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Charles Ellertson
- Thread starter alinwa
- Start date
Al, we (me, Joel Pendergraft, Jeff Rogers, Tony Z, etc.) have used Aluminum, usually 1.50 o.d. with 1/8 wall. 6061 T-6 recommended. Best quality (lowest wall thickness/runout) you can find. Machine as if you were chambering (i.e., tight tolerances).
I have also used 1.375 o.d. I've also had success with 1.375 o.d. welded steel, 1/16 wall, with lots of holes drilled in the tube. Steel seems to require more tension. I don't know what you mean by "pre stretched." On the light guns, we use a nut with a shoulder, not jacking screws. Muzzle brakes fits on the same thread as the nut; the nut acts a a stop for the brake.
Most of the tensioned barrel rifles that weren't 1K Heavys were 1K LGs at 17 pounds. But the tube assembly doesn't weigh much... I made a 10.5 pound PPC with a stretcher, too. Still, a 10-pound .338 is going to be hard to bring off. We've always used a steel nut, I suppose you could make that of aluminum, too.
Right now, for my 1K light gun, I'm shooting one of Joel's old rifles, a .338/404 with a tensioning tube made of 1.50 o.d. with 1/8 wall (6061 T6 aluminum). 30-inch barrel. The case holds 114 grains water, full to overflow, so that's .338 Lapua country. More than 10 shots & heat becomes an issue. Make the fit of the barrel (should be about 1.250 at the breech, right?) a close fit to the tube, and there is better heat transfer.
Dave Tooley took the idea the other way; he put the barrel under compression. This on a .300 Win Mag. While excess heat could still cause deflection, you don't lose tension under heat (well, compression, in this case) A little more work, probably a little more weight than tensioning. Main thing is to control the muzzle, whether by tensioning or compression doesn't seem to matter.
* * *
I know Berger has just finished a run of thick-jacket 300 grain Hybrids -- I won 300, & one of the guys at Berger called & chatted. I'd prefer the thin jacket as I keep them under 2,800 fps, but they had just finished a run of the thick jacket (aka "tactical"), so that's what was available.
BTW, that .338/404 was part of the reason I won the bullets. It shoots very well indeed. Most consistently accurate load for me is 79 grains of 4831 behind a 300 Berger Hybrid, but it's "only" starting out at 2,630. Next most accurate load was 88.5 grains of Rel-25. As you probably know, the burn rate of Reloader powders can change from lot to lot. H-1000 seemed to shoot well, with a few more occasional, unexplainable flyers than Rel-25, which itself has more than the 4831. Even if only 1 or two inches at 1,000 yards, flyers aren't good in competition.
You had mentioned success with Retumbo -- what's a good starting charge? For me, accuracy over speed...
Hope this helps
I have also used 1.375 o.d. I've also had success with 1.375 o.d. welded steel, 1/16 wall, with lots of holes drilled in the tube. Steel seems to require more tension. I don't know what you mean by "pre stretched." On the light guns, we use a nut with a shoulder, not jacking screws. Muzzle brakes fits on the same thread as the nut; the nut acts a a stop for the brake.
Most of the tensioned barrel rifles that weren't 1K Heavys were 1K LGs at 17 pounds. But the tube assembly doesn't weigh much... I made a 10.5 pound PPC with a stretcher, too. Still, a 10-pound .338 is going to be hard to bring off. We've always used a steel nut, I suppose you could make that of aluminum, too.
Right now, for my 1K light gun, I'm shooting one of Joel's old rifles, a .338/404 with a tensioning tube made of 1.50 o.d. with 1/8 wall (6061 T6 aluminum). 30-inch barrel. The case holds 114 grains water, full to overflow, so that's .338 Lapua country. More than 10 shots & heat becomes an issue. Make the fit of the barrel (should be about 1.250 at the breech, right?) a close fit to the tube, and there is better heat transfer.
