Experience with 30-338 LAI vs. 300 NMI / velocities on both, etc.

[Sgt. Brumbaugh]

I am still getting my feet wet with my 300 NMI. I am 550 rounds into a 26 in barrel that with 89.5 grains of N568 shoots around .25 MOA at 2900 fps with 245 Bergers. Throat wear is .0036-004 per 100 rounds. I have a 30 in barrel ready to screw on that I expect will gain around 100-125 fps with the same powder- maybe N570 will spice up the velocities a bit. This is a competition ELR rifle, so I am looking for temp stable powders as I travel from Washington state to Texas, Kansas, etc.

I am tossing around the idea of a 30-338 LAI (I know it will be a barrel burner- probably .006 or worse throat death per 100 rounds) but I am wondering about the experiences of guys who have run them and maximized their velocities and accuracy. Would a 34-36 in tube on a 30-338 LAI be 100-200 fps faster than a 300 NMI? 3250-3300 FPS doable with reasonable brass life?

Any feedback from guys who have run the 30-338 LAI's?

 

[ShaunBrady]

I did a series of wildcats based on the 338 Lapua case about 10 years ago to provide data for modeling the effects of increasing the case capacity to bore ratio and pressure. I wanted to use the same case for all of them because I was estimating pressure from extractor groove expansion.



The bottom is the parent 338 Lapua

The top was the first. The parent case was necked down to 7mm with a 35 degree shoulder.

The second one down is necked down to 7mm and 40 degree Ackley improved. This one was pretty much a scale model of a 338 Snipetac, 375/416 Barret, or 30/33XC.

The third one is a 30/338 40 degree improved, but short chambered 0.100 to fit in an AICS magazine. The case capacity to bore ratio was between a 26 and 28 Nosler.

The fourth is a CIP 300 Lapua made from 338 Lapua brass. It's metric is similar to the 7/300PRC, 33XC and 416 Barret.

I turned a lot of bullets inside out. The guy whose ranch hosts my test range wants to make a gate from the barrels I've been through.

The direct answer to your question is it's very likely you'll meet your velocity goals at pressures similar to what you appear to be running now. Your 300 Norma Improved load looks reasonable. Figure 80-100 fps from the 30" barrel.

The bad news is the velocity gains won't be worth the other impacts. "Barrel Life" is a colloquial for a larger
series of overheads you'll bring down if a 30 caliber case with the capacity of an improved 338 Lapua is used for the string lengths required for most ELR matches. They are significantly compounded by the use of double base powders.

Straying into unsolicited advice, there are 4 factors affecting impacts at distance.

100 yard precision
Velocity Spread
BC Spread
Uncertainty in the aiming point.

From your initial post, it looks like you're working on the wrong end of the elephant. The ELR problem cannot be solved with raw velocity or BC and the precision will take care of itself when you're working on the right things. 10 years ago, a lot of us attempted it. Some are still trying to sell them as solutions. It's also still the most common starting point for people looking to compete.