AI AT 308 20" 1:12 : bullets, burn rates and accuracy

[joe.grey]

Hello all,

I've been shooting for years because of my career in the military and as you well know, we used what the military had issued us as rifles. Now that I am retired, I decided to buy myself a precision rifle and begin reloading. As mentioned in the title, the rifle is an Accuracy International, model AT chambered in .308, factory 20" barrel with 1:12 twist.

As of now, I've only shot Federal Gold Medal Match 168gr SMKs (factory loads) out of it and when I do my job, the results were there to support the rifles capabilities. In the past, my experience with the 308 had us use the 175gr pills when we pushed it out passed 700m. And now, having the possibility to try out many new things as a civilian, through reading, I discovered the Lapua Scenar 155gr bullet with its BC of 508...very interesting, but can a 20" barrel help produce that 2950 fps it needs to be stable out to 1000m?

Would a faster burning powder allow a full burn out of that 20" barrel and enough push for the 155 Scenar to reach 2950 fps? Or should I stick to the 175gr pills because of the short barrel?

Thank you for your input, looking forward to reading it.

 

[shoot4fun]

You are not likely to get the number you're looking for with any powder. The F-Class FTR guys are getting very high numbers from the 155 but, I believe, with 30 to 32" barrels.
When I had an AE MKII 308 with that same barrel I got great accuracy with 168 FGMM out to around 800 yards. Then, at the 1000 yard mark, I experience trans-sonic bullet tumble.
Load the 175 SMK (or TMK) ahead of 44.5 Varget in Lapua brass and I think you will be happy.

 

[shoot4fun]

Agreed on the Berger 175 OTM. I use the 185 Hybrid for long range but did my son's rifle shoots the 175 OTM as easily as the 175 SMK (tune wise) and performance is better especially at longer ranges. Another powder to try may be Alliant 2000MR. I have had very good performance with it.

 

[jlow]

I've looked at the 185 Hybrid but I think it is too long and don't think it is recommended for the 1:12 twist of our barrel. The highest BC/heaviest bullet I have shot out of my 24" AT is the 185 grain Juggernaut under 44.3 grain of Varget seated long around 20 thousands from the lands and still fit in the AI mags. MV was around 2,650 fps. Accuracy under 0.5 MOA.

 

[shoot4fun]

I've looked at the 185 Hybrid but I think it is too long and don't think it is recommended for the 1:12 twist of our barrel. The highest BC/heaviest bullet I have shot out of my 24" AT is the 185 grain Juggernaut under 44.3 grain of Varget seated long around 20 thousands from the lands and still fit in the AI mags. MV was around 2,650 fps. Accuracy under 0.5 MOA.

I agree on the Hybrid not being as good for 12 as 10 twist. That is the reason I was recommending the 175. Your velocity/accuracy seem right on to what I found.

 

[joe.grey]

Thank you all for the great advise, very technical and informative and that's what I was looking for. I will look into those Berger 175 OTMs for sure.

 

[joe.grey]

Powders: i live in an environment where temperatures vary from -30 celcius to +40 celcius. Looking at the different powders, I fing that Hodgden seem to offer good choices of powders that are not sensitive to temperatures such as: Varget and 4166.

Varget is reported to vary from lot to lot and there is not much info on 4166 but they advertise it as very consistent to temperature swings because of the Enduron.

Any Opinions?

 

[shoot4fun]

I tried, albeit not seriously, 4166 so I can't really condone or condemn.
My experience with 4451 is much greater and I can tell you it has shown very promising results. Consistent SD and velocities across variables in humidity and temp.
Buying Varget by the 8 pound jug is the best option there.

 

[joe.grey]

Once again, great input! Thank you all. I guess I need to start doing some testing. Looking forward to it. Now to order powder and bullets !

I'll chime in once I've ran a few tests and let you all know how I'm doing. Here's a pic of my new rifle.

 

[shoot4fun]

I presently own an AW and an AX rifle. Same action as the AT and I've never seen a bad shooting AI rifle.
Good luck!

 

[Cujo]

Your scope looks like it might be mounted a bit too far forward. Try moving it back about an inch or so and see how that works for you. Pick up the target adjustable butt pad that will increase your LOP.

Congrats! You'll love the AT and its ability to quickly and easily swap barrels.

 

[joe.grey]

Cujo,

I am 6'3" so in order to get a perfect eye relief for my physiognomy, that's the set up that works for me.