.243 Twist Rate

300magman · December 7, 2009, 11:09 AM

I previously posted this in the general section, but I didn't get any replys that were on topic so I'll give this a try here.

I'm wondering, If I have a fast twist barrel (about 1 in 8") that is designed to fire heavy bullets like the 105gr nosler competition bullet, can I still fire light 55gr bullets out of that barrel (at 3800fps+) or will the rapid spinning imparted on them cause them to fly apart?

kwells6 · December 7, 2009, 12:04 PM

possibly...

rwilson452 · December 7, 2009, 12:17 PM

best bet would be to pick a Sierra bullet from their web site and ask Sierra how it would perform in your barrel. They are usually good about this sort of thing. I suppose you could compare an equal weight bullet from a different mfg but I wouldn't put any money on it.

Crapulence · December 7, 2009, 12:22 PM

342000 rpm is more than 2 times the recommended spin rate of 55gr jacketed bullet. I am pretty sure it would self destruct (363600 G's)

**Unclenick** · December 7, 2009, 12:36 PM

Too fast with a light bullet can spoil accuracy by causing core stripping, which is where the jacket is spun faster than the core in the bore. A bonded core bullet should withstand it better than a standard cup and core bullet. It does deteriorate accuracy. Harold Vaughn was able to use a magnetometer to measure it in bullets that were running around 3200 fps, IIRC? I think they were maybe 6 mm, too, but I'd have to double-check. May have been .270's.

In addition, when you spin a bullet too fast, every tiny imperfection in mass symmetry is exaggerated as wobble. It is the trade-off between that and fast settling that caused Vaughn to estimate a gyroscopic stability factor of 1.4 was about nominal, while Don Miller put it about 1.5. Close enough to each other that I usually put 1.45 into my calculator for nominal results.

Your 8" twist at 3800 fps with the 55 grain Sierra BlitzKing, for which I show a length of .747", would give a stability factor of 3.66. Sierra recommends not exceeding 3.00, generally, so I think your in potential problem territory. A 12.7" twist would give 1.45 with that bullet at that velocity.

I don't know if the bullets will actually fly apart or not? If they "disappear" on their way to the paper, then that's what happened. You'd have to try it to see? I would not expect great accuracy, even if everything holds together. Some of the bullets designed for extreme high velocity have thicker jackets and may do much better than expected. Jacket thickness being variable means there is no fixed spin limit for all bullets of the same caliber. Only those of the same caliber with the same jacket thickness.

300magman · December 7, 2009, 03:18 PM

Thanks for the great information so far guys. Perhaps I should also be asking this question (particarly if anyone here has been firing 243's at long distance) Just what would be the optimal rate of twist for a bullet in the 105gr range? (or actually, the minuimal twist rate that I could get away with?)

And this one seems very important to me: IF I spin a light bullet so fast that it fails catastrophically, could it do so while in the bore and cause damage to either rifle or shooter?

mapsjanhere · December 7, 2009, 04:02 PM

There have been cases reported of jackets coming off the bullet in the barrel, don't know if due to fast spin. That is catastrophic, because you still get regular recoil etc unlike a squib, but you end up with a barrel obstruction for your next shot. The infamous exploding Blaser R93 was claimed to be due to that.

edward5759 · December 7, 2009, 04:20 PM

I have four custom 243s
Two with the 1-14 twist for shooting coyotes. I like the 55 grain bullets but even they like the 75 grain bullets better.
one of the rifles is 1-12 twist I shoot most all weights in it, except the 55 and real heavy ones. I get about 1.25 inch groups with the 107 grain bullets.
My last rifle was my sons a savage with a 1-10. Still the 107 didn’t do as well as the 100 grain, 5/8 inch group with H450. it would not shoot the 55 grain bullets at all.
I liked the 1-12 twist the best; with 75 grain bullets it bucked the wind well.
It worked well on coyotes also.
have fun and happy shooting.

Ed

tom234 · December 7, 2009, 05:04 PM

Check out:
http://www.shilen.com/calibersAndTwists.html

http://www.riflebarrels.com/products...wist_rates.htm

**Unclenick** · December 9, 2009, 06:14 PM

300 Magman,

Bullet length has more to do with the right twist rate than weight does, which plays a smaller role. Check out the JBM calculators online. Look for Don Miller's calculator there and you can plug your bullets in. I have an Excel file based on Miller's method which includes some additional explanation of what you are looking for. You can download it here. You will need to know the length for any method of estimation, though. Often, the best way is to call the bullet maker's 800 number and ask what the average length is?

Blue Grass · December 9, 2009, 06:42 PM

This may be slight thread drift, but I was just wondering. Would a sold bullet like a Barnes hold together better than a copper jacket/lead core bullet at fast twist/high velocity levels? Doed anyone have any experience with these type bullets? Just curious. Thanks.

December 7, 2009, 11:09 AM	#1
300magman Senior Member Join Date: September 12, 2008 Posts: 714	.243 Twist Rate I previously posted this in the general section, but I didn't get any replys that were on topic so I'll give this a try here. I'm wondering, If I have a fast twist barrel (about 1 in 8") that is designed to fire heavy bullets like the 105gr nosler competition bullet, can I still fire light 55gr bullets out of that barrel (at 3800fps+) or will the rapid spinning imparted on them cause them to fly apart?

