Copper Mono Stability

[OXN939]

Recently traded into a Howa 1500 Alpine in .243 and currently in the process of putting everything together. Since there are quite a few members on here whose knowledge of gunsmithing and physics far exceeds mine, I figured I'd get y'all to double check me here.

Planning to shoot copper monos as its hunting load- looking Federal Trophy Copper 85 gr., to be exact. The rifle's twist rate is 1:10 with a 20" barrel, which should be just about right to stabilize a standard 85 grain projectile. Since copper monos have a lower sectional density than standard lead/copper cup-and-cores, however, and are therefore longer bullets than lead projectiles of the same weight, would a faster twist rate than 1:10 be optimal for this load or is 85 grains light enough to do the trick? Are my assumptions about the interactions between bullet construction and requisite twist rate correct? Take me to school here.

 

[Capt_Craig]

They will work fine, as will Barnes TTSX. The only issue is determining if your rifle likes them snd finding THE load it likes.

 

[OXN939]

They will work fine, as will Barnes TTSX. The only issue is determining if your rifle likes them snd finding THE load it likes.

Yep, got that on the agenda for this weekend.

So, in the vein of doing some homework before hitting the range, crunching numbers gives conflicting information. The closest load available (87 gr. Very Low Drag bullet) for Berger's "Twist Rate Stability Calculator" has a gyroscopic stability factor of 1.32- marginal, according to them. Shilen, however, recommends that 1:10 twist rate is good to go for .243 projectiles up to 95 grains. Any input from the gurus? Does this 85 grain load fall into a grey area in terms of what manufacturers deem acceptable?

 

[Elnicko]

What I have found with copper bullets is standard twist rates on barrels are not optimal for non-lead projectiles unless you drop down in weight. I had a Tikka .243 that was a 10 twist and it would not group with anything 85gr and up. I loaded up some 80gr TTSX’s with superformance and it shot great. If you plug in Barnes’ 85gr TSX in Berger’s calculator at standard .243 speeds it shows optimal twist being 9 or faster. Not sure what bullet Federal is using but that should be close. Not saying the 85’s won’t work in your rifle but you may save yourself some frustration by dropping down in weight or replacing the barrel if you’d like to shoot heavier non-lead bullets.

 

[El Gavilan]

This is a timely post, I drew a deer tag for AZ unit 45 rifle and I'm looking at loading up some ttsx 100 gr for my 6.5mm Rem mag. That calculator says it's should be a good round.

Sent from my Moto Z (2) using Tapatalk

 

[Yote Klr]

They will work fine, as will Barnes TTSX. The only issue is determining if your rifle likes them snd finding THE load it likes.

I agree, my barrel likes them .005" from the lands despite what Barnes suggested about jumping them .050" off the lands.

 

[OXN939]

What I have found with copper bullets is standard twist rates on barrels are not optimal for non-lead projectiles unless you drop down in weight. I had a Tikka .243 that was a 10 twist and it would not group with anything 85gr and up. I loaded up some 80gr TTSX’s with superformance and it shot great. If you plug in Barnes’ 85gr TSX in Berger’s calculator at standard .243 speeds it shows optimal twist being 9 or faster. Not sure what bullet Federal is using but that should be close. Not saying the 85’s won’t work in your rifle but you may save yourself some frustration by dropping down in weight or replacing the barrel if you’d like to shoot heavier non-lead bullets.

Yep. I think the 85s are right on the edge of a grey area- maybe not perfectly stabilized, but if I can get 1.5 MOA from them I can live with it. Will go out this weekend and check em out, and if they don't do the trick, will try the 80 gr. Barnes TSX.

 

[Capt_Craig]

If the 85s don’t work in your rifle, the Barnes 80 gr TTSX should be just enough shorter to stabilize, and generally do a great job on game.

 

[TauPhi111]

While most responses here gave good advice, please let me clear up a few things surrounding all copper bullets, which is all I shoot at game. First, regardless of construction, all bullets of X diameter and Y weight have the same sectional density. SD is simply a measure of the amount of mass behind a bullet's frontal area. The reason they are longer is because copper is less dense than lead, and keeping ogive shape and diameter constant, the only way to have a bullet made of a less dense material be the same weight as lead is to make it longer, usually in the shank.

Now, longer things are harder to stabilize. Often, standard twist rates are not optimal for those who want to shoot heavy for caliber copper bullets. However, I've talked to Barnes engineers on many occasions and they have told me that MOST of their bullets are designed for standard twist rates. If they weren't they wouldn't sell nearly as many bullets as they do. They also however usually recommend dropping down a weight class since you'll usually have near 100% weight retention and the bullet will penetrate as good as a much heavier bullet. Since 100 grains is usually pretty standard for 243 bullets for big game, I think the 85 would work well. I'd buy a box and shoot them at 100 and 200 yards. If you are not seeing key holes in the paper, you're probably ok. If you do, you can try the Barnes 80 gr TTSX, and if those are giving you trouble, actually try the 85 grain TSX. It is actually a bit shorter although it is 5 grains heavier. A final trick would be to remove the tip from the 80 grain TTSX. This should remove enough length to stabilize the bullet, although your BC will take a hit. If you are within 300 yards though, I don't think it would matter much.

