7mm Questions and Idea's

[IanP]

I agree with Bruce, the 9.5 twist should be fine with 180gr VLD Bergers at sea level. I just did the calc for the 180gr bullet at 4m (altitude) which is the altitude at Lower Light. At 4 m the air pressure is 29.91inHg and at 2800fps gives a Sg = 1.36, (at 24C). Pretty close to the optimal Litz recommended Sg = 1.4.

I will post on the safclass.com.au a new altitude to air pressure calculator on which I am adding all the altitudes of the SA rifle ranges. I am getting the altitude of the ranges from satellite data off Google Earth.

So far Lower Light at 4m and Mt Barker at 406m provide the greatest air pressure difference. Its nothing to worry about but it does make a small stability diffence. 4m = 29.91inHg and 406m = 28.51inHg.

The conversions are done using the ICAO Standard Atmosphere model and the Excel spreadsheet calculator converts altitude in metres to both hPa and inHg.

Download Spreadsheet here: http://www.safclass.com.au/Spreadsheets ... essure.xls

IanP

[Cameron Mc]

I am definately keen on trying the new 180 mk. I have always believed that you should only spin the bullet the required amount to stay stable. This seems to be more important with the larger calibres. I guess I have stayed away from the Bergers because of availability and price, so I have not tested these enough to form a solid opinion.

It's funny, on the Sierra 175mk box it says "use 1-8.5" or faster".

Bruce, I am going to run that barrel till I kill it. It has helped me win alot of shoots. I am curious to find out how it dies, slowly or quickly. Just my luck it will be on the last day of a queens coming into 1000yds.

I have another 284 barrel going. Same make, reamer, load and it is shooting just like the old one. Might rechamber at around 1500 for curiousity.

[RAVEN]

when you rechamber Cameron up your load .3 gr you will be back in the block hole

[bruce moulds]

if all those 308 buulets fired every week are stable, then 180 bergers fired from a 9.5 twist are more stable.
the 308s do become unstable in the transsonic zone, as evidenced by match rifle, and the 7mms would probably too, but we don't get to the transsonic zone at our ranges.
i have shot a 9" twist with 180 bergers at 1100 metres with no stability problems.
i have seen 80 gn sierra 224 bullets go unstable at 1000 yd out of an 8 twist barrel (button rifled, so it might not have been exactly 8 twist), and the problem went away when the velocity (load) was increased. talk about being on the ragged edge. the gun had shown no problems up to 800 metres and shot well.
cameron, you mention the price and availability of bergers. in usa they are not priced much differently than sierra. could this suggest a bit of gouging somewhere along the line when prices are compared here? certainly the new 180 sierra will attract a lot of attention for that reason.
the 162 amax and new bullet from hornady at 3000 fps becomes a 6.5/284, with good barrel life, in the wind. not to be sneezed at when the guy using it can use it. if those new jackets are as described look out 168 berger.
bruce.

[Paul Janzso]

Bob, forget the HV profile go for the1.25 inch straight profile, you will not regret it.
Cheers
Paul

[bobeager]

Thanks guys for all the really good info...much appreciated

[Ovenpaa]

At the risk of going off topic slightly how do the SMK's compare to the Bergers price wise in Australia? A check this morning shows UK prices shows:

SMK 180 = AUD61.55
Berger 180 VLD =AUD80.45

It is accepted that 7mm gets you into some very high BC bullets but the recent price rises for Berger by the time they get to the UK makes the SMK offering very appealing.

I have just ordered 500 Berger Hybrids direct from the USA to try and offset the cost of my shooting slightly as everything is getting so expensive

[RAVEN]

FYI

Proj - 7mm - 175gn Sierra MK $53.60
Proj - 7mm - 180gn Berger Hunting VLD $83.30
Proj - 7mm - 180gn Berger Match VLD $76.50 might have to get me some of those

[RAVEN]

The new Berger 7's
we will soon be spoiled for choice
plus hornady and sierra's new offerings

28404 - 7mm 180 gr BT (Medium Tangent Ogive) - G7 = .314
28405 - 7mm 180 gr VLD (Long Secant Ogive) - G7 = .337
28406 - 7mm 182 gr XBT (Extra Long Tangent Ogive) - G7 = .332
28407 - 7mm 180 gr Hyb (Extra Long Hybrid Ogive) - G7 = .345
28408 - 7mm 175 gr XLD (Extra Long Secant Ogive) - G7 = .336

[BATattack]

do you have any idea of when the new berger hybrid and the 180SMK are going to be avalible in australia?

RAVEN thats a very long list of 7mm bullets!! if we are not carefull the supplyers could end up with an under or over stock of new offerings.

[RAVEN]

WHAT you DON'T have any yet??? BAT