510 Whisper Build Advice (Stock/Bottom Metal/Magazines/Twist/Barrel Length)

[Airwolf...]

Hi all,

After my first and mostly successful foray into custom bolt actions with my 338 Lapua Improved build, it's time to start the next one. I have decided to build a 510 Whisper bolt action. I was wondering if anybody could help with some questions regarding parts selection for this build. So far, I have purchased the action, which is a Remington 700 footprint Long Action that supports 4.050" magazines.

• Will 510 Whisper cartridges fit in a 338 Lapua Magnum AICS magazine? For my 338 Lapua Improved build, Fritz at Black Canyon Customs machined out the shoulder guides of my MDT 3.850" AICS magazines and I am curious if I would have to have something similar done for these to fit, if at all.
  • Is there any point to using 4.050" magazines that have a max COAL of 3.970"? I see that the 750 AMAX load on SSK's load data has a COAL of 3.620" and a standard CIP AICS magazine allows 3.740". It's always nice to have some extra room to work with, but if it is going to make everything else a pain, I won't bother.
• Are there any chassis-style stocks (like the MDT ACC Elite or MPA BA etc) that accept 4.050" AICS magazines? I have not been able to find any.
  • If no chassis style stocks would work, what stock would you recommend? I would prefer to keep it at or less than $700 if at all possible.
• What length barrel would you recommend? I am happy to SBR the action and go with a short barrel. I was looking at the SSK load data and they are using an 18" barrel. I think this is a bit long for my needs, as I was planning on developing my loads with Vihtavuori N110 and it is a very fast burning powder.
• What twist rate would you recommend for a 510 Whisper? I see that Maker Bullets offers a 1000gr 50 BMG Subsonic REX and a 900gr 510 Whisper Subsonic REX that both have a recommended twist rate of 1 in 10.

Thank you in advance!

 

[Dirty D]

I haven’t built one (yet) but looking at the specs I would assume that a CIP length magazine would be the easy button. The COAL is listed at 3.34” with a 750 grain bullet and the CIP magazines are 3.8”

 

[chance553]

I built mine with CIP length mags. I had to machine out the shoulder guides on the MDT mags, while AI mags worked ok. I am thinking I may shorten up a mag similar to those 6BR mag kits, as the M33 ball projectiles end up at about 3.20" COAL and theres a ton of room in the mag.

I like KRG stocks at that budget. I put a whiskey 3 on mine.

You will need a 1 in 10 or faster barrel. Mine is 17", but may SBR it later down the road.

 

[45-90]

This is what I used a new Rem 700 mag action with a new Lapua bolt... which has to be machined a bit to fit the action.
The barrel is 1-10 twist was a McGowen blank 26" long.
I purchased a pt&g 510 whisper finish reamer, and threaded and chambered it.
Used the finish reamer to make a cartridge gauge.
Bought 1000 pcs of brass 338 Lapua and mostly 300 Norma brass to convert .
Did this on an industrial scale with lathe and mill.

Used an aluminum chassis, with 3.715" MDT detachable mags. Open up the bullet guide, and mess with the front to feed the .510 bullets.

The military 650 fmj bullets are around 3.2" and 750 ATips around 3.615" for COAL.
I have not used the 900 gr Maker subsonic.
But have been messing with some light supers, like 350 gr .510 HG bullet that supposed mushroom at 900 fps but run them at 2450 fps in the Whisper accurately.

Here is some load data...adjust to fit your barrel length.
First set of data is 650 fmj or 610 gr APIT.
2nd set is for 750 gr Atip.

The subsonic loads are easy on the shoulder, but you'll notice a difference as one goes to supers like a 750 gr at 1450 to 1500 fps. Even the light bullet super wiith almost 5000 ft/lbs of energy seem to have less recoil.

The APIT are fine at subsonic speed at 100 yds, but start damaging 3/8" AR500 plate at 1200 fps, and penetration starts at 1200 to 1400 fps, and almost penetration above that.
The tips ignite as low 800 fps on many surfaces, blow up on fairly light targets...just have a giant grave pit with no dry flammable materials....and Not in fire season anywhere.
This is one of the most fun sub/ super calibers available...and I already shoot the 300 blk, the 8.6 blk, the 338 Spectre.

