OzFclass

G'day All,

At the beginning of 2016 I tuned a 168gn VLD load for my 32" .284W. The barrel before this tune had 220 rounds on it. I finished on 52.0gn of ar2209 @ 2940 fps with brilliant accuracy and waterline @ 100y out to 600y. At 100y it would drill a small rugged hole, 300y out to 600y was capable of high X counts. One of those tunes you feel absolute confidence in with good conditions.

I haven't shot it for a while. Admittedly the last couple of shoots with it weren't brilliant and I thought I was out of practice. I shot 300m Fly on Saturday and was left baffled at its lack of performance in mildish but switchy conditions. It had terrible vert and seemingly ghost winds kept moving it a lot.

When I got home, I cleaned and pasted the barrel and borescoped it. The lands and leade still look quite good. Barely any fire cracking, no gouges or scrapes from rods, etc.
I loaded up a powder charge test of 5 shot groups from 52.0gn to 52.7gn in 0.1gn increments. I've been using the same powder batch, bullet batch, primer batch and cases.
I went to the 100y range this morning to re-test. 52.0gn shot awful groups and the MV is now down to 2865 fps Ave. 52.7gn is 2920fps and the groups closing up tighter again. It's still to be seen if I can get the groups AS tight as they were.

I have been keeping this barrel very clean between shoots and short stroking the throat with paste and lightly pasting the rest of the barrel every 200 ish rounds.
The barrel now has 1050 rounds down it.

My thoughts are, "Is this muzzle velocity drop attributed to normal wear of a .284W barrel or more likely a result of overzealous pasting?" I guess I'd have to slug the barrel to work that out?

I've previously been advised on this forum that a lot of shooters will re-chamber a .284W every 1k rounds.

Wondering if anyone has some advice or an opinion on this one for me?

Cheers,
Denis.

Is it the same powder batch?

Rebel105 wrote:Is it the same powder batch?

Yes it is. All components are the same batch numbers as when the 52.0gn load was developed.

At 1050 round count I would give it a freshen up especially now it's "gone off".(take a little off the crown & chamber) FWIW I don't think your cleaning would slow MV.
Have you been chasing the lands as the throat has worn, depending on if you were jamming or jumping, may have some influence on speed but maybe not what you have experienced.

Just a thought Dennis, are you jumping these bullets? if so have you re checked you jump? Perhaps the lands have eroded and your jumping further than you think and thats dropping pressures/muzzle velocity.

Hi guys,

Thanks for the replies. This tune is jammed .005". I do chase the lands. Every time I load ammunition I seat the bullets long, I check the land position every time and set the seating die from there.

I learnt that lesson a long time ago and vowed never to get caught out with that again. I found that in the first few hundred rounds of a barrels life, the lands erode quickly and then they settle down to a ball park rate of a couple of thou. every 150 - 300 rounds, depending on the cartridge, rate of fire and working temp (as in, they last longer if you don't cook them).

Denis,
Did you note somewhere the initial reading of your jammed load and the projectile? Also the throat angle does change when it burns away. It would interesting to know how much your jammed load has changed in length. You keep pushing the projectile out to keep the same tune position but in turn you get more cartridge air space as well.

Rebel105 wrote:Denis,
Did you note somewhere the initial reading of your jammed load and the projectile? Also the throat angle does change when it burns away. It would interesting to know how much your jammed load has changed in length. You keep pushing the projectile out to keep the same tune position but in turn you get more cartridge air space as well.

I do keep detailed load records. Looking back, from 220 rounds to 1015 rounds (loading for the last test), the lands have eroded 0.007". Measurements taken from base to ogive.

I have received some very fitting advice from a reputable shooter today that clarifies things for me. It might help someone else one day with a similar query.

Obviously as usual, all barrels are different and the below numbers are a rough guide.

This shooters experience with his .284's has been that the powder charge needs to be increased by approximately 0.1gn per 200 rounds to keep it in tune. This is with a good cleaning regime including removing carbon every 150 - 200 rounds and chasing the lands.

I've had 2 x .284W barrels that I've worn out. But, through their life I had changed powder, primer and bullet batch numbers a few times which meant that they had to be re-tuned / tweaked periodically.

With this barrel in question, it's the first time that I had purchased the same batch number of all components to last the life of the barrel. Because of that I didn't feel the need to check speeds or short range groups while it was scoring well in F-class.

I believe the re-tuning of the first 2 barrels due to component changes disguised this characteristic that I'm only just experiencing now with this barrel.

I've been caught out and now I know better. I'll be chronographing all guns every 100'ish rounds from here on.

It's a funny game. Just when you think you have a process down pat and a good understanding, you realise that you don't. 2016 was an interesting year for me. A 300WSM that kept speeding up and a .284W that's slowing down.
Thanks to wealth of knowledge on this forum and great people that are willing to share information and help out, I've been able to wade my way through some not so straightforward experiences.

This person has come to my aid a few times now. Thank you very much Champion, I appreciate your help so much.