Looking into a R700 build... any downsides of 22" 1:8 twist?

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pneumagger
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Looking into a R700 build... any downsides of 22" 1:8 twist?

Post by pneumagger » Sat Apr 13, 2013 5:49 pm

Looking into getting/building my first bolt action. Just a .308 since it's easier to find than other calibers and it seems like a great "beginner gun". Plus I already have a 308 AR so that means no new calibers. The goal of the rifle would be mid/budget priced bench/target gun; 500-1000 yards - so I was considering a 22" stick with AAC Muzzle Brake mount. Since 762SDN-6 finally showed up at my dealer I figure a bolt gun would be a great host. Trying to stay around $1400-$1700 sans optics.

Looking at a simple Remington 700 build, factory receiver & barrel in a Bell & Carlson stock with a quality scope and mounts should shoot pretty decent for the cost. However, since I have a can waiting at my dealer, I'm a bit put off by the 1:12 twist... not ideal for subsonic suppressed as I'm not sure it would stabilize anything over 175gr. I'm considering using a different barrel of 1:10 minimum... but now am looking hard at a 1:8 twist.

I'm thinking that a 22" 1:8 twist would pretty much guarantee the ability to use the large 220gr pills and still throw lighter bullets out to longer ranges easily. I'm pretty sure that typical 155gr scenars & 168gr Amax/SMK will still be stabilized at 1:8.
What would the downside of a 22" 1:8 twist with 762SDN6 be for a target/bench gun? Any silencer/stability issues? What's the lightest bullet I can shoot full speed through 1:8? What would be the heaviest subsonic?

I haven't began reloading, but plan on it someday when my work life settles down.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by 700PSS » Sun Apr 14, 2013 2:58 pm

Mine has the AAC 18" barrel with 1:8. Especially for use with a silencer, I'd go shorter than 22".

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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by pneumagger » Mon Apr 15, 2013 10:44 am

Is there a problem with trying to work up a 200+ grain subsonic load out of a 22" barrel? I realize the 18" is probably a bit better for subsonic primary or dedicated use, but I do want to use the rifle to shoot long range as well (whether suppressed or unsuppressed). I feel like an 18" barrel would limit my velocity/range on long distance loads.

Have you tried 168gr SMK/Amax or 155gr Scenars in your 1:8 twist? Do they stabilize at full velocities?

Thanks.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by JohnnyC » Mon Apr 15, 2013 11:36 am

You should be fine. I'd skip the 155's and 168's and stick with 175's for the super. You can give 155's a shot but it's still not going to buck the wind at long range as well as the 175's. 168's are just sorta there. Nothing wrong with them, but generally eclipsed by other bullets.

Put the variables into the bullet stabilizer on JBM and see what it spits out. I highly doubt you're going to overspin a bullet with any negative outcome other than maybe poor accuracy but you won't know until you try it.

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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by doubloon » Mon Apr 15, 2013 11:51 am

I'm searching for the article that did a long range comparison on different length barrels. When I find it I'll post it but what it boils down to is there are no real long range limitations on the shorter barrel.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by robpiat » Mon Apr 15, 2013 12:09 pm

The 155s are somewhat deceiving because they are so long. They may need a faster twist than a standard 168/175

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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by doubloon » Mon Apr 15, 2013 12:29 pm

Agreed, bullet length has a direct correlation to twist rate. Barrel length is a very minor consideration in stabilization. But I think you got that the other way around. Longer heavier bullets want a faster twist like 1:10 and shorter lighter bullets want something more like 1:12.

And it's really the bullet length that matters even though the weight is how the topic is most commonly discussed. There are a couple examples where a bullet in the right weight range won't stabilize as well as another bullet of the exact same weight and it's due to the weight distribution along the length.

The 155gr pills would end up "over stabilized" in a 1:10 or faster barrel. You can shoot them out of a 1:10 with some success at short ranges but a 1:10 really wants a longer bullet 165/8gr and above. I haven't read about a lot of benefit to anything faster than 1:10 for long range shooting. Without doing any math I wouldn't shoot anything lighter/shorter than 168/170gr through a 1:8.

I've read about people successfully shooting subsonic/suppressed through a 1:12 twist barrel with the right ammo, something 180gr or smaller.

It's all about tradeoffs and knowing the limitations and benefits of the tradeoffs.

I settled on a 1:10 20" barrel for my long range bolt gun. It's plenty good for reaching out to 1000 yards and still manageable for hauling through the woods and swinging around in a deer stand. My AR-10ish is a 1:10 18", still good out to 100 yards if I want but much better for swinging around and follow up shots like sniping at a herd of pigs.

