7mm Rem Mag for Long Range

[Vaalbos]

Some comment to some of the issues below from anyone with experience using the 7mm Rem Mag for long range (800 to 1600m) would be appreciated.

What twist is ideal for use with the new generation of ultra high BC VLD bullets such as the 180gr and 190gr?
What is the limit of the std 1 in 10" twist with regard to the VLD range of bullets, and a 26" barrel with typical velocities achievable? (Gauteng/Dullstroom Altitudes)
When cutting a chamber for this specific application what reamer design is best, taking into consideration the bullet to lands geometry and longer than standard overall cartridge length due to the VLD profiles? (Rem 700 LA)
Is there a specific tried and tested reamer available from someone in SA for this purpose?
What cases are recommended for this application and is neck reaming mandatory for any specific chamber reamer?

The new bullets available in various calibers for Long Range applications demand a different approach when building dedicated rifles and if there are any additional factors to be considered please raise them.

Thanks

[LoopSoosStroop]

Vaalbos, I have some limited experience with a Howa 7 mm RM. It had a thin 24" barrel and 1 in 9.5 " twist. It was only accurate with the lighter 130 and 140 gr bullets, and the BC of those ruled it out for real long range use.

A 10 or 9.5 twist is not fast enough for even the 162 gr Hornady bullets, never mind the 180 gr and 190 gr modern VLD long range bullets. You will need a 8 twist as a minimum for a proper long range rifle.

Another thing is local powder. With S385 you get 80% case fill on max loads, and poor SD and ES. We cant get the most out of the 7 mm RM here in SA.

No Lapua brass either, but at least there is Norma. In my humble opinion, if you want to shoot far you ideally want a caliber that has Lapua available, or sort and prepare your brass meticulously.

The 7 mm RSAUM is the better option, but will require a custom build as well.

[Capt. Yoda]

Met al die nuwe kruit beskikbaar in SA is die 7mm rem verseker nie die slegste keuse vir n 1600m geweer nie.
Om die langer VLDs te skiet en 100% te stabiliseer sal ek na n 1/8" loop kyk, doppe sal jy maar Norma moet gebruik.
Oor die reamer moet jy maar met n GS praat en besluit hoeveel freebore jy wil he vir jou koel, onthou ook maar net omdat jy n reamer spec vir koel X beteken dit nie jou geweer gaan daai koel skiet nie so hou maar nog n ander koel dalk met n ander ogive ooo in gedagte

[LoopSoosStroop]

Hoe lank gaan daai kruit nog hier wees...

[Vaalbos]

Thanks for posts on the subject.

I ran a QL simulation with 26" barrel using 180gr Berger VLD and S361.

Around 2800fps seems achievable as per att.

7mm Rem Mag - 180gr Berger VLD - S361.JPG

Is this realistic for 7mm RM?

Based on this result I ran some calcs for Stability Factors using 1 in 10"T and those came out as below;

7mm 1 in 10 twist stability.pdf

Some calcs list the bullet as "Marginally Stable" and others as Unstable.

Regarding the stability of the 7mm and 168gr SMK, I shoot a 7mm-08 Rem with 1 in 9,5"T and it groups 5 in 8,00mm and less at 100m. Velocity is around 2350fps.

I am looking for this accuracy level with a 7mm 180gr VLD at about 2800fps.

I would prefer to stay with the more conventional case of the 7RM but possibly the 7mmWSM and 7mm Dakota could be in that window.

[JPS]

Vaalbos,

My mening is as jy iets soek om tot 1600m akkuraat te skiet gaan jy baie lae ES moet kry op jou patrone en deur somchem kruit te skiet teen 60500 psi met pmax van 61000 psi is.nie die moeite werd nie veral nie teen 91% dopvulling nie ons het nou al baie keer gesien somchem kruite "peak" vinniger as wat QL voorspel sodra jy by max druk kom. Ek sou daai geweer herkqmer na ander kaliber as jy hom in alle geval gaan oorsny. Maar ek weet nie of jy die regte twist loop sal kry soos Loop soos stroop tereg wys hierbo in fabrieks geweer nie. Ps. Bygesê ek dink Daar mag dalk iets in Remington wees..

Ek ken nie die 7mm RM nie maar ek ken so effe van 284Win. Met 10gn minder kruit skiet ek 180gn vld's teen 2820-2840fps maar met 30" loop en Somchem S385. Met VV 560 skiet ek met nog laer druk en laer ES teen 2870fps die 183 SMK's. 7mm SAUM sal ook goeie keuse wees.

Praat dalk met Pinkes hier op die forum hy het 7mm remington fabrieks geweer gekry met die regte twist vir 180gn koeëls as ek dit reg het en hy het sy geweer laat kamer na 7mm SAUM toe. En die geweer skiet barshou. Daar is erens topic op die forum oor die roete wat hy gevolg het.

Tem minste is 7mm baie goeie platform om mee te begin vir LA. Sterkte met jou besluit.

[Capt. Yoda]

Your sitting with less than 92% fill rate in that big case with 361, one of the problems that loop SS was talking about with the big magnum cases and our powder. Not n show stopper but for consistant ignition especialy in a 1600m rifle I would look at a powder that gives me more than 95 and as close to 100 or even 101%.



Wel daar het Jan dit nou mooi op gesom.