 

[NHPiper]

This is what I used a new Rem 700 mag action with a new Lapua bolt... which has to be machined a bit to fit the action.
The barrel is 1-10 twist was a McGowen blank 26" long.
I purchased a pt&g 510 whisper finish reamer, and threaded and chambered it.
Used the finish reamer to make a cartridge gauge.
Bought 1000 pcs of brass 338 Lapua and mostly 300 Norma brass to convert .
Did this on an industrial scale with lathe and mill.

Used an aluminum chassis, with 3.715" MDT detachable mags. Open up the bullet guide, and mess with the front to feed the .510 bullets.

The military 650 fmj bullets are around 3.2" and 750 ATips around 3.615" for COAL.
I have not used the 900 gr Maker subsonic.
But have been messing with some light supers, like 350 gr .510 HG bullet that supposed mushroom at 900 fps but run them at 2450 fps in the Whisper accurately.

Here is some load data...adjust to fit your barrel length.
First set of data is 650 fmj or 610 gr APIT.
2nd set is for 750 gr Atip.

The subsonic loads are easy on the shoulder, but you'll notice a difference as one goes to supers like a 750 gr at 1450 to 1500 fps. Even the light bullet super wiith almost 5000 ft/lbs of energy seem to have less recoil.

The APIT are fine at subsonic speed at 100 yds, but start damaging 3/8" AR500 plate at 1200 fps, and penetration starts at 1200 to 1400 fps, and almost penetration above that.
The tips ignite as low 800 fps on many surfaces, blow up on fairly light targets...just have a giant grave pit with no dry flammable materials....and Not in fire season anywhere.
This is one of the most fun sub/ super calibers available...and I already shoot the 300 blk, the 8.6 blk, the 338 Spectre.

What's the case fill % look like with some of those powders?

How far out have you pushed the subs?

 

[MK20]

This is what I used a new Rem 700 mag action with a new Lapua bolt... which has to be machined a bit to fit the action.
The barrel is 1-10 twist was a McGowen blank 26" long.
I purchased a pt&g 510 whisper finish reamer, and threaded and chambered it.
Used the finish reamer to make a cartridge gauge.
Bought 1000 pcs of brass 338 Lapua and mostly 300 Norma brass to convert .
Did this on an industrial scale with lathe and mill.

Used an aluminum chassis, with 3.715" MDT detachable mags. Open up the bullet guide, and mess with the front to feed the .510 bullets.

The military 650 fmj bullets are around 3.2" and 750 ATips around 3.615" for COAL.
I have not used the 900 gr Maker subsonic.
But have been messing with some light supers, like 350 gr .510 HG bullet that supposed mushroom at 900 fps but run them at 2450 fps in the Whisper accurately.

Here is some load data...adjust to fit your barrel length.
First set of data is 650 fmj or 610 gr APIT.
2nd set is for 750 gr Atip.

The subsonic loads are easy on the shoulder, but you'll notice a difference as one goes to supers like a 750 gr at 1450 to 1500 fps. Even the light bullet super wiith almost 5000 ft/lbs of energy seem to have less recoil.

The APIT are fine at subsonic speed at 100 yds, but start damaging 3/8" AR500 plate at 1200 fps, and penetration starts at 1200 to 1400 fps, and almost penetration above that.
The tips ignite as low 800 fps on many surfaces, blow up on fairly light targets...just have a giant grave pit with no dry flammable materials....and Not in fire season anywhere.
This is one of the most fun sub/ super calibers available...and I already shoot the 300 blk, the 8.6 blk, the 338 Spectre.

Could one use a standard 700 long action and just open the bolt up to 338 bolt face? The pressure level in the gun will be relatively low anyway but does the action have the required length?

Thanks.

 

[45-90]

Could one use a standard 700 long action and just open the bolt up to 338 bolt face? The pressure level in the gun will be relatively low anyway but does the action have the required length?

Thanks.

Yes, any Remington LA and open the bolt face.
Or buy a Lapua mag bolt, that may have to be fitted to your action...or measure the bolt bore dis under the front and rear bridges with gauge pins and order a bolt .001 ot .002 smaller from pt&g.



