Twist rate for .50 conicals?

I apologize for worrying this site to death with newbie questions but I am doing the critical research for a new custom rifle and I want to get it right the first time for my limited budget. I think I want to build a bullet gun, one that will shoot conicals like the TC slugs or Buffalo bullets or the Hornady HBHPs. What twist rate will be ideal for .50 cal and bullets from 300 to 400 grains with the emphasis on maybe 320-350 grain slugs? I can't seem to get a straight answer from GM or from my two custom gun builders and I really need to know what will really shoot these bullets. Thanks in advance.

Not to worry, these guys live for questions. I have very good results with my .50 percussion with a 1:32 twist 32" barrel and shooting hornady's great plains bullets (385 grain hbhp). I strongly suspect that Green Mountains 1:28 twist barrels may do even better.

From what I have seen,used,and read about conicals it seems that a twist rate of 1/32 to 1/28 is what would work the best for the weights you are wanting to use. The 1/48 twist works well with conicals from what I have read in posts about them; but I have never owned one other than a TC Hawken and conicals were not legal in PA when I owned it so they never got tested in that rifle. One poster said his 1/48 twist TC shoots real well with the 370 grain Maxi balls. My experience is limited but others will help.

I have a 1/28 twist GM LRH barrel in .50 caliber but the bore is a bit too large for the Great Plains bullets to fit snug enough. It also has .005 deep grooves and wide lands. This type of barrel shoots saboted bullets really well but doesn't do real well with conicals unless you think 4" at 100 is good enough. I have been advised that if I put a mmp sub-base under the Great Plains bullet in this barrel it will tighten up to less than 2" and I have the stuff I just have not gotten around to it yet.

I think a deeper groove depth of around .008-.010, a twist from 1/32-1/24, and a land to land bore of .50 would be about ideal. The Great Plains Hunter rifle from Lyman would probably do it as well as any production rifle out there.

There will be a few here that have some real life experience with conicals and will join in soon I am sure. Good luck to you.

markd, If you get a Green Mountain 1-28 twist I can absolutely guarantee you that a 50 cal with 1-28 twist will shoot a 410 gr Hornady Great plains bullet so good you will be bragging to us all in a very short time. Both of mine will shoot under 2" groups about any day of the week at 100 yards. My first 10 groups averaged just over 1" at 100 yards. Here is my best group. You will like it I promise. Ron

For a 50 cal bullet rifle I'd go with 1-28 twist.

WOW!!! YEEE HIIII! Now that is what I am talking about!!! Ron, You are da'man! Finally, I got the info. and the proof. Thanks to all for your input, but a special thanks to Ron for the group picture. I am amazed that so few people on here and other places I am researching are using conicals when they will shoot like that. Maybe round balls will shoot like that too and I am too inexperienced to make them do so. Maybe I just ain't got the right set up yet. I am admittedly new but my quest is for a custom gun that will shoot like Rons with a bullet that will buck the wind and slam a critter at 100 yards. Sounds like a good 1:28 might fill the bill. Thanks again to all and do please keep your experiences coming. The more info. I have the greater my confidence will be in my project. I really cannot afford to have a rifle built and it not be exactly what I need it to be.

My 50 cal GM does well with 385 gr buffalo bullets over a lubed wonder wad and 80 gr FFg (90 gr shoots well too but recoil is much sharper)

The group below is 5 shots at 50 yds with open sights

Well if you looking for bucking wind these won't do it. I do have a lot of punch with these, but bucking wind is not what ML's do much of. I have to remind you that this is my best group. I average under 2" all the time with that gun.
My 45 is a great shooting gun and right now it is averaging well under 2" at 100 yards. That gun is a 1-18 twist and I am shooting bullets in the 385 to 475gr range. Ron

Yep! In roundball you go up in caliber to get weight. You don't need a big caliber to throw serious weight with conicals. The 45 would likely be my choice if I was building a slug gun. The choice on rifling depends on the bullet range you intend to use. Bullets start at about 200 grains and run to about 500.

Unless you know you are going to be taking shots at over 500 yds, I think you would be better served making a gun in .40 caliber. A 1:18 ROT will shoot conicals, and give fine accuracy. You have to be conscious of the amount of pressure you put on your breech when you build a conical gun, and the .40 gives you a margin of safety, and less recoil.

I suppose if you are shooting bang plates, go with the .45. If you intend to hunt, use the .40.

markd, I am sure a .40 would be nice but is it legal? Here in Idaho and in many other states 45 is legal for deer and Antelope. You have to go 50 or bigger for about everything else. If you want to go .45 I made a 45 this spring. It is a .458 with a 1-18 twist. From the very start this rifle was designed to be a deer and antelope gun. Here are some groups out of it. Ron

I work on a lot of old Winchester barrels and find it strange the way they did their rifling for the 50EX (50-110), The early ones had a twist of 1 in 60, then went to 1 in 56 and ended up with 1 in 48. The 50-100 using a 450 grain bullet started at 1 in 48 and ended up with 1 in 36. Winchester did this with a lot of calibers, speeding up the twist to get them shooting better. The 95 Winchester ended up with a 1 in 11 twist for all calibers.
If I were building a new 50 caliber slug gun for myself I would probably go with a twist of 1 in 24 - 1 in 32 depending on the size of bullet I use. The slower twist has a slight edge in velocity but may not stabilize at long range ( 500+).

another thought. The 45-70 with a 500 grain bullet and 1 in 22 twist held many records at 800 yards.