Well, here we are, barrel and dies sitting on my bench, donor is a 300 RUM 700P with a Talley 20MOA rail. It hasn't been trued or the barrel fitted yet and I'm wondering if I should shelf this project for awhile and just enjoy the 300 RUM barrel until it is cooked. I have a scope mounted and some reloading supplies for the 300 too. IT is indeed a fearsome round as well and it makes little sense to reinstall a factory tube, so I should really enjoy wearing it out first no??
twist rate for 6.5-300 Ultra
- Thread starter jtoews80
- Start date
LongBomber
CGN Regular
- Location
- Fernie, bc
Buy an action wrench ($70 Brownells - Surgeon action wrench) and a barrel vice (under $100 for a vice on Ebay) and do both. Once the action is trued have both barrels fitted, the swap between them is an easy job.
Best of both worlds.
Best of both worlds.
You got me curious as I have a .264WM in a 10 twist and have run into issues with bullet instability. It was marginally OK with 140 grain Sierra's and 140 grain Nosler Partition in warm weather. However, when the weather turned cold they both went unstable.
I did a calculation on both bullets using the Border Barrel site, which has a calculator based on McGyro code. They both came out to a stability of very close to 1.0. Recommended is 1.4, but that has a margin of safety in it. In any case the code was quite accurate in predicting when the bullet goes unstable.
So I ran McGyro on Berger match bullets starting at 130 grain, and working down in bullet weight. Have a look at the second graph at the bottom of the page. It shows stability vs velocity. As you can see velocity does not make that much difference. Just for reference I'll list the Stability Factor at 4,000 fps.
130 VLD - SF@4000 fps = 0.70 McGyro Results
120 BTHP - SF@4000 = 0.93 McGryro Results
100 BTHP - SF@4000 = 1.23 McGyro Results
So my thoughts are that there is virtually no chance the 120 or 130 will stabilize. The 100 probably will be OK. I don't think the 123 SMK has any chance. I rather doubt the 107 SMK will work either. If it does, probably only in warm weather. I have some, but don't have the dimensions handy, but I recall they were also an issue for my 1 in 10 twist.
I wish you well with the gun, but I don't think those heavier bullets are going to happen in a 12 twist...
We'll find out when we start shooting it. I do know it will wear out fast anyway, so that is life. I ran a couple of ballistic calculators and they said close to the same. 123's sure, 130's not likely, 140's never, one variable that a calculator isn't going to show is the affects of the 30" tube. Most likely, those figures are for 24" barrels and using those bullets inside of a conventional velocity range, I doubt that anybody tested a 130 or 140 grn 6.5 bullet to that velocity. Nonetheless, areodynamics are a function of math and the formula could very likely be true regardless of barrel length or velocity. I'm not to sure, but there was a 10 twist 6.5-300 wby barrel floating around on the EE awhile back that would work if this doesn't. I have the reamer on my bench, so a different barrel is an option, but a costly one. To be truthful, I never really planned on using the 140 VLD at all because the SMK has a thicker jacket and will handle the velocity a bit better. Realistically, neither bullet would be operating where they were designed or expected to when they start crossing 3500FPS.
Here is the 700P in her 300 RUM factory configuration.
My 264 is overstabilized @ 8.5 twist with 140 VLD's and is limited velocitywise. I should rechamber to 260 and stop wasting powder.
Here is the 700P in her 300 RUM factory configuration.
My 264 is overstabilized @ 8.5 twist with 140 VLD's and is limited velocitywise. I should rechamber to 260 and stop wasting powder.
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I already found that out with another action I had on my bench. If I have the action trued, I'd have to have both fitted, but for the barrel life of either, it may be a moot point. If you shoot a RUM all summer 50 rounds a week it would be unlikely to shoot within MOA by summer's end. If it still shot after 500 rounds of 6.5 or 750 of .308 I'd be happy.
Best plan to date, wear out 300 RUM, wear out 6.5 barrel, rebarrel to something sane like a 338 edge, 338 lm or lmAI. I'd would have to open up the bolt face for the lapua, but would get to shoot it longer.
JT.
Best plan to date, wear out 300 RUM, wear out 6.5 barrel, rebarrel to something sane like a 338 edge, 338 lm or lmAI. I'd would have to open up the bolt face for the lapua, but would get to shoot it longer.
JT.
I think a 34 or even 36" barrel would provide big velocity gains.
Let us know how it goes.
A very cool project....Errr...Supernova!
The Lord hates a coward and you guys aren't one of those!
