SuperKirby

When I ordered my SMI barrel, Ron said they use a 1:32 twist that works great with the .458 325 gr. FTX with Harvester smooth black sabots. I can get a .458 FTX down the barrel, but it takes everything I have to get it there. I would hate to have to reload in a hurry in the field. I figure I might get a pack of .458 sabots and see if that makes a difference, but I'm not getting my hopes up too high.
So now I'm looking for a new bullet to try. I thought I had more than I do, but I'm about out of bullets in general, so I don't have a lot to experiment with, and I don't want to start randomly buying bullets to find out they don't work well with this twist rate. I looked at the calculators that use the greenhill formula, and they work off caliber and length. Here's my question - when figuring caliber, do you figure the caliber of the bullet itself or the bullet/sabot together? If I figure a .45 bullet, it looks like I want a bullet 1.09". In a .50 I should look for something 1.34".
Any recommendations for a bullet?

sabotloader

I am not really sure I am reading this post correctly? Who said that a 1-32 was the best twist?

I mean it is not a bad twist but I really think it is limited in what can be shot from it...

Hopefully Lee will pick up on this thread - he knows the Greenhill backwards and forwards...

Personally, in just my limited experiance - I really prefer 1-24.

Josmund

Before you start buying bullets, spend $5 on a pack of Harvester Crushed Rib Sabots. I shoot the 325 FTX out of a .52 Knight with very good results. However, it does have a 1/26 twist.

When I have used the Greenhill formula it always has me needing bullets longer that what id commercially available.

lemoyne

SuperKirby
If you will give me the exact length and diameter of a bullet I have a program that will give the ideal twist for it.
A .458 bullet .96 to .98 would be considered an exact match at 1800 FPS, since it takes 3x as much to over-stabilize a bullet you could push that up quit a bit in FPS and still be OK if your barrel vibrations are complimentary.

SuperKirby

Sorry for the confusion, I should have be more clear. Ron Name, the owner of SMI that makes the barrels. I debated a lot what twist rate to go with before ordering the barrel. I almost went with 1-24, but then Ron was very insistant that 1-32 was a good twist rate for .50's and I ultimately decided to go with what the guy making the barrels recommended. And I'm not saying it's a bad twist, I'm just wondering if there's certain bullet lengths and or weights that I should look at so I'm not buying a bunch of random bullets that won't work.
If I'm correct (and I very well may not be), in general the slower the twist the shorter that works? Not to say longer bullets won't work in a fast twist? I'm not sure. It confuses me.
Lee, for whatever it's worth, the next bullet I want to try is the Hornady .452 250 gr. FTX. I looked at hornady's website and didn't see a length on it, but I'll look some more.

sabotloader

It would really be hard not to go with the advise of the guy making the barrel... He should certainly know. I am not much of a information source when it comes to SMI barrels but it seems to me that PACNOR and Savage have gone the other way. Did he provide any examples of what bullets might be the best. My guess is common ordinary lead/copper bullets shorter in length would be the ticket if you can get them down the barrel.


I think you are correct going or thinking shorter. Lyman offered a 1-32 twist in their GPH barrel as sabot shooter but I am positive they were looking at the shorter more common pistol type bullets.

SuperKirby

SMI's preferred twist was 1-36 for a long time. When the .458 FTX came out he said he really like the bullet and was getting good accuracy out of it. He said he sped up the twist a little and can achieve MOA or a little less with it. He now recommends a 1-32 twist with a .458 FTX.
I really like this idea. I like heavy bullets and was quite excited about using this bullet for hunting. Unfortunately there's no way I could get a quick reload in the field. It takes all my weight to get one down and destroys my hand (I should look into a palm saver.)
As of now I plan to try to order some .458/50 sabots, but I hate to order them to find out they don't work. If those don't work I'll try out some of the .452 250 FTX. I just thought I would see if anyone thought they would or wouldn't work before I bought them.

sabotloader

SuperKirby

I guess I am at a loss because all the information I have leads to a faster optimum twist but also that is for basically BP, so there really must be different information for Smokeless.

I wonder about putting this question in to the smokeless guys over on Dougs and see what they say...

http://dougsmessageboards.proboards....oard=smokeless

lemoyne

The 250 grain FTX is .750 long and well with in the capability of a 1-32 twist. You are correct in believing that the slower the twist the shorter bullet that matches it.
I ran a few numbers to give you some ideal length bullets:
.452 ideal length .95
.458 " " .97
There are a couple of things to remember about this:
It is much harder to over stabilize a bullet that it is to under stabilize it, this means that to long a bullet will be harder to get to shoot that one that is a bit short.
Also remember that changing a bullets velocity changes the speed of its spin all of these are calculated at 1800 FPS some times when a bullet is on the fringe a faster or slower velocity can help. A LOT of the bullets we normally shoot will do fine in a 1-32 twist. You may have to push the 300 grain bullets at least 1800 FPS to get them to shoot well.

SuperKirby

Thanks for the help guys. I really appreciate it. I'll play around and see what happens. It turns out I have a while before I have to get to serious about it.
I appreciate the advice and it gives me an idea of where to start looking.