7BRAW re-Visit

[ktm571]

Hi. Searched a bit but this topic seemed to pop up and fade a couple of years back.

I'd be interested in a 7-08 with a standard or 25 degree shoulder and .200/.230-ish FB with std 1.5 degree throat. I've looked long and hard at the WTO 7 SAW but I'm too chicken to put $1000 worth of barrel blank + chambering at risk with their stepped throat in 1k benchrest. That throat design presumably helps with speed and they intend it for PRS. I'm not sure how erosion of the straight step in that throat would affect accuracy for benchrest over the life of a barrel.

Anyone try a 7 SAW for benchrest? Or know where Alex W left the 7BRAW topic? Thx.

 

[ballisticdaddy]

I run a 7SAW for hunting and NRL hunter matches but it's a bit much for PRS imo. Curently running the Hornady 162 grain ELD-M at 2,788 fps and Sierra 150 grain TGK at 2,755 fps with Alpha brass. I shot f-class 1,000 yard for years and if you are looking at a 7mm why not just use the tried and true .284 Win?

 

[ktm571]

Hi. Searched a bit but this topic seemed to pop up and fade a couple of years back.

I'd be interested in a 7-08 with a standard or 25 degree shoulder and .200/.230-ish FB with std 1.5 degree throat. I've looked long and hard at the WTO 7 SAW but I'm too chicken to put $1000 worth of barrel blank + chambering at risk with their stepped throat in 1k benchrest. That throat design presumably helps with speed and they intend it for PRS. I'm not sure how erosion of the straight step in that throat would affect accuracy for benchrest over the life of a barrel.

Anyone try a 7 SAW for benchrest? Or know where Alex W left the 7BRAW topic? Thx.

Recoil & muzzle blast simply. I have a 284 now. A properly throated 7-08 with a 180 HT ought to be within 100 fps or so of a 284 using 8-10gn less powder. My particular matches are about 65-70 rds with a 17lb gun and lighting off that many rounds with a 284 on a Sunday just isn't fun.

 

[ballisticdaddy]

Recoil & muzzle blast simply. I have a 284 now. A properly throated 7-08 with a 180 HT ought to be within 100 fps or so of a 284 using 8-10gn less powder. My particular matches are about 65-70 rds with a 17lb gun and lighting off that many rounds with a 284 on a Sunday just isn't fun.

If you push a 180 grain projectile within 100 fps of a .284 I would venture to say it would have VERY similar recoil and muzzle blast. I shoot my 7SAW suppressed as neither the recoil nor muzzle blast are enjoyable!

 

[DHuffman]

7-08 40° improved is competive running 180s in 600 & 1000 in BR
Will run 2700 without wrecking brass and recoil in a 17#:gun is mild IMO

 

[std7mag]

Your gonna laugh. Shake your head. And just flat out think I'm crazy.

My first 600 yard F-Open match, I shot my Stevens 200 with the 22" sporter barrel that I reamed to 7mm-08AI (7mm-08 Imp 40°).
It was the last horrah on the barrel as I had put about 6,000 rounds through it. (Yes, you read that correctly)
So rifle with an Atlas knock off bipod, Sightron STAC 4-20X56 weighed in about 8lbs.

For cartridge I was using PPU brass.
Alliant PP2000MR powder.
Fed 210M primer.
140gr Berger VLDH at 2.898" COAL (Reamer has a 0.06" FB)
Velocity 2,832fps with ES-6, SD-2 run over (2) ten shot strings.

Muzzle blast wasn't bad.
But after the second string of 20 rounds recoil was getting to me.
By the end of the third string, I was hurting!

I think a 17lb gun, throated for the 160-168gr class of bullets, the 7mm-08AI would probably shine.

 

[mike mccormick]

Or....and I know it sounds crazy.....you could just throttle back on the 284, find a lower accuracy node, and achieve your goal.

 

[Fire Dog]

Your gonna laugh. Shake your head. And just flat out think I'm crazy.

My first 600 yard F-Open match, I shot my Stevens 200 with the 22" sporter barrel that I reamed to 7mm-08AI (7mm-08 Imp 40°).
It was the last horrah on the barrel as I had put about 6,000 rounds through it. (Yes, you read that correctly)
So rifle with an Atlas knock off bipod, Sightron STAC 4-20X56 weighed in about 8lbs.

