Home Forums Reloading Big Game Rifles 7mag/160Partition/ H4831

Ahh...good catch. I. Missed that.

southtexas,

Dirtfarmer's explanation of the reason for the slightly lower SAAMI pressure standards for the 7mm RM is exactly correct. The pressure variations have been documented in many laboratories, many times, but can vary with powders and primers.

I was visiting a new pressure lab a dozen years ago when the head guy told me about the variations he was seeing with some loads. He'd called the head guy at the lab of a major ammo factory, and the other guy said, "Yeah, that's what happens sometimes in that cartridge!" (Members of SAAMI--the Sporting Arms and Ammunition Manufacturer's Institute--tend to cooperate with each other, since the whole point of the organization is to make sure handloading data and factory ammo works safely and reliably in factory rifles.)

Another problem was variations in chamber dimensions between manufacturers, especially when the cartridge was at its peak of popularity from 1962 through the 1980's. Various companies were really cranking out 7mm RM's, and differences in throats were common.

This doesn't mean the pressure variations happen with all loads, in all rifles, but SAAMI members don't want their customers blowing up rifles, or themselves--and not just because they'll get sued. SAAMI is an organization of VOLUNTEER members, who want their products to be safe. Injuring or killing customers isn't good for business.

MD: Thanks for all the intel. Interesting stuff.

I've got a good supply of IMR4831. May be a little faster than optimum for the 7Mag, but looks like I should be able to ease above 2900 fps without a problem, and that would be enough to suit me.

Sounds like a plan. Single-based powders like IMR4831 are generally less touchy than double-based powders that an produce a little more velocity.

In my loading manual, there is a caution regarding 7mm mag loads.

It says loads worked up in Norma brass must be reduced by 10% and worked back up if changing to different brass, this was due to variations in case wall thickness and case capacity.

In this manual it lists the top loads coming from RL 19 and RL 22

Nick Harvey's Reloading Handbook

I can get in the low 2900 's with H4831 & the 160 AB in a 280 AI and that IS NOT hot ridding the round.

Loading 160's in the 7 Rem Mag to about 3000-3050 or so fps in a bunch of 7 Rem Mags, a few thousand times the last four decades, has kept me out of any trouble with the cartridge.Never blew a primer nor had a hint of a problem and a few of those barrels were shot until they were worn out.

I don't reach for H4831 for the cartridge so much anymore,although it works very well with 150 gr bullets. 160's can start to get stubborn IME,and I like to start with slower powders for the cartridge these days once bullets hit 160 grains and up.

I load 160s at 3000, 150s at 3100, and 140s at 3200 generally. I've only been loading half as long as Bob but have also never had a pressure issue of any kind in 7RM. I'm usually a couple of grains over max to get these velocities. Most of my loads are slightly below max in older manuals. Using a chrono is a must working up max loads. My favorite powder the past couple of years for 160s is H1000.

Agree with Bob and Horseman. My fave/most accurate powder for 140,s, 150's, and 160's is RL22. Velocities in line with Horseman's experience.

I like H4831 in my 7mm Remington Magnum too but I ran out months ago. I've still got a pound of H4831SC but that's reserved for my .260 Remington. I've found IMR-7828 to be just as good as H4831 in my 26 inch Rock Creek barrel. Here's my hunting load (velocity 15 feet from the muzzle).

Bullet: Nosler 160 gr. Partition
Powder: IMR 7828 64.0 grs.
Primer: Federal 215
Case: Federal
LOAL: 3.285 (2.745 Base to Ogive with Stoney Point)
Average Velocity: 2919.70 fps
Extreme Spread: 27.44
Standard Deviation: 10.53

RL 22 works well also. My favorite round in the 280 AI is a 150 NBT with H4831SC just under 3000 fps. I have no desire to try and make the 280 AI into a 7RM.

Nosler 150 BT - 58.0 IMR4831 WLR 3043 fps
Nosler 160 AB - 57.0 IMR4831 WLRM 2922 fps
Hornady 162 AMAX - 60.0 RL22 WLR 2930 fps


These days speed only gets my attention if it starts getting too fast and then I know its time to back off. I just don't believe there is much difference between a 160 being pushed say at 2750 or 3050. Its going to do its job if we do our job.

Randy

I won't comment on the lethality and effectivenes of 160gr Partitions, because that has already been proven.
My factory 7mm Mag (Savage 110) shoots MOA at book speeds/loads (I lucked out) both in 150gr and 160gr pills with IMR4831 and RL22 respectively. ~3100 for the 150s and ~3000fps for the 160gr PTs.
160gr PTs, 64gr RL22 Rem 9 1/2 Mag primers WW brass
OAL 3.29"
150gr BTs 60.5gr IMR4831, Rem 9 1/2, WW brass
OAL 3.33"

I have not tried other primers or powder since I don't see the need.
I will vouch for 160gr Sierra Gamekings shooting very close to POI, though they can stand a bit more powder than the 160 PTs.
They kill whitetails very well too.

Tip top velocity is not everything. I've found H4831 very reliable and stable in the 7RM with every weight from 162 down. In one rifle with both 154 HSPs and 160 NPts it shrinks my groups 1/3 from the top velocity powders, and lets me use them both with the same zero. That is a more than fair trade for 50-100fps, to me.