.30 caliber twist rate question

[wmitty]

Kreiger has a .30 caliber blank with a 1-17" twist rate. Asking for opinions; would the 311466 be stabilized at such a slow twist rate? Looking to build a dedicated cast boolit shooter in .30-06 and don't want to go to an extreme twist if it will be useless except for very light boolits.

[Outpost75]

I have a .30-'06 with cut rifled Obermeyer 1:16" twist barrel which is scary accurate shooting 152-grain Ball M2 and 160-grain cast bullets which fit the military chamber at charges which function my M1 Garand and provide about 2200 fps with 40 grains of IMR4064. I expect that #311466 and similarly blunt cast bullets having similar a ratio of length-to-diameter will shoot fine in the 17" twist, but will probably need to be driven to velocities equivalent to the .30-30 Winchester to be stable.

My circa 1942 Winchester Model 70 is chambered the same as an M1 Garand National Match barrel and is glass bedded into a WW2 Van Orden pattern "Marksman" stock which resembles the butt shape of the '03 Springfield "C" stock, without handguards, with the fore-end shaped into a semi-beavertail with rail. Scope is an external adjustment 10X Unertl Vulture with return spring and clamp. The rifle is also equipped with a long slide Lyman 48 receiver sight and has an M1 Garand front sight fitted onto an integral base machined into the muzzle of the 24 inch straight-tapered barrel which is 0.80" diameter at the muzzle.

I cast bullets about 16 BHN using 50-50 scrap linotype and wheelweights. Bullets are sized .311" to fit the somewhat worn throat and are lubed with 1 part Dextron ATF to 4 parts of beeswax. I assemble my loads in LC Match cases, primed with Winchester WLRs or Federal 210s. I would start with 35 grains of either IMR4895, IMR4064, RL15 or Varget and use a 1 grain Dacron fiber filler tucked loosely into the case neck, its final position being determined by the base location of the seated bullet. Once you find the sweet spot for your rifle you should expect quality bullets to produce ten-shot groups in the 3-4" range at 300 yards.

Larry Gibson has a similar rifle and I believe shoots very similar loads.

Hopefully he will chime in here and elaborate on anything important which I may have left out.

[Rcmaveric]

Use a bullet stability calculator. There are numerous on the web. Then just plug in the bullet length and velocities you plan on shooting and your local weather. See if it works.

Sent from my SM-G950U using Tapatalk

[Outpost75]

I have found many of the so-called stability calculators do not agree with empirical experiments.

I prefer ten-shot groups at 100, 200 and 300 yards, looking to confirm that the groups are circular normal with vertical and horizontal variances are approximately equal and that the dispersion maintains proportionality to the range.

Some typical 7.62mm, ten-shot, 200-yard test groups, fired off sandbags with 10X Unertl, Mauser with 12" twist NATO STANAG chamber, Winchester Model 70 10" twist SAAMI chamber:

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[Larry Gibson]

Concur with Outpost75; "many of the so-called stability calculators do not agree with empirical experiments" as there are other factors that enter into "the when" a bullet is stabilized. The 311466 can be stabilized in the 17" twist but, as Outpost75 mentions, it will have to be driven relatively fast. If fast is your game then the 17" twist will be okay with the 311466 or the slightly longer 165 gr NOE 30 XCB (310-165-FN). I've found the 16" twist to be superb with those bullets also up through 3000 +/- fps yet that twist also allows a bit of leeway at the lower velocity level. I use (and highly recommend their barrels) a 16" twist 3 groove Broughton barrel (920-922-4882) chambered in 30x60 (short chambered '06) and get excellent results.

If you want an "all around" cast bullet twist for 30 caliber including the 30-06 I recommend a 14" twist with a minimum length of 26" (the longer the better). With a 14" twist it will stabilize cast bullets up through the 311299 (200 gr) in length the faster end and the 311466 down to a very low end velocity. My 14" twist 27.4" long Palma barrel (.308W) is very accurate with the 311041 at 2600 fps which makes for an excellent deer/antelope hunting load out to 300 yards but my 16" twist will not shoot them as well which indicates they are only marginally stable in the 16" twist.

Again, if rebarreling with a new barrel, I highly recommend Broughton barrels. If another make barrel then I suggest, for higher velocity use, a 4 groove with not less than .004" deep grooves and several makers even make a 15" twist which may be a decent "compromise".

As to jacketed bullets the 14" twist will stabilize them up through 180 gr SPs with the exception of the longer 175 - 178 VLD types. However, the 14" twist will stabilize a 175 Sierra MK at 2800 fps quite nicely which is easily doable in a 26" barrel. It also improves the accuracy of milsurp M2 and M80 bullets by lowering the RPM. The same M80 ammunition that gives 2 - 3 moa accuracy in 10" twists gives 1 1/2 - 2 moa in 12" twist and basically moa accuracy in the 14" twist.

[wmitty]

Thanks for the input, gentlemen. I think I'll be looking for a 1-14" twist barrel.

[lar45]

I have a Mauser that was built by Tim Malcomb of MBT, Goodsteel, I asked for a full length 30.06 chamber with his 30XCB reamer. I need to turn the necks just a little bit and then can load with regular 30.06 dies. My rifle has a 14 twist Krieger barrel and shoots the 30XCB very well. I've pushed it to around 2800fps useing 2500+ and Carnauba Blue. The 2500 + seemed to give the best accuracy, but the Carnauba Blue wasn't very far behind.
I'm sitting in a deer stand right now or id post some pics. If you're looking for an ultra precession rifle, I'd seriously consider Tim Malcomb of Malcomb Ballistic Tool, Goodsteel here on the forum, He's an aerospace machinist by day and pours that level of precision into his love of building accurate rifles.

[redhawk0]

I'm sitting in a deer stand right now or id post some pics. .


LOOK!!! Behind you!

[lar45]

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[Larry Gibson]

Concur with Lars on his 2500+. It's all I use now on my cast rifle bullets pushed from 1400 to 3000+ fps.

Gotta love Tim's work.......

Just under moa accuracy with 11 shots at 600 yards........2900 fps with 30 XCB, 2500+ lube, Broughton 16" twist barrel chambered in 30x60 XCB (short chambered 30-06...same reamer Tim used in Lar's rifle)

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Certainly no complaint with Kreiger barrels either. They just didn't make a 16" twist is all but do make 14" twist barrels.....:-)

As good as that is a 14" twist is still the best "all around" twist for cast in 30 Caliber and is quite sufficient with the most used jacketed bullets, especially in a 308W, 30x57 XCB, 30x60 XCB or 30-06.

[GBertolet]

Ditto on the 1-14 twist. I installed a 30-30 Douglas barrel on my 788 Rem. It was a free barrel blank. I had my doubts about the 1-14 twist, but I tried it anyway. Not disappointed. It shoots fine at 200 yards with a 311291 bullet @ 1600 fps. Last time I shot at 200 yards, the groups were in the 2.5" range.

[Forrest r]

If outpost75 & larry say the 1 in 17 will work, take it to the bank.

I asked about a 1 in 14 and got excellent advice. Spent some $$$ on a shilen bbl with a 1 in 14 twist and never looked back. Just wish I would of put my listening ears on and bought the slower twist bbl years ago.

[Larry Gibson]

Thanks for the input, gentlemen. I think I'll be looking for a 1-14" twist barrel.

A little more specific example as to your original question concerning the 311466; the 311466 in my 14" twist 27.4" barreled Palma rifle (Schultz & Larson 4 groove barrel).

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I see no reason an '06 with a 14" twist barrel can't do the same.