Vihtavuori's new powder N555 is in the house!
Ah yes, the fun and excitement of new load development. The experiments begin.....
This first post is about muzzle velocity testing for my first loads fired with Vihtavuori's "new" N-555 in my old Tikka .260 Rem:
(Warning and disclaimer: Everyone knows the drill: Do not assume my powder charge test is safe in your rifle. Read the reloading manual, start at the minimum powder charge, and work up carefully watching for pressure signs. Your rifle will be different than mine
).
Rifle: Tikka T3X Stainless Varmint in .260 Rem
Barrel: Factory original, 1:8 twist, 24 inches, approaching 3000 rounds fired.
Stock/Chassis: MDT XRS
Brass: Lapua fired 6x, neck sized and then neck expanded using 0.263 expander mandrel. (After 5x fired this brass was annealed and full length resized).
Bullet seating felt smooth and even across cases.
Bullet: Lapua Scenar-L 136gr.
Bullet seating depth: 0.004" off lands. (found to work well with this bullet and H-4350).
Chronograph: Magnetospeed V3.
Vihtavuori online reloading manual for N555 and 136gr Lapua Scenar states:
Min load = 40.1gr. V0 = 2523 fps
Max load = 44.3gr compressed. V0 = 2802 fps
The bench setup:
In our deep cold winters here, I am fortunate that my local range has a heated shooting house for the 100m range. We shoot through window ports with various window port contraptions to attempt to seal the air flow. The photo below shows the bench setup:
I left a gap at the top of the window port so that I could get my hand out and manipulate the Magnetospeed bayonet, and did not replace the cloth blocking the air flow. This was a mistake! That gap caused too much inside warm air to mix with the outside very cold air, resulting in terrible mirage at the scope/air interface. However it is impossible to completely stop the air flow and we are plagued with mirage issues all winter at this range.
The mirage tube on my scope (zebra stripe thing), extends to just shy of the muzzle, in order to isolate as far away as possible from the cold/warm air mixing, but its often not enough.
Mirage Factors: Outside temp was -18C. Inside temp was +17C. Therefore 35C differential air mixing at the window interface, causing intense mirage directly in front of the scope, despite dampening by the mirage tube. Point of aim was blurrily jumping about an inch in all directions, making group size irrelevant for this test.
(I have since modified the window port seal and improved the mirage issue somewhat, and we'll see if that improves things in future thread posts).
The Magnetospeed bayonet likely has an effect on group size. On this rifle the Magnetospeed typically elevates the point of impact by 1/2 to 1 inch at 100m, which was indeed the case this day.
Other factors:
Winds were 15 km/hr, gusting to 30 km/hr. Wind chill was -28C. That wind was drawing heat from the barrel end. Therefore the outside of end of the barrel remained cold, whereas the inside part of the barrel got quite hot. This effect would no-doubt affect barrel harmonics, but its unknown how it would affect muzzle velocity.
Ammo Temperature: Ammo box on the bench is assumed to be about same as inside, about +17C, but there is some cold air mixing around the bench, so it may be a little colder.
RESULTS:
My test loads, 5 rounds each: 40.1gr to 44.0gr in 0.5gr increments.
Data: ("Row" refers to the rows in my ammo box)
Interpretation:
There were no signs of excessive pressure. Primers showed no cratering, and all had rounded edges. One case head in row 10 (44.0gr) did show an ejector mark, so maybe it was getting close.
The clean bore/cold bore fouling round (blue highlight) using Min load was significantly slower, which is typical for this rifle with all powders. Shown for record, but I never use the clean/cold bore data point for stats.
Rows 7 (42.5gr) and 8 (43.0gr) in green highlight had an outstanding ES of 7 and 8 respectively, and SD of 3.0 and 3.3 respectively.
Velocity climbs fairly steady. No obvious "velocity nodes" except for the 0.4gr increment for rows 2 and 3, but I need over 2600 fps so I will not consider these. (The 0.5 gr increment is a little coarse to see fine velocity nodes IMO).
As mentioned above, group size was irrelevant for this first test using the Magnetospeed, mirage issues, and considering the crazy temperature differentials in the barrel.
Conclusion:
Stats-wise, 5-round groups per charge are a small sample size, so take everything with a grain of salt. That said, based on the very low ES and SD I am going to chose 42.5gr and 43.0gr loads for further load development and tune with bullet seating depth. For long range shooting where I may want more velocity, I may work on load development for 43.5gr and 44.0gr charges (orange highlight).
In the warmer weather where the barrel will get hotter and more evenly hot, I would predict the velocities to increase slightly.
