Mauser M03 - Good Accuracy with 270 Win

In some earlier posts to this Mauser M03 Blog I promised to see if my M03 270 Win and 30-06 barrels could produce better accuracy with hand loads than with the factory ammunition I'd been using so far. Well (cue fanfare), with my first attempt to live up to this promise I have some results from my 270 to share. Pics below.

After over a week of rain and wind it was calm and sunny on Tuesday this week so I gathered my Wilson reloading dies and other bits and pieces and headed out to the rifle range, hoping it wouldn't be too crowded. I got there just as a break between firing serials was about to end and quickly stapled a clean card to a target board. I was about to run it out to the 100 meter mark when the range officer, who was kindly waiting for me, said, 'Don't you want to put something to aim at on it?' Good point! I didn't want to hold the others up so quickly drew just the one square, seen in the picture below. While more aim points could have been handy, working with just one made for a good photo in the end.

My tests were with Berger 150gn VLD Hunting bullets. While these are called 'Very Low Drag' by Berger, with a G1 ballistic coefficient of .531, they are not too long or pointy to feed properly from the M03 magazine. Just before heading to the range I worked out the maximum cartridge overall length (COL) for these projectiles in this barrel, using the method outlined below (now with a nice title to help the search engines find it):

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How to Measure a Rifle Chamber for Maximum Cartridge Overall Length and Depth of Bullet Seating From the Lands.

- I carefully inserted a snug fitting cleaning rod down the bore from the muzzle end until the flat end of the rod was resting against the face of the closed bolt. I'd checked that the chamber and barrel were clear of course, so I was happy to cock the bolt to ensure it was tensioned and its bearing surfaces were engaged with those in the barrel. I put a small but strong hand clamp with stiff rubber clamping pads on the cleaning rod and snugged it up against the muzzle crown, while checking that the cleaning rod was still pressed against the bolt face.

- I opened the bolt and carefully withdrew the cleaning rod by about 15cm, then left it resting in the barrel. I was careful not to disturb the clamp.

- With a case that had been neck-sized but not yet primed or filled with powder I fitted one of the Berger 150gn VLD Hunting projectiles so it was barely finger tight. I put this into the chamber and used the bolt to push it in gently until it stopped, with the projectile resting against the lands of the rifling.

- I slowly eased the cleaning rod back into the barrel until its flat face rested against the tip of the projectile.I used the inside measuring tips of my vernier calipers to measure the distance between the pad of the clamp and the crown of the barrel it had rested against before. This distance equals the maximum length of a loaded cartridge for that combination of barrel and projectile.

NB: If the end of the cleaning rod is female threaded, recessed, hollow, angled or simply higher on the outside than in the centre, the bullet tip might protrude into the recess or low spot while taking the measurement, resulting in a shorter maximum COL measurement than you'd get with a flat ended rod. This won't be dangerous, as you'll be seating your bullets further from the lands than you think. It could be confusing though.

- I subtracted 20 thousandths of an inch from that maximum to use as a starting point for COL. Upon firing, the projectile would have to move that far before meeting the lands and engraving into the rifling, while still being held by the case neck. Makes for good accuracy, so they say.

Another NB: Developing hand loads in general and seating bullets close to the lands to improve accuracy (possibly) is not something to be doing if you're not completely right in the head. If going down this route, use your brain, don't drink alcohol or use fancier substances, study your reloading manual carefully and don't be stoopid. :-)

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Once I was at the range I looked up Nick Harvey's Reloading Manual (which has advice on starting and maximum loads for Australian ADI rifle propellants) and settled on 49 grains of AR2209 for my first two shots. ADI make the propellants used in Australia's military ammunition and I've found it to be very good. It's designed to be more temperature stable than other powders and can produce very fine accuracy. I don't have a set of wind-proof digital powder scales, so measured the loads using a powder thrower that I'd calibrated for maximum loads with my scales at home. A full turn inwards of the adjustment screw would equal a 1.5 grain reduction in the measured load, with 2209. Two turns would take me down from 52 grains to 49.

The two shots with (what should be about) 49 grains were aimed at the middle of the square. 'Wow, they're close together!' I thought, looking through the 10x magnification of my Zeiss scope. They landed about 3 cm to the right of where the rifle is sighted for the Norma 150 grain spire point factory ammo I've been using.

Next, I rotated the powder funnel's load adjusting screw out by 1 turn, to deliver around 50.5 grains of 2209. When I was about to fire I realised the new shots could land near the previous ones if I used the same aim point, so rested the cross hair on the top right corner of the square. A figure-eight! 50.5 grains is looking pretty good. Now let's push up to what ol' Nick reckons is a maximum load and see what happens. My two shots with 52 grains were aimed at the bottom left corner of the square and produced another figure-eight. The RWS primers were not too flattened so I went up another half turn, to 52.75 grains. I'd drawn another square lower on the board during a break and aimed at that. These loads were still not too hot for the rifle but spread out like those at 49 grains, about 10 mm centre to centre, which is very good but pretty crap compared to overlapping holes.

Three pairs of hand load test shots fired with a Mauser M03 270 Win 

I'd been reloading the same five fire-formed cases throughout and decided to make up three rounds at 50.5 grains, a moderate load with the best accuracy so far. My cases would last well with that charge. The bottom photo shows this last group, aimed at the middle of a new square, after moving the scope's reticle two clicks to the left. I'd let the barrel cool a bit, but it was still pretty warm at the start of this group. What makes me happy is that the third shot landed between the first two. That's a good sign that the combination of rifle and ammunition is working well. I measured this three shot group at a touch over 10 mm. I am wondering if I can do better by using the full suite of case preparation tools and techniques, to turn the case necks, do some length trimming, neck chamfering, primer hole deburring and case sorting by weight. It won't hurt and might help. I might even put a scope that's bigger than 10 power on next time. And get up earlier to dodge the wind that was picking up.

A 10.5mm group fired from a Mauser M03 270 Win with Berger 150 projectiles

Conclusion: This Mauser M03 with its 270 Winchester barrel is capable of outstanding accuracy, which can be achieved with a bare minimum of load development with projectiles that are not as easy to work with as others, such as flat base bullets with less pointy noses. If the piggies want to grumble about me shooting at them with a rifle that isn't accurate enough, they won't have a leg to stand on.