High Std. Dev. in 204 Ruger

[carrollshooter]

I have a puzzleing problem. My reloads in 204 have a very high S.D. and extreme spread. Shooting a Cooper 21 using Sierra 32 gr., 28 gr. Benchmark, Fed 205M, Hornady or Laupa brass. The SD's on ten shot strings run from the 30's to the 50's with as much as 151 f.p.s. ES. Velocity runs about 4060 f.p.s. I weigh all charges to plus or minus .05 grain. Reloader 10 and 4198 give similar results. Old military surplus WC 846 gives the most consistent velocities but SD is still in the mid 20's. Benchmark gives the best groups at 100 and 200 yards usually averaging in the 4's for five shot groups but vertical stringing starts showing a little at 200 yards and is very pronounced at 300 yards as would be expected with such velocity extremes. I am used to seeing SD's in the 7-15 range for my more careful loads. What gives here?

 

[RonAKA]

Do you trust your chronograph? Have you tried shooting through two chronographs and comparing the velocities?

Edit: Sorry I did not see your comment about normally getting much lower SD's.

 

[carrollshooter]

I am using an Ohler with a proof channel. This is the only cartridge that I am having this problem with.

 

[Laurie]

I've had the same experience with some combinations. The entire 222 Rem family of cartridges is prone to the problem and it looks like .204's greater case capacity and powder charge in relation to bore area has made it worse - no proof, just a gut feeling.

Looking at my handloading notes, there seems to be no rhymne or reason to it at times. Some combinations will produce very similar ES values irrespective of charge weight, while others range from single to three figures across a 2gn charge weight range. Also, it's not uncommon for three shots out of a 5-round string to have a tiny spread (I've even had four with identical recorded MVs) but one or two way, way adrift.

While many cartridges see ES values decline when a powder with a burning rate on the fast side is used, that doesn't seem to apply either. Some of my biggest spreads came from Reloder 10x and H. Benchmark combinations. I can't find a powder anywhere in my notes that would have me think "that one consistently produces smaller ES values" either. It applies to several makes of brass including neck-turned and fully prepped Nosler and Norma, across CCI-450 and BR4 plus Remington 7.5BR primers. I can't experiment with seating bullets into the leade to see if that would change things (either way!) as my Savage LRPV is very long-throated, but at least I know there is no question of some ogives just kissing the leade and others not. It applies equally to several weights of Berger and Hornady bullets too.

So, it's still a mystery to me. I simply quit worrying about it. The rifle shoots in the twos and threes at 100yd with combinations it likes, and I don't shoot at long enough ranges for 40-60 fps spreads to affect bullet strike. At some point in the near future I plan to have a Remington 700SPS Tactical rebarrelled to .20 Tactical, and I look forward to seeing how it compares in this regard. I expect much smaller values from the smaller capacity case, but may be disappointed!

Laurie,
York, England