SIZING – HOW MUCH IS POSSIBLE?

A few months back I happened upon a second hand, double cavity, Lyman 280468S, a Loverin pattern mould original cut for the .270 Winchester. At 110gr nominal weight it must have been a great bullet for small game in the .270 Win and would be perfect for the new 6.8 SPC; neither of which I own but not one to pass up a bargain I bought the mould based on my hopes that it would be possible to size the bullets to .269 for my FAT 41 6.5X52 Carcano. 0.280 down to 0.269? How so?

In recent times many very favourable reports have been posted involving substantial diameter reduction when nose first sizing of cast lead alloy projectiles in Lee push through style dies. Bullets designed for the 8X57mm (.323-.325 inch) are being successfully sized to .314 and shooting well, something that is in stark contrast to any of the historical readings suggested that even minimal sizing will be detrimental to accuracy. Traditionally the best accuracy is achieved from bullets cast as close to throat diameter as possible that require little or no sizing as the more a lead alloy bullet is handled the more likely it is to become damaged or distorted. In fairness the accuracy reports are not coming from winning targets at CBA matches and indeed until such material appears I will reserve judgement on primo accuracy however the vast majority of cast bullet shooters are not trying to achieve match winning results as much as field accuracy or groups to match jacketed ammo at least.

Back to my new 280468S. The first order of work was to make a push through, press mounted sizing die. This I did matching it to the die body of a Lee factory crimp die I had on hand not being used. The sizing die fits snuggled into the FLC die body and is held neatly by an ‘O’ ring. Next a push rod was fashioned to fit in the spent primer hole of a case holder mounted on the press ram in similar fashion to the Lee system. The sizing die worked perfectly and sizing even heat treated alloy at near 20 BHN was easy enough.

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From the outset the 280468S, sized 0.269 for the Carcano, showed potential but groups were not stella and tended to be inconsistent. Not until a fellow cast bullet chucker stopped in home for a chinwag did the situation remedy itself when he reminded me to completely fill the grease grooves on the bullet BEFORE sizing. The purpose of prelubing was to maintain the structure of the bullet as the lube is non compressible and as the bullet is squeezed down 0.011 from 0.280 to 0.269 the grooves remain fairly unchanged whilst the bullet length increases due to the displacement of the metal. The displacement and growth is very controlled thanks to the lube and this control was the difference between average, inconsistent groups and primo results.

L to R: 280468S base first sized .269 Lyman 4500, push through sized .269, PRELUBED push through sized .269 (lube removed for photo), as cast .2805.

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The Carcano rifle is open sight equipped only but with a correctly sized bullet accuracy of around 1 inch at 50m is being achieved reliably.  The load is 14gr of Alliant 2400, air cooled wheel weight alloy, over a CCI large rifle primer and a crimp into the third grease groove. Velocity is 1750fps and the gas check is made from rather hard 0.010 aluminium formed in a Freechex III die.

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After 20 odd years of cast bullet shooting I thought I was a dedicated Lyman lubesizer fan but I can now see the benefit of the push through style dies. What this exercise has taught me is it’s not how MUCH you size but HOW you size. Anyone who has based first sized long bullets the likes of the 6.5mm Cruise Missile will know it is possible to bend a bullet in the process. Further, bullets with long bore riding noses can be and often are ‘bumped’ during sizing base first where the unsupported nose of the projectile squashes slightly during sizing and increases in diameter. This ‘bumping’ is dependent on the amount of inertia present during the process. Inertia is created by factors such as an oversized gas check requiring swaging down onto a bullet shank and/or oversized moderately hard bullets; the more you have to lean on that press handle the more the chance of ‘bumping’ that nose. In contrast, nose first sizing puts all the force, square and plumb on the base of the bullet without stressing the top end of the projectile. Food for thought ah?

Keep your powder dry. Jeff.

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About JeffinNZ

Dedicated cast bullet shooter, runner, fisherman and father for two beautiful girls.
This entry was posted in Casting, Handloading, Moulds. Bookmark the permalink.

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