You might want to make a friend in the barrel industry.
Speaking of which....
Do you like single malt Scotch Ian?
I know Gaillard does!
Let us know how it goes.
A very cool project....Errr...Supernova!
The Lord hates a coward and you guys aren't one of those!
You might want to make a friend in the barrel industry.
Speaking of which....
Do you like single malt Scotch Ian?
I know Gaillard does!
I built a 6.5-300 Wby many years ago, with a 1-10 twist if I recall. Surplus powders and Thunderbird powders kept it going, but I never really saw the velocities I expected. I have all the bits and pieces to build a 1-8 6.5 STW laying around, but have had no time. Things are much better now with many more powder and bullet choices. With a 1-12, I think you will have a LR varminter, but I see no reason why you can't make it successful for your stated purpose. Have fun and keep us posted. - dan
- Location
- Ft. Mac. Alberta
No, it will be more like a 6.5STW!Seems like your going to end up with what amounts to a 7mm stw with a different name. Oh well have fun doing it.
Cat
Should be a little quicker then that, more case capacity. - dan
LongBomber
CGN Regular
- Location
- Fernie, bc
You will notice that I said fitted both barrels... ie re-chamber and thread the factory barrel. Had it done on one of mine for an extra $75 while the rifle was being built. An extra $75 and I can shoot two calibers with a quick swap.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Consider H50BMG. You are going to have way too much case capacity with any ball powder.
Sounds like a hoot. Hope the bullets stabilize.
Look forward to the report.
Jerry
Sounds like a hoot. Hope the bullets stabilize.
Look forward to the report.
Jerry
gunrunner8
CGN Ultra frequent flyer
- Location
- Kamloops, B.C.
260Rem rifle with 9" twist barrel shooting various 140 gr bullets at 2800 FPS will stabilize them while they turn at 224 000 RPM past the muzzle. That supermagnum of yours with 12" twist must spit the same bullets at 3733 FPS for them to have the same RPM and stabilization. With 130gr bullets that might be possible but it still could be a borderline result IMHO.
How do you fit a factory barrel after it has been trued..am I missing something..
how do increase the thread size on a factory barrel? specially with a long chambering like an Ultra mag..honestly I would like to know. Any smiths can chime in...
Good choice. With US869, which has a burn rate next to charcoal, and is very dense, you'll top out at about 100.0 grs with a 140gr bullet, which is well below its capacity of about 105.0 grs with that powder.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
When the world was safer, we could get WCC872 which is pull down 20mm VULCAN powder. It is right beside wet sawdust on the powder burn chart.
I would want a powder that top out at under 60,000psi at 95% load density (higher better).
US869 should be a bit faster then H870 which is inturn faster then H50BMG. I shot a fair amount of H50BMG in a 300RUM and it was a very nice powder to work with. It might be a bit fast for a 6.5-300RUM
BUT a keg sure don't stick around for long
Enjoy...
Jerry
I would want a powder that top out at under 60,000psi at 95% load density (higher better).
US869 should be a bit faster then H870 which is inturn faster then H50BMG. I shot a fair amount of H50BMG in a 300RUM and it was a very nice powder to work with. It might be a bit fast for a 6.5-300RUM
BUT a keg sure don't stick around for long
Enjoy...
Jerry
When the world was safer, we could get WCC872 which is pull down 20mm VULCAN powder. It is right beside wet sawdust on the powder burn chart.
I would want a powder that top out at under 60,000psi at 95% load density (higher better).
US869 should be a bit faster then H870 which is inturn faster then H50BMG. I shot a fair amount of H50BMG in a 300RUM and it was a very nice powder to work with. It might be a bit fast for a 6.5-300RUM
BUT a keg sure don't stick around for long
Enjoy...
Jerry
H50BMG might do that, so should US869.
With respect to US869, I have found it to be slower than both H870 and H50BMG - it's much more dense than H50BMG as well. In the 6.5 RUM with a 140gr bullet, you'd top out at about 100.0 grs in the 60K psi range, and be close to 95% load density. US869 gives the highest MV's in the various high capacity cartridges I shoot: 6.5-300 Win Mag; 300 RUM; 8mm ARP; and soon 6.5 RUM (I have the reamer, barrel and components), but has not been the most accurate. That could be because at the MV's where it's at its best operating pressure, the barrel-bullet combination is not most accurate and not be that it's an inaccurate powder per se.
I am awaiting Alliant Reloder 50's availability, and I'd like to try Vihtavuori 20N29.
