Maximum load for 7mm Rem Mag 160 gr Nosler Accubond

[r.atkinson]

Hi,

I am looking for some advice.
I have just got my 7mm Rem Mag and working up a load for it. I am using 160 gr Nosler Accubond and Viht N-165 which is easy to get hold of in the UK, so that is my definite powder of choice, although I do have plenty of N-160 but it’s a bit fast for a 7mm RM.

I have the 7td edition Nosler reloading manual. It states the starting load should be 57.0 gr and the maximum load should be 61 gr. The 61 gr load was the most accurate being sub 0.5 MOA. I have seated the bullet 20 thou off the lands.

When I chronoed the load the average was a mere but very consistent 2633 fps. The manual says it should be more like 2900+ fps. Their test barrel was 24" whereas mine is 25.5", so in theory should have a higher velocity than the Nosler test.

I realise all the manuals seem to over state the velocity but surely not by 300+fps!!

Looking at other reloading info, the Vihtavouri manual says for a Speer Grand Slam 160gr bullet the start load for N-165 should be 59.1gr and the maximum is 68.1gr this should produce 2982fps. The maximum load is 7.1 gr higher than Nosler state for their similar bullet.

The Hornady manual states for N-165 starting load of 52.7gr and maximum of 62.3gr for a similar bullet offered by Hornady.

My question is, how safe would it be to ignore the Nosler manual and try the Viht suggestion? I am wanting to get as close to 3000fps as possible.

I know I can make some rounds at say 1 grain increments and watch for pressure signs as I go, but I wonder if anyone else may have also done the same. I know all rifles are different so what is safe in someone else’s 7mm Rem Mag may not be safe for mine.

I am using brand new unfired Norma brass and Federal Gold Medal Large Magnum primers.

When I have shot 90 rounds I will neck size some brass and compare the same load vs unfired brass.

Any other suggestions would be appreciated.

Cheers

[Randy Bohannon]

Could be many things mate, the lot of powder, the precise nature of your barrel, the size of your chamber, etc.

As a start can you measure the water capcity of a fired case and an unfired case as per: http://www.gsgroup.co.za/faqcasecap1.html

and let us know please?

We can at least eliminate that variable.

[r.atkinson]

Right, well I ended up going with the viht data and went over the Nosler maximum load.

I got an average of 2850fps when I went up to 66.3 grains. Interestingly enough 66.6 grains had pretty much the same average fps as 66.3 grains did.

I am now in a position where I have used 80 of the 100 pieces of brand new Norma brass. I have neck sized and cut to my desired length.

I have measured my case expansion, new VS once fired brass. On average the cases have expanded by 3.5%.

I know that every rifle is different, but any idea what the likelihood is that my load will not lose, first and foremost accuracy and secondly velocity.

I will more than likely make 3 rounds using 66.3gr with new brass and the same charge with once fired and see what difference it makes on accuracy and velocity.

I will also try a load working up to a 3.5% increase as I now have 3.5% more case capacity. This will mean my load could be 68.6 grains. Although the viht data says the maximum is 68.1 grains.

I am leaving for South Africa for a PG hunt on Tuesday so I have limited time available for another serious batch of load testing!!

Any help/advice would be appreciated.

Cheers

[Randy Bohannon]

Right, well I ended up going with the viht data and went over the Nosler maximum load.

I got an average of 2850fps when I went up to 66.3 grains. Interestingly enough 66.6 grains had pretty much the same average fps as 66.3 grains did.

I am now in a position where I have used 80 of the 100 pieces of brand new Norma brass. I have neck sized and cut to my desired length.

I have measured my case expansion, new VS once fired brass. On average the cases have expanded by 3.5%.

I know that every rifle is different, but any idea what the likelihood is that my load will not lose, first and foremost accuracy and secondly velocity.

I will more than likely make 3 rounds using 66.3gr with new brass and the same charge with once fired and see what difference it makes on accuracy and velocity.

I will also try a load working up to a 3.5% increase as I now have 3.5% more case capacity. This will mean my load could be 68.6 grains. Although the viht data says the maximum is 68.1 grains.

I am leaving for South Africa for a PG hunt on Tuesday so I have limited time available for another serious batch of load testing!!

Any help/advice would be appreciated.

Cheers

3.5 % more capacity does not equate to 3.5% load headroom.

if you give me the raw water capacity figures I can run a Quickload simulation for you which although in no way definitive, will at least give me some idea based on the velocities you have provided.

What is your barrel length, incidentally?

[r.atkinson]

3.5 % more capacity does not equate to 3.5% load headroom.

if you give me the raw water capacity figures I can run a Quickload simulation for you which although in no way definitive, will at least give me some idea based on the velocities you have provided.

What is your barrel length, incidentally?

You are an absolute star Randy.

The new brass case capacity is 5.456 ml.

The once fired case capacity 5.647 ml.

Barrel length is 25.5"

Cheers

[Randy Bohannon]

Ok so first the caveat that quick load may very well not accurately model what is going on in your rifle, cannot account for free bore, is bad at modelling over pressure, etc.

that said from the data it gives me things correlate pretty well. 66.3 grains gives a predicted mv of 2870 fps at a estimated pressure of around 52kpsi assuming an oal of 3.290.

