My project - 260 INCH

[R.G.C]

Hi RGC,

Very nice to have you on the forum.

I've ended up making my own version of the 260 INCH by running the 260 Rem. reamer in another 0.2 inches and using a shortened (by 0.25 in.) 30-06 Lapua case. Point taken regarding neck-length but I wanted something a bit more robust for 1000 yard benchrest shooting.

Yes - I could use the 260 Rem. die to full-length size but I was afraid it might a) not re-size the bottom bit of the case and b) it might actually bulge the case. Only time will tell.

I've just chambered the barrel this afternoon and prepped all the brass. I will try and shoot it on Thursday - then we will find out about re-sizing.

Cheers
Vince

Vince,

I understand you appoach, although, personally, I would not have started from a longer case than needed.

On question of resizing, there is little chances that you cannot use a longer caliber die to reform correctly the bottom of the case. It os not att his palce that it deforms, except in case f overpressure.

I do not agree on your comment about short necks being weaker than longer hoses!!....

R.G.C

[woody_rod]

I've ended up making my own version of the 260 INCH by running the 260 Rem. reamer in another 0.2 inches and using a shortened (by 0.25 in.) 30-06 Lapua case. Point taken regarding neck-length but I wanted something a bit more robust for 1000 yard benchrest shooting.

Robust in what way? I shoot the round, it averages 3060fps with a very moderate load and zero case problems - I could probably get 3150 out of it, but it would be difficult to extract. 1000 yard benchrest does not put any more pressure on a case than any other discipline. We have people in AU that say the same thing, which is of course not based on any engineering evidence or proper scientific process. Pressure is a constant, it has nothing to do with the discipline. If my case is operating at 60k psi, yours operating at the same pressure will mean the same mechanical forces being present; it is as simple as that.[/quote]

[ovenpaa]

Robust in what way?

The BR shooters I have spoken to in the past seem to have mad moments where the conditions are ideal and they shoot, flags have dropped, mirage is steady and so on, at that point they try to fire their card in one go, certainly in under a couple of minutes. I assume when throwing rounds into a rifle like that the last thing you need is the worry of knocking the bullet out of alignment as you bash it on the receiver of fumble and drop it.

Personally, shooting an F Open class rifle I would dearly like to know what the difference a shortened neck on my 7mm SAUM would make. I am even tempted to go and shorten back a few cases to see. Tempted.... They are so expensive and awkward to get I am not sure I dare do it!

[R.G.C]

Robust in what way?

The BR shooters I have spoken to in the past seem to have mad moments where the conditions are ideal and they shoot, flags have dropped, mirage is steady and so on, at that point they try to fire their card in one go, certainly in under a couple of minutes. I assume when throwing rounds into a rifle like that the last thing you need is the worry of knocking the bullet out of alignment as you bash it on the receiver of fumble and drop it.

Personally, shooting an F Open class rifle I would dearly like to know what the difference a shortened neck on my 7mm SAUM would make. I am even tempted to go and shorten back a few cases to see. Tempted.... They are so expensive and awkward to get I am not sure I dare do it!

Ovenpaa,
I decidedly start to like this forum very much…. Hope it will quickly grow up...

If the BR shooters could even avoid to have to pull their triggers, I think they would adopt the principle immediately!!!
In Target, F-Class, Match Rifle, whatever, firing is controlled. Difference..
Fast feeding can be eased by different means, one of the most efficient being the cone breech.
On question of neck length, I believe a long bullet in an action with feeding difficulties can be more detrimental than a neck length difference..
Shortening the neck of your actual 7 SAUM without altering the chamber as well would not bring you very mch I think. It wll alwo not do any good to your actual chamber (probable flame pitting f the neck area).

Cost of cases: use an improved round using a cheap once-fired case as a basis.. The Bisley armouries bins are now full of excellent .308 RWS/RUAG ones!!!
A 7mm INCH could even be envisaged, it would be no more than a 7-08 with its shoulder moved forward 3,5mm
R.G.C

[ovenpaa]

I decidedly start to like this forum very much…. Hope it will quickly grow up...

I am pleased you are enjoying the forum Robert. Dare we tell the Listoids of our new discovery? I know Christel has great hopes for the new year both on the Forum and of course at the Range!

I like the idea of the 7mm INCH, where is Woody when you need him? As you point out, Bisley is full of RUAG 308 brass which is of a top quality, this is the problem with the SAUM, the better brass made by Norma is twice the price of Lapua etc. I recently shipped around 8kgs of .308 Berdan DAG to Filippo who tells me it is also made by RUAG so he was pleased.

I agree the SAUM as a short neck in the standard chamber would serve no purpose, my curiosity would be purely to see any change in run out and as Woody is shooting the 260 INCH the data he has *should* apply to the SAUM. Possibly the short neck is the way forward, is anyone else exploring this type of chamber?

Pesonally, using a Barnard action I have no feed problems, but I have plenty of time to chamber the round, shoot and remove the case afterwards, this is the second rifle built for us by Sanselm who posts on this forum and both rifles shoot very nicely (Thank you Stuart and Vince for two very accurate rifles)

[R.G.C]

I decidedly start to like this forum very much…. Hope it will quickly grow up...