Still looking for the article, it's on one of the sniper forums but I can't remember which one.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by pneumagger » Mon Apr 15, 2013 12:51 pm

The more I think about it, I think I'll probably be happy with a 1:10 Howa or something else and just throwing 175gr subsonics when I feel the need. Plus, a 1:10 should have no mysteries involved with using many of the high BC 155gr and 175gr match rounds available with good success. Also, I wont have to order some expensive custom barrel just to stick it in a factory action with just average stock and scope.

On the flip-side, I think I might have a 1:8 LR308 barrel made or something similar. A carbine length 1:8 308AR pushing 220gr loads probably wouldn't have any trouble cycling .308 subsonic with an adjustable gas block. The only real question, as with a 1:8 twist bolt gun, is whether it shoot the lighter ammo well (?). I would have to think that 110gr TAP @ 2800fps out of a lightweight 16" .308 would be NASTY for anything standing in the way.
doubloon wrote:...
The 155gr pills would end up "over stabilized" in a 1:10 or faster barrel. You can shoot them out of a 1:10 with some success at short ranges but a 1:10 really wants a longer bullet 165/8gr and above. I haven't read about a lot of benefit to anything faster than 1:10 for long range shooting. Without doing any math I wouldn't shoot anything lighter/shorter than 168/170gr through a 1:8.
...
Don't the 300BLK (.308) rifles shoot 110-125gr supersonic loads as standard - albeit only 2100-2300fps or so? And those all stabilize without excessive yaw for suppressed use.
Would the 2800-3000fps from a 20+ inch .308 really be so bad for those bullets?
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by doubloon » Mon Apr 15, 2013 1:10 pm

pneumagger wrote:...
doubloon wrote:...
The 155gr pills would end up ...
...
Don't the 300BLK (.308) rifles shoot 110-125gr supersonic loads as standard - albeit only 2100-2300fps or so? And those all stabilize without excessive yaw for suppressed use.
Would the 2800-3000fps from a 20+ inch .308 really be so bad for those bullets?
Yessir!

When I say "over stabilized" I'm really talking about long range shooting and mostly I'm talking out my ass because I am far, far away from any kind of expert.

I shoot 145gr PPU fodder out my 1:10 barrels out to 100 yards all the time. I look at it as a way to get relatively cheap trigger time (purchased a few back when they were ~$0.40/rnd) and collect usable brass for handloads.

Out to 100 yards I get reasonable accuracy with the 145gr pills ... I could aspire to be a tennis ball's nightmare. But I've noticed if I try to take those same bullets out to 300 yards the groups open up unpredictably.

Pushing 168gr pills out the same rifle I can stack 5 shots in a 0.6" hole at 100 yards and just under 2.5" at 300 yards. There are, of course, a lot of other factors at play but my personal experience out to 300 yards coupled with reading all the wisdom the internet has to offer says short bullets in fast barrels just gets frustrating at long ranges. Kinda the way long bullets in slow barrels is flirting with destroying a good suppressor.

This is all based on my limited experience and personal bias so please don't let it curb your desire to seek the truth and feel free to smack me up side the head through the ethernet with any facts to correct any misinformation I may have inadvertently distributed.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by pneumagger » Mon Apr 15, 2013 7:31 pm

I'm learning here too. I've never owned a bolt gun nor a rifle suppressor... so picking a desirable twist & length to accomodate both is multitasking in new territory for me.

I think I'll make life easier and just go with a Howa 1500 and factory 1:10 barrel... then have it cut to 22" and threaded for an AAC 51T 762 Brake. With a decent B&C stock I think this is my most affordable route to good accuracy in a suppressed bolt. I really wanted a R700 action in a B&C stock, but a 1:12 sacrifices alot for subsonic use and a barrel change would have been a few hundred extra more.

So for now, I think the Howa 1:10 22" .308 is the route I'd take.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by 700PSS » Mon Apr 15, 2013 9:14 pm

pneumagger wrote:Is there a problem with trying to work up a 200+ grain subsonic load out of a 22" barrel? I realize the 18" is probably a bit better for subsonic primary or dedicated use, but I do want to use the rifle to shoot long range as well (whether suppressed or unsuppressed). I feel like an 18" barrel would limit my velocity/range on long distance loads.

Have you tried 168gr SMK/Amax or 155gr Scenars in your 1:8 twist? Do they stabilize at full velocities?

Thanks.
I shoot mostly 168gr SMK Fed GM in mine. Only subs I've used are Cor-Bon. As some have said here, use a ballistics calculator to determine at what point your supers go subsonic and you'll know your max range.

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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by johndoe3 » Tue Apr 16, 2013 1:06 am

In 308 subsonic, the 22" barrel will work OK and an 18" will work. In practice, the 18" barrel gives a lower ES in velocity over the 22". The reason is that the cold bore subsonic for the longer barrels causes a higher velocity variation.

