.284 win: GRT data vs VV official data

[marchx]

VV reloading data shows 57.7gr of N165 is perfectly safe for .284 win whereas GRT show huge overpressure. 180gr bullets in both cases.

 

[jelenko]

Very interesting. Second one you've found, yes?

 

[Stumpy1]

Question(s)? Are you using dimensions for the Scenar L bullet in GRT? Would it make a difference in the final outcome?
Also, the OAL that is spec in both are different by a good bit -would this make a difference? (the OAL difference is a bit more than 0.100").

Not trying to be a richard, but trying to learn. (and trying to learn if simulations are worth the time and money).

Frank

 

[Tangent]

I think the old advice of start low and work up still stands. I wouldn't take any data at face value. Too many variables. No substitute for testing with your particular components in your rifle.

 

[Laurie]

I've used N165 in the straight 284 for years with the 180gn SMK marginally into the lands, and in the rifle's early years, the 180 Scenar-L jumped. Lapua brass (6.5-284 necked up) and the mild PMC (Russian) LR primer. COAL: 3.1-inch; actual fireformed case water capacity 66.7gn. Bartlein 30-inch 4-groove gain twist ending up as one in eight inches.

Early on with the barrel new, I worked up to 57.0gn which gave around 2,830 fps. This later speeded up to over 2,850, maybe a bit more, and a short-range check showed groups had opened up. The charge was dropped and fine-tuned in the 54-55.5 gn range ending up at 55.0 which is what I still use with 2,300 rounds down the barrel and still shooting well. At the time of charge adjustment, that gave 2,825 fps. Throat wear has been modest, the COAL increased to put the ogive back into light engagement sometime between the 1,200 and 1,500 round count level.

I've never had the slightest pressure issue with this combination (irrespective of what QuickLOAD calculates); primer pockets on the original cases are still tight with one batch having been fired 13 times. I don't even FL size, using a Forster Bushing-Bump die (modified 6.5-284 as Forster doesn't make this model for the 284 proper), and bolt opening and extraction are very, very easy (Barnard 'P'). This is 980 ft ASL on an exposed range in northern England, so no very hot days here (in fact, not very many mildly warm days!).

However, to reinforce the caveat that every rifle / barrel / chamber is different, a friend who shot a similar rig (Barnard / Bartlein) in BR Heavy Gun also with Lapua brass (IIRC with the CCI-BR2 and Berger 180gn Hybrids) had to drop charges pronto after blowing a couple of primers with 57gn.

 

[jelenko]

Question(s)? Are you using dimensions for the Scenar L bullet in GRT? Would it make a difference in the final outcome?
Also, the OAL that is spec in both are different by a good bit -would this make a difference? (the OAL difference is a bit more than 0.100").

Not trying to be a richard, but trying to learn. (and trying to learn if simulations are worth the time and money).

Frank

I used the defaults in GRT for Sierra 180 SMK. Shows a peak pressure of 80K - a wannabe Fury.

 

[marchx]

Thanks Laurie. It seems to me that VV data show surprisingly low velocity at 57.7- 2651 fps. 57gr in GRT and 2851fps seems plausible.

In most cases discrepancies between VV website and GRT are within reasonable margin of error. Like the one popular load below in 6.5 creed (13fps difference).

 

[bks22345]

In my 284 with 32” barrel, I ran .4gr ladders from 55 to 57 of N165 on a new barrel. I was getting 2860 at 57 and I didn’t list any pressure signs in my notes. I settled at 55.6 at around 2770 or so, thinking the barrel would speed up. With about 300 rounds on it I’m still getting about the same velocity. I shoot at about 165 MSL and we always have humidity.

I don’t remember if I ran a GRT estimate on it before I started, but my procedure lately with a new cartridge (or barrel/bullet/powder) is to take my laptop with me to the range. After your first ladder group, you can sync GRT to your velocities. That will give you a pretty good idea of where to start looking for pressure issues. It will still be a little off at the upper charges so you may need to adjust again about midway. Not exact but it’s a better guesstimate tool than using the default values.