It's probably just me but I can't find the answers I'm looking for using this sites search function. So I thought I'd ask you all directly.
I have been working with a BPCR with an 18 twist barrel chambered to .40-65 Win. I have used a variety of bullets and length with fairly good results out to 600 yards which is as far as I plan to push this rifle/cartridge/twist combination. The mold I am working with at the present is a nose pour adjustable mold. That will allow me to fine tune it to what should be the best length for my goal, at least within the limits of mold's design. I'm really looking at silhouettes as the primary target so bullet weight is another question. What weight in .40 caliber can be expected to push the rams over assuming reasonable shot placement and that the hand of God isn't bracing them.
I'm wondering what other shooters with .40 caliber rifles having 1 in 18 twist barrels have found to be the workable limit in bullet length? What do the various formulas say is the longest bullet that will remain stable enough to shoot in at least somewhat windy conditions out to 600 yards?
One more thing! How much does bullet design affect stability and effectiveness on distant steel critters?
Any information that relates will be appreciated, load and rifle info too. What actual bullets are being used could be useful? If there are threads that talked about this I like to know where to find them?
Jim - zero experience with that slow a twist, but a number of folks are the shooting the BACo 400gr "Kidwell" Money bullet out to 1000yd, so it must fly pretty good and "could" work in that twist. 400gr should be plenty to knock over a ram, considering that a 360gr 38cal bullets does so quite handily. Let me know if you need some to test.
Unless the nose is VERY blunt, a 400gr bullet would not be stable is a 18" twist barrel - it barely is in a 16" twist barrel. Soomething lighter than 400gr would be the thing.
I have 4 or 5 different bullet length calculators. For an 18 twist barrel with a velocity of 1275, they predict that the longest bullet would be in the range of 1.202" on the long side (Greenhill with 130 constant), down to 1.156" (also the GH with a 125 constanct). Carr, Crawleys and Lilja formulas all produce numbers that are intermediate to those estimates of maximum length.
Generally, pointier noses allow a little more length, and paper patch bullets require a little less length.
These are all just guidelines, but I don't see anyway a 400 gr bullet is going to fly well in an 18 twist barrel. Certainly, I would not gamble on one.
Glenn - I appreciate the offer and I'll look at that bullet to see if my rifle "might" work with it. I didn't know how far to venture into the weeds on my rifle's chamber because it is a bit complicated.
My understanding is that it was designed to use the RCBS 40-400-CSA bullet. It has a free bore that is nearly .400" long and will accept a bullet .4095" diameter, but no bigger. I have done fairly well on rams with a 420 grain Leeth bullet at 1.344" OAL, but I know hat bullet is mathematically too long. I can get 70 to 75 grains of 1 1/2 Swiss behind that bullet. The problem with these longer bullets is that they just don't seem to shoot as well or as consistently as I'd like. Probably due to the length.
The bullet it really shoots best is the RCBS 40-350-CSA at 1.177" OAL. While this bullet weighs 362 grains from my mold and has worked on rams fairly well, I know it could be a little longer and heavier. How much is the question?
The Lyman Snover at 409 grains and at 1.364" OAL had pretty much the same results and the Leeth 420 grain. I took the Snover and shortened it to 1.328" OAL thinking it might improve, but that did not shoot as well as I had hoped.
The adjustable mold I am working with now is set at 1.240" OAL and runs 390 grains. It is shooting like I'd like to see this rifle shoot. I will test it at 600 yards hopefully this weekend. So it is looking like somewhere over 1.177" but shorter than 1.328" is going to work. The 1.240" length seems to be good, time will tell. So how much longer than 1.240" can it be? That is really what I'm looking to find and will eventually. I was hoping to shorten the journey at least a bit by finding out what some of you guys here have found works or doesn't work in their 18 twist 40s.
I can be happy at 1.240" and 390 grains, but this bullet is not exactly a high BC design, having a short flat nose. So once I get the length thing nailed down I plan to make a mold that will give me the best possible compromise in stability, weight, and a ballistic coefficient from.
That is the plan. Not sure how close I can get to the prefect bullet, but I intend to have fun making a run at it.
Look at the Saeco #640. Casts at 370gr and have used as a chicken bullet, but never at distances longer than 300m. I have to run through a 0.409" sizing die as my mold casts a bit large at 0.410" and, like yours, my rifle doesn't like anything that big around.
