Precision Rifle

What do we mean by accuracy cartridges?

 

Some cartridges have more 'inherent' accuracy than others. It's all to do with burning the powder consistently from shot to shot. Short fat cases seem to do this better than long thin ones.

 

A long neck is also useful - not just to firmly hold the bullet in alignment but also to keep the 'turbulance-point' within the neck. The turbulance-point is the intersection of the lines following the shoulder angle. Steep shoulder-angles also help keep the turbulance-point within the neck. Most accuracy cartridges will have a shoulder-angle between 30 to 40 degrees. 

We should also consider the bullet. Some cartridges using long bullets require a fast-twist barrel, those using short bullets can get away with a slower twist. The faster we spin the bullet, the more we show up any minor defects. The 6PPC using a 68 grain flat-base bullet requires only a 1 in 14 twist, whereas the similar size 6BR using a 105 grain bullet will need a 1 in 8 twist.  

 

 

220 Russian

This is a neck-down of the infamous 7.62x39 Kalashnikov case. The Russians developed it for their 300m rifle teams in the sixties. Some benchrest shooters still use it but most ‘blow-out’ or ‘improve’ the case to give it a steeper shoulder-angle (the PPC) and more capacity. Small primer-pocket.

 

22PPC

This was the earliest improvement to the 220 Russian case. In 1974 Ferris Pindell and Doctor Lou Palmisano made every other short-range accuracy Cartridge obsolete overnight with this round. The 22PPC still has a following even at the highest level of benchrest but the case is usually shortened by about one tenth of an inch to give it slightly less capacity. The ‘short’ version is sometimes called the 22Ski. I'm currently shooting a 22PPC 'short' in benchrest competition.

 

22BR

This round is a neck-down of the 6BR Remington. It has been used in serious benchrest competition but not now. It is more likely to be used on a mid-range rifle, shooting 80 grain bullets at over 3000 fps. Utilises a 308 bolt-face. Small primer-pocket.

 

22Dasher

This is a phenomenal little round. The cases are a bit fiddly to form but it’s worth it. We first neck-down the 6BR, then blow the shoulder forward and at the same time steepen the angle to 40 degrees. We lose a little neck-length but gain a ten percent capacity increase. It will now push out 80 grain bullets at around 3250fps. Another great 600 yd BR round. I've recently built a rifle for the 22Dasher. It is an excellent performer giving 0.75 inch groups at 300 yards with 80 grain Sierra bullets.

 

6PPC

A legend amongst wildcats! This is the most famous accuracy cartridge of all time. The 22PPC was soon necked-up to 6mm and this round now dominates benchrest competition out to 300 yards. If you are looking to shoot benchrest, don’t even think of any other round. The 6PPC holds all the world’s accuracy records out to 300 yards. Flat-base bullets in the 66-68 grain range are most popular and velocities are around 3250 fps.

 

6BR

Is this the most efficient and versatile round ever? No longer a serious contender in short-range benchrest but it is a formidable performer at all ranges even out to 1000 yards. It currently dominates 300m ISSF competition. Bullets from 70 to 105 grains can be used. It is currently the most popular round in 600 yard benchrest competition. Uses the popular 308 bolt-face.

 

6BRX

This is a simple ‘improvement’ to the 6BR. By blowing forward the shoulder, we gain a little extra capacity. Is it worth it? Maybe.

 

6mmDasher

As the 22 Dasher but retaining the 6mm bullet. Cases are a little easier to form. A great round even out to 1000 yards.

 

6XC                                                                                                                                                                                                                                                                                This round is very similar to the Swiss Match (below) but was developed by American Highpower shooter, David Tubb. The cases can be formed from the 22-250 but Tubb offers his own brass and dies. He uses his own 115 grain DTAC 6mm bullet to great effect even out to 1000 yards. Over here, the Swiss Match is probably a better option.

 

6x47 Swiss Match

The 300m ISSF shooters love the 6BR but it can sometimes hang-up on chambering because it is a little nose-heavy. To overcome the problem, the Swiss simply lengthened the 6BR by 0.3 of an inch. The extra capacity now makes it a great round at all ranges using the 105 grain bullet. Brass is only available from Ruag but it can be formed by necking-down the new Lapua 6.5x47. It will shove a 105 grain projectile out at around 3000fps. Uses the 308 bolt-face and a loaded round will fit a standard 308 magazine. Uses a large primer. I have a tactical rifle in Swiss Match. It is very accurate and easy to shoot with little recoil. A great alternative to the 308 for mid-range paper-punching.

