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Old December 27, 2013, 10:33 AM   #26
mehavey
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The only spin rate (that I know of at least), with an
impact on the coriolis effect is that of the earth.

...a aleisurely 0.00694 RPM I believe.

Throw in lattitude, azimuth & range for a fun afternoon
w/ EXCEL's trig functions.


.

Last edited by mehavey; December 27, 2013 at 10:40 AM.
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Old December 27, 2013, 10:34 AM   #27
CharlieDeltaJuliet
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When I had my SPS Tactical I had best lck with a 178 AMAX. I never got up into the heavier weights such as 190-220grs in .308
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Old December 27, 2013, 10:56 AM   #28
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Quote:
Eppie, how much does a bullet's coriolis effect influence its trajectory if the twist goes from 1:12 to 1:11, or 1:11 to 1:10 for a given 30 caliber bullet leaving at a given muzzle velocity? MOA units at any range are fine to describe the change.

I ask because I've shot .308 Win's with 190's at 1000 yards from 1:12, 1:11 and 1:10 twist barrels with no difference in accuracy.
Bart I have no experience with that. I defer to you.

I only mentioned because I am having a 6XC rifle build and out to 1,000 yard with a 115 grain bullet it was mentioned as a theoretical consideration when going from a 1:11 to 1:8 twist rate. At that range wind is the real challenge not the theoretical spin factor.
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Old December 27, 2013, 11:15 AM   #29
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Quote:
1-12 also worked very nice for +P loads using 190's in Garands
Bart : I've heard you talk about the 190s shooting just fine from a 1-12 308 Win . How ever the quote above may suggest that the 190s need 30-06 +p load to work best out of a 1-12 twist .

I don't know what a 30-06 +p load would give me using a 190gr smk but I'd think it would be in the 3000fps area or faster . So far the best I can get with my 190s out of my 24" 308 Win is in the low to mid 2400fps range .

How much would the 600fps difference impact the ability for the 1-12 to stabilize that bullet at any range or temp ?

To the OP I think the heavier the bullet the better in a 1-10 twist . Right now I'm shooting sub moa with 175 smk , 178 A-max and 190 smk . Each bullet is being pushed by a different powder . I'm going to try the 208gr A-MAX soon just to see how it does from my 1-10 308 Win
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Last edited by Metal god; December 27, 2013 at 11:26 AM.
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Old December 27, 2013, 11:15 AM   #30
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In 1997 with a 308 Bart Bobbitt shot a 3.325" 20 shot group at 800 yards with Sierra's 155-gr. Palma bullet with 45.3gr. of IMR4895 and RWS Primers in full-length sized WCC60 match cases.

In 2013 with a 7mmRM I shot an 8" 3 shot group at 500 yards with Nosler 140 gr Ballistic tip bullets with 70 gr H4350 and Win large rifle primers in once fired RP brass surplussed out of St Marks testing.

This is the difference between a top competitor, and just some schmuck that goes hunting.

My contention is that it takes skill to react to recoil in the same way every time. Low skill shooters will improve more than others with reduced recoil.

The best round for shooting groups in a 308 that I have found [and I own more than a dozen 308s] is 110 gr Vmax moly .308 LC or WW brass, 44.9 gr IMR4895 2.815" OAL.

This is a wimpy load with a wimpy bullet and seated long. The long seating assures that the bullet will jam into the lands, and thus be concentric on at least ONE end of the bullet.

90% of the shooters at the average range will shoot smaller groups with this wimpy load.
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Old December 27, 2013, 12:45 PM   #31
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Your rifle will have to decide that
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Old December 27, 2013, 04:02 PM   #32
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Quote:
I don't know what a 30-06 +p load would give me using a 190gr smk but I'd think it would be in the 3000fps area or faster . So far the best I can get with my 190s out of my 24" 308 Win is in the low to mid 2400fps range .
Not safely. The fastest I've seen anyone push the 190 SMK from a 30-06 is a hair over 2900 fps. He used a 28" barrel to get that velocity.

Most folks shooting the 190 SMKs in 30-06 are in the 2750 to 2850 fps range, any more than that they need longer barrels to get more velocity.

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Old December 27, 2013, 09:03 PM   #33
Bart B.
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The Garand barrels I shot 190's out of were loaded in new 7.62 NATO M118 match cases with 44 grains of IMR4320. That pushed them out at about 2585 fps in the 24" barrel; I shot two or three of them one evening across a chrony just to see what they did.

Hodgdon's site lists a few tenths grain less for a 190 with a bit over 58K psi in their web site but the barrels I used had tight bore and groove dimensions. They were a the high end of pressure specs and probably went over the line a bit; I've called them +P loads for years but they were safe in Garands with well fit op rods and no high pressure signs on cases. They did make the op rod sing the loudest of any load used.

I and others have worn out a few 30 caliber magnum barrels shooting 190's out at 3000 fps from 1:12 twist barrels. Excellent accuracy for 20 to 30 shot strings; sub 5/8 MOA easily at 1000 yards. I've even shot 200's from the same 1:12 twist barrel leaving about 2950 fps and got equal accuracy with as many shots.
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Last edited by Bart B.; December 27, 2013 at 09:15 PM.
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Old December 27, 2013, 10:36 PM   #34
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Very good , thank you both
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