c-g-designs

A recent thread on the French forum ‘Les Copains du TLD" about the wildcars of the title .The subject deserve some clarification.

Once again, the idea came from a discussion at Bisley between Laurie Ingram, Peter Campbell and myself around the F-Class Short Magnum calibres actually in favor and their barrel fast wearing reputation, the necessity of specific bolt head  recesses and the cost,short lifespan and dubious uniformity of the available brass.

At that time the NRA just changed  from RG as issued ammunition for the RUAG 155 grains. This conversion let presume good quality boxer-primed, once-fired brass was  becoming available at low cost and of a far superior quality.

Having always been favourable to the short neck concept (cf the .300 Savage) and standard 40° shoulders allowing a much better gas flow, I oriented the discussion on the oissibility to move forward the standard .308 case, moving the shoulder forward thus reducing the neck height. This modification allowing showed many advantages and few issues, although the later not neglectibles.

Advantages　:

1°) Use of good quality once-fired brass and available in quantity.Also possible to test the Lapua "Palma" brass with SR primers.

2°) The shortened neck would ensure a better gaz sealing in ensuring better  adherence when firing.

3°) The 40°　neck being kept, ensuring a better gas flow with no turbulences.

4°)The neck diameter  being constricted from 7,62 to 7 or 6,5mm, it result a slight increase in neck wall thickness, allowing to turn the neck to a desired diameter.

5°) The shortened neck allow a better centering of the bullet thus a better cartridge concentricity.

6°) Although specific sizing dies being recommended, it remain possible to use standard .260Remington and 7-08 dies, a resizing of the case base being always possible using a die intended for longer cases, such as  30-06 or 7x64.

7°) Every rifle in .260Remington or 7-08Winchester can simply be transfprmed in .260 INCH and .284INCH respectively by simply reaming the shoulder forward;

Drawbacks:

1°)Necessity to fire-form cases.

2°) Cases lifespan possibly reduced,however largely compensated by cheap availability of good mother-brass.

3°) The shorter neck could allow a less satisfactory hold of the bullet in the case,but this was not evidented in the practice and the bullet extraction valus was more constant than with longer necks.

Back from Bisley, I started work and noticed it was possible to extend the powder chamber lenht by some 3,5mm (.138’) with no problem. The conventional CIP dimensions L1 (from base to top of shoulder) and L2 (from base to bottom of shoulder then became:

--For the .260: L1 increased from 39,62 and L2 from 45,10 to 48,6mm

--For the .284　: L1 increased from  39,62 tp 43,32mm and L2 frpm 44,47 to 48,17mm.

Thus allowing a capacity increase of some 33 cubic millimeter.

The two calibres were immediately baptized "INCH" and the reamers ordered to Triebel.

Laurie installed a Border 5R in .260 on his INCH rifle and started his fire-forming…and blew an extractor on his first attempt..I then learned him to create a false .260 shoulder  on his .308 cases in order to create a good chambering for fire-forming. This worked perfectly, but later we barreled a Mauser 98 action with an old .308 barrel. The Mauser extractor resisted the firing pin blow no problem and the cases accepted all kinds of cheap bullets, plinkers; etc; including .32 lead bullets (ignoring bore leadng)… Remainuning only the neck sizing,turning and trimming after this brutal treatment.

Inbetween; specific dies were ordered at Redding.

Laurie shot  the .260 INCH with success at Bisley for 2 years before he had to cease shooting,,even at 1200yards. I do not have his loading datas nor the velocities he obtained, just a few excellent group targets shot at 300 metres.

Several rifles were made in Australia in .284 INCH and we have excellent reports on them regularily.

14/12/2015

R.G.C