Guys,
Are the two compatible? I am in the process of getting all the gear needed to build a 300Whisper with 1:8" twist and would very much like the option of using a light cast projectile to duplicate 30Carbine ballistics. I reckon it would hammer Mr Fox when he's whistled in to within 100yards . Very much looking at a "fat" 22WRFM if you wish.
Cheers...
Con

Excessive twist is not helpful but may not be the end of the world as long as velocities are sedate. Ditto a short cast bullet in a long throat, which seems likely to be the case in a 300 Whisper. Just armchair theory -- I don't have any experience with the 300 whisper.

Speaking only from my own experience the faster the twist the more limited you'll be on velocity and getting carbine like speed won't be easy with an 8 twist. Jacketed shooters are using 17 or 18 twist barrels to shoot inch long bullets although of course they're shooting much faster. An 8 twist barrel would most likely stabilize an 1 1/2 long bullet easily so if fox with a light bullet is going to be a primary use for the gun I'd suggest thinking about at the fastest a 14 twist.

Pat

Thanks guys,
The 1:8" twist is to allow all projectiles to be used from the 85gr pistol projectiles through to heavy match 240gr. The cast projectiles are to be a side line. Having said that, the suggestion of a 1:14" is a good one as the rifle will use 110gr through to 125gr as its "bread and butter". Might need to give this one a little more thought. On the flip side, will a fast twist like 1:8" be detrimental to shooting a heavy 200gr cast successfully? My only expereinece with cast is in a 45/70 Marlin, so this is a learning experience!
Cheers...
Con

The problem with the fast twist is it tries to tear the bullet up if the velocities are higher. A 1-12 twist is still friendly to cast, and 1-10's aren't too bad, but under 1-10 and you're really putting a strain on the bullets.

You only need the 1-8 if you're looking to drive the 240 gr subsonic loads.

It's a pretty tall order to expect everything from 85 gr to 240 gr bullets to shoot well in any twist barrel. Just my opinion but if 110 or 125 grain bullets are going to be the bread and butter of the gun build it around them and forget the rest. You could use a 14 or 15 twist barrel which should not only shoot the jacketed bullets well but do very well with something like the RCBS 165 gr. sil bullet. I doubt many fox shot through the lungs would know the difference between that and a heavier bullet and it seems to be one of those bullets that people have luck with, more bullets to the pound also.

I don't know if an 8 twist would be detrimental to anything cast bullet related but I do believe it'll be harder to find a good shooting load with any kind of velocity.

quote:

Originally posted by Con:
Guys,
Are the two compatible? I am in the process of getting all the gear needed to build a 300Whisper with 1:8" twist and would very much like the option of using a light cast projectile to duplicate 30Carbine ballistics. I reckon it would hammer Mr Fox when he's whistled in to within 100yards . Very much looking at a "fat" 22WRFM if you wish.
Cheers...
Con

Accuracy with your 1-8" twist barrel will go south (given quality cast GC'd bullets) between 1500 and 1600 fps with the lighter 30 carbine type bullets. Heavier cast bullets should give good accuracy into the 1700 fps range. The twist of the barrel correlates into RPM. Your barrel will generate 135,000 RPM at 1500 fps. Most cast bullets will lose good accuracy above 140,000 RPM. In short cast bullets (i.e. the 30 carbine type) those with a long bearing surface and short nose will most often produce the best accuracy at the highest velocity. There are always exceptions and only testing in you barrel will give you the "right" answer.

Larry Gibson

I don't see why cast bullets and fast twists should be a problem. I shoot cast in my .223, 1 in 9", all the time and get consistent less than 1 moa groups at over 2400fps. Also, I use cast in my Swedish Mauser, 1 in 7.5", without problem.

andrew375,
There are at least two potential problems with a fast twist.

One problem is that all bullets and particularly cast bullets are imperfectly balanced. Even if the bullet is perfect when you load it, it may well be damaged and become unbalanced as it travels down the barrel. When this unbalanced bullet exits the barrel, it is going to wobble. The faster it spins, and the greater the imbalance, the more it will wobble. This problem is well understood and there is an exact formula to predict the effect of imbalance and twist on group size -- though there is no practical way to measure the imbalance. You can find the forumula in either Mann's book (The Bullet's Flight) or Vaughn's book (Rifle Accuracy Facts).

In fact, Mann concluded that the imbalance-induced wobble was the primary limitation of accuracy.

The other potential problem is that the bullet may "strip" the rifling, though this rarely occurs and people worry about it too much.

The twist problem is more complicated than "X" velocity or "Y" twist or "Z" RPMs because the diameter factors into the equation as well. Smaller calibers can tolerate more RPMs than larger calibers. Yes, you can shoot 22s at 2400 fps with a 1-9 twist, but good luck doing it in a 45 caliber with 1-9 twist. The aforementioned equation accounts for the diameter.

As I stated, I have no experience with the 300 whisper, but I've shot thousands of cast bullets in 7mms with 1-9 twist, and they were quite satisfactory at sedate velocities. It's just that if you want to push the velocity, the twist is going to open up groups.

Push the 6.5 OldFeller 170 grain bullet past 1600 fps in a Swede and things get real snakey, real fast. Below that velocity, they shoot very well. I'm told that shorter cast bullets allow somewhat more velocity in the Swede's fast twist.

The very long .30 HBC bullet (210 grns?) behaved similarly for me in a 1-10" .308.

If you want .30carb ballistics, get a .30carb barrel. It is a wonderful small game round out of a Contender pistol or carbine just as it is, at its best with bullets/boolits in the 100-120gr range.
The Whisper is designed to shoot its best with heavy bullets (150gr & up) at sils, and building one with a fast twist will make it less able to stabilize them. There is no reason at all why you can't use a cast boolit (GC's & ww alloy) in the 130-160gr range to hunt small game with it.
As I am sure you are aware, for deer, it really doesn't have what it takes energywise except at extremely short range, though its big brother the .30/223 does, with ballistics up into the .30-30 & 7.62x39 range. For that matter, either of those would in my opinion be a better choice than the Whisper for two reasons, greater versatility and much greater availability of inexpensive brass. Both are also readily available in a number of different action types right off the rack, new or used, where the Whisper would pretty much limit you to a Contender or other single shot custom job.