December 7, 2009, 12:04 PM	#2
kwells6 Senior Member Join Date: October 24, 2008 Location: Central Arkansas Posts: 437	possibly... __________________ "Make the lie big, make it simple, keep saying it, and eventually they will believe it."

December 7, 2009, 12:17 PM	#3
rwilson452 Senior Member Join Date: June 10, 2004 Location: Tioga co. PA Posts: 2,647	best bet would be to pick a Sierra bullet from their web site and ask Sierra how it would perform in your barrel. They are usually good about this sort of thing. I suppose you could compare an equal weight bullet from a different mfg but I wouldn't put any money on it. __________________ USNRET '61-'81

December 7, 2009, 12:22 PM	#4
Crapulence Senior Member Join Date: November 12, 2008 Location: Manly Flower Mound Texas Posts: 126	342000 rpm is more than 2 times the recommended spin rate of 55gr jacketed bullet. I am pretty sure it would self destruct (363600 G's) Last edited by Crapulence; December 7, 2009 at 04:15 PM.

December 7, 2009, 12:36 PM	#5
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	Too fast with a light bullet can spoil accuracy by causing core stripping, which is where the jacket is spun faster than the core in the bore. A bonded core bullet should withstand it better than a standard cup and core bullet. It does deteriorate accuracy. Harold Vaughn was able to use a magnetometer to measure it in bullets that were running around 3200 fps, IIRC? I think they were maybe 6 mm, too, but I'd have to double-check. May have been .270's. In addition, when you spin a bullet too fast, every tiny imperfection in mass symmetry is exaggerated as wobble. It is the trade-off between that and fast settling that caused Vaughn to estimate a gyroscopic stability factor of 1.4 was about nominal, while Don Miller put it about 1.5. Close enough to each other that I usually put 1.45 into my calculator for nominal results. Your 8" twist at 3800 fps with the 55 grain Sierra BlitzKing, for which I show a length of .747", would give a stability factor of 3.66. Sierra recommends not exceeding 3.00, generally, so I think your in potential problem territory. A 12.7" twist would give 1.45 with that bullet at that velocity. I don't know if the bullets will actually fly apart or not? If they "disappear" on their way to the paper, then that's what happened. You'd have to try it to see? I would not expect great accuracy, even if everything holds together. Some of the bullets designed for extreme high velocity have thicker jackets and may do much better than expected. Jacket thickness being variable means there is no fixed spin limit for all bullets of the same caliber. Only those of the same caliber with the same jacket thickness. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

December 7, 2009, 03:18 PM	#6
300magman Senior Member Join Date: September 12, 2008 Posts: 714	Thanks for the great information so far guys. Perhaps I should also be asking this question (particarly if anyone here has been firing 243's at long distance) Just what would be the optimal rate of twist for a bullet in the 105gr range? (or actually, the minuimal twist rate that I could get away with?) And this one seems very important to me: IF I spin a light bullet so fast that it fails catastrophically, could it do so while in the bore and cause damage to either rifle or shooter?

December 7, 2009, 04:02 PM	#7
mapsjanhere Senior Member Join Date: August 6, 2009 Location: Albuquerque Posts: 2,832	There have been cases reported of jackets coming off the bullet in the barrel, don't know if due to fast spin. That is catastrophic, because you still get regular recoil etc unlike a squib, but you end up with a barrel obstruction for your next shot. The infamous exploding Blaser R93 was claimed to be due to that. __________________ I used to love being able to hit hard at 1000 yards. As I get older I find hitting a mini ram at 200 yards with the 22 oddly more satisfying.

December 7, 2009, 04:20 PM	#8
edward5759 Senior Member Join Date: September 15, 2009 Location: Phoenix, AZ. 30 miles from water, two feet from Hell. Posts: 355	243 I have four custom 243s Two with the 1-14 twist for shooting coyotes. I like the 55 grain bullets but even they like the 75 grain bullets better. one of the rifles is 1-12 twist I shoot most all weights in it, except the 55 and real heavy ones. I get about 1.25 inch groups with the 107 grain bullets. My last rifle was my sons a savage with a 1-10. Still the 107 didn’t do as well as the 100 grain, 5/8 inch group with H450. it would not shoot the 55 grain bullets at all. I liked the 1-12 twist the best; with 75 grain bullets it bucked the wind well. It worked well on coyotes also. have fun and happy shooting. Ed

December 7, 2009, 05:04 PM	#9
tom234 Senior Member Join Date: February 14, 2008 Location: Kansas Posts: 753	Check out: http://www.shilen.com/calibersAndTwists.html http://www.riflebarrels.com/products...wist_rates.htm

December 9, 2009, 06:14 PM	#10
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,063	300 Magman, Bullet length has more to do with the right twist rate than weight does, which plays a smaller role. Check out the JBM calculators online. Look for Don Miller's calculator there and you can plug your bullets in. I have an Excel file based on Miller's method which includes some additional explanation of what you are looking for. You can download it here. You will need to know the length for any method of estimation, though. Often, the best way is to call the bullet maker's 800 number and ask what the average length is? __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

December 9, 2009, 06:42 PM	#11
Blue Grass Senior Member Join Date: August 12, 2009 Posts: 398	This may be slight thread drift, but I was just wondering. Would a sold bullet like a Barnes hold together better than a copper jacket/lead core bullet at fast twist/high velocity levels? Doed anyone have any experience with these type bullets? Just curious. Thanks.