2 Grains?

[Hawk]

I recently bought a 7mm RUM Sendero and was looking at handloading the 162 grain Hornady A-Max bullet. I'm not reloading yet but did notice that:

Hornady shows the 162 grain A-Max as requiring a twist rate of 1:9 or faster. The Remington Sendero is spec'd with a twist of 1:9.25.

Further, Remington loads 160 grain partition bullets for the round.

So, howcome a 160 grain bullet works in 1:9.25 but a 162 grain doesn't??

Is Hornady "sandbagging" the requirements for the 162 grain A-Max or is Remington shipping 160 grain unstable bullets, or neither or both? Or does the lousy 2 grain difference actually make a difference?

TIA
Hawk
Not a good start for my reloading adventure

 

[Black Snowman]

It's possible it's not just the weight but the ballence and profile of the bullets that change the twist requirements as well. IIRC tail heavy bullets tend to be more stable and more accurate for whatever odd reason. Seems just the opposite of what makes sense to me but the Sierra Match Kings will prove my "common sense" flawed every time

 

[HSMITH]

It will work fine, just shoot them. 1 in 9 works nicely with 175's too if you can push them a little in plain 7 mag, and the Ultra should be even easier to get them stabilized. I have not found a 7mm bullet weight over 110 grains that won't shoot reasonably well in a 7 mag with a decent 1 in 9 barrel on it. If I were going to shoot 160-175's and NOTHING else I might look at some of the 1 in 8 and 1 in 7.5 barrels out there, otherwise the 1 in 9 makes more sense as it will shoot all of the commercially loaded ammo on the market.

 

[dakotasin]

you really won't know for sure until you sit down at the bench and fire a few rounds off. my bet is that it will be fine.

the 7 rum produces so much velocity that you will likely be able to get away w/ a little less twist than hornady speculates. hornady probably spec'ed that for 7 rem mag shooters.

i shoot 162's in my 7 mag, and they shoot very well. my brother's rifle won't handle anything heavier than 150's, and the rifles have the same twist...

also, i was told that my 308 w/ its 12 twist would not stabilize 175's or heavier - i sat down at the bench and it groups 180's very well out to 400 yards... just gotta try it out.

i think you'll be fine, though.

 

[lycanthrope]

The A Max has a different profile than the Partitions. It has a sharper taper to the point (a bullet like this carries more weight that actually does not contact the riflings). Hornady SST's in 162gr won't stabilize in my 7mm STW, but 160 Partitions will. In order to get SST's to shoot decent I have to seat them longer to get the olgive closer to the lands. When I do this they won't fit in my magazine!

 

[Jim Watson]

Bullet stabilization depends on length, not weight. A needle-nosed boattail requires a faster twist than a flatbase spitzer of the same or even heavier weight but shorter length. A roundnose will be even easier to stabilize, ref all the pre-1904 military rounds with heavy roundnose bullets.