61 grains produces estimates of 2650 fps and 40kpsi.

since you have been good enough to provide two data points and the necessary information it has been possible to see that in this case the burn rate of the vit165 QL's guys measured and the batch you have seem to be pretty close as he predicted results are pretty close to your measured results.

On on that basis i would say that as long as you are not seeing any pressure signs, noticing anything unusual, etc the vit data seems ok to use.

I would note however that the difference between 2850 fps and 3000 is going to make bugger all difference to your plains game hunt, with perhaps an inch or so less drop at 300 yards and no difference at all in killing power. In order to achieve that 150 fps you will be in pressures approaching 62kps according to QL.

ive been on a few trips abroad and the most important thing is reliability. Keep the load moderate and you will have no sticky extraction problems on the second round after lying on your belly for an hour in the hot sun waiting for the shot for example... I would personally full length resize the brass for this same reason, it is better if a hair or grass seed is not able to prevent the chambering of that second round by getting between the chamber wall and the cartridge...

take me what you have and best luck, it will work just fine.

[Randy Bohannon]

Ok, I think I may have found a meaningful answer to this.

it appears that the CIP dimensions for bore size are different for the 7x57 and 7mm rem mag. Therefore a given barrel or bullet manufacturer can use slightly different nominal values for a "7mm" which would explain the wild differences in load data.

a tight bullet would bring pressures up and need less powder to get the same velocity and a freer fitting bullet more powder to get to the Same pressure and hence velocity.
http://www.t2ammo.com/data/_uploaded...oove-twist.pdf

[pjinoz]

Your maximum load will be constrained by PERMANENT case expansion and loading guides relate to what the publisher found with their gun/components. Of coarse SAAMI data will be obtained in a defined pressure gun but again it will be with their components and these components means bullet, primer, case and powder. if you are getting 0.001" case expansion after firing then BACK off, if not it may well be safe to increase your load until you get near this limit. However, KEEP all components constant when working up to this level. BTW take no notice of those who outright say that the best accuracy is with mild loads, how do you know until you try? Some years ago I built up a .378 Weatherby Magnum which I "improved" as I wanted 3200 fps from the 270 gr. bullet not Mr. Weatherby's optimistic 3180 fps. staring with Remington 9 1/2 mag primers I had to back off at 112 gr 4831 and a miserable velocity of less than 2900 fps, however, using CCI 250 mags I achieved 3206 fps using 118 grs and less pressure than the Remington primers. My conclusion was that Remington primers were too brisant and that CCI were less so. The same was with my .264 mag. So, if you try lighting your BBQ with petrol (brisant) you will likely only singe your beard whereas using kerosine it will light very well (without singed beard). This is not to encourage the use of any given primer but to advise you that you don't just try one combination in your load development and that you DO NOT swap around components without first working up again. Estimated velocities are VERY WISTFUL indeed! Better to ban the use of pressure guns, chronographs and targets so we can live in blissful ignorance!

Have fun and stay safe

[r.atkinson]

Finally I have a load that meets all my requirements.

66.3gr - 2863fps
66.6gr - 2923fps
66.9gr - 2940fps
67.2gr - 2951fps

The 67.2gr load started showing pressure signs. There was a circular mark from the extractor plunger. Plus there was only 11fps increase from the 66.9gr load.

Given there is negligible difference between velocity of the 66.9gr and 66.6gr, I made my decision based on accuracy. The 66.6gr load was just over a 1/2" group. More than accurate enough for my PG hunt next week.

I went home and promptly pulled the 9 remaining rounds.

I dare say if I had more time before I went to SA and played with the seating depth, I could tighten the group a bit more. The bullets are seated 20 thou off the lands, when I get home I will try 10 and 15 thou off the lands to see if that reduces my group size, although a 1/2" group is plenty good enough for hunting.

[pjinoz]

Finally I have a load that meets all my requirements.

66.3gr - 2863fps
66.6gr - 2923fps
66.9gr - 2940fps
67.2gr - 2951fps

The 67.2gr load started showing pressure signs. There was a circular mark from the extractor plunger. Plus there was only 11fps increase from the 66.9gr load.

Given there is negligible difference between velocity of the 66.9gr and 66.6gr, I made my decision based on accuracy. The 66.6gr load was just over a 1/2" group. More than accurate enough for my PG hunt next week.

I went home and promptly pulled the 9 remaining rounds.

I dare say if I had more time before I went to SA and played with the seating depth, I could tighten the group a bit more. The bullets are seated 20 thou off the lands, when I get home I will try 10 and 15 thou off the lands to see if that reduces my group size, although a 1/2" group is plenty good enough for hunting.

If you had a circular mark from the extractor plunger @ 67.2gr then it is very likely that you were WAY OVER a safe load and whilst you have backed your load to 66.6 gr (0.6gr reduction) I think you might find that this load is still too hot. What is your case head expansion?
Remember that when dealing with Max. or near Max. loads small changes may send pressures vertical!
Stay safe