Barnes used to list all the required twists on their web site, which unfortunately they do not any more. Other all copper bullet makers though, like Hammer bullets or Cutting Edge Bullets do. You can compare the bullet length and twist rate on Hammer to Barnes bullets of similar length and weight (which they do list) and get and idea of what twist rate is required. I've found that their twist rates are not suggestions, they are required for good stability. Good stability is essential for terminal performance on tough bullets like a Barnes. Hammer and CEB both list 80 grain bullets that are shorter than the Barnes by a couple hundreths, and recommend a 1 in 9 twist, so there is a possibility you will have marginal stability or worse. Again, I'd check out to 200 yards. I've had bullets look ok at 100 and totally unstable at 200.

If you handload, there are still more solutions for your slower twist. Both hammer and CEB make bullets less than 80 grains (and shorter) for rifles with a slower twist. They'll still take deer with no problem, so I'd suggest you check them out. Hope that helps. Feel free to message me with any questions.

 

[OXN939]

While most responses here gave good advice, please let me clear up a few things surrounding all copper bullets, which is all I shoot at game. First, regardless of construction, all bullets of X diameter and Y weight have the same sectional density. SD is simply a measure of the amount of mass behind a bullet's frontal area. The reason they are longer is because copper is less dense than lead, and keeping ogive shape and diameter constant, the only way to have a bullet made of a less dense material be the same weight as lead is to make it longer, usually in the shank.

Now, longer things are harder to stabilize. Often, standard twist rates are not optimal for those who want to shoot heavy for caliber copper bullets. However, I've talked to Barnes engineers on many occasions and they have told me that MOST of their bullets are designed for standard twist rates. If they weren't they wouldn't sell nearly as many bullets as they do. They also however usually recommend dropping down a weight class since you'll usually have near 100% weight retention and the bullet will penetrate as good as a much heavier bullet. Since 100 grains is usually pretty standard for 243 bullets for big game, I think the 85 would work well. I'd buy a box and shoot them at 100 and 200 yards. If you are not seeing key holes in the paper, you're probably ok. If you do, you can try the Barnes 80 gr TTSX, and if those are giving you trouble, actually try the 85 grain TSX. It is actually a bit shorter although it is 5 grains heavier. A final trick would be to remove the tip from the 80 grain TTSX. This should remove enough length to stabilize the bullet, although your BC will take a hit. If you are within 300 yards though, I don't think it would matter much.

Barnes used to list all the required twists on their web site, which unfortunately they do not any more. Other all copper bullet makers though, like Hammer bullets or Cutting Edge Bullets do. You can compare the bullet length and twist rate on Hammer to Barnes bullets of similar length and weight (which they do list) and get and idea of what twist rate is required. I've found that their twist rates are not suggestions, they are required for good stability. Good stability is essential for terminal performance on tough bullets like a Barnes. Hammer and CEB both list 80 grain bullets that are shorter than the Barnes by a couple hundreths, and recommend a 1 in 9 twist, so there is a possibility you will have marginal stability or worse. Again, I'd check out to 200 yards. I've had bullets look ok at 100 and totally unstable at 200.

If you handload, there are still more solutions for your slower twist. Both hammer and CEB make bullets less than 80 grains (and shorter) for rifles with a slower twist. They'll still take deer with no problem, so I'd suggest you check them out. Hope that helps. Feel free to message me with any questions.

Great SA in this; thanks a ton for all the info. I'll be adding 200 and 300 yard paper tests to my homework at the range to confirm projectile stability.

Also, during my research, found this article by Jim Carmichel that is pretty illuminating. Re-enforces the idea that even minute differences in bullet construction can become large differences in the real world, and that range confirmation is absolutely necessary for ethical hunting before taking a load into the field.

 

[TauPhi111]

yes that is a very good point that not a lot of people pay attention too. Bullets can weigh the same but be very different in length. A bullet with a long point ogive and longer boat tail (VLD style) can be much much longer and therefore require much faster twist than the same weight round nose, flat base bullet.

I've run into the slow twist problem with an old Savage 99 in 250 Savage I bought. I had thought it was recent enough to have the more current 1:10 twist that should be fine for both the 80 and 100 grain Barnes TTSX bullets, and not the 1:14 twist that came with earlier guns. Well IDK what the twist is because I've had a hard time measuring it, but it doesn't stabilize either. Pulling the tips from the 80 grainers solved the problem and gives me a nice hollowpoint to smack deer with. I use it as a super handy, light recoil deer drive gun, so not having the BC is ok with me.

My other twist problem came from trying to shoot the very very long 140 grain Cutting Edge MTH in a 7.5 twist 260 AI. Even though that is fast compared to the standard twist, there was misinformation on their website and they actually require a 7 twist. These ones looked ok at 100 yards, but by 200 they had totally went unstable. Dropped down to the 130 grain with only .05 less BC and picked up about 200 FPS and they work great.

I hope the Federals or Barnes work for you. Depending on if you hand load and how far your want to shoot this gun, either pull the tips or get some CEB or Hammers and you'll be set.