Thread: .308 significant speed differences?

i have just finished using a new lab radar lx to re-zero all my rifles and iron out the drop sheets. Interestingly (to me anyway) there was around 125fps speed difference from 2 rifles, (2735fps average vs 2602fps) both 16", same box Sako 150gr game head. Both rifles have a known history in the family, very few shots down each barrel and in very good condition. Tikkakoski LSA-55 and Winchester mod 70. Is this unusual? both shot lovely tight groups, just seems a lot to me. Cheers

Is the Tikka the higher-speed ? I'd expect tighter-tolerances than the mod.70 ( both are proven models though , lucky you ) but you can't ask for more than nice tight-groups and the deer won't notice the difference

My model 70 in 270 had very long throat and rather loose bore so in theory would have been slower....

Originally Posted by rewa

Is the Tikka the higher-speed ? I'd expect tighter-tolerances than the mod.70 ( both are proven models though , lucky you ) but you can't ask for more than nice tight-groups and the deer won't notice the difference

Yeah the tikka is higher speed. Was expecting way less to be fair out of 16" but pretty happy with the result and that gamehead 150 is a hell of a round for putting deer down.

Originally Posted by Micky Duck

My model 70 in 270 had very long throat and rather loose bore so in theory would have been slower....

Doesn't matter with .270 mate, the deer often hop in the back of the ute to save you the carry out of respect for gods callibre.

Each rifle is an individual.
It depends on how tight the chamber or the bore is; how long the throat is. Even rifles of the exactly the same manufacturer will show a difference. (In my experience the greatest difference in rifles with the same load is the 7x57 - an old cartridge that has been made in different throat lengths, twists and many manufacturers over a hundred years, and I can get 2950ps with a certain load in one rifle and 2800 with the same load in another, mostly due to longer throat.

I have experienced differences in batches of the same powder that added up to a significant difference as well, needing another half a grain or more to match.

My T3x was spitting same ammo at 2663fps 16” suppressed.

Originally Posted by Northlandnewbie

My T3x was spitting same ammo at 2663fps 16” suppressed.

Arnt T3x slow from factory though? Or is that just an old wives tale?

How many rounds from each did you measure?

Originally Posted by Tentman

How many rounds from each did you measure?

I found the old Gamehead and pro stock used to have around 20fps spread the last lot I ran over Chrony were similar speed but 40fps spread. 10-15 shots of each over a Garmin.

Originally Posted by Tentman

How many rounds from each did you measure?

15 through one and 20 through the other

Originally Posted by Williamfga

i have just finished using a new lab radar lx to re-zero all my rifles and iron out the drop sheets. Interestingly (to me anyway) there was around 125fps speed difference from 2 rifles, (2735fps average vs 2602fps) both 16", same box Sako 150gr game head. Both rifles have a known history in the family, very few shots down each barrel and in very good condition. Tikkakoski LSA-55 and Winchester mod 70. Is this unusual? both shot lovely tight groups, just seems a lot to me. Cheers

Greetings,
This is from what I have read but could explain the difference. Most rifle barrels are cold hammer forged these days and due to a little spring back in the steel have a little choke toward the muzzle. this is likely to vary with manufacturer. I suspect that dimensions are tinkered with to get the barrels to produce roughly factory specs. When the barrel is shortened, especially when the chop is 6 to 8 inches, this choke is removed so the velocity loss can be highly variable. Also those that have progressively shortened and chronographed barrels have found that the loss in not even but varies up and down from an average of around 30 fps per inch.
GPM.

Originally Posted by grandpamac

Greetings,
This is from what I have read but could explain the difference. Most rifle barrels are cold hammer forged these days and due to a little spring back in the steel have a little choke toward the muzzle. this is likely to vary with manufacturer. I suspect that dimensions are tinkered with to get the barrels to produce roughly factory specs. When the barrel is shortened, especially when the chop is 6 to 8 inches, this choke is removed so the velocity loss can be highly variable. Also those that have progressively shortened and chronographed barrels have found that the loss in not even but varies up and down from an average of around 30 fps per inch.
GPM.

Cheers, good logical answer there.

Interesting data…worthy of more research..