More load development to come.....
Ah yes, the fun and excitement of new load development. The experiments begin.....
This first post is about muzzle velocity testing for my first loads fired with Vihtavuori's "new" N-555 in my old Tikka .260 Rem:
(Warning and disclaimer: Everyone knows the drill: Do not assume my powder charge test is safe in your rifle. Read the reloading manual, start at the minimum powder charge, and work up carefully watching for pressure signs. Your rifle will be different than mine
).Rifle: Tikka T3X Stainless Varmint in .260 Rem
Barrel: Factory original, 1:8 twist, 24 inches, approaching 3000 rounds fired.
Stock/Chassis: MDT XRS
Brass: Lapua fired 6x, neck sized and then neck expanded using 0.263 expander mandrel. (After 5x fired this brass was annealed and full length resized).
Bullet seating felt smooth and even across cases.
Bullet: Lapua Scenar-L 136gr.
Bullet seating depth: 0.004" off lands. (found to work well with this bullet and H-4350).
Chronograph: Magnetospeed V3.
Vihtavuori online reloading manual for N555 and 136gr Lapua Scenar states:
Min load = 40.1gr. V0 = 2523 fps
Max load = 44.3gr compressed. V0 = 2802 fps
The bench setup:
In our deep cold winters here, I am fortunate that my local range has a heated shooting house for the 100m range. We shoot through window ports with various window port contraptions to attempt to seal the air flow. The photo below shows the bench setup:
I left a gap at the top of the window port so that I could get my hand out and manipulate the Magnetospeed bayonet, and did not replace the cloth blocking the air flow. This was a mistake! That gap caused too much inside warm air to mix with the outside very cold air, resulting in terrible mirage at the scope/air interface. However it is impossible to completely stop the air flow and we are plagued with mirage issues all winter at this range.
The mirage tube on my scope (zebra stripe thing), extends to just shy of the muzzle, in order to isolate as far away as possible from the cold/warm air mixing, but its often not enough.
Mirage Factors: Outside temp was -18C. Inside temp was +17C. Therefore 35C differential air mixing at the window interface, causing intense mirage directly in front of the scope, despite dampening by the mirage tube. Point of aim was blurrily jumping about an inch in all directions, making group size irrelevant for this test.
(I have since modified the window port seal and improved the mirage issue somewhat, and we'll see if that improves things in future thread posts).
The Magnetospeed bayonet likely has an effect on group size. On this rifle the Magnetospeed typically elevates the point of impact by 1/2 to 1 inch at 100m, which was indeed the case this day.
Other factors:
Winds were 15 km/hr, gusting to 30 km/hr. Wind chill was -28C. That wind was drawing heat from the barrel end. Therefore the outside of end of the barrel remained cold, whereas the inside part of the barrel got quite hot. This effect would no-doubt affect barrel harmonics, but its unknown how it would affect muzzle velocity.
Ammo Temperature: Ammo box on the bench is assumed to be about same as inside, about +17C, but there is some cold air mixing around the bench, so it may be a little colder.
RESULTS:
My test loads, 5 rounds each: 40.1gr to 44.0gr in 0.5gr increments.
Data: ("Row" refers to the rows in my ammo box)
Interpretation:
There were no signs of excessive pressure. Primers showed no cratering, and all had rounded edges. One case head in row 10 (44.0gr) did show an ejector mark, so maybe it was getting close.
The clean bore/cold bore fouling round (blue highlight) using Min load was significantly slower, which is typical for this rifle with all powders. Shown for record, but I never use the clean/cold bore data point for stats.
Rows 7 (42.5gr) and 8 (43.0gr) in green highlight had an outstanding ES of 7 and 8 respectively, and SD of 3.0 and 3.3 respectively.
Velocity climbs fairly steady. No obvious "velocity nodes" except for the 0.4gr increment for rows 2 and 3, but I need over 2600 fps so I will not consider these. (The 0.5 gr increment is a little coarse to see fine velocity nodes IMO).
As mentioned above, group size was irrelevant for this first test using the Magnetospeed, mirage issues, and considering the crazy temperature differentials in the barrel.
Conclusion:
Stats-wise, 5-round groups per charge are a small sample size, so take everything with a grain of salt. That said, based on the very low ES and SD I am going to chose 42.5gr and 43.0gr loads for further load development and tune with bullet seating depth. For long range shooting where I may want more velocity, I may work on load development for 43.5gr and 44.0gr charges (orange highlight).
In the warmer weather where the barrel will get hotter and more evenly hot, I would predict the velocities to increase slightly.
More load development to come.....
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