300 RUMBO chamber reamer drawing--take a look please

[jmden]

Here's the fifth draft of a chamber reamer that I'm planning on having made.

http://mysite.verizon.net/respg9za/

I'm sorry if the image doesn't come through too clearly. Actually I see that it didn't come through at all in the body of the message. Obviously, I need help with that process as well. The link should still work.

I tried to set this up so that the body/boatail junction of the 200g Accubond would be about .020 below the neck/shoulder junction with a 2.850 case length and a .270 neck length. This should give me a few thousandths worth of rifling to play with before the bullet is set out to far. That's the plan anyway.

Dave at PTG thinks this will work fine but he doesn't care for the short neck. Neither to I, but I'll risk it to maximize volume. I remember STL and S1 awhile back with their 30 Wolf (about the same volume--338 Lap case made into a 30-338 Lap Imp. with a short neck to max volume)project that had a much shorter neck than this and S1 was saying that he was having pretty good barrel life. The idea is to maximize available volume from the 300RUM case.

I'm for additional comments/suggestions...I'm putting on body armor as I write this.

Thanks,

jmden

 

[Fiftydriver]

Jmden,

Just a couple comments on your design. Baically it looks good but there are two areas that I would be worried about.

The first is the amount of taper in your case. From your print it looks like your running roughly 0.004" of body taper for every inch of body length. You will find that if you load to top pressures that this very limited amount of body taper will result in extraction problems on the 4 and 5 firing of the cases. Possibly on the 3rd firing.

The reason is because with such a min taper body, the Full Length sizing die simply can not reduce the body diameter enough to not bare on the chamber walls.

Once the case tempers a bit from firing, the case will spring back more from the sizing die and chambering and extraction will become an issue and eventually this can cause chamber scratching. I would recommend more taper in the case.0.008" taper per inch of case body is min in my opinion.

Second dimension I would change slightly would be the chamber diameter. Most RUM cases mic 0.5450" to 0.5453" in case head diameter. Again, if you run at top pressures the 0.5510" diameter you are using will allow excessive case head expansion and will result in lose primer pockets relatively quickly.

I would get several differnet lots of brass and get a head diameter measurement on them and tighten up your case head diameter more. This will allow your cases to handle top loads and offer longer case/primer pocket life as well.

Other then that things look good!! Should be a great round.

With the dimensions of your throat I assume this is designed for a single shot use only? The 0.3085 diameter would be perfect for the 200 gr Accubonds I have as they measure an even .3080" in diameter.

IF you want to possibly use any other long range bullets such as the SMK or Wildcat Bullets I would contact those companies and find out what their bullet diameters are running. SOme can vary by quite a bit so this is the time to look into this area, not after the reamer is made.

Designing the reamer for one specific bullet is not always the best option. Make sure other top quality bullets will also function in the chamber just in case.....

Good Shooting!!

Kirby Allen(50)

 

[jmden]

Thanks, Fifty. Dave Kiff called as I was reading your post this morning and the body taper issue was one thing I wanted to question him again about before he made this reamer. He wasn't too concerned about it as he's seen cases with less body taper than that do just fine. He made one reamer for a WSM guy who had no body taper whatsoever and apparently didn't have any problems with extraction. Dave was surprised at this, but it's the facts. At any rate, we increased the body taper a bit and the reamer should be made today.

He's had a number of guys running 300RUM reamers up to .555 at the case head area with apparently little issue with primer pockets loosening up but there seems to be to be some physics there that can't be ignored. In other words, I can't imagine that pockets aren't opening up. I see your point.

Nope, not a single shot. I put a Wyatt's center feed mag box in last year. Only two down instead of three, but controlled center feed and a whopping 4 inch magazine lenth. I'm 4.115 OAL with Sinclair comp to reach the lands now with the 180 Accu and I made sure I could position the 200 similarly and have it fit in the mag. The longer bullets might be a problem, however.

Thanks for the input,

jmden

 

[coupalr]

This looks like what I want. I have a 300 rum police that I would be willing to rechamber to test your reamer out. If this is a possibility let me know. I want to put a custom barrel on it in the near future but I would like to see your reamer tested before I chamber a $500 barrel.

 

[Fiftydriver]

What barrel are you using that costs $500? I just got a 40" stainless Lilja 338 1-10 with a 1.750" straight cylinder in for alot less then that.

If your paying $500 for a barrel blank your paying to much!!

Just my opinion, even including fluting!

Kirby Allen(50)

 

[jmden]

6mm Shooter,

I've been gone for a few days hunting--sorry for the delay.

At this point, and at the risk of sounding like a scrooge on this board (sorry!), I'm not willing to loan out my reamer. I got it a couple of days ago and would like to use on my barrel. It will likely take me several months to get around to doing at this point the way finances are. Dave Kiff at Pacific Tool and Gauge can probably get the reamer to you pretty quickly now that he has it on file if you'd like to go that route. One thing to keep in mind is that in it's current configuration, mine is made for the 200g Accubond--it's a finish reamer for close to optimum bullet seating (I hope) for that bullet while just on the lands. So if you want one from Dave, you'll have to spec it out for the bullet(s) you want or finish reamer you want, etc.

jmden