.395 barrels: Preferred twist?

07 December 2006, 13:11

Gerard

Ron,
I will send e-mail over the weekend with more detail but, in short, here is my thinking. The twist should be 1:12". This will make possible an HV in the 330/340gr weight range that will deliver good terminal ballistics from muzzle to 500yds (SF 1.5). It will also result in an FN in the same weight class with a SF of more than 2.5 for similar or better linearity as the 380gr 416 Rigby and 270gr .375 H&H. Here is the cherry on top: An SP of 340gr or so with a BC of 0.700 plus will deliver supersonic flight to silly distances. Doing a 1:10" twist will do little to enhance the HV and FN and seriously hamper the design of a usable SP, given the case capacity. Could be a real do all rifle and load development would be a snap.

07 December 2006, 16:06

jeffeosso

quote:
Originally posted by Gerard:
, in short, here is my thinking. The twist should be 1:12". .... Doing a 1:10" twist will do little to enhance the HV and FN and seriously hamper the design of a usable SP, given the case capacity.

Gerard,
and once again, we perfectly agree.

jeffe

07 December 2006, 16:09

jeffeosso

Ron,
where do I send a check for a chipin?
jeffe

07 December 2006, 21:09

boom stick

wow...thanks rip and gerard for getting the bullets going

what do you think rip...should we bump up the weight by 10 grains??? that would give a s.d. .311

07 December 2006, 23:31

RIP

quote:
Originally posted by Gerard:
Ron,
I will send e-mail over the weekend with more detail but, in short, here is my thinking. The twist should be 1:12". This will make possible an HV in the 330/340gr weight range that will deliver good terminal ballistics from muzzle to 500yds (SF 1.5). It will also result in an FN in the same weight class with a SF of more than 2.5 for similar or better linearity as the 380gr 416 Rigby and 270gr .375 H&H. Here is the cherry on top: An SP of 340gr or so with a BC of 0.700 plus will deliver supersonic flight to silly distances. Doing a 1:10" twist will do little to enhance the HV and FN and seriously hamper the design of a usable SP, given the case capacity. Could be a real do all rifle and load development would be a snap.

That clinches it then.
The Bullet Maker has spoken.
AR has spoken.
I am very happy with a 1:12" twist.

I do not want to collect any money for this.
It would be nice if folks would order barrels from McGowen and bullets from GSC.

The pipeline from RSA is pumping machined copper parts quite reliably.

08 December 2006, 00:05

boom stick

so are we going with 340 grains???

good to see everyone getting along

08 December 2006, 00:19

RIP

boom stick,
Whatever Gerard says on the bullet weight. 330 to 340 grains is the ball park, though 320 to 340 would suit me fine too.

I do tend to wish they would all turn out to the same weight in HV, FN, and SP, but 330 grains +/- 10 grains on any of the final specs would be compulsive enough to obsess me.

Now for the barrel contour:

My thought is that 0.650" at a 25" muzzle would be the skinniest for a featherweight. 0.700" at a 25" muzzle would be the heaviest I would want to put up with.

Splitting the difference and we have 0.675" at a 25" sporter's muzzle. This is near identical to the contour on the CZ 550 Magnum .375 H&H, .416 Rigby, and .458 WM and Lott.

Even the SIGARMS Mauser 98 Magnum in .450 Dakota uses a barrel that is about 0.675" at the 25" muzzle.

I suppose McGowen will do whatever contour is specified within reason and could supply it as an unturned cylindrical blank even cheaper.

Our dreams are now in the hands of THE BULLET MAKER.

08 December 2006, 01:27

boom stick

quote:
I do tend to wish they would all turn out to the same weight in HV, FN, and SP,

completely agree...

having the same load and poi is mucho importante

08 December 2006, 07:55

RIP

McGowen taught Krieger how to button-rifle, when Krieger started supplying a big contract for barrels on Weatherby rifles.

Krieger taught McGowen how to cryo-stress relieve, in return.

Now McGowen cryo's all his barrels routinely.

Here's the specs:

groove diameter: 0.3950"
bore (land) diameter: 0.3870"
twist: 1:12"
contour: your choice
(chrome-moly or stainless, your choice)
The standard shank is 1.200" and lengths up to 28" standard, IIRC.
Start planning your boom sticks. Maybe a 27" straight cylinder shop mule and a 23" featherweight sporter?

08 December 2006, 09:59

Gerard

Bullet weight is unimportant. Given the application, bullet length is important. All three styles should be the same weight so loads will be pretty similar but point of impact, no chance. The first 100 yds will be close but after that there is no way that three bullets going at similar speeds but with BCs spanning 0.200 to 0.700 will follow the same path.