..

 

[45-90]

What's the case fill % look like with some of those powders?

How far out have you pushed the subs?

I'd have to look it up, but some are rather full with the slower powders. And the full would depend on how far out you seat the bullet.
I use these for plinking especially the military bullets.

I have some super loads to try that are close to 100% fill with win 296, and s 300 grain bullet and may get to 2700 to 2800 fps.
The 510 Whisper is rated at 50,000 psi for the break open Contender, but one can run a bit higher in a bolt action.

 

[NHPiper]

I'd have to look it up, but some are rather full with the slower powders. And the full would depend on how far out you seat the bullet.
I use these for plinking especially the military bullets.

I have some super loads to try that are close to 100% fill with win 296, and s 300 grain bullet and may get to 2700 to 2800 fps.
The 510 Whisper is rated at 50,000 psi for the break open Contender, but one can run a bit higher in a bolt action.

Maybe at some point I will get one built. I love shooting subs. I did not like the accuracy I got with SBRed 300blk bolt guns. 16" barrels produced much better subsonic groups.

It's a miserable subsonic round to load for because all of the variables become much more sensitive. Seat the bullet deeper, spike the velocity up. Pour .1gr off with the powder, damn that's a larger variance of the total load. Etc.

Would be curious if the 510 whisper has been easier to find good nodes and groups.

 

[45-90]

So I am not at this point shooting for accuracy in the 510 Whisper.
But using up out dated deteriorated powders, various primers from decapped primed pulled cases, and lots of 650 gr fmj and a few APITs.
When is the last time you purchased IMR powders for $3.89 per pound?
These are plinking rounds...

How did they shoot at 60 yds?
First shot high, over adjust scope low, next us close to center with 1 shot way off to the right, could be the shooter of the resized 650 fmj bullets not known for accuracy...this is with deteriorated powder, various reused primers, no idea as to the mix of magnum or standard LR primers.
Just cheap plinking ammo.

There are not many match bullets in .510 caliber, and the ones available are expensive. So this is a way to have cheap shooting with the 510 whisper.

For sub hunting one should consider the 900 or 1000 gr Maker bullets. They bring a whole new dimension to wound channel and energy on target....but I have not tried them yet. For super hunting you have an elephant gun available in the .510 Whisper.

I no longer use short barrels below 16" ...no more SBR or pistols. Even the 9mm AR has went from 10" to 14.5" pined and now 16" no suppressor. The 16" is much better and faster, one can get 750 ft/ lbs of energy out of a 9mm hand loaded with plus p ammo 124 gr HST at 1600 fps. 1720 for 115 gr. Or 2640 fps for 50 gr copper hp out of a 9mm.

 

[45-90]

Maybe at some point I will get one built. I love shooting subs. I did not like the accuracy I got with SBRed 300blk bolt guns. 16" barrels produced much better subsonic groups.

It's a miserable subsonic round to load for because all of the variables become much more sensitive. Seat the bullet deeper, spike the velocity up. Pour .1gr off with the powder, damn that's a larger variance of the total load. Etc.

Would be curious if the 510 whisper has been easier to find good nodes and groups.

I have found the best subsonic round to be the 338 Spectre in the AR 15 platform with a 16" barrel.
It comes with a 6.5 twist almost identical to the new 338 ARC with about a grain and a half less capacity because the one is a shortened 224 Valkyrie case or 10mm Mag case and the other a shortened grendel case.
The 338 Spectre has high load density, single digit S/D with subs or supers, bullets from 160 Barnes to 300 Maker...
and great accuracy...in a 16" barrel no suppressor.
Only one powder needed LilGun. 100 % burnt, high load density. Small Rifle primers or large pistol primers still small S/Ds. But the SR primers are the way to go for top super velocities.
I have shot the Maker 300 gr and 350 gr sub bullets and their 165 copper slit super bullets around 2120 fps in the Spectre,
plus cheap Speer 200 & 225 gr.
Here is exact load data in AR 15. Running a titanium bolt carrier.

