work the action, check function and a good excuse to go have fun at the range. Custom rifles cost too much for boring cartridges : I can figure out what twist barrel I need with the velocities you guys are giving me, which is very much appreciated. My next hurdle is the reamer, my action has the Wyatt's Extended magazine cut, so I am going to try and have a reamer cut to fully take advantage of case volume and bullet seat depth. I do want to shoot some of the heavier bullets 150+g, I am funny that way.
I can figure out what twist barrel I need with the velocities you guys are giving me, which is very much appreciated. My next hurdle is the reamer, my action has the Wyatt's Extended magazine cut, so I am going to try and have a reamer cut to fully take advantage of case volume and bullet seat depth. I do want to shoot some of the heavier bullets 150+g, I am funny that way.The 284 was very very high on my list, but, 7mm-08 ammo is much easier to come by if I somehow loose mine during transport, practice what I preach so to speak. Also, feeding could be an issue that I don't want to tackle. I am also planning on a 6mm barrel for small to medium predator calling in the winter months, 6mm-284 is way more than I want for that. This rifle is going to be a lighter version of my heavy 358 Norma, stock and all, though the Norma has a 21" barrel, and "similar" action.
Berger suggests a 1 in 9 inch twist rate for the 180 grain bullets they make, 1 in 10 is good all the way down to the 140's. I would opt for the faster twist rate if I was going to hunt bear so I could shoot the heavier bullets.
As far as building the A.I. I say go for it! I have a 280 A.I. and I love it. I can almost get 7 mag velocities with alot less powder. Straight 280 rounds are easily purchased across the counter if I lose loaded rounds in transport. Good luck and keep us in the loop on the new build, BK.
As far as building the A.I. I say go for it! I have a 280 A.I. and I love it. I can almost get 7 mag velocities with alot less powder. Straight 280 rounds are easily purchased across the counter if I lose loaded rounds in transport. Good luck and keep us in the loop on the new build, BK.
i too have experience with the 280AI - 2 of them with 26" bbl, great- 3140fps with 140s and 2955 with 160's
the 7-08ai gives me within 100fps from a 24 in bbl on the 140 and 125fps on the 160s 7-08 ammo also will fire in the Ai camberif you loose your reloads
if you want a light short rifle go the 7-08AI i did and dropped 2lbs of carry weight
Bob
the 7-08ai gives me within 100fps from a 24 in bbl on the 140 and 125fps on the 160s 7-08 ammo also will fire in the Ai camberif you loose your reloads
if you want a light short rifle go the 7-08AI i did and dropped 2lbs of carry weight
Bob
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