375 RUM Improved (Box Monkey Express)

[yorketransport]

York,

 You wouldn't happen to have GO gauges also, would you?

I certainly do! And I have a die reamer for the 375 BME. Why pay $300 for custom dies when you can pay $120 for a reamer to make your own.

How many reamers do you own man! Sounds you need to open up a local business. Call it: Gunsmith of Savages. That way savage owners will know you will work on their stuff! 

Right now I just have the 338/375 and the 375 BME. If I had my own lathe, I'd probably have a lot more. I just don't have time or space to have too many more projects going. Right now I have 4 project guns which need some attention. There's the 6mm BR pistol, 338/375 rifle, 358 Win, and now the 375 BME. Plus I have a 308 Norma Mag barrel which should be done in a couple weeks. I should really spend less time building, and more time shooting!

Andrew

[Biggerhammer]

You have to have them to shoot them!

[yorketransport]

I got a couple more cases fireformed. This time they were 404 Jefferey cases. These are a little easier to form than the 375 RUM brass. No necking up, just run them into a 378 Weatherby die to neck them down enough to get the brass to chamber. If I try to neck them down in the 375 BME die, the necks will crush every time. The shoulder angle is just too sharp.

 
I only got about 25 of these done before my wife said I can't fireform them in the garage any more. It wasn't the noise, but the smell that she didn't like.

Hopefully I'll get out next weekend to do some more load work.

Andrew

[Biggerhammer]

That's what I did with 450 Ultra Magnum, I ordered .404 Bell cases from Buffalo Arms. Used cornmeal to partially fire form them. Then seated a 500 gr Hornady into the lands, so the case head was pushed tight against the bolt face and ran a mid range load of Win 748 to fully form them.

[yorketransport]

Well I got out for the first round of full power load development today. So far I'm happy with the results.

This trip was using H1000 and the 350gr MK. H1000 is not ideal. It's too slow to get max performance. I started with this powder because I figured I couldn't fit enough into the case to get myself into too much trouble. I ran the powder charges up to 115 grains, and even using an 8" drop tube the loads were over compressed. The good news is that I was able to hit 3100 fps with no pressure signs. I could cycle the bolt with one finger and the brass practically falls out of the chamber. 3100 fps with a 350gr bullet! That's not bad at all! Plus I'm still getting single digit extreme spreads.

The accuracy wasn't as good as I expected, but that had a lot to do with the over compressed powder charges. The bullet was hard into the lands and in my experience the MK doesn't work well when jammed. A faster powder should let me seat the bullets back off the lands a little bit and hopefully improve the groups. Right now I'm geting around .75 MOA. I know it will do better.

The next lesson learned is that I need a better recoil pad. I rarely complain about recoil, but with the full power loads this gun is "peppy" to say the least. Recoil is straight back, but still feels about like my 9# 375 Ruger, or at least mid weight 338 Win mag. The recoil pad on the HS Precision stock really wasn't intended for this sort of caliber. It came off a Savage LRPV in 22-250. The 375 BME is slightly bigger  I could also add a little weight to the stock. Right now the rifle weighs just under 12# which may be a little on the light side for a target gun in this caliber. It's pretty muzzle heavy anyways. A little weight in the but would help balance it pretty well I think.

I'll post more results the next time I get out.

Andrew

[Biggerhammer]

Cool set up York! Maybe some RL-22 and a 5 thou jump or so. Welcome to the super magnum recoil club! My right eye is sometimes fuzzy for a little while after a bench session with my 450 Ultra Mag. Like you said, STRAIGHT BACK! recoil.

[yorketransport]

RL-22 and IMR 7828ssc are the next to try.  Then it will be a pile of RL-17 and a 235 TTSX. That should be screaming!

Andrew

[Biggerhammer]

You should be able to flat CRUISE that 235!!!!! It would make a great Rockchuck bullet out of that chambering.

[Frank7mm]

Do you still have the reamers? What load did you settle with? What Velocity? I was thinking of a 375 RUM but this looks like more fun.

[lghtnquik]

7500lb-ft of energy hahahahahahahahahahahahaha I guess why not!

[yorketransport]

Do you still have the reamers? What load did you settle with? What Velocity? I was thinking of a 375 RUM but this looks like more fun.

Sadly, I haven't had much time to work with this rifle yet. Just as I finished the rifle I had an unexpected business expansion which will consume all of my time for the next few months. I went from a one man corporation to buying two more vehicles and hiring two new employees over the course of 2 weeks. This now puts me working 6 days and more than 80 hours every week.  I'm glad that the business is growing, I just wish it wasn't at the beginning of hunting season!

Right now I have a load using 114gr of H1000 under the 350gr MK moving at about 3050fps with single digit standard deviations. The groups are not as good as I want though. It's hanging in the .75 MOA range and I really expect better. I need to fine tune the seating depth and charge when I get time. I've tried a few other powders (IMR 7828ssc, H4831, and Reloader 17), but none gave me the results I wanted. Reloader 17 was throwing 300gr Sierra boat tails at nearly 3400fps, but it gave pressure spikes, so I dropped that powder. The extreme spread was over 30fps but the groups were amazing. It's a shame that the powder was so unpredictable.

I still have the reamers and gauges, but I would probably just go with a standard 375 RUM unless you are just looking for something different. Most of the gains I'm seeing are from extending the throat to increase case capacity and the 30" barrel.  If you stretched the throat on a standard RUM you would be pretty close to the same numbers without the need to fireform. I will say the that I'm not happy with Remington 375 RUM brass. It's only good for 2 firing before the primer pockets open up. The Norma 404 Jefferey brass holds up much better and actually give a slightly longer neck, which is nice.

I probably won't get much done with this until after the Christmas rush has passed. Hopefully I'll have a little more time to work on it then.

Andrew

[coachcw]

Bad Ass ! enough said .

[Biggerhammer]

Try some of the BELL .404 Jeffery brass from Buffalo Arms. It has worked well in my .450 Ultra and is stout stuff. I'm going to neck some of it down , turn the necks and try it in my .338 Edge when I have some time after the hunting season.

[b23]

You're primer pockets are blowing out because your load is over 80,000 PSI and if your still jamming those 350 SMK's the pressure spikes up to almost 88,000 PSI !!!  That's using your 4.2 OAL and 114gr of H1000

SAAMI spec is barely over 63,000PSI for the 375 RUM

You might want to think about backing it off a bit before you hurt yourself because you're flirting with disaster.

[yorketransport]

You're primer pockets are blowing out because your load is over 80,000 PSI and if your still jamming those 350 SMK's the pressure spikes up to almost 88,000 PSI !!!  That's using your 4.2 OAL and 114gr of H1000

SAAMI spec is barely over 63,000PSI for the 375 RUM

You might want to think about backing it off a bit before you hurt yourself because you're flirting with disaster.

Your numbers would be accurate if I were using a standard 375 Rum case, but did you enter the actual dimensions for the case I'm using? It's also worth considering the throat dimensions I'm using are not the standard RUM specs either. I assume that you're using QuickLoad to calculate those numbers.

I haven't had any pressure problems with H1000, only with Reloader 17. I can't fit enough H1000 in the case to really get into trouble. That's one of the reasons I started with that powder. And I'm not the only one who feels that Remington brass is on the soft side. I do appreciate your concern for me though. I wouldn't be too worried about it though. This isn't my first day.  If somebody else wants to try these loads they're going to need a gun chamber for this caliber first.

Andrew