Optimum barrel length & twist rate for .510 Whisper?

[Thunderclap]

Hi everyone! I’m new to this forum. I’ve been searching for information for a .510 Whisper project but there doesn’t seem to be a whole lot out there. I was wondering if anyone could tell me what would be the optimum barrel length & twist rate for subsonic shooting.

[THE DOCTOR]

1/8 twist is optimal and 16-18 inches is adequate for stabilization

I make brass from 338 lapua if you need some

good luck with your project

[Thunderclap]

Thanks man. I will be needing brass. I'll send you an E-mail when I get to that point.

Can anyone give me the names of a few people that make barreled actions for these (besides SSK Industries) and about how much they cost? I would like to shop around.

[Titleiiredneck]

Contact the user spook on these forums, I belive he knows the skinny on the 510.

[THE DOCTOR]

S1 of artactical.com also builds them among many other fine weapons

you might send him an email

[onechance]

The Doctor, you have a PM

[LouBoyd]

I've been watching this thread and am puzzeled. How can you discuss useful barrel lengths and twists without specifying the bullets you're trying to shoot? A 600 grain cast lead Postell certianly doesn't need the same barrel length or twiist as an 800 Grain Barnes solid. The bullet style also determies what length of action is needed and the shape of the throat.

For supersonic bullets barrel length determines how much velocity you can squeeze out of given case capacity and peak pressure. But for suppressed subsonics you just need a barrel long enough to allow the cartridge to get the bullet up to speed. Any longer just hurts accuracy from velocity dispersion. Typically 8 to 12 inches is plenty. For legal reasons a lot of subsonic barrels are 16 inch. For unsuppressed rifles a long barrel can reduce muzzle pressure to where the propellant gas escapes the muzzle subsonic, which makes the rifle fairly quiet, but then barrel friction becomes a major issue.L Lubricated cast lead is the usual solution. I have subsoinic rifles with barrel lengths from 10 to 36 inches. They each have their place but not for all bullets. For twist rate you have the choice of selecting a barrel which shoots one style bullet very well or any bullet with only fair accuracy. It's unlikely to find one barrel which works right for all bullets.

Maybe another thread on selecting bullets for subsoniic use would be useful . The target and it's terminal ballistics mainly controls bullet selection. Range and atmosphere also play a part. The name of the cartridge or it's diameter and powder capacity (like stating it's a 510 Whisper) have much less to do with selecting barrel length and twist than does bullet selection.

[Thunderclap]

LouBoyd, thanks for chiming in. There are a lot of variables that I’m not aware of, that’s why I’m on here asking questions. Primarily the rifle will be used for killing feral hogs quietly at long range. My thinking was that I would experiment with different types of bullets after I have the rifle to determine which one works the best, but from what you’re saying it sounds like I need to have the bullet picked out before I order the rifle.

It seems like most .510 bullets should have enough energy to take care of a hog a 500 to 600 yards so its probably most important to pick a bullet that flies accurately. Is there any reason to use soft point or hollow point bullets? I’ve read before that they don’t actually expand the way they are supposed to at subsonic velocities but I don’t know if that’s right.

Anyway, I was thinking about using the Winchester M33 650 grain full metal jackets. Anyone have any other recommendations?

[THE DOCTOR]

Lehigh makes some great hunting bullets

http://www.lehighbullets.com/products.asp?cat=10

The pre cut 680 gr. bullet is devastating on hogs and is the most impressive 50 cal subsonic bullet i have found.

[redtazdog]

Both of my 510 guns shoot great with 500grn to 800grn bullets, 1050fps subs and 1600+fps supers.
Hawk has good bullets for subsonic hog killers.
I have used the 500grn hawk and the 600 grains x .035 RN..........$59.50
http://www.hawkbullets.com/Pricelist.htm
.
http://i197.photobucket.com/albums/aa166/redtazdog/510Whisper1w.jpg

[redtazdog]

Lehigh makes some great hunting bullets

http://www.lehighbullets.com/products.asp?cat=10

The pre cut 680 gr. bullet is devastating on hogs and is the most impressive 50 cal subsonic bullet i have found.
I have some of the lehigh 680's and yes they work good but they didnt
kill the hogs any better than the Hawk bullets.
The performance and the price is nice at 1.20 each

[LouBoyd]

Primarily the rifle will be used for killing feral hogs quietly at long range. My thinking was that I would experiment with different types of bullets after I have the rifle to determine which one works the best, but from what you’re saying it sounds like I need to have the bullet picked out before I order the rifle.

What do you consider to be "long range". I shoot supersonics out to 2000 yards. For me anything over 1000 yards is long range. For subsnoics though in my opinion long range starts where you HAVE to use a rangefinder to hit anyting. That starts somewhere around 300 yards. A 510 whisper will >easily< launch 700 grian bullets, and over 1000 grains is practcal in cast lead. Bullt shape harldy matters to 500 yards. I shoot 700 gn flat nose 458's.
The heavy VLD's Hornady's and Barnes solits have plenty of retained energy over 1000 yards, but your chance of hitting anthing due to velocity dispersion is low at that range.

I'd suggest you do some "what if's" using a ballistic computer. I use the Quickload/Quicktarget pair from Neco. Quickload can calculate chamber pressures, loads, effeects on seating depth, and the effects of barrel friction. Here are some other useful calculators free on line. http://www.eskimo.com/~jbm/calculations/calculations.html The drag and twist calulator here is excellent based on work done by Robert McCoy at the US Armys Ballistic Research labs. It's tediouis to use though. Note that most bullet dimensions are in calibers (decimal fractions of bullet diameter). The Greenhill formula isn't of much use for subsoinics. Unfortunately that calculator doesn't allow adjusting air density or speed of sound It's fixed.at standard conditions. With subsoinics the two rules are that the bullet weight alone (just under Mach 1) sets the muzzle energy and the bullet's BC and air density sets how much of that energy is retained dlownange. Ultra high BC's don't gain much, but BC's over about .5 are desirable for "practical" ranges. (300+ yards). To 100 yards a 700+ gn flat nose cylinder is ok.

As to bullets expanding, There was a Sherlock Holmes storry about a a sniper killiing people (and attempting to shoot Holmes) using a big bore air rifle shooting soft cast lead. A.C. Doyle knew of such rifles which were available tthen. Pure lead is excellent for it's subsonic terminal ballistics. No 50 BMG bullets will expand in flesh at subsoniic velocities, nor will solids.. The slitted Lehigh solids will (at least should). I have some but haven't shot them. A major problem for subsonics is bore friction. You need a very short barrel to shoot hard jacketed bullets they have to be lubed. Cast lead is simpler and for practical length actions can typically carry more energy just because of lead's density. With subsonics you're fighting primarily the time filght squared drop which is essentially the same for all heavy subsonics for a few hundred yards.

I cant' advise what's best. I'm still experimenting.