That said, I have a number of 308 rifles and have shot subsonic with a 24" barrel (1in10 twist) with 220 grain bullets and for me they were stable. However, I am shooting at 5000' altitude and above, and the density altitude and air pressure gives a significantly higher bullet stability than at sea level.

I also have a 308 rifle with a 21.5" barrel (1in11.25) and another 308 rifle with an 18" barrel (1in10).

For occasional subsonic shooting, you will be happy enough with the results of the Howa with a 22" barrel with 1in10 twist. That choice will also give you better long range supersonic shooting. Run the stability calculator at JBM and you can see the results for yourself. It's accurate in relation to real world experience. Be sure to set your altitude in it to get the most accurate output for where you live; and it is done by setting the "Pressure". It defaults to sea level (29.92), whereas for 1000' (in Ohio?) the station pressure for a standard day is 28.86. Here are a few bullet lengths you can use in the calculator.

Sierra 175gr MK -- 1.240"
Sierra 220gr MK -- 1.489"
Lapua 200GR --1.340"
Hornady 208gr AMAX--1.532"
Sierra 180gr Gameking -- 1.287"

For each bullet in the calculator, determine the stability at temp settings 0F and 100F, and you'll see that using the temperature extremes, you have much more bullet stability in hot weather. The result is that during the hot summer you might be able to shoot 220gr bullets OK with a 1in10 twist, subsonic; while in the cold of winter they'll keyhole.

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by pneumagger » Tue Apr 16, 2013 7:50 am

Thanks for the link! I'll play around with it some and see whats up.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by robpiat » Tue Apr 16, 2013 9:03 am

Just FYI, the 155 Palma bullets (I.E Scenar) are LONGER than the 168/175 MK bullets.

You are basically approaching 260 performance without buying a new gun. Like a 260, you will have less barrel life than a 308.

1:10 is still my preference

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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by doubloon » Tue Apr 16, 2013 3:31 pm

robpiat wrote:Just FYI, ...
Cool!

I've not yet been far enough along in my long range education to have run across the Palma but it seems to still fit into what I've read about stabilization being more dependent on bullet length than bullet weight.

FWIW everything I've read about "overstabilization" seems to be unproven theory and a subject of much debate.

Also, 1:10 is my do it all preference for 308 as well.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by pneumagger » Tue Apr 16, 2013 11:14 pm

I was looking at the BC on the 178gr Hornady Match and it's WAY higher than even the 155gr scenars! And the 168gr Nosler BT & 178gr Amax both have good BCs and should offer good terminal performance too. Finally, I'll be trying some of those Hornany 180gr RN for subs that everyone talks about.
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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by JohnnyC » Wed Apr 17, 2013 5:18 pm

Any of the 175/8's have close enough BC's that realistically I don't think you'll be able to shoot the difference. Work up a load for each and keep the data on the best ones that way no matter what you can always load something accurate regardless of component availability, etc.

I mean, if a 175 gives you .25 MOA at 100 and the 178 gives you .20 MOA, first are you capable of that accuracy to begin with (let's be honest, at 600 yards most "1/4 MOA shooters" aren't), then are you capable enough to see the accuracy difference between the two, considering that's if it's that much difference in the real world to begin with. At long range, where BC really matters, is it really worth the time and energy chasing down the highest possible BC you can find, or is it a far better usage of your time going with a proven load and learning to shoot it well.

While I understand the appeal of wanting to eek out every bit of velocity, drop, wind handling, with something like a .495 BC vs a .505 BC vs a .508 BC, is it worth the time, cost, etc. to source components, develop loads, et. al. when you're most likely not going to see a tangible benefit?

As an example, a 155 Lapua Scenar with a .508 BC, 2900 FPS has only about a .1 mil difference compared to a 175 SMK with a .505 going 2550 FPS at 1k yards. At some point the chase is nothing but diminishing returns. Find something good that works and stick with it, without putting too much headache into it. It's a .308, don't overthink it, it's not like anything you're going to be doing is new, and chances are all the homework you'll really have to do is half an hour on the interwebs with some range time thrown in for good measure.

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Re: Looking into a R700 build... any downsides of 22" 1:8 tw

Post by RJT » Wed Sep 11, 2013 1:29 pm

pneumagger wrote:On the flip-side, I think I might have a 1:8 LR308 barrel made or something similar. A carbine length 1:8 308AR pushing 220gr loads probably wouldn't have any trouble cycling .308 subsonic with an adjustable gas block. The only real question, as with a 1:8 twist bolt gun, is whether it shoot the lighter ammo well (?). I would have to think that 110gr TAP @ 2800fps out of a lightweight 16" .308 would be NASTY for anything standing in the way.

Don't forget about COA(cartridge overall length). You may have magazine/feed issues on a semi-auto running subs.
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