Lands shifting..

[gixer1]

I noticed a bit of a drop off in velocity in my 6.5cm load - nothing wrong with the accuracy, it just slowed down by about 100ft/sec…I had a node at 2,665ft/sec with 140gr ELDM’s and 42.5gr of RS62, SMRP’s and seating at around 2.190” OGIVE which was a .067” jump.

I noticed recently that the velocity had dropped a little, accuracy is still good, so I decided to measure the lands again with an OAL gauge.

The lands are measuring at 2.277”…whereas when new the lands measured at 2.257” (.020” change)

The rifle has fired 1,267 rounds, would this be a normal amount of wear to lose .020”?

My plan is to increase the length to 2.210” and then go in .1gr increment charge increase until i get back to the node and see if it’s at the same velocity.

regards,
Gixer

 

[Andyquadra]

Sounds plausible

 

[andy R204]

Accuracy would be more important to me.
My 6mm br when relatively new I switched to 87gr Vmax with a 35th jump.I did OAL measurements to the lands last year & to get the same jump to the lands I'd have next to nothing in the case neck.
My gunsmith told me to not chase the lands if your loading with a jump into them with your "pet" load.
My FPS is still the same 3070 FPS as it was when it was developed around 3 year ago.

 

[Utectok]

If it still shoots we’ll leave it alone? I think chasing the lands is pretty old skool. These days I’ll shoot the same load till the barrel is shot out or they become inaccurate

 

[gixer1]

If it still shoots we’ll leave it alone? I think chasing the lands is pretty old skool. These days I’ll shoot the same load till the barrel is shot out or they become inaccurate

It’s more the drop in velocity that I don’t like - I want to get it back up to 2650-2700fps if I can get a node there…

I was just a little surprised that the lands shifted .020”…but I guess after 1200 rounds that’s not a big deal…

 

[Ronin]

Perfectly normal wear

 

[Utectok]

I’ll be honest mate I’m not even certain there is a lot of evidence nodes exist. If you shoot enough to properly define nodes you actually see a fairly direct relationships between speed and powder charge. Nowadays I pick a speed I like for other reasons ie terminal performance or to retain supersonic speeds beyond 1k or something and, so long as it’s safe, load to that speed. If it doesn’t shoot accurately I change powder or primer or bullet and spend very little time on COAL save to give copper more jump than lead. I’ve done all the length and lands and node stuff and all I did was waste ammunition and time really. You can kid yourself with 3 shot groups that something is actually happening but it’s not really.

 

[Andyquadra]

It’s more the drop in velocity that I don’t like - I want to get it back up to 2650-2700fps if I can get a node there…

I was just a little surprised that the lands shifted .020”…but I guess after 1200 rounds that’s not a big deal…

The drop in velocity could just be a temperature sensitive powder?

 

[andy R204]

The drop in velocity could just be a temperature sensitive powder?

Good call that Andy

 

[gixer1]

I’ll be honest mate I’m not even certain there is a lot of evidence nodes exist. If you shoot enough to properly define nodes you actually see a fairly direct relationships between speed and powder charge. Nowadays I pick a speed I like for other reasons ie terminal performance or to retain supersonic speeds beyond 1k or something and, so long as it’s safe, load to that speed. If it doesn’t shoot accurately I change powder or primer or bullet and spend very little time on COAL save to give copper more jump than lead. I’ve done all the length and lands and node stuff and all I did was waste ammunition and time really. You can kid yourself with 3 shot groups that something is actually happening but it’s not really.

There are definitely nodes…one of the best things I bought was a Garmin, makes it way easier to see and figure out ES drops…and it correlated with the most accurate loads from what I have seen.

And it’s not 3 shot groups, it was 5 and as I said it’s been a accurate rifle since but just the change in velocity has changed all the settings for longer range.

Regards,
Gixer

 

[gixer1]

The drop in velocity could just be a temperature sensitive powder?

Nah, it wasn’t just in the colder weather…I’ll report back once I’ve tried extending the length and ladder tested.

 

[Utectok]

There are definitely nodes…one of the best things I bought was a Garmin, makes it way easier to see and figure out ES drops…and it correlated with the most accurate loads from what I have seen.

And it’s not 3 shot groups, it was 5 and as I said it’s been a accurate rifle since but just the change in velocity has changed all the settings for longer range.

Regards,
Gixer

I’m quite wary of making judgments on ES or SD from low sample sizes. About 30 shots gives you some decent evidence. What I found was a lightly compressed load brought down SD quite a lot. Garmin is quite amazingly useful right! I guess nodes vs sample sizes is the question I’d say ten shot minimum but each to his own mate so long as your enjoying it and learning right.

 

[ColinBr]

Temperature lower than when you first built the load?

 

[gixer1]

Temperature lower than when you first built the load?

Nah, not especially Col.

 

[Greenmist]

I have a picture somewhere of two rounds from my .22-250, one just off the lands when I did the first load development, the second just of the lands when it was sent for a rebarrel, there is a visible difference after a few thousand shots

 

[gixer1]

So I guess the drop in velocity could be some pressure escaping past the bullet before it has a chance to contact the lands?

 

[Andyquadra]

What powder are you using?

 

[Utectok]

So I guess the drop in velocity could be some pressure escaping past the bullet before it has a chance to contact the lands?

Lots of things can change MV in my experience. Sometimes it’s barely detectable changes to the interior of the barrel sometimes it just needs a bare metal clean? Sometimes it’s a different batch of powder or anneal regime. Consistency is more important than speed?

 

[jthyttin]

So I guess the drop in velocity could be some pressure escaping past the bullet before it has a chance to contact the lands?

Rather the longer jump allows bullet to accelerate and having greater speed when contacting lands. This results in lower pressure (for powder burn) and thus lower MV.

 

[Bavarianbrit]

Perhaps the barrel is unscrewing see my other post.