Rebarrelling my old 243 to another 308 based cartridge

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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by bladeracer » 01 Oct 2022, 4:53 pm

SCJ429 wrote:But the 243 can shoot a 107 grain bullet in excess of 3000 fps and with a bit of coaxing at 3100 fps. This is about the same speed a 260 can produce with the same weight of bullet but worse BC. Hitting a goat at 500 metres with either projectile would be quiet similar but the 243 has the edge. It is like comparing the 7mm08 to the 308, they are very similar but the 7mm has the edge.


Certainly, it can by running it very hot, but you can do the same with the 6.5x55mm or 7mm-08 if that's how you roll. With the larger calibres you don't need to work the rifle that hard to make up the shortfall. You could also go with a .240 Weatherby if you really want to get the most out of 6mm bullets, but you're still only achieving what larger calibers can already achieve without all that heat, noise and expense.

At 500m the 3000fps 107gn SMK has about 460mm of drift in 10mph of crosswind. The 6.5x55mm with the 143gn ELDM at 2650fps (without having to push it hard) has the same wind drift, and 20% more energy.

I like the .243 but it is not in the same class as the 6.5mm or 7mm chamberings.
The .243 and a few cases of 87gn VMax ammo will deal very effectively with most of what a lot of shooters are likely to want from their rifle.
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by bigrich » 01 Oct 2022, 6:16 pm

SCJ429 wrote:But the 243 can shoot a 107 grain bullet in excess of 3000 fps and with a bit of coaxing at 3100 fps. This is about the same speed a 260 can produce with the same weight of bullet but worse BC. Hitting a goat at 500 metres with either projectile would be quiet similar but the 243 has the edge. It is like comparing the 7mm08 to the 308, they are very similar but the 7mm has the edge.


horses for coarses i guess . a 6.5mm 120 BT travelling at 2950-3000 fps is going to be devastating on a goat . me personally , i'm not too keen on shooting past 300 yards with any of my sporter rifles . at most hunting ranges BC's are splitting hairs . but with regards sectional density/projectile weight/ versus energy transfer i'd rather a 6.5 than a 6 . besides that , 243's have a obnoxious muzzle crack :P

also i have it on good authority from big pete 6mm is no good :lol:
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by SCJ429 » 01 Oct 2022, 6:46 pm

bladeracer wrote:
SCJ429 wrote:But the 243 can shoot a 107 grain bullet in excess of 3000 fps and with a bit of coaxing at 3100 fps. This is about the same speed a 260 can produce with the same weight of bullet but worse BC. Hitting a goat at 500 metres with either projectile would be quiet similar but the 243 has the edge. It is like comparing the 7mm08 to the 308, they are very similar but the 7mm has the edge.


Certainly, it can by running it very hot, but you can do the same with the 6.5x55mm or 7mm-08 if that's how you roll. With the larger calibres you don't need to work the rifle that hard to make up the shortfall. You could also go with a .240 Weatherby if you really want to get the most out of 6mm bullets, but you're still only achieving what larger calibers can already achieve without all that heat, noise and expense.

At 500m the 3000fps 107gn SMK has about 460mm of drift in 10mph of crosswind. The 6.5x55mm with the 143gn ELDM at 2650fps (without having to push it hard) has the same wind drift, and 20% more energy.

I like the .243 but it is not in the same class as the 6.5mm or 7mm chamberings.
The .243 and a few cases of 87gn VMax ammo will deal very effectively with most of what a lot of shooters are likely to want from their rifle.

It is not a hot load for a 243, it would be very safe. My tiny 6mmBR shoots 107s at 2800 fps and my 243 when load testing shot them at 3180 fps.
My thoughts are if you wanted something to knock over things that the 243 isn't suited you would be better off with a 270 Win or a 308. If you want a 6.5mm all good. But they are not much of a step up from a 6mm.
When comparing the 6mm to the 6.5 ballistics, you shoot the same weight bullet and the 6mm has the BC advantage and can shoot them around the same speed. Or you shoot the heaviest available and the BC is about the same but the 6mm has a speed advantage.
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by bladeracer » 01 Oct 2022, 9:20 pm

