Bullet stability in 7mm RM

01 April 2019, 00:19

Alec Torres

i've been shooting my 7mm RM for decades. I did some load development for elk hunting early on and found that 175 CoreLokt bullets did not always stabilize and would sometimes keyhole through the target. I was using H870 and IMR4831 for these loads. The rifle has a Hobaugh barrel and (I assume) a 1-9" twist. Consequently, I use 160 grain bullets (Nosler Partitions, mainly), which perform very well in this rifle.

Maybe I'm just trying to push the heavier 175s too fast? Is there another bullet that I might use to get better accuracy results? Should I just be happy with the 160s I use now?

01 April 2019, 09:16

eagle27

Why not check the twist of your barrel so you know for sure what it is as a starting point.

p dog shooter is right, normally the faster you drive a bullet the more it will stabilize if it is struggling to do so in a given twist.

1-9" or 1-10" should be adequate to stabilize a 175gr 7mm projectile. I know 1-12" does not always.

For decades I exclusively used the Sierra 160gr SPBT projectiles in my 1-12" twist 7x61 S&H Schultz & Larsen rifle with unbeatable success. Never had cause apart from experimenting around on target and feral goat to try anything else.

01 April 2019, 11:22

JMJ888

Just a preference thing based on personal experience but I would shoot a partition over a corelokt bullet every time regardless of bullet weight.

I have had good luck with partitions and Barnes tsx’s but if you are having a problem with twist rate stabilizing bullets then a longer solid copper tsx isn’t going to help.

I would measure the barrels twist rate and go from there but would not feel under gunned with a 160 partition with a bit more velocity over a 175 on elk.

02 April 2019, 04:14

Alec Torres

Thanks everybody for your thoughts and comments.

quote:
Originally posted by JMJ888:
Just a preference thing based on personal experience but I would shoot a partition over a corelokt bullet every time regardless of bullet weight.

I have had good luck with partitions and Barnes tsx’s but if you are having a problem with twist rate stabilizing bullets then a longer solid copper tsx isn’t going to help.

I would measure the barrels twist rate and go from there but would not feel under gunned with a 160 partition with a bit more velocity over a 175 on elk.

The rifle is at my gunsmith now having new rings and scope fitted. He will slug the bore for me and we can see what the twist rate is.

I'd like to have the option of 175 grain bullets, but have never suffered from shooting 160s.

AT

02 April 2019, 19:55

Jim Knight

I had a factory Mod 700 7mm RM that shot the 175 corlokts OK, but when I tried some older "Bitterroot" 175s, they keyholed. I was only shooting deer with it so settled on the 150 Partition. I loaned the rifle along with some ammo I had loaded witht he 160 Partition and he killed an elk with it. Some say that the 7mm caliber ( any of them) "balances" with the 160 grain bullet. Not a bad thing. When it comes to any slow twist, "speed is your friend". A 140 TTSX is a great all around bullet.

02 April 2019, 22:12

Alec Torres

quote:
Originally posted by eagle27:
... a 1-9" or 1-10" should be adequate to stabilize a 175gr 7mm projectile. I know 1-12" does not always.

For decades I exclusively used the Sierra 160gr SPBT projectiles in my 1-12" twist 7x61 S&H Schultz & Larsen rifle with unbeatable success. Never had cause apart from experimenting around on target and feral goat to try anything else.

This rifle was originally chambered in 7 X 61 S&H. It's a good cartridge, but can be hard to find ammo and cases. This is the reason I had it re-barreled to 7mm RM many years ago. The 7 X 61 barrel was rifled with 1 in 12" twist rate and I couldn't get it to stabilize 175 grainers either

02 April 2019, 23:41

eagle27

quote:
Originally posted by Alec Torres:
quote:
Originally posted by eagle27:
... a 1-9" or 1-10" should be adequate to stabilize a 175gr 7mm projectile. I know 1-12" does not always.

For decades I exclusively used the Sierra 160gr SPBT projectiles in my 1-12" twist 7x61 S&H Schultz & Larsen rifle with unbeatable success. Never had cause apart from experimenting around on target and feral goat to try anything else.

This rifle was originally chambered in 7 X 61 S&H. It's a good cartridge, but can be hard to find ammo and cases. This is the reason I had it re-barreled to 7mm RM many years ago. The 7 X 61 barrel was rifled with 1 in 12" twist rate and I couldn't get it to stabilize 175 grainers either

Over the years Norma has made batches of cases for the 7x61 S&H and I played around and formed cases from 7mm RM, not that I was short on cases anyway. When I sold my 7x61 to go down to a 7mm-08 as a better rifle for my boys start to shoot with I had 3 packets of the original 7x61 S&H Norma ammo to hand (not the later 7x61 Super). These packets were printed with "Exclusively made for Sharpe and Hart & Associates ….."

I could easily get an honest 3000fps with the Sierra 160gr SPBT bullet with good case life in my 26" barreled M60 Schultz and Larsen rifle with Norma factory rounds delivering 3080fps
(3100fps advertised MV). Some say Sierra is too soft but I never found it so. I found at most any range it punched through making a nice quick killing mess of vitals on the way. The original Norma 160gr SPBT did the same but the later 160gr in their Super ammo was a different bullet, too hard and punched through without doing the necessary damage. I suspect this ammo was made for African animals which their catalogue advertising with lions etc., seem to indicate.

05 April 2019, 00:27

Alec Torres

quote:
Originally posted by England:
I have a 1990 vintage Browning Stainless Stalker in 7mm Rem Mag with a 1/9.5" twist. It will not stabilize 175gr Trophy Bonded Bear Claw bullets reliably and doesn't shoot 160gr TBBC well either. But it does well with other 160gr bullets, including Nosler Partition, which is what I usually load.

Interesting. I have a box of Federal Premiums with the TBBC 160s. I have not tried them yet, but a range session is in order when I get the rifle (with new S&B Summit) back from my 'smith. My usual load - which works really well on elk - is H870 with 160 Nosler Partitions.

Mike

What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.