The difference between the 338 Spectre and 8.6 Blkout with hybrid cases, which id great for supers but too much case capacity for subs and requires an AR 10 platform...so if your into subs the smaller case 338 Spectre is easy to tune for accuracy...most everything is accurate, with LilGun...and it shoots the same bullets. Except these 350s are a bit much, and I make bore riders out of them to get 1100 fps, or cut 6 grains of copper off the front in the lathe.
This SR primer and reformed case shows super low S/Ds.
The new 338 Spectre vs the 338 ARC...very similar but the ARC has an 8 twist the 6.5 twist has been my favorite for accuracy, versility, and consistency with these sub calibers. Do not go 3 twist in the 8.6 blkout, its inaccurate, inconsistent, blows up jacketed lead bullets, and dangerous if pushing velocities to your muzzle devices and bystanders.
With the 338 Spectre and LilGun you can run your 300 gr Maker specifically made for 6.5 twist right up to 1100 fps to give you max sub velocity for max energy transfer to the animal, without going super...it's very consistent in 16" barrel.

Cheaper to shoot than the 510 whisper, but if you want maximum subsonic energy, and killing power the .510 Whisper and 900 gr Maker bullets will be the way to go.
And solids from armor piercing to brass and copper should take care of any elephant on the menu.

 

[45-90]

In case ya need to open up the bullet guides on a 338 Lapua MDT magazine to .510 whisper...here's how it did mine.
Use an adjustable parallel inside the mag so you can put aluminum packing blocks on the outside and clamp down tight on the OD with the milling vise...level the top before machining.
I used a 4" long 1/4" carbide end mill.
Touch and go about .040" in .010" increments on plunge cuts then mill back and forth to flatten.
Do the same to the other side, & done.
Polish with 320 grit sandpaper, clean and reassemble.

 

[Airwolf...]

This is what I used a new Rem 700 mag action with a new Lapua bolt... which has to be machined a bit to fit the action.
The barrel is 1-10 twist was a McGowen blank 26" long.
I purchased a pt&g 510 whisper finish reamer, and threaded and chambered it.
Used the finish reamer to make a cartridge gauge.
Bought 1000 pcs of brass 338 Lapua and mostly 300 Norma brass to convert .
Did this on an industrial scale with lathe and mill.

Used an aluminum chassis, with 3.715" MDT detachable mags. Open up the bullet guide, and mess with the front to feed the .510 bullets.

The military 650 fmj bullets are around 3.2" and 750 ATips around 3.615" for COAL.
I have not used the 900 gr Maker subsonic.
But have been messing with some light supers, like 350 gr .510 HG bullet that supposed mushroom at 900 fps but run them at 2450 fps in the Whisper accurately.

Here is some load data...adjust to fit your barrel length.
First set of data is 650 fmj or 610 gr APIT.
2nd set is for 750 gr Atip.

The subsonic loads are easy on the shoulder, but you'll notice a difference as one goes to supers like a 750 gr at 1450 to 1500 fps. Even the light bullet super wiith almost 5000 ft/lbs of energy seem to have less recoil.

The APIT are fine at subsonic speed at 100 yds, but start damaging 3/8" AR500 plate at 1200 fps, and penetration starts at 1200 to 1400 fps, and almost penetration above that.
The tips ignite as low 800 fps on many surfaces, blow up on fairly light targets...just have a giant grave pit with no dry flammable materials....and Not in fire season anywhere.
This is one of the most fun sub/ super calibers available...and I already shoot the 300 blk, the 8.6 blk, the 338 Spectre.

Thank you so much for all of the great information! I will report back as soon as I get mine in.

 

[45-90]

So I did some 510 Whisper shooting today.
300 gr Barnes supersonic maximum effort loads. Along with some IMR 4227 650 fmj loads that were subsonic.
The 300 gr Barnes orginial reached 2875 fps for a max load...that's 5500 ft/bs of energy. One if the flattened 300 gr bullets was over 1.300 dia recovered from the dirt bank.
The 510 Whisper is not a small case here compared to the 338 Ruger compact magnum. So it can deliver 458 magnum energy to the target if needed...I wasn't kidding about elephants.