I am pleased you are enjoying the forum Robert. Dare we tell the Listoids of our new discovery? I know Christel has great hopes for the new year both on the Forum and of course at the Range!

I like the idea of the 7mm INCH, where is Woody when you need him? As you point out, Bisley is full of RUAG 308 brass which is of a top quality, this is the problem with the SAUM, the better brass made by Norma is twice the price of Lapua etc. I recently shipped around 8kgs of .308 Berdan DAG to Filippo who tells me it is also made by RUAG so he was pleased.

I agree the SAUM as a short neck in the standard chamber would serve no purpose, my curiosity would be purely to see any change in run out and as Woody is shooting the 260 INCH the data he has *should* apply to the SAUM. Possibly the short neck is the way forward, is anyone else exploring this type of chamber?

Pesonally, using a Barnard action I have no feed problems, but I have plenty of time to chamber the round, shoot and remove the case afterwards, this is the second rifle built for us by Sanselm who posts on this forum and both rifles shoot very nicely (Thank you Stuart and Vince for two very accurate rifles)

Ovenpaa;

You can always sacrifice one or a few old SAUM cases, shorten the necks by case trimming, resize, top a bullet on it at your 'normal' OAL, and check for runout ad behaviour in rough hangling....

Exceptt he intensive tests Laurie made few years ago 'and also the shortened necks variants of the 6mmBR), there is here, due to our regulations, quite a lot of shooters having drawn a lot of accuracy fron the .300 Savage.Here are a few necks lenghts for comparison:
.308 Win: 7,70mm
7-08 : 7,51
.300 avage: 5,60mm
.260 Inch: 3,78mm
As you can see, there is plenty potentila to increase the powder sleepig room of a 7-08..

Now, do consider all the shortened necks variants of the 6mm BR: Dasher, XC, etc... They all claim to perform much better that the original 8,18mm long neck of the parent 6BR Norma case.

I do not have at hand their neck lenghts, but they are all in the area of the .260 Inch, and maybe even shorter.

R.G.C.

[The Gun Pimp]

Guys,

This 'short neck' thing is something which, to my knowledge, has not been expored on any other forums.

It's a very interesting topic which we can all easily test and maybe learn something.

We could be on the verge of a new discovery - let's give it a try!

Cheers
Vince

[R.G.C]

Guys,

This 'short neck' thing is something which, to my knowledge, has not been expored on any other forums.

It's a very interesting topic which we can all easily test and maybe learn something.

We could be on the verge of a new discovery - let's give it a try!

Cheers
Vince

Vince;
For me, ot is fun, and all what I can bring in is for everyone’s benefit (!!!!!!!!i hioe it wikk be beneficial).

There is one point I think I should warn you on your appoeach:
Every ‘case improvement’ tend to move the shoulder forward, or at least increase its shoulder angle without moving it.
Case lenght reduction is reserved to forming cases to make ammunition for an obsolete caliber for instance, when research of the precision is not the determining factor. It is however the way you have choosen. I will try to explain on metallurgy and metal working points of view!

This might be well know of you, but memebers might need to be infirmed:
Punching cases is a multi-steps operation (12 to 14 in sequence usually), the first ones producing a ‘cup’, externally cylindrical to the bottom diameter, and the inside punched to a female taper form, with wall thicker at bottom than at top. This wall thickness at top is calculated for, once the bottleneck of the case finally formed allow the neck thickness to become the desired final one. Effectively, starting from a thin wall tube of 12mm OD, to end in several operations to a some 6,5mm ID (for a .260 calibre), the process can only result in an increase of the wall thickness. This is simple mathematic metal displacement….
Note that all the operation before starting to form the bottleneck and external tapers are made with an internal support (a die and a punch), when the subsequent operations will be without this internal support (a die only), therefore difficult to control accurately the inside shape. Metal stresses are important at the level of the two folded junctions at top and bottom of the shoulder cone. This is where the even thickness is the most difficult to obtain…..and, in shortening the longer case by .250” as you say, it is exactly the area you have choosen to rebuilt the neck of your new round…
I wold consider a weakness at this point..spitting parts of neck together with the bullet is ot a good thing…
Would it not be possible for you to envisage to start from a case such as 8x57 or 7x57 instead if you want something longer than the .308? Yhis ould allow you to build you neck on a better basis.
Hope my complicated explanations tentatives are understandeable.
R.G.C

[R.G.C]

Guys,

This 'short neck' thing is something which, to my knowledge, has not been expored on any other forums.

It's a very interesting topic which we can all easily test and maybe learn something.

We could be on the verge of a new discovery - let's give it a try!

Cheers
Vince

Hi all,

There is one point I forgot to mention : heavy artillery ammunition have necks often no longer than 1/4 the calibre..They are not reputed to be sensitive to rough handling..

We do ot refer often enough to artillery in our balistics!!!

R.G.C

[ovenpaa]

This is true, I handled the 35mm Bushmaster fairly recently and the cases have very short necks, however they are also made out of steel and have a significant crimp around the neck as well as appearing to be glued in (Maybe a lacquer instead?) They are also very well contained for transit.

I am with Vince on this, it is unusual and interesting and I would like to see someone try the short neck over here. Come on Vince, you have no excuses with Diggle all but in your back garden and a workshop as well, you could chamber and test all in the same day