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6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

 
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Old 01-22-2012, 03:51 PM
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6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

There has been a lot of discussion around comaparing the 6.5's and I have personally had a lot of pm's asking questions about the 6.5 Sherman so I thought this might be a good time to try to cover it all on one thread. What I would like to do is try to explain the differences, and similarities, of some of the 6.5's in question. Some of the differences that I can easily explain are based on actual measurements, so can be taken as fact, and some of my comments may be my own beliefs and interpretations.
Let me start by saying that I shot a 6.5 A.I. for many years and believe it to be a fine cartridge, and was in fact the reason for the development of the 6.5 Sherman. When it was time to re barrel my last A.I., I decided that since I was wildcatting anyway, why not try to improve on what I thought to be an already good thing. My intent was to keep the '06 sized bolt, increase velocity while maintaining accuracy, barrel and case life, as well as brass cost and availability, and ease of forming.
To back up for a minute, my first thought was to build a Gibbs, which is also a proven performer. I went so far as to order some brass from Quality Brass, but when I looked it over, I really didn't like the extremely short neck on the Gibbs, so on to the Sherman.
The Gibbs was limited at its inception, because it was based on the '06 case which is .046" shorter than a .270 or .280 case. In order to gain the case capacity, the sacrifice was made in the neck. The A.I has a good neck, but lacks the case capacity of the Gibbs. I WANTED BOTH!
I started by taking the exact case specs of each, and then easily decided on the .270 as a parent case to gain the extra length needed. I spoke with some knowledgeable people as to what minimum body taper would be and what I thought a good neck length should be for the caliber. I chose the 40 degree shoulder for two reasons. First of all, it gives maximum case capacity and more importantly IMO, in conjunction with the neck length, it keeps the flame point more confined inside the neck rather than directly into the throat. It is my belief that this is why the A.I. and Sherman barrels last longer than many 6.5/.284 barrels that hold approx. 11% less powder than the Sherman. The body taper I decided on was less than the A.I., and far less than the Gibbs, which left me with a .460" diameter at the shoulder. The shoulder was moved forward farther than the A.I. but still maintains a .300" neck length which is plenty for a 6.5; Less than the A.I. and far more than the Gibbs, resulting in more capacity.
The end result was a case with the same capacity as the Gibbs with the good qualities of the A.I. Field tests so far have proven the value of each. I can reach 3200"+ with 140's in a 26" barrel. Accuracy is great, and case and barrel life have proven to be very good. (You could add approx. 40'/sec/inch of barrel length) i.e. 30" barrel = 3360'.
The case performs very well with a large variety of powders from 4350 to retumbo, all giving good accuracy and velocity. I currently have fired around 1300 rounds with no apparent loss of accuracy.
This cartridge will exceed any other '06 sized bolt face and in fact, will equal the 6.5 WSM, which is also a great cartridge, although I doubt the barrel will last as long as the Sherman. The Gibbs will equal the Sherman velocity as well, but, IMO, is an inferior design for the above reasons. I have had very good feed back on another build, and look forward to seeing some more out there!
I have had comments that "it is nothing more than a Gibbs or an A.I. by another name", but if that is the case , we only have about a half dozen cartridges in existence! The truth is, the only dimension the Gibbs shares is the case head and the A.I., the case head and shoulder angle.
I hope this clears up some of the questions, and myths. Feel free to pm me if there is something that can't be handled on the open forum.......thanks.......Rich
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Old 01-23-2012, 04:07 PM
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Re: 6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

I have the AI and the Gibbs. The Gibbs is a little faster. The .25" neck has not been an issue and mine is very accurate. If yours has the same capacity as the Gibbs I will verify that it will shoot with a 6.5-300 wsm because I have owned both. Actually it will perform right on the heels of the 264 winchester. The 270 and 280 cases are the ones to use because you can get the performance of the Gibbs while retaining the optimum case neck length. My 7mm JRS off the 280 case will shoot virtually right with a 7mm remington.
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Old 01-23-2012, 05:38 PM
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Re: 6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

Quote:
Originally Posted by Long Time Long Ranger View Post
I have the AI and the Gibbs. The Gibbs is a little faster. The .25" neck has not been an issue and mine is very accurate. If yours has the same capacity as the Gibbs I will verify that it will shoot with a 6.5-300 wsm because I have owned both. Actually it will perform right on the heels of the 264 winchester. The 270 and 280 cases are the ones to use because you can get the performance of the Gibbs while retaining the optimum case neck length. My 7mm JRS off the 280 case will shoot virtually right with a 7mm remington.
LTLR.....I would agree with all of what you say. I think the advantage of the longer neck is that it is a little more forgiving accuracy wise unless your chamber is PERFECTLY concentric, which they rarely are. I also believe that it does give better barrel life in conjunction with the 40 degree shoulder. Either,way, they all are great cartridges and fun to shoot........Rich
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Old 01-23-2012, 06:14 PM
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Re: 6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

Quote:
Originally Posted by elkaholic View Post
I also believe that it does give better barrel life in conjunction with the 40 degree shoulder.
You believe it gets better barrel life because the flame path is contained better compared to the shorter neck correct?

Scot E.
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Old 01-23-2012, 07:16 PM
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Re: 6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

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Originally Posted by Scot E View Post
You believe it gets better barrel life because the flame path is contained better compared to the shorter neck correct?

Scot E.
Longer neck plus sharper shoulder. If you draw a line down both sides of the shoulder angle, where it converges should be well inside the neck. This has always made sense to me because if you compare to a cutting torch, the flame is ALWAYS the hottest right at that point.......Rich
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Old 01-23-2012, 07:41 PM
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Re: 6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

I have owned several 6.5-06AI's and love them so the Sherman has me very intrigued. My current AI shoots 3105 w 59 Retumbo and a Fed 215. I have also owned a 6.5 WSM that I was not all that impressed with. How many grains of Retumbo are you using in the Sherman to get to your 3200+ Vel's out of a 26" tube?
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Old 01-23-2012, 10:23 PM
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Re: 6.5'S APPLES to APPLES (Sherman, Gibbs, A.I.)

Quote:
Originally Posted by CPGfan View Post
I have owned several 6.5-06AI's and love them so the Sherman has me very intrigued. My current AI shoots 3105 w 59 Retumbo and a Fed 215. I have also owned a 6.5 WSM that I was not all that impressed with. How many grains of Retumbo are you using in the Sherman to get to your 3200+ Vel's out of a 26" tube?
It depends on the lot, but around 64 grs. It will also reach 3200' with 7828, rl22, rl,25, and various others. That is with BR2 primers though. With 215's, I'm sure it would be less........Rich
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