Help - QuickLoad 80gr Barnes .243 TTSX IMR4350 Load Calc?

[wytonpjs]

Help - I'm after a big favour pleaseeeee.......

I have a 20" barrel Sako 75 in .243 that I spent time on a range on Saturday firing off a ladder of IMR4350 with 80gr Barnes TTSX. Speeds (Magnospeed V3) were a little disappointing (not a surprise many will say with a 20" barrel) and my max tested load of 42.5gr yielded only 2876 fps. For obvious reasons I'd like to reach a minimum of 3100 fps for legal use on roe as well as muntjac. I have just run GRT and it says a 43.0gr load of IMR4350 should reach 3123fps (personally sceptical since the 42 load measured an average of only 2831) but more worringly, it says that the 43gr load is overpressure (4166 bar).

Could anyone check these parameters and advise what QL says please? All rounds fired at 42.5 showed absolutely no signs of pressure and the bolt operated freely (as always).

Many, many thanks

BTW - to forestall the obvious, I'm sitting on large stocks of IMR 4350 and 4895 I'd like to use up in preference if I can but, if the answer due to barrel length is to move to a REACH compliant powder, so be it as this is a lovely handling rifle.

 

[Andyquadra]

What's your COAL?

 

[wytonpjs]

What's your COAL?

Measured to the ogive, 2.140" (exactly the same as factory VOR-TX rounds)

 

[wytonpjs]

After a very useful pm, I've measured my .243 reloaded brass (mixture of Sako/Norma but all the TTSX loads are with Sako cases) and my COAL is actually 66.34mm with a case length of 51.92mm. The TTSX heads measure 27.52 and not 30.49 as per GRT and I'm also guilty of not putting my exact case figures into GRT; the actual bullet seating depth is 13.1mm. If I re-run GRT with these specific values it still gives me a 100% burn within the 20" barrel and whilst the pressure is very near max, its not now over-pressure. Importantly, it also suggests a speed of 3116 fps which will meet the minimum legal roe muzzle energy I seek. Revised picture attached:



Whilst this is very close to maximum pressures, its not now over-pressure.

 

[borbal]

For what it is worth, I just ran your numbers through P-Max, using a usable case capacity of 47.54 grains H20, (the same as the "Combustion chamber" in GRT), and I got a predicted muzzle velocity of 3162 ft/sec, which is close enough to be generally in agreement with GRT. The maximum pressure in P-Max was a little lower at 3671 bar. That shows that the powder models in P-Max and GRT are very similar, via separate channels of research.

Do you have access to another chronograph...?

 

[wytonpjs]

Do you have access to another chronograph...?

Many thanks @borbal

Sadly no although I might ask a colleague............. Someone else did wonder about the battery but although it was only reading 7.4v (9 volt PP3) all functionality worked and I'd expect it to be a cliff-edge issue, it either works or it doesn't rather than being inaccurate. Another random thought of mine is that the powder is quite old - it has no smell/discolouration but could ageing account for a 7% performance reduction? It was fairly consistant at ~200fps low (6.6-6.9%) across the ladder...........