 

243 Win.Imp.

The 243 Wnchester was never noted for its accuracy. Rifles are usually 1 in 12 twist so bullet-weight is limited and the 20 degree shoulder doesn’t help. Improve the case by blowing forward the shoulder and increasing the angle to 40 degrees and suddenly we have a much more effective round, especially with a 1 in 8 twist barrel using 105 grain bullets. Nontheless, capacity is more than necessary and the Swiss Match offers similar performance. Again, 308 bolt-face. Uses a large primer.

 

6-284

The 284 Winchester has been around for over forty years and was originally developed as a hunting round for use in the lever-action rifle. No one took any notice until Bill Shehane necked it down to 6mm and set a new 1000 yard benchrest world Light Gun record with it a few years ago. It has a capacity of around 60 grains though again, not all the capacity is used with the 105 grain bullet. Velocities can easily exceed 3250fps but this speed tends to offer best accuracy. I had a rifle in 6-284 and it was very good for 1000 yard BR but barrel-life was only 1000 rounds. Bill eventually went for a shorter version which was even more effective. The case is unusual in that it has a rebated rim but this fits the standard 308 bolt-face meaning that a standard 308 can simply be re-barrelled. Uses a large primer.

 

6.5x47

This is a brand-new round from Lapua. The case is almost identical to the Swiss Match so it will feed better than the 6BR and is claimed to offer better ballistics even out to 1000 yards than either the 6BR or the 308Win. Bullets from 108 to 140 grain can be used. Brass is small primer-pocket and uses the 308 bolt-face. It was developed as a target round, so it should be accurate. I've just built a tactical rifle chambered for this round - see 'Projects'.

 

260 Rem. AI

This is the latest edition to the list. Initially, I didn't include it but after having shot a couple of rifles chambered for this cartridge, it seems to deserve a place on the list. It's no more than a necked-up 243Win with the shoulder blown-out to 40 degrees. To make it work, you need a reamer that will seat the 123 or 139 grain 6.5mm bullet well out, otherwise, powder capacity will be compromised.                                                                                                                                                                                             

 

6.5x55 Imp.

The 100 year old 6.5x55 had lain dormant on the competition scene until Steve Dunn set a new UK 1000 yard Light Gun record with this round and eventually America woke up to it - but in the 6.5-284 form. The 6.5x55 Sewde case is Improved by blowing out the taper and increasing the shoulder angle to 40 degrees. Unfortunately, the case-head is larger than the 308Win. and the bolt-face needs to be opened-up a little so the 6.5-284 (below) is a better option.

 

6.5-284

This round has achieved tremendous popularity over the last two or three years. The case is very similar in capacity to the 6.5x55 Imp. but it has a little more capacity (which isn’t used) and a 308 case-head. Accuracy is outstanding out to 1000 yards making it a popular F Class and benchrest round, usually with a 139/140 grain bullet. Expect a barrel-life of about 2000 rounds. I'm currently using a 6.5-284 for F Class and I like it but I might try the 7mm next time.

 

6.5mmWSM

The new range of SAUMs and WSMs are very exciting to the accuracy-seeker as they offer the ideal short, fat powder column. The 6.5 version is a grossly over-bore 'wildcat' and barrel–life will be less than 1000 rounds. Unfortunately Lapua don’t do brass but Norma do (form from 270WSM) and it's very good. Uses the standard magnum bolt-face.

 

284 Winchester

Shooters of the 6.5-284 are finding that the standard 7mm version gives increased barrel-life, equal accuracy and the heavier (175/180grain) bullet performs better in the wind. Lapua make 6.5-284 brass which is easily necked-up.

 

7mmWSM

This cartridge can use the factory case or be formed by necking-down the 300WSM – which gives a slightly longer neck and is thus favoured by accuracy-seekers. Case-capacity is about 69 grains and it will shove a 180 grain bullet at well over 3000 fps. This round currently holds the UK Light Gun record for a 5-shot group at 1000 yards measuring 2.67 inches. It is also becoming a popular F Class round but again limited barrel-life of around 1000 rounds. 

 

7mmBooBoo

This round was developed by Dave Tooley and Bill Shehane for 1000 yard benchrest. It’s about as big as you can go with a 17lb Light Gun. The cases are formed by ‘improving’ the European RWS 8x68 cases, which are belt-less and of excellent quality. It's now used for F Class and won the UK F Class League in the hands of Peter Wilson.(See www.f-class.org.uk)

 

300WSM

This could just be a better option than the 7mm version – especially barrel-life but as yet I don’t know of anyone using it in serious competition.