09 December 2006, 08:50

RIP

quote:
Originally posted by Gerard:
Bullet weight is unimportant. Given the application, bullet length is important. All three styles should be the same weight so loads will be pretty similar but point of impact, no chance. The first 100 yds will be close but after that there is no way that three bullets going at similar speeds but with BCs spanning 0.200 to 0.700 will follow the same path.

Outstanding!

Here is the barrel price:

$180 for chrome-moly
$280 for stainless
all are cryogenically stress relieved
any standard contour (same as Douglas contours)
lengths up to 28" long standard pricing
12" twist

McGowen Rifle Barrels
5961 Spruce lane
Saint Anne, Illinois 60964

Phone: 815-937-9816

You can find his "Accuracy Got you Over a Barrel?" ad in _Rifle_ magazine.

Give Harry McGowen a little time to tool up before overwhelming him with orders please.

09 December 2006, 23:24

boom stick

good price rip!

10 December 2006, 07:13

RIP

Good barrels.

Waiting for good bullets.

10 December 2006, 20:08

Gerard

Ok, basic work up is done for 1:12" twist. Bullets are .395"/.387" and all three, HV, FN and SP weigh 340gr. Subject to confirmation by field testing, the HV will start expanding from an impact speed of 1200fps and will be completely expanded by an impact speed of 1500 to 1600fps. Weight retention up to 2500fps or so should be pretty close to 100%. Over that it will start losing petals depending on the medium encountered and petal loss should be complete at around 2700fps. The remaining cylinder front with boat tail rear end will be almost indestructible and will be better than 80% retention. BC is a calculated 0.610 and should be good for spitting distance to 400/500m depending on MV. The bullet will be snoring loudly (sound asleep) from the muzzle.

The FN is good for major calamities up to 120/130m. Any action that feeds one caliber RN bullets will feed the FN as well. It has a stability factor well above 2.5 and even severely angled shots (high angle of incidence) will result in good transition and linear penetration. It will be interesting to see if a Cape Buff can be perforated lengthwise.

The SP is 1.89" in length with an ogive length a hair over 1". Calculated BC is over 0.700. It will not be stable through the transonic range so you must hit before it drops below 1200fps.

Drawings will be done in the coming week and prototypes will be run 27/28/29 December.

10 December 2006, 20:39

RIP

Gerard,
Sounds like just what the doctor ordered for a .395/.338 Lapua Magnum, AKA .398 Lapua Magnum.

SD = .311 for the .395/340gr, FWIW or not worth.

I predict an easy 2700 fps for the .395/340gr SP with the .398 Lapua, likely 2800 fps.

It will be close to 1600 fps at the 1000 yard mark. Supersonic well beyond 1000 yards, even if started off at only 2700 fps.

This is the perfect rifle for all us Bubba's wishing to challenge the 1000 yard shooters with our "elephant rifles."

In summary, regarding your speedy work on the GSC .395 SP, HV, and FN:

11 December 2006, 01:22

boom stick

quote:
Originally posted by Gerard:
Ok, basic work up is done for 1:12" twist. Bullets are .395"/.387" and all three, HV, FN and SP weigh 340gr. Subject to confirmation by field testing, the HV will start expanding from an impact speed of 1200fps and will be completely expanded by an impact speed of 1500 to 1600fps. Weight retention up to 2500fps or so should be pretty close to 100%. Over that it will start losing petals depending on the medium encountered and petal loss should be complete at around 2700fps. The remaining cylinder front with boat tail rear end will be almost indestructible and will be better than 80% retention. BC is a calculated 0.610 and should be good for spitting distance to 400/500m depending on MV. The bullet will be snoring loudly (sound asleep) from the muzzle.

The FN is good for major calamities up to 120/130m. Any action that feeds one caliber RN bullets will feed the FN as well. It has a stability factor well above 2.5 and even severely angled shots (high angle of incidence) will result in good transition and linear penetration. It will be interesting to see if a Cape Buff can be perforated lengthwise.

The SP is 1.89" in length with an ogive length a hair over 1". Calculated BC is over 0.700. It will not be stable through the transonic range so you must hit before it drops below 1200fps.

Drawings will be done in the coming week and prototypes will be run 27/28/29 December.

bravo gerard!

11 December 2006, 01:27

boom stick

question...i know i am getting ahead of myself but is there a need to make 300 grainers with the still respectable s.d. of .275???

there is no need for extra speed or range but flatter shooting maybe???

anyway, small point but wanted to see what you think.

thanks for everything, i am having a blast seeing things come together.