Question on Rifling and twist rate for Monolithic Bullets

[GAnderson]

I've got a .243 factory rifle with the standard 1-10 6gr barrel that shoots lead core bullets exceptionally well. I have come to acquire a substantial stash of Barnes 80gr TTSX monolithic bullets and have tried everything to get them to group acceptable and they just won't. At BEST I can squeak out an 1 1/4" group every now and then at 100yds. I have tried all the suggestions and powders that Barnes gives on this bullet and I realize that mono bullets aren't known for superior accuracy...but I do feel as though the 1-10 twist may not be stabilizing this bullet as good as it should since these bullets are somewhat longer than traditional bullets in the same weight category...Barnes maintains that a 1-10 should stabilize them.
So I got to looking at the various barrels that are available with different rifling and twist rates. I see 6mm 1-9 6gr, 1-8 3gr, 1-8 6gr, 1-8 5R gr and 1-8 3R gr as well as faster twists in the 1-7 area. The 1-9 might work better than the 1-10 but I am thinking a 1-8 will be the best hopefully. My question is in regards to the number of grooves and potential of the 3R or 5R rifling? Has anyone been down this road with mono bullets and felt that the 3 groove is better than the 6 groove and/or would one of the "R" riflings be even better? I am thinking the 5R 1-8 might get me what I want. Please share your thoughts.

Thanks,
Gene

 

[Walt Krafft]

Either one will work fine. I use a lot of Bartlein 7.5 twist 5R barrels. Also have used 3 groove Lilja's with great success. Pick one and don't worry about it.

 

[SKWERLZ]

Either one will work fine. I use a lot of Bartlein 7.5 twist 5R barrels. Also have used 3 groove Lilja's with great success. Pick one and don't worry about it.

I’m currently running a bartlein 338 5r 7.5 twist with solids.

 

[GAnderson]

I’m currently running a bartlein 338 5r 7.5 twist with solids.

I assume accuracy is good for your application...can you compare your accuracy between the solids and conventional? Better, same or only slightly worse?

 

[SKWERLZ]

I assume accuracy is good for your application...can you compare your accuracy between the solids and conventional? Better, same or only slightly worse?

Solids definitely seem a bit more temperamental.
When they are happy they can be impressive.

 

[Preacher]

Most of them need a long jump before behaving..

 

[Herzo]

Understand that solids are longer for their weight as opposed to jacketed bullets and the length of the bullet is what determines the twist required to stabilize them.

 

[GAnderson]

Most of them need a long jump before behaving..

Yes, that's what I got from Barnes and while it might have helped some, it just has not panned out.

Thanks,
Gene

 

[GAnderson]

Understand that solids are longer for their weight as opposed to jacketed bullets and the length of the bullet is what determines the twist required to stabilize them.

Yes, I think I explained that in my original post...Quote "I do feel as though the 1-10 twist may not be stabilizing this bullet as good as it should since these bullets are somewhat longer than traditional bullets in the same weight category".
This is why I am wanting to know if a faster twist will indeed help these "solid" bullets group better and will the 5R rifling even help more.

Thanks,
Gene

 

[GAnderson]

Solids definitely seem a bit more temperamental.
When they are happy they can be impressive.

That's what I have found most people that have experience with them claim...that they can be finnicky, but if you can get them to work, they are great.

Thanks,
Gene

 

[Herzo]

Yes, I think I explained that in my original post...Quote "I do feel as though the 1-10 twist may not be stabilizing this bullet as good as it should since these bullets are somewhat longer than traditional bullets in the same weight category".
This is why I am wanting to know if a faster twist will indeed help these "solid" bullets group better and will the 5R rifling even help more.

Thanks,
Gene

My apology for not reading more carefully.

 

[dellet]

I’m curious if you ran the bullet though any of the stability calculators?
Best I can come up with is below 1.1, as low as 1.05 depending on velocity. I’m not sure marginally stable is what I would call that.

Something else to check is groove diameter, solids are much less forgiving concerning a loose fit. They just don’t bump up and fill the groove like a lead core bullet.

 

[Coyotefurharvester]

Barnes load data shows 1/10 twist test barrels thru 85 gr. bullets.

 

[dellet]

Barnes load data shows 1/10 twist test barrels thru 85 gr. bullets.

I’m not certain Barnes is showing a minimum required twist, looks like normal twist for the cartridge. Note the same bullet in a 6mm Remington requires a different twist as do other cartridges.





JBM using the bullet library,

 

[Will Henry]

A 10 twist will stabilize a 100 grain Sierra boattail just fine. Unless the 80 gr TTSX is longer than that bullet, twist isn't your problem. Nonetheless, if you re-barrel, it doesn't hurt to go with an 8 or even 7.5. BTW, I have an almost pathological aversion to 5 groove barrels. WH

 

[dellet]

A 10 twist will stabilize a 100 grain Sierra boattail just fine. Unless the 80 gr TTSX is longer than that bullet, twist isn't your problem. Nonetheless, if you re-barrel, it doesn't hurt to go with an 8 or even 7.5. BTW, I have an almost pathological aversion to 5 groove barrels. WH

Longer if you count the tip, shorter without.

My personal experience with monolithic bullets is they seem to do better with a little faster twist. Comparing the 100 sierra to the 80 Barnes with the same length, all the stability calculators look at them using generic profile. Most monolithic don’t fit that profile. Add in the groves and the balance and pressure points change. It’s not a straight up comparison. Using a drag model would be better, if you can include the grooves in the calculations.

I would still question groove diameter and gas cutting do too poor fit and not full obturation.

 

[Fuj]

I Have had dismal tests with quite a few of the differing makers in the
real short bullets, for closer range applications. Best results though was
from long jumping, and a higher then normal twist rate......i have taken
barrel stubs and pushed solids thru them on a hydraulic press with gauge.
Results were all over the map. Best overall tests came from "Cutting Edge
Bullets" and this may be due to their oversize ring they machine in. Either
way, I was never impressed with any target I shot solids with......

 

[GAnderson]

Barnes load data shows 1/10 twist test barrels thru 85 gr. bullets.

Yes, in talking with them they say a 10 twist works fine for this bullet...I guess we need a definition of what is "fine" as far as accuracy goes for their test standards.

Thanks,
Gene

 

[GAnderson]

I’m curious if you ran the bullet though any of the stability calculators?
Best I can come up with is below 1.1, as low as 1.05 depending on velocity. I’m not sure marginally stable is what I would call that.

Something else to check is groove diameter, solids are much less forgiving concerning a loose fit. They just don’t bump up and fill the groove like a lead core bullet.

I'm inclined to think this might be the case...I don't see anything about the bullet holes that would indicate an unstable bullet. Attached are some group pics. Seating deeper(more jump) had the best effect on shrinking the groups but for me they are still unacceptable. The first pic#4372 is an extreme group but in the beginning a lot of them were really bad...better than the first pic but still bad. After discussing with Barnes and seating for more jump, the last 3 pics are the results...while a great improvement, really not what I want.
Since this is a factory barrel(looks good with borescope) I am inclined to believe what you are saying in regard to groove diameter.

Thanks,
Gene

 

[GAnderson]

I’m not certain Barnes is showing a minimum required twist, looks like normal twist for the cartridge. Note the same bullet in a 6mm Remington requires a different twist as do other cartridges.

View attachment 1675168

View attachment 1675169

JBM using the bullet library,

View attachment 1675176

I noticed that also between the 243 and 6mm on the twist rates they published. That's what got me to thinking of a faster twist.

Thanks,
Gene