Jim,
we have a mutual friend and fellow cheddar-head who built a beautiful .40-72 around a 17 twist (IIRC) barrel. I don't know how long the bullet was that he used, but it was, apparently, much too long. YOu might check into that.
Brent - I agree with your math. I have run this question through various calculators too and I get the same results, usually between 1.180" and 1.202" just like you say.
What happens at 1.240"? Does that bullet just fly true out to the turkeys and then somewhere between there and the rams it gets all wobbly and go in unintended directions? What if the bullet is 1.220" long? Or 1.210"?
I know if you have a marginally stable bullet it will continue to fly true in light wind, but once the wind gets a little nasty such a bullet can become even less stable and accuracy suffers. I've seen this at 1000 yards.
I guess I'm hoping to walk right up to the line of being unreliable and then back off just a little. I just need to reach the rams on days when the wind isn't trying to prove something and knock those critters of the rail with some feeling that a hit isn't going to leave the ram doubled over in laughter. It's bad enough the chickens start snickering when I walk to the line before I even raise my rifle. I hate that!
Brent - That conversation will happen soon enough. I am hoping to have the upper hand when it does. Let's just make it any sooner than it has to be! Please!
Brent - The length of the bullet or who made the mold had nothing to do with the problems that were encountered. At least in my opinion. I think the case may have been a little high in capacity for the bore size and case design. I really don't know for sure. I would like to work with that rifle myself and see what I could do with it, but I have trouble enough already! The focus now is making this project work the best possible and have fun doing it. The fun part is working pretty much as planned. The other part remains to be seen.
The rifle I am currently shooting has an 18 twist Badger barrel. I had thought it was going to be a 16 twist, but it showed up an 18 and it was a good enough deal that I did not want to return it. It seems to shoot pretty well. The bullet I like is a 395 grain BACO 409 Creedmoor. It is 1.29" long. The bullet that came with the gun is a 410 grain Postel that is 1.365" long. I have only used the Postel a couple of times, but did not notice any particular instability. I have shot several thousand of the Creedmoor now and it seems to like them. A couple of nights ago I shot a 1 1/2" tall by 1" wide five shot 200 yard group with it. I have cleaned the rams several times and shot in some nasty wind. I seem to be able to call all of the misses, so it hasn't seemed at all unstable at distance. I am entered in the midrange match at Byers this weekend, so we will see what happens there. I am using 55 grains of 1 1/2 Swiss and a CCI large rifle primer. I don't believe I have run a single ram with this load. I don't know if all this is right or wrong, but I think it is working. I hope this helps, Cody
Cody - Thank you for the info. This is why I wanted to hear from other shooters with 18 twist 40s. Like I told Brent, I've run the numbers several times using different calculators and they all spit out the same numbers pretty close. They'll indicate that any bullet over 1.200" or so will not stay stable. I have shot bullets as long as 1.370" and never noticed any problems with stability. I don't plan on going that long with my new mold, the only reason I would consider a longer bullet would be for a little more knockdown on the rams. I'm thinking that 390 grains should work there.
Seeing my rifle seems to favor bullets that are a bit shorter I'll stay with the 1.240" for now. I'm not getting groups as small as the one you got, but 2.0" to 2.5" at 200M is pretty darn good for me. The new mold will be an elliptical and I'll give up some weight going to that style, but I figure the improved BC will be worth giving up a little. It doesn't sound like I'd be in any real trouble if I had to lengthen it a little to recover some of the weight I will lose.
This is a journey and there are lots of places where things can and will go wrong before I arrive at my destination, that's all part of it. Again, thanks for your reply, you've been very helpful. I'll look at that BACO bullet for it's design.
Don't forget, Cody shoots 9 chickens. He doesn't NEED 10 rams like the rest of us
Lots of folks report success with bullets longer than the calculators predict. That has not been my experience (esp when using the GH constant of 130). It will be interesting to see. My .40 caliber bullet is 1.417" long and weighs 415 grs roughly that should be on the ragged edge of acceptable stability I think.
Brent - I've never seen 10 rams! and I've sure as hell never seen anything close to 9 chickens!!! More than a little in stability seems to be my problem there!
I'm just thinking hear, but if you can hit 9 chickens......., (Just kidding there Cody, don't take it to heart!)
Anyway, I just want to hit the majority of the rams and the turkeys. All of the pigs. Then if I can just scare 2 chickens enough that they faint, well I'm a happy man!
So I thought I'd ask you all directly.