SCJ429 wrote:It is not a hot load for a 243, it would be very safe. My tiny 6mmBR shoots 107s at 2800 fps and my 243 when load testing shot them at 3180 fps.
My thoughts are if you wanted something to knock over things that the 243 isn't suited you would be better off with a 270 Win or a 308. If you want a 6.5mm all good. But they are not much of a step up from a 6mm.
When comparing the 6mm to the 6.5 ballistics, you shoot the same weight bullet and the 6mm has the BC advantage and can shoot them around the same speed. Or you shoot the heaviest available and the BC is about the same but the 6mm has a speed advantage.


Comparing bullets of different diameters but the same weight is denying the inherent advantages of the larger calibre. The larger calibres work better because they can run longer heavier bullets that have better BC, hang onto their velocity and energy for longer, and carry more energy. This is why we've moved to tighter twist rates, to allow us to shoot longer bullets for their BC advantages.
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by bladeracer » 02 Oct 2022, 1:53 pm

SCJ429 wrote:But the 243 can shoot a 107 grain bullet in excess of 3000 fps and with a bit of coaxing at 3100 fps. This is about the same speed a 260 can produce with the same weight of bullet but worse BC. Hitting a goat at 500 metres with either projectile would be quiet similar but the 243 has the edge. It is like comparing the 7mm08 to the 308, they are very similar but the 7mm has the edge.


I had a think about this. I reckon I can push the 105 above 3000fps without too much trouble, though I would still consider it very hard on the brass and throat and not something I would want to run regularly. But I really don't think I could make 3100fps. Are you running a 22" barrel to make these velocities?

I might consider the very hottest of the 6mm's to _almost_ be riding on the same "edge" as the 6.5's and 7mm's, but the .243 is nowhere near that edge. It's in the ballpark, and the .223 is in that same ballpark with modern bullets and twist rates, but they're in the middle of the ballpark, not near the edges.

Even at conventional sub-300m hunting distances, the larger calibers have a real edge by carrying a lot more energy. The .243 has the edge on small game as the lighter bullets are likely to evaporate with less penetration while the heavier bullets are going to carry a lot of their energy into the hill behind the target, but they are still going to devastate the target.
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by Peterwho » 03 Oct 2022, 8:29 pm

Could go somewhere different - try a 338 Federal. It will put a big punch on any goat. Won’t hurt the shoulder as much as a 358.
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by SCJ429 » 04 Oct 2022, 6:04 pm

You would be mad to shoot a 243 with heavy pills and slow powder out of a 22 inch barrel, the flames licking out of the muzzle would be over a metre long. If you want to use shorter barrels, I would go for a 308 using faster powder and you loose only a little velocity. My barrel was a more sensible 26 inches and still spat out some impressive flames and had a destnctive crack, also used it to achieve nearly 4,100 fps with lighter projectiles. The chrono stopped reading the speed after that so I am not 100% sure of the final speeds achieved.
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by bigpete » 04 Oct 2022, 6:11 pm

Peterwho wrote:Could go somewhere different - try a 338 Federal. It will put a big punch on any goat. Won’t hurt the shoulder as much as a 358.


358w is pretty mild
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by bigrich » 05 Oct 2022, 5:58 am

bigpete wrote:
Peterwho wrote:Could go somewhere different - try a 338 Federal. It will put a big punch on any goat. Won’t hurt the shoulder as much as a 358.


358w is pretty mild


Agreed. And a better choice of medium game bullets than 338. Most 338 bullets are to stout as they are designed for the win mag. That’s why I went with 358.
If I was the OP I would look at 260 rem or 7-08 depending on whether the mag length is over 2.8”
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Re: Rebarrelling my old 243 to another 308 based cartridge

Post by Jakethefake » 09 Oct 2022, 9:12 pm

bigrich wrote:If I was the OP I would look at 260 rem or 7-08 depending on whether the mag length is over 2.8”
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I'm home now (I was about 12000km away when I made this post), so I got the old girl out of the safe for a closer look. The magazine length is 2.875. I'm still leaning towards 7mm-08. But I kinda want a 260 as well now.
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