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7mm RM FPS data

06 Apr 2012
@ 11:29 am (GMT)

Danny Strong

Hi,
Firstly let me say what a great site this is. Good, practical, real world gained knowledge. It cuts through all the internet trash talk and the marketing hoopla that floats around about products and their performance.

I just bought a 7mm RM in a Rem 700 with a Zies Conquest 3x9 x 40. The rig is intended for Red Deer, but other quarry that gets in the way will be shot. I will be reloading. The rig is probably a little over gunned for Red Deer, but I figure dead is dead, but there are all different levels of wounded.

I note you highly recommend the 162gr SST. I currently use the .270 x 130gr version in a 270-308. I find they blow up at close (50 meter) ranges, but it pole axes Red Deer at close to mid range.

I have 2 questions.

1. Given annealing will slightly reduce the diameter of the wound channel and also, given the decisive perform I have with the 270-308 even though they blow up, would you suggest annealing to limit blow up (IE. separation) for the 7mm RM.

2. I note the ballistics table for teh 162gr SST shows 3100 for 24" and up to 3400 for 26". I was not aware that a 2" extension would give such a significant increase in FPS. Have I read this right. I would add that it is all rather acedemic as all I'll get is what ever my rig gives me.

Thank you for a great site. I will take photos of projectile performance and provide details of internal and external ballistics for future kills.

Replies

10 Apr 2012
@ 09:24 am (GMT)

Quote this

Nathan Foster

Re: 7mm RM FPS data

Hi Danny, thanks, I am glad you are enjoying the site.

Regarding the 130 grain SST, due to the SST bullet design combined with the low sectional density of the 130 grain .277" bullet weight, the SST is prone to jacket core separation and eventual full fragmentation. The SST has a stout jacket, thicker than many bullet designs but as Hornady describe, it has a rapid expanding 'super shock tip'. On impact, the SST expands immediately but once it has expanded, the frontal area tends to remain wide. A cross section of the expanded SST, especially at lower velocities, can look like a capital T. This T shape causes rapid arrest of the jacket. The heavy lead core cannot cope with this rapid braking and is forced to leave the jacket behind. The effects can be much more pronounced at low velocities.

Annealing the SST ogive helps the frontal area to swage back against the shank but there are limitations. SD is an important factor, the higher the SD the better. Annealing the 130 grain SST does not produce uniform results when used in the .270 Win at ordinary hunting ranges, however, in your .270-08, you may see some benefits, the lower MV being kinder to the SST on impact.

Annealing the SST does not cause a reduction in wound channel diameters. A reduction in bullet frontal area after initial expansion does not translate into a reduction of wounding. Wound channels remain disproportionate to caliber, in other words, the half inch frontal area of the SST will still create a 2 to 3" internal wound etc. Furthermore, one of the main advantages of annealing the SST besides penetration, is to promote faster expansion at long ranges / low velocity as a means to increase wounding.

I have now put annealing videos in the knowledge base. Please use the side menu on the left, scroll to the bottom and you will see videos on annealing the SST and VLD projectiles.

Regarding the 162 grain SST, yes you have read that wrong, must have accidentally read the energy figures. The fast barrel figures were for a 26" barrel yielding 3100fps. Please bare in mind, 7mm rem Mag rifles do differ widely, some 26" barreled rifles give best accuracy at 2960fps regardless of a 26" barrel length and regardless of pressures being mild at 3100fps and regardless of the rifle being tricked up and true.

It can take a great deal of experimentation to achieve accuracy at 3100-3125fps in some rifles. The key is usually experimenting with smaller steps in incremental loading (.2 grain steps) combined with 3 different seating depths or more. For most users, this can be quite a pain as it involves a large range of variables, a lot of time and can be quite costly. For those who want to chase the velocity, the experience can be rewarding but it must always be remembered that a 7mm Rem Mag producing velocities in the 2900fps range is still something to be reckoned with at 1000 yards.

Recoil is yet another factor, for example, an SPS 7mm Rem Mag is a lot easier to shoot accurately at 2900fps than at 3100fps. The velocity gain may work out well over the sand bags, but can be lost in the field due to difficulty controlling the rifle under recoil. A heavier platform like the Sendero is better to work with if chasing 3100fps- but again, a great deal of experimentation can be required, the shooter has to weigh up whether its worth investing time and money in this direction if the rifle does not respond immediately to basic load development. Chances are 50/50.

The SST can be finnicky to hand load. I suggest a close seating depth to start with, a jump of .2mm or 10 thou. If results cannot be achieved with this bullet jump, .5mm or 20 thou is the next step, if this doesn't work, 1mm or 40 thou as a third step. Radical changes involving seating right back several mm (over 100 thou) can be useful for experimentation in short magazine rifles. I definitely recommend annealing the 162 grain SST for use on Red deer. On its own, the 162gr SST is acceptable but the enhanced performance of the annealed 162 grain SST is well worth it, especially on the large body weights you are targeting.

Photos in the future would be great thanks!