For cartridge I was using PPU brass.
Alliant PP2000MR powder.
Fed 210M primer.
140gr Berger VLDH at 2.898" COAL (Reamer has a 0.06" FB)
Velocity 2,832fps with ES-6, SD-2 run over (2) ten shot strings.

Muzzle blast wasn't bad.
But after the second string of 20 rounds recoil was getting to me.
By the end of the third string, I was hurting!

I think a 17lb gun, throated for the 160-168gr class of bullets, the 7mm-08AI would probably shine.

Mass x Velocity is going to equal the same amount of recoil impulse no matter what cartridge is used… 180gr x 2,800+fps
The heavier gun will soak up the felt recoil effects and adding a RAD system will make your shoulder thank you following a long string match.

 

[ktm571]

Mass x Velocity is going to equal the same amount of recoil impulse no matter what cartridge is used… 180gr x 2,800+fps
The heavier gun will soak up the felt recoil effects and adding a RAD system will make your shoulder thank you following a long string match.

Thx guys. Ya, it's Mass x Velocity squared . So yes, muzzle velocity of a 180 at 2700 is only 7-8% less than 2800. There is the muzzle blast factor too using 8-10 grains less powder. And in theory better barrel life comes along for the ride.

I'll look into the RAD system as well. I shoot for fun. Will never be a Nat'l Champ. The 284 isn't fun right now at that many rounds. Wouldn't be as bad for 1-2 relays at Williamsport on a Saturday.

 

[ktm571]

Thx guys. Ya, it's Mass x Velocity squared . So yes, muzzle velocity of a 180 at 2700 is only 7-8% less than 2800. There is the muzzle blast factor too using 8-10 grains less powder. And in theory better barrel life comes along for the ride.

I'll look into the RAD system as well. I shoot for fun. Will never be a Nat'l Champ. The 284 isn't fun right now at that many rounds. Wouldn't be as bad for 1-2 relays at Williamsport on a Saturday.

Muzzle energy that is...

 

[std7mag]

Mass x Velocity is going to equal the same amount of recoil impulse no matter what cartridge is used… 180gr x 2,800+fps
The heavier gun will soak up the felt recoil effects and adding a RAD system will make your shoulder thank you following a long string match.

That's the kicker, so to speak.
I was shooting a 22" barrel with a 140gr bullet at 2,832fps. But from an 8ish lb rifle.

My wife's Savage 111FP with the 24" heavy varmint barrel and a Choate stock puts it right at 14lbs.

Even with a longer barrel, I'm not sure that the 7mm-08, AI, or SAW would have enough case volume to push a 180gr bullet to the 2,800fps range.
I could be wrong, but I think if you were able to, it would be hard on the cases.

 

[Fire Dog]

That's the kicker, so to speak.
I was shooting a 22" barrel with a 140gr bullet at 2,832fps. But from an 8ish lb rifle.

My wife's Savage 111FP with the 24" heavy varmint barrel and a Choate stock puts it right at 14lbs.

Even with a longer barrel, I'm not sure that the 7mm-08, AI, or SAW would have enough case volume to push a 180gr bullet to the 2,800fps range.
I could be wrong, but I think if you were able to, it would be hard on the cases.

I think you are right as I am using 180’s & 184’s in a 280AI {basically a 7mm-30-06} and to get them moving at 2’800fps requires 56.7gr of 4831sc and the 308 case of the 7-08 just may not have enough capacity but some other powders may be a bit less volume and able to produce that velocity… As always advised, go slowly and with caution as you approach maximum loads.

 

[ktm571]

I think you are right as I am using 180’s & 184’s in a 280AI {basically a 7mm-30-06} and to get them moving at 2’800fps requires 56.7gr of 4831sc and the 308 case of the 7-08 just may not have enough capacity but some other powders may be a bit less volume and able to produce that velocity… As always advised, go slowly and with caution as you approach maximum loads.

All good stuff. But we have drifted away from my initial inquiry: Anyone try a 7 SAW for benchrest? Or know where Alex W left the 7BRAW topic?

Alternatively, I have plans to get there myself. I have a 7mm rental throater on the way and a $70 used 7mm-08 barrel. I plan to throat that barrel so the start of the boat tail of a 184 LRHT is about 0.060 ahead of the neck-shoulder junction. Then just check for a max reasonable speed with probably H4350. All of the book data uses 2.800 - 2.950 COAL,. A 184 sitting where I want it has a COL of about 3.125. There is room for more powder at 3.125. WTO claims 2800 with a 180 HT in their SAW but they have a modified throat that presumably improves speed. I want to see what speed a typical 1.5 degree throat would give at ~3.125 COAL....unless someone else has done this.