Dave Tooley took the idea the other way; he put the barrel under compression. This on a .300 Win Mag. While excess heat could still cause deflection, you don't lose tension under heat (well, compression, in this case) A little more work, probably a little more weight than tensioning. Main thing is to control the muzzle, whether by tensioning or compression doesn't seem to matter.
* * *
I know Berger has just finished a run of thick-jacket 300 grain Hybrids -- I won 300, & one of the guys at Berger called & chatted. I'd prefer the thin jacket as I keep them under 2,800 fps, but they had just finished a run of the thick jacket (aka "tactical"), so that's what was available.
BTW, that .338/404 was part of the reason I won the bullets. It shoots very well indeed. Most consistently accurate load for me is 79 grains of 4831 behind a 300 Berger Hybrid, but it's "only" starting out at 2,630. Next most accurate load was 88.5 grains of Rel-25. As you probably know, the burn rate of Reloader powders can change from lot to lot. H-1000 seemed to shoot well, with a few more occasional, unexplainable flyers than Rel-25, which itself has more than the 4831. Even if only 1 or two inches at 1,000 yards, flyers aren't good in competition.
You had mentioned success with Retumbo -- what's a good starting charge? For me, accuracy over speed...
Hope this helps
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Thank You Charles..... I'd guessed (wrongly, it seems) that AL would collapse under the load. My plan is to stretch the barrel to a measured length, snug everything up and remove the tension.
Regarding loading Retumbo, I just bought a 300RUM donor setup last week and will soon be able to run 338L and 338RUM head-to-head. blown out 338L, 300gr Berger, Retumbo powder VS 338RUM. I'm a little hesitant to assume direct crossover between the cases since I've never measured water capacity of my 338L and I've never even seen a 338RUM but I'll happily PM you my loads if you wish.
al
Regarding loading Retumbo, I just bought a 300RUM donor setup last week and will soon be able to run 338L and 338RUM head-to-head. blown out 338L, 300gr Berger, Retumbo powder VS 338RUM. I'm a little hesitant to assume direct crossover between the cases since I've never measured water capacity of my 338L and I've never even seen a 338RUM but I'll happily PM you my loads if you wish.
al
I'd guessed (wrongly, it seems) that AL would collapse under the load. My plan is to stretch the barrel to a measured length, snug everything up and remove the tension.
Well, you can collapse the thinner aluminum tubing. I'd suggest that might be too much tension, though. Early on, with a rail gun (1/2" wall aluminum), I heated some things up to get a lot of tension -- never computed, just "a lot." Talk about nice patterns...
a.JR reports with his (aluminum tube) that as long as there is some tension after it gets warm from 10 quick shots, it seem to work. Don Neilson reported that with his steel tubing (used in a PPC), he needed to use a fair bet of tension -- IIRC, about 40 ft pounds on a torque wrench (using a cap instead of multiple jacking screws). Might be that's too much for thin-walled aluminum.
Another guy, with a 1K HG (no weigh limit), didn't use tension at all, but rather screws through the end cap to secure the barrel's muzzle -- just like a spider for a lathe. It shot very well, too, and same characteristic group shape as a well-done tensoned/compressed barrel.
All this led me to speculate that the phenomena we're after is to get the barrel closer to a double-cantilevered beam. In passing, we also get pretty close to Calfee's "stopped muzzle." Any way you get there, tension, compression, or restraint, seems to work. Likely one way works better, and likely there is an optimum value, but nobody's done the work yet.
Greg Tannel, who used a set of jacking bolts, also reported you could tune the setup by adjusting individual screws. In this case, I believe "tuning" was for group size rather than group shape. It's been a while, and it was a telephone conversation, so I might be miss-remembering.
Be careful. If you get positive results, you might have opened a study that will take the rest of your life...
I'll happily PM you my loads if you wish.
Yes, please, I'll be careful. If I recall, the .338 RUM has a little less capacity than the .338/404. And the blown out .338 Lapua has more. You once mentioned you'd found a fairly light load with Retumbo that shot well in your improved .338L.
al[/QUOTE]
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