Range Report 185 groups great at 300 lousy at 1,000 What happen

[Trevor]

Hey

was hoping for some insight into what happened.

I recently developed a load for 185 class bullet the chrony showed 2,800+ in a 308 win case, (SG according to JBM) is 1.162. G1 .525(no G7 reported as of yet was estimated to be .270). Again using JBM I am supposedly reaching 1,400fps at 1,000 yards. Even accounting for errors in the chrony I was above 1,100. Initial testing showed the load was excellent my best groups at 300 yards. Took them out to 1,000 and I could hardly keep them in the 8 ring it wasn’t simply vertical either shots would be high left low right water line left and right. Now I had my 155 load with me and twice when I went from shooting the 185 to 155 the 155 would shoot X’s while the 185 were all over.
Conditions on testing day were ideal, 78 degrees, blue skies, light mirage 1-3 mph winds. 500 ASL

Bullet is a Flat base not the typical boat tail. Which is supposed to transition better between supersonic to transonic into sub…

The low SG is because I have a slow twist barrel 1-14 but even with the slow twist I was above 1 and they shot excellent at 300. does anyone have any ideas.

I know 1.4 SG is the standard but this is a fair weather rifle and will never see below 32 and most likely never below 45 degrees.

Thanks
Trevor

 

[MontanaMarine]

Re: 185 groups great at 300 lousy at 1,000 What happen

I'd guess the 1/14 twist just isn't cutting it as the bullet slows down.

 

[MontanaMarine]

Re: 185 groups great at 300 lousy at 1,000 What happen

Stability factor of 1.16 is really on the verge of unstable. 1.3+ is where you want to be.

 

[LawnMM]

Re: 185 groups great at 300 lousy at 1,000 What happen

I would agree with Montana, you are shooting a heavier bullet with a slow twist barrel and the bullets are destabilizing in flight.

 

[Xcount]

Re: 185 groups great at 300 lousy at 1,000 What happen

Trevor,
a FB 185 bullet has less wind fighting ability, they are known for short range accuracy only, so what gains you would make in increased BC would be lost to wind at 1000 anyways. a 14 twist, even a 30 inch Palma, is probably not going to stabilize a 185 and especially near sea level. my closest 1k range is 5k'asl so you might get away with it here, but there is never, ever 1-3mph of wind.

seems to me you pushed too many factors out of the known norm's, 185 typically needs 12 twist for most conditions, and flat based bullets are typically used for 100 and 200 yards benchrest.

 

[ChadTRG42]

Re: 185 groups great at 300 lousy at 1,000 What happen

Yes, the bullet is unstable at that range. We've had the same issue with the 208. It shoots awesome at 600 and in, but at 800 and out would fall apart with a marginal twist rate and short barrel. You need more twist for that bullet. Stick with the palma 155's and you'll be ok.

 

[Trevor]

Re: 185 groups great at 300 lousy at 1,000 What happen

thanks guys

i have a 13 twist on order should be getting it this week and will see if it can stablize these bullets.

I also have a pratice session out to 800meters this weekend so i will see were along the yaradage line the bullet falls off.

Trevor

 

[sinister]

Re: 185 groups great at 300 lousy at 1,000 What happen

Flat base and slow twist is definitely not going to cut it.

Try at least a 1-11 (1-10 probably better).

The flat base is going to give you drag -- I doubt you'll get 800 yards with accuracy

 

[Tactical]

Re: 185 groups great at 300 lousy at 1,000 What happen

My 1x11.27 twist is handling 185s at 1000 yards well but I am pushing them around 2800 fps

 

[TiroFijo]

Re: 185 groups great at 300 lousy at 1,000 What happen

Tactical, that's a boat tail 185 gr bullet (lapua??), right?

 

[Tactical]

Re: 185 groups great at 300 lousy at 1,000 What happen

Yes, 185 Scenar or 185 FMJ both Lapua

N550 or Varget for powders out of an F TR Rifle so loaded too long for magazine use, in 308 Win, in Lapua case