155 Scenars 24" Tikka t3 tactical wierd data

[sharac]

I've ran load testing session and trying to get a fast load for 155 scenars and got some funny results.

Temperature was 26°F with sunny weather, shooting of the table with bipod&sock for rear support. Powder was N540 for all testing loads. I've shot also 185gr/155gr scenar with N140 as a baseline to compare speeds to and two 170 lockbase loads for N540 comparison. Wasn't shooting for groups (my excuse for poor results

) and was really cold so i didn't do all to well.

Forgot to add: All bullets are hBN coated
Primer: RWS5341 LR
Brass: Thun(Ruag) 2.007"
COAL: 2.91" (for 155 only)
Vihtavouri N540

There were absolutely no pressure signs up to 49gr when i got cratered primers, no sticky bolt, no flattened primers and no case head or primer pocket expansion. I am baffled by lack of pressure signs as by all accounts my loads should be WELL beyond max. As for the speed differences i am totally at a loss as speeds for known loads are correct but speeds for 155 from 47 to 49 are not consistent to actual loads (and yes i'm positive i've loaded correctly as i hand weigh each load).

I find it odd as to why no pressure signs and i'm having doubts whether shooting around 47gr (where by my guess node should be despite not being obvious due to poor shooting) is safe. I don't dare to increase load beyond 49,5gr to get other pressure signs as i fear the next sign will be busted rifle...

And also 3000fps with 155gr from 24" is making me doubt my Chrony (too cold for it and started acting up???)

Loads are from 1-3 going from bottom left and up and 4-6 from bottom right to up.

Just to put into perspective (first load accuracy - 185gr) what rifle shoots when shooting from prone and under normal conditions

 

[vman]

Re: 155 Scenars 24" Tikka t3 tactical wierd data

Hbn coating will reduce pressure but still i would not take it 2 grains above max... if your not seeing signs perhaps your not looking hard enough or your bolt is just in such a way that you probably wont get a hard lift on that rifle and bolt combo.

Loads 2 and 5 look decent

 

[sharac]

Re: 155 Scenars 24" Tikka t3 tactical wierd data

The signs should be there as a load i tried a while ago with 185gr Scenars and N540 did flatten primers and also primer pockets were enlarged. I think i will do another round of testing from 46,5 - 47,5gr and watch closely for any signs of overpressure. Also i've found that N540 is a bit more temperature sensitive than N140 so i'll also have to adjust for temperature changes...

For N140 155 load (#2) i had the same problem getting good grouping even with varying COAL (Tikka has long throat - 2.95"). 170lockbase and 185gr Scenar are both very forgiving bullets and they shoot extremely well (it almost doesn't matter what i do the always want to group).

hBN might be the cause of this, i've read that it increases bullet speed :

Patent

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Summary of results

20 uncoated rounds had an average muzzle velocity of 2368 feet per second and a maximum barrel temperature of 120° Fahrenheit. A first set of 20 boron nitride powder-coated rounds had an average muzzle velocity of 2732 feet per secondand a maximum barrel temperature of 138° Fahrenheit. A second set of 20 boron nitride powder-coated rounds had an average muzzle velocity of 2719 feet per second and a maximum barrel temperature of 150° Fahrenheit. The average gain inmuzzle velocity by coating rounds with boron nitride powder was 157 feet per second. The average gain in barrel temperature was 18° Fahrenheit.</div></div>

 

[sharac]

Re: 155 Scenars 24" Tikka t3 tactical wierd data

Also some might find useful new Lapua reloading data, some numbers are revised (especially N540 powder) and new data are more inline with my experiences with N540 (i also wrote Lapua a year ago about N540 powder with no response to 44.9 max N540 and 2900fps speed - impossible IMO)

Link to Lapua site..

 

[Grump]

Re: 155 Scenars 24" Tikka t3 tactical wierd data

Those 155 Scenars seat just like 175 Sierra Matchkings. They are long. Soooo, I wouldn't trust any load with conventional powders pushing them more than 3,000 fps from a 24-inch barrel. Regardless of the ambient temperature.

There are just too many ways for "pressure signs" to be absent when a load it using up our safety margins. Any more, the pressure sign I rely on is velocity.

On top of that, the law of diminishing returns has manifest itself in reloading--more than once--in getting LESS velocity with MORE powder (small increments like yours). I have personally seen it when my Dad was exploring the possibility of reducing port pressure in an SKS with loads of a fast-burning powder. That's another way velocity can serve as a pressure sign.

 

[sharac]

Re: 155 Scenars 24" Tikka t3 tactical wierd data

Thanks for the input i also think anything above 48gr is pointless and really pushing it (also Lapua now confirms that and that i'm not insane - getting 2900 with 44.9gr N540 almost started screaming dude where is that advertised nitroglycerin). I will explore loads around 47gr i think that is the real target.