The Applications of different twist rates

[Laurie]

The Russians altered the twist rate on the Dragunov,my barrel has a twist of 1:320mm or 1:12.6 inches which is the original SVD twist before they tightened the SVD to 1:240mm or 1:9.4 inches to better stabilise the longer tracer and armour piercing bullets.

You rightly note the issue of tracer bullets in military ammunition which are generally significantly longer than same weight ball projectiles and therefore need a faster twist rate. (For any given bullet length increasing the weight actually reduces the spin rate needed, so the 0.224" 65gn BTSP Sierra GameKing can get away with a significantly slower twist rate than the similar weight but much longer 68gn Hornady HPBT Match and 69gn Sierra HPBT MatchKing.)

The other issue is that of the military have to be prepared to fight in any season in any corner of the world in the most extreme conditions recorded for 100 years. So, chamber pressures have to remain manageable in 130-deg F in the shade with a rifle and ammunition that are sit in full sun (the US M118LR 175gn SMK 308 loaded with Alliant Re15 failed that test in Iraq and Afghanistan and has been reformulated with a less temperature affected propellant); likewise minus 40-deg C in the Arctic winter. The original AR15 prototypes started with the .222 Rem cartridge and its standard 1 in 14" rifling twist, the latter carrying over to the early .223 / 5.56mm with a 55gn FMJBT bullet in the XM16 trials rifles. 500M Arctic conditions trials at Thule soon finished that - the rifles couldn't hit the proverbial barn doors at anything over 100M thanks to the super-dense air needing a much greater amount of gyroscopic stabilisation and the 12" rate was quickly adopted despite 14" having been effective in continental US conditions. Even that was barely adequate in extreme cold with the old M193 cartridge, but the rifle was being rushed into service in a tropical theatre, Vietnam. However, the later 5.56mm NATO standard for the M855 / SS109gn bullet and its longer tracer version was set at a very fast 1 turn in 7". The standard SS109 ball projectile actually needs a 1-10" twist or maybe a little faster for full stabilisation in British conditions.

[Laurie]

My struggle with the 175gr SMK in my Remington was I figured that I just wasn't getting enough muzzle velocity from the shorter barrel. [Countryman]

Been there, got that T shirt! When FTR started up as an offshoot of F-Class I switched to it from 6BR using an out of the box 24-inch FN Special Police Rifle which was touted as 'FTR-capable' - it wasn't, not by a long chalk.

With the 175gn SMK at a little short of 2,700 fps it shot fantastic short-range groups performed well in club comps to 600 yards, just managed OK at 800 if conditions weren't too bad, started to struggle at 900 ands would hit the target but rather randomly at 1,000. My first ever (Blair Atholl) Glen Tilt range outing was on a rough early May weekend in 2009 or maybe 2010 shooting into a very strong quartering and turning headwind with regular rain squalls that saw wind speeds rise by 50-100% in irregular gusts. After my performance that weekend, a sensible person would have found some other cheaper and more satisfying way of spending lots of money - in one match I lost a point by not converting my 'sighters' which had scored 2 and 1 !!

The longer term answer was a competitive rifle; the short-term was to load the 190gn Sierra MK which is famed for its ability to handle transonic speeds and even dropping into subsonic flight over a stiff dose of Viht N550 high-energy powder for 2,550 fps or thereabouts.

[Countryman]

Sounds exactly where I am at Laurie. I've run the whole gambit and it's become a bit of a matter of principle that it will not beat me.

The randomness of my efforts at 1000 yards has driven me nuts!

[Matt]

Guys, hope you don't mind me pulling this back up.

My Remington is a McQueens machine but I'm just not getting there at 1000 yards which bugs me.

I've just agreed to buy a rifle with a 30" Truflite 1:12 barrel. I have 155gr Lapua Scenars as well as 155gr Palma match and 175gr SMK's. What's it going to like?

Can anybody help me with some load data for that elusive 1000yard Vbull?

What action is this on, reason I ask is that people often think that shooting at 1000 yards is easy, when I first started in FTR I was using a remington action with a decent aftermarket barrel that I had put on to get into competition, this was a good combo but I never wanted to be above 2950 for practical safety reasons..... Once I got a little more into it I upgraded to a full custom gun (Dolphin FTR rig - great rifle) which allowed me to push a 155.5 berger a little quicker (which in reality you need to do if you want to be competitive in FTR) - the point I'm trying to make is that your 1:12 with a 155 will be fine but you will need to carefully select a powder and work up a load that will suit your set up....

Then also remember that there's more to it than just twist rate, reloading technique and quality, shooting technique, bipod and rear bag set up and of course wind reading

Whatever you do remember that it's great fun at 1000 but it can be infuriating at the same time as any slight changes or inconsistencies can look dreadful on the target aaarggh

[Countryman]

It's a rebarrelled Accuracy International AE.

I know Mik Mak and he has done great work on my other rifles but I'm not committed to a career in 1000 yard + comps nor will my budget stretch to one of his excellent creations right now.

If I can reliably get on the board it will be a start! I think I can do my part otherwise but we will see.

[Matt]

Sounds good, the AI and barrel combo should be good for 1000.

As Laurie said earlier in the thread, a 155 at around 3000 should be good, not sure what powder you were going to use but it would be worth trying some RS52 in your load development

Also worth investing in Lapua brass and a resizing die that will allow you to adjust neck tension, either neck sizing only or if you prefer full length then go for something that will do both such as the redding.

It all makes a difference when shooting long range, a good thing to remember is that you're trying to remove inconsistencies in the whole process.

[Countryman]

I have both Lapua and RWS brass. With the 155gr I am using N140 and TR 140. This works on a settled day.

I have been using these with the 175gr too but I was wondering if this was part of the problem.

I have Benchmark and Reloader 19 to hand.

[Matt]

I used to use N140 but found better results with other powder, you also get better MV for less pressure with RS52, useful if you find an accurate node in the quicker speeds that would have had you with possible pressure problems with N140 (which is still a good powder for 308)

I tried 175SMK once, still got most of them in a box once I'd pulled the remainder after trying them at 1000 (don't know of any FTR shooters using them in competition)

[ovenpaa]

The AE with standard 24" Border barrel performs well with the Lapua 170 Lockbase which is still available over here, a reasonable load of N540 behind it does the trick and my original AE shot well with such a combination for years.

Incidentally the 170 Lockbase was the basis of the original Lapua .308 HPS (High Performance Sniper) ammunition used in theatre and is also still readily available as is the latest 170HPS ti and both run at around 2750 with the later ti being less temperature sensitive.

[Racalman]

I have a Rem 700 with AI stock and Armalon barrel, 1:12 twist.

A couple of years ago I started using 185gn Berger Juggernauts at 1,000 yards and they consistently give me high scores in our club's snap shoots.

My load is 45gn Viht N550 (YEMV) which gives a modest MV of 2650fps but thanks to the bullet's excellent BC the calculated velocity at 1,000 yards is 1250fps. It's a very stable load which doesn't burn out the barrel.