.300 Laupa vs .300 RUM

[Rich Coyle]

.300 Lapua vs .300 RUM: Anyone know at what pressure these two cartridge run? At the same pressure which brass would last longest?

 

[Engineering101]

300 Lapua 63.8K PSI (per Wikipedia)
300 RUM 65K PSI per SAAMI

Lots of variables in the brass life equation. Probably depends more on what brand of brass you are using since metallurgy varies somewhat by brand but I don't really know which would last longer (assuming same pressure and same metallurgy).

 

[THEIS]

Hello,

Rich, Are you speaking a "true" 300LM brass or the wildcat 30-338 version more common in the USA?

I do know 300LM head stamped brass never made it to the USA from Lapua on a "commercial" basis but a few pieces might have come in through "private" channels.

Thanks,
THEIS

 

[Rich Coyle]

Thanks, guys. My ignorance is going to show even more. Maybe I should just ask for advice. I want a big 7 with a long neck about .350". Would you go the expense and trouble to get the Lapua or push the shoulder back of a RUM case?

The max length in this action is 3.78". And I will use VLD bullets.

 

[MudRunner2005]

Thanks, guys. My ignorance is going to show even more. Maybe I should just ask for advice. I want a big 7 with a long neck about .350". Would you go the expense and trouble to get the Lapua or push the shoulder back of a RUM case?

The max length in this action is 3.78". And I will use VLD bullets.

Just buy a .28 Nosler or 7mm STW and be done with it. Both cartridges nearly carbon-copy each-other's ballistics. That's about as big as you can efficiently go in the .284 bore without too many diminishing returns.

Compare equal barrel lengths and all other equal factors, the 7mm STW and 7mm RUM are within 25-50 fps of each other...The difference is the RUM uses about 25+ more grains of powder to achieve that extra 25-50 fps of MV. That means you only gain 1-2 fps PER grain of powder, over the STW. But from the extra burn time and flame on the throat, the barrel has about 1/2 the barrel life of the 7mm STW/.28 Nosler. Hardly worth the investment, if you ask me.

 

[Rich Coyle]

I had a 28'" 7STW and eventually rechambered to 7RUM. It gained 25fps. You made a sell. I will go with a shortened RUM with a long neck.

Thanks for the push.

 

[bigngreen]

Going a 7mm I'd look at using the 300 Norma Mag as a parent if looking at the RUM or Lapua case size, over all length is much better.

 

[el matador]

Going a 7mm I'd look at using the 300 Norma Mag as a parent if looking at the RUM or Lapua case size, over all length is much better.

My thoughts exactly.

What kind of velocity are you looking for, and with what bullet? People have been getting great results with the 28 Nosler lately, running the 180s and 195s above 3200 fps. That's pretty dang decent for most people. Of course the Lapua-based 7mms are going to exceed that quite handily but then you're into the realm of wildcats and their accompanying complications.

 

[MudRunner2005]

I had a 28'" 7STW and eventually rechambered to 7RUM. It gained 25fps. You made a sell. I will go with a shortened RUM with a long neck.

Thanks for the push.

Yep, that's basically all the .28 Nosler is. Is a short, long-necked RUM, with the capacity of a 7mm STW. Being the case is short and fat, you should be able to seat the long Berger 195's out to within .015" of the lands (which is where most Bergers perform best), and still be able to run them in the internal magazine as a repeater.

I have two 7mm STW's, one is a factory Sendero SF that I ordered brand new in 2002, the other is a custom that was built off a CDL 7RUM action. Being the feed rails are already widened (factory RUM) I have been debating on a .28 Nosler build just to diversify my collection.

 

[Rich Coyle]

Yep, that's basically all the .28 Nosler is. Is a short, long-necked RUM, with the capacity of a 7mm STW.

What's the length of the neck on the .28 Nosler?

 

[THEIS]

What's the length of the neck on the .28 Nosler?

Hello,

Page 87 of SAMMI here http://saami.org/specifications_and...ns/download/Z299-4_ANSI-SAAMI_CFR.pdf#page=13

THEIS

 

[Rich Coyle]

Thanks.

 

[RockyMtnMT]

Hey Rich we have a reamer on the shelf for the 7mm-338 Lap improved. We just have not got around to building one yet. We could build yours first. We have a barrel on hand as well. If you have the action we could get it rolling pretty fast.

Steve