Weighing charges with electronic scales: a note of caution

[Finman]

Hi all,

 

I thought I'd share with you one of my recent experiences whilst on the range. I was testing some loads for my 6mmBR (built on a Tikka M590LH action, with a Border Barrel). I was shooting a load that I am familiar with and not particularly hot (31.7gn VihtN135, 75gn VMax, Rem 7.5, COL 1.760'), after I had shot another 3 strings of 5 shots. The first shot went where it was supposed to and then I shot the second one.

 

A loud noise came from the rifle, gasses were escaping from the ports, and my ears were ringing. When I examined the round, I noticed a burst primer (and no other signs of pressure). The bolt was not showing any signs of damage, but there was no firing pin protruding... I thought it was broken by the backlash (as it turned out a small piece of brass was preventing it from cocking, and once this was removed all was back in working order again).

 

As you can imagine I was totally perplexed: Had the load been hot, I would have had signs on the first round (no stiff bolt, no extractor marks, no primer cratering). I started tracing the story of this round back. I then realised that this was a batch that I had loaded using a new Lyman electronic scale (apologies, I cannot remember the model but it is the one that can weigh up to 1500gns). This scale, I noticed at a later stage, had the habit of losing its calibration to zero and weigh almost 0.5 grains more than the intended load. I tend to think that this was the reason for having the blowout and, at least, I am thankful I still have eyes (although my left ear is still not functioning properly, having had the gases passing right infront of it).

 

The lessons I have learned:

a) shooting with a moderator is not an excuse not to wear hearing protection (I wasn't)

Tikka makes really strong actions, but I don't want to find out how strong...

c) need to get a pair of glasses (eyes are not sold by Sinclair...)

d) From now on I shall retire the electronic scale and use it only for sorting cases.

e) The beam scale will be my 'baby' from now on!

 

I would be very interested to hear whether you have an alternative explanation for the failure of that load or whether you have had similar experiences in the past.

 

Finman

[ejg223]

I use my Lab scales, also electronic.

These would be from Bizerba with 0,001 gram increment

and cost somewhere around £2000-£3000.

Even with these, I put the empty pan on scales and

look if she is still at zero then fill powder into pan.

Even the best scales seem to have some "slip stick" so

a little tap or touch with the powder scoop to see where she

settles is needed.

We have a very solid chipboard base that is sitting on three silicon

drops on the table to keep level and vibrations away.

Electronic scales can be a nightmare, they way they can lie is

only beaten in politics.

edi

[Andrew]

Finman: Were these loads the first fired in a newly barreled rifle? If so, did you have the chamber cast to check it's dimensions with the loaded round you were using? ~Andrew

[Guest varmartin]

Hi finman.

 

31.7 grains of Vit 135 is not a hot load...and if the scales did add an extra 0,5 grains I don't think that would be an over hot load either ??

 

Did you pull and weigh the other loaded rounds to prove they were over loaded ??

 

May have been a duff primer. I only use CCI BR4 and Federal Match so dont have any knowledge of the Rem 7.5`s.

 

Martin

[6mmBR]

One of the loads I use in my 6BR is 32gn N135 with the 75 V max. No pressure problems however I use Fed Gold Match primers.

Cheers

Dave

[Finman]

Cheers for the responses chaps.

 

Andrew: I have had this rifle for 2 years now and never before had I any trouble with the chamber or this type of load when I shot it in the past

 

6ppc: I did not pull any of the other rounds, but I shall do so to see whether this (wrong charge weight) has been repeated in any of the others. Indeed 0.5 of a grain should not give any pressure problems. One of my 'pet' loads is 33gn VihtN135, 65gn VMax, Rem7.5, COL: 1.770, and that one shoots .2groups all day with no pressure signs...

 

as for the Rem7.5, is a primer that I use only when I use Viht or Alliant powders. For some reason the loads seem to be working better with them than with the Fed205M or the CCI450M. Never before did I have a problem with the Rem7.5.

 

I shall try and find some time to pull and re-weigh the charges in the remainder of that string and see whether they are the correct weight.

 

thank you for your contributions,

 

Finman

[Zaitsev]

I'll second the need to wear ear protection when shooting with a moderator (range) as I had a PES moderator part company with the rifle using .300 win mag full house loads (178gr A max). Fortunately I have most of my hearing back but I had whistling in my ears for weeks. Ditto the sentiment on the eye protection.

 

 

 

 

Z

[nuttyspaniel]

After chronoing my loads tonight and seeing the variance my digis are of the bench and the old fashioned sclaes are getting rigged up!! My scales from cabelas were giving me a hell of a time last night!!! A 19.1grn powder charge would weigh 21.5grns then removed and then replaced it would weigh 18ish grains before trying another charge it would perhaps do the same, eventually once I got the same charge weighing the same twice I would then put it in the case!!!!

[ejg223]

Nutty, I'd rather use a lee scoop than those

scales.

edi

[Guest varmartin]

I also had a set of cheap Digital scales....CRAP or what ?

I tried trickling up a charge on them. It did not work, the read out was jumping all over the place. they are sort of OK if you weigh a case or similar but if you wanna trickle...forget it.

I think you got to spend good money for a proper set.

 

Martin