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Sierra 30 Cal. Jackets - Information

 
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  #1  
Old 01-06-2010, 09:45 PM
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Sierra 30 Cal. Jackets - Information

Anyone have any idea of what the jacket thickness on these would be?

Are they tapered, straight and is it safe to figure that since they are "match" jackets, they are the 'same' as SMK jackets?

Thanks in advance.

Roy
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Old 01-07-2010, 10:15 AM
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Re: Sierra 30 Cal. Jackets - Information

Roy---they are different depending on the bullet.
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Old 01-07-2010, 10:48 AM
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Re: Sierra 30 Cal. Jackets - Information

Boss Hoss,

I'm particularly interested in the 30 cal jacket offering. The length is a little short, 1.155" but if tipped properly may be made to work.

From looking at their price, there must be some gold in the mix.

I sliced a 375, 350gr SMK. Pretty thick. The jacket may have started life as a copper pipe.
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Old 01-07-2010, 11:57 AM
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Re: Sierra 30 Cal. Jackets - Information

Roy,

If you're looking at the 30 cal jacket at 1.155", that's the standard jacket for the 168 MK, if the seller isn't listing it as such. These have been sold through R.W. Hart and Bob Cauterrucio for many years now, so I'm assuming that's where you found them? If I recall corrrectly, they should run between .028" to .032", depending on caliber, etc.. As Boss said, they vary from one application to another, but all of the match bullets tend to be thinner than a hunting jacket of the same caliber. Most are straight walled, though there are a few that utilize a double taper, or a stepped thickness. Unless they started doing it recently, these aren't ones they sell as jackets, but are used only for their own internal production.

What's your project here, anyway?

Kevin Thomas
Lapua USA
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Old 01-07-2010, 12:46 PM
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Re: Sierra 30 Cal. Jackets - Information

Kevin,

Thanks for the info.

I got the price from Sierra's web site.


What's your project here, anyway?

There isn't a bullet maker on the face of this earth, that has shown him/herself, that makes a 270 Cal VLD/ULD 170 Class hunting bullet that is robust enough to consistently stand up to the rigor of an 8 twist 3 groove barrel.

The bullet making industry is pretty set in its ways with little desire by the makers to tackle such a small niche market considering the high initial costs. Thus I came to a brick wall and am attempting to build a door to get through it.

Conversations with the barrel maker indicate that more robust jackets are the solution. I've been turning them out, in the experimental state one-off on the lathe.

I've been using pure copper rod and a reamer that Dave Tiff make to my specs. So far so good........

I figured that the Sierra jacket, would be possibly enough tougher than pure copper. When drawing down to 277 from 308 thickness could go up to as much as 0.0356" which is very close to the 0.040" base thickness that I've started with. I'm using a straigh taper.

Questions lead to more questions which lead to challenge after challenge.

That's my project.

Roy
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Old 01-07-2010, 01:15 PM
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Re: Sierra 30 Cal. Jackets - Information

Roy,
I know the feeling, and I feel your pain! Sounds like a worthy endeavor, but as you noted, not one that the major makers are likely to bother with. Besides, most (including Sierra) are having enough trouble just keeping their heads above water in routine production these days. There may be some issue of "set in their ways" but mostly, it just comes down to a matter of return on investment. Most don't want to be the first to dive in and find out just how frigid the waters may be. After suggesting them I had a major fight to get the 77s and 80s (.224" MKs) into production, since none of the other major makers were producing anything similar. Smaller makers like JLK were already cleaning up on them, but it's hard to get the Titanic to make a sharp turn like that, if you know what I mean.

Sierra uses standard 95/5 gilding metal for their jackets, but I suspect you were already aware of that. A thicker jacket may be a solution here, but have you seen the stuff that Eric Stecker of Berger posted about bullet blow-ups? Berger had some issues with this some time back, and revamped their jackets to deal with the situation. Eric took the question to MIT and invested some serious $ in determining precisely what was going on. In the end, it seems that heat transfer is the culprit, not just jacket thickness per se. So, anything that may result in developing/transfering less heat to the jacket may also be of assistance in keeping things together. As far as the difference in heat transfer between pure copper and 95/5 gilding metal, that might be interesting.

Keep me posted hre, you've got me curious now!

Kevin
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Old 01-07-2010, 07:30 PM
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Re: Sierra 30 Cal. Jackets - Information

I understand what you are saying regarding ROI and turning the Titanic.

I seem to find myself on the 'bleeding edge' of most things I do. The last one worked out well enough, allowing time to push ropes like this one.

The heat transfer concept tends to make sense.

In this case the bearing surface appears to be an indicator. Heavy for bore bullets have very long bearing surfaces.

Also note that 7mm 200 grain offerings in the same barrel and twist are exhibiting prefect performance.

The longer bearing surface presents greater problems.

Bullet shapes such as the Hornady 277 140 BTSP with their very shot bearing surface can't be made to fail in my rifle. Neither can any of the Nosler solid based bullets be made to fail. The Noslers shoot exceptionally well, even at this stage of barrel life. The problem being that 150 gr is a little on the light side for this cartridge and their is dismal. I'm hoping for a 160, 170 and 180 high bc offering. The 180 being about optimum for LRH at deer sized animals and smaller.

It may be that the solution will be a simple one and most probably right in front of my face. But the time and expense are spent looking for the needle in the haystack, not actually finding it. Also, there ain't no free lunches.
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