Loading to magazine length/bent tips

[Briant_az]

I've got a 300 RUM that I am unable to load close to the lands due to internal mag length. This hasn't really been an issue as far as accuracy of the rifle goes.
I have been shooting 200gr Accubonds in the rifle for 3-4 years. Last year I had the tip of one of the Accubonds come off in the reloading box. I thought this was weird but never really gave much thought to it. I just assumed it was a faulty bullet and shot it the next time I went to the range. This year after shooting a deer I took the other two rounds out of the internal mag and I noticed that the tip of the other two bullets were bent. Obviously the recoil of the gun if making the loaded rounds hit the front of the mag box.

Is there a way to stop this? What length are you guys loading to, under you mag length?

Any help or insight is greatly appreciated.

Brian

 

[sturner]

I took out the internal plate on my magazine to get more room

 

[QuietTexan]

Wyatt's mag box. I've already talked to my shop about the big 3.990" one that requires a cut in the action, CFE-9?

Or Hammers set to factory mag length. The reason I haven't done the box yet is I spent the money on some 180 HHs.

 

[eschafer]

how does a longer mag box stop recoil from bending bullet tips?

 

[MagnumManiac]

I have the same issue in 300, 338/340 and 375 Weatherby.
I run them .005"-.010" from max mag length. This helps slow them down, the tips still get hit, but not as bad.
My light Kimber's are the worst, they flatten the tips real good no matter how close I keep the tips to the mag box. Funny thing, my Win Model 70 EW in 338WM is only half a pound heavier than my Kimber's and it doesn't deform the tips at all.

Cheers.

 

[QuietTexan]

how does a longer mag box stop recoil from bending bullet tips?

.2" more clearance so the tips don't contact the front of the box. If the bullets are sliding around hard enough to break the tips off you have a different problem than clearance, replace the mag box spring.

 

[billflangjr813]

how does a longer mag box stop recoil from bending bullet tips?

So what are you really saying??

 

[CONatureBoy]

I have a Remington Sendero SS II in 300 RUM. I had a gunsmith install a longer Wyatt's magazine box. That required machining away around 0.07" of the aluminum bedding block where it runs across the stock at the back of the magazine. The gunsmith also machined a little of the steel at the back of the port (I think they call it) on the action proper. Now I can put in the magazine a couple of 210-grain VLD cartridges loaded to a COAL that's within a few thousandths of the lands. My gunsmith says he does this sort of thing all the time. Love it.

A bit of elementary physics: if the bullet tip is close to the inner wall of the magazine box, recoil has less time to accelerate the magazine to the rear before making contact with the tip of the bullet. From then on, the bullet will either deform or move with the magazine. Once they're both moving the same speed and direction, subsequent acceleration of both occurs continuously, gradually--not suddenly--which will deform the bullet tip less. A faster-moving magazine will strike the bullet tip with more force. So moving the bullet towards the magazine wall (either by having a longer cartridge or a shorter magazine) is one way to decrease the force on the bullet tip due to the initial impact. Another way is to have a bullet tip that resists deformation. This suggests that a longer magazine box is only a good idea when you need it to hold long-for-caliber cartridges.

I'm a little surprised your bullet tips deform. The physics would be pretty obvious to a ballistician.

 

[drborsos99]

What's wrong with hand loading your cartridges so the COL (cartridge overall length) is .060" off the lands?

 

[CONatureBoy]

What's wrong with hand loading your cartridges so the COL (cartridge overall length) is .060" off the lands?

Nothing, if it shoots straight. I get better accuracy from VLDs when I load them close to the lands. My understanding is the bullet has less distance/time to get off center from launch to engagement with the lands, so it enters the barrel closer to being perfectly centered, and positioned more consistently. (I wonder whether powder loads that are close to 100% reduce this effect by doing a better job producing a spatially symmetric pressure gradient behind the bullet, at launch?)

I am under the impression that loading close to the lands has another effect, namely to increase resistance to the pressure building behind the bullet earlier, because the gases produced by the burning powder can't escape around the bullet for as long. This would tend to produce a sharper pressure peak, requiring more care with near-maximum loads to avoid overpressure conditions. (I have read that this effect at least partially motivated the design of most Weatherby chambers, which--the 240 Weatherby aside--have long throats to give the gases more time to escape around the bullet, while ultimately allowing more powder to burn behind the bullet. Weatherby cartridges are overbore, and this was a way to handle all that powder before our era of abundantly available slow-burning powders.) I'm no expert, but this hypothesis is consistent with my experiences handloading for a dozen or so rifles. I get a bit more speed out of a bit less powder when I load close to the lands. I haven't tried to quantify that effect.

 

[azarcher10x]

It was always my understanding, 300 RUM was designed to have a substantial jump for the bullet. This was a way it produced higher velocities. I can't see where any bullets are going to allow gases to escape around the bullet before it reaches the lands, unless it's an extremely short, light projectile. I've run max load, 165 gr. Barnes TTSX just short of standard mag length, and never had any issues with deformed tips. I believe the COAL is 3.690. Even there, I'm .150 off the lands. I run a very efficient brake from LR Customs. Perhaps that's the difference!

 

[CONatureBoy]

Here's the SAAMI 300 RUM chamber spec:

If I read that right, it has 3.2487" - 2.9880" = 0.2607" of leade and 2.9880" - 2.8780" = 0.11" of throat. Or if I should use the inner number, that would be 2.988" - 2.860" = 0.128" of throat. By way of comparison, here's the 280 AI spec:

The throat here would be 2.754" - 2.560" = 0.194", about half again as much as the 300 RUM. So I don't see extraordinary jump in the RUM's chamber design. . . .

The Wikipedia article on the RUM concludes that it was "conceived as a long range hunting cartridge" well suited to shooting heavy/long-for-caliber bullets. Comparing it to the 30-378 Weatherby, the article says, "The .30-378 Weatherby Magnum is considered the most overbore production sporting cartridge available and is not considered as efficient as the .300 RUM cartridge. In part due to its excessive freebore lengths the claimed velocities by Weatherby is a resultant factor of this freebore length. If chambered to allow bullets to seat to the lands of the rifling the large Weatherby cartridges would exhibit overpressure signs immediately. All things equal the .300 RUM and .30-378 Weatherby if chambered with the same throat and freebore would be comparable." I don't know who wrote that, but it's consistent with my speculations about pressure peaking faster when you seat close to the lands. Weatherby chambers have lots of freebore to flatten out the pressure peak, so they can maintain peak pressure longer (by burning oodles of powder), to get the speed that made Weatherby famous.

 

[Lenny Foffa]

I have been considering Regulating my ammo for one of my rifles. .270 Weatherby Magnum. Make the length that I know is longer at the ogive and shoots the best , and make the other two rounds suitable to function in the the internal magazine. ( Shorter) When I am ready to hunt my way to the blind, Chamber the Longer round last, so it will be the first shot. Rifle loaded with the preferred first round , and safety on. Some of you ,may remember when the guys who hunted Africa, turn of the century , with big magnums in beautiful double rifles needed to to have Regulated Loads for the left and the right barrel , so the they could zero both barrels at the same range. Just a thought. Yes, I am open to all kinds of criticism!!!

 

[Gone Ballistic]

I've never experienced any problems in my custom 300RUM with any Nosler Accubond 200gr. or 210gr. bullets. But, it has been my experience that loading anywhere off the lands and grooves makes it shoot lousy groups. I have done better tuning my groups by measuring from the SAMMI specs and on my previous barrel, I got my best sub MOA group from going shorter. This has told me that this caliber needs a lot of jump for accuracy.
I'm curious about how many other 300RUM reloaders have had the same experience?