 

[64Rambler]

Last year I ran a 7mm-08 with a long throat for 600 F-Open. With a Berger 180 Hybrid I had CBTO lengths of 2.318" and 2630 fps with 45.8 gn of N555. Was starting to get an ejector swipe at 46.1gn and 2650 fps. With 168 VLDs I was getting 2750 with 45.5 gn H4350 at 2.290" CBTO.
I have another barrel in 7mm-08AI with a 32.5* shoulder that I need to get dies for, but in fire forming I was getting 2740 with 46.5 gn of H4350 and 168 VLD at 2.366" CBTO and hard jam with groups in the 1s by 3rd firing - zero pressure signs and easy bolt lift with plenty of room for more powder.

 

[std7mag]

All good stuff. But we have drifted away from my initial inquiry: Anyone try a 7 SAW for benchrest? Or know where Alex W left the 7BRAW topic?

Alternatively, I have plans to get there myself. I have a 7mm rental throater on the way and a $70 used 7mm-08 barrel. I plan to throat that barrel so the start of the boat tail of a 184 LRHT is about 0.060 ahead of the neck-shoulder junction. Then just check for a max reasonable speed with probably H4350. All of the book data uses 2.800 - 2.950 COAL,. A 184 sitting where I want it has a COL of about 3.125. There is room for more powder at 3.125. WTO claims 2800 with a 180 HT in their SAW but they have a modified throat that presumably improves speed. I want to see what speed a typical 1.5 degree throat would give at ~3.125 COAL....unless someone else has done this.

Paging Mr. Wheeler!!!
@Alex Wheeler to the thread, please...

 

[Alex Wheeler]

Never did a 7BRA. Tried a 7-08ai. Not sure if this is getting confused with the 7PRCW (7-6.5prc)

 

[ktm571]

Thanks all. I did get that 7mm-08 Remington take-off barrel and throated it (1.5 degrees) until the start of the bearing surface of a 180 HT was just ahead of the start of the shoulder as shown in the pic. This put the bullet base about 0.050" above the shoulder-body junction, so lots of room for powder due to the 20 deg case. Faced the barrel tennon shoulder for the thicker recoil lug of my long action 700 to get the headspace close. 20" barrel incidentally. $79 for the used barrel + shipping + about $60 for throater rental with shipping. Economical test in my mind to explore 7mm-08 with properly seated 180 bullets..

COL was 3.115 with 0.015 jump for this test. Stopped at 44 gn H4350 which gave 2475 fps with the 180 and no significant case pressure signs.. And there was room for a bit more powder + I used necked-up Federal 260 Rem cases whose heads were .215" thick, so Lapua brass would hold about another grain in this configuration. Note: this was just a speed test - shot into the bank.

So this is the end of my 7-08 story. Pretty sure I could get to the 2700 fps range easily with 10" of additional barrel length to work with while using ~10gn less powder than a 284. So I got my answer and confirmed a couple of affirmative comments that came in above. Take care.

 

[ballisticdaddy]

So how was the recoil / muzzle blast in comparison to the 284 with same bullet?

 

[ktm571]

Recoil was horrible. But this test was done in a 7-ish pound long action Rem CDL. No brake so the muzzle blast wasn't as bad as my 284 with radial brake. But the short barrel seemed loud.

 

[ELR LVR]

Recoil & muzzle blast simply. I have a 284 now. A properly throated 7-08 with a 180 HT ought to be within 100 fps or so of a 284 using 8-10gn less powder. My particular matches are about 65-70 rds with a 17lb gun and lighting off that many rounds with a 284 on a Sunday just isn't fun.

So youre saying with a 7/08
you can get approx 2700 fps, with a 180 gr, with approx 40 grns of powder?
Not doubting just asking, since I am debating the next 7mm to build also
-----
I don't prefer my current 7/08 with its 9.5 tw (it sits in the closet mostly even though its alright with 162's)
But if 2700 with a 180 is easily achieveable I may put an 8 twist on it.
-----
Otherwise I would prefer a 284 pushing 2800-2850 with a 180 gr