Temp sensitivity out of accuracy node

[LongWalker]

Took a rifle I'm going to be using in a couple weeks to check zero and reconfirm DOPE out to 300. Load is 30-06 running a Berger 180 EH in front of VV-N550 in Lapua brass at 2851 avg fps.

Reader's digest version is the temp was in the upper 80s and it was walking at 100 for zero and then would do the 2 rounds in 1 round out group. The node is at the higher end and when I put the chrono on it velocities were 10-21 fps over average. I think the hotter loads we're enough to put it outside the node. Load development was done in the spring so it hit the 70s a couple times but not 80 degrees or above.

Load was sub-moa out to 500 verified twice before so temperature sensitivity out of the node is the only explanation I could come up with. And yes I triple checked scope, rings, etc.

Anyone else ever have a similar experience?

 

[Stammster]

Yep. Been there, but usually with load development at warm temps and then actually shooting 20-50 deg colder in the fall/winter.

When I load develop now, I look for a range over 1-1.5 gr that gives similar POI and decent SD and groups, rather than a charge weight that just gives the smallest group size.

When you did your load development, how did the 0.3-0.5 gr higher powder load shoot? Similar POI and group sizes to what you see here?

Other issues could be different lot numbers of components, mirage at higher temps, shooting conditions (bench stability, shooting position), etc.

 

[LongWalker]

The node above this one (.3) is where I started to get pressure signs so I didn't really pay attention to the group during the OCW.

There was a good bit of mirage but I wasn't having issues with the other rifle so I thought I could eliminate that. Powder, primers, bullets all the same from load development.

 

[Stammster]

Hotter ambient temps could mean hotter barrel temps. Might explain the flyer if it was the 3rd shot, but not necessarily the POI shift. How much are we talking (inches at 100 yds)?

 

[DENRIK89]

How old is your powder and are you leaving it exposed for long periods during loading? Powder has a certain (albeit low) moisture content, if left out to dry too long your burn rate can speed up a little. Also as double base powder ages the nitroglycerin moves closer to the surface also affecting burn rate. First thought would be temperatures tho especially when you know every progressive shot heats the chamber and soaks the next round

 

[LongWalker]

Hotter ambient temps could mean hotter barrel temps. Might explain the flyer if it was the 3rd shot, but not necessarily the POI shift. How much are we talking (inches at 100 yds)?

Inch and a half and it wasn't always the third shot. Sometimes the 1st and 2nd too. POI shift was high and right

 

[LongWalker]

How old is your powder and are you leaving it exposed for long periods during loading? Powder has a certain (albeit low) moisture content, if left out to dry too long your burn rate can speed up a little. Also as double base powder ages the nitroglycerin moves closer to the surface (gas out) also affecting burn rate

Powder is a six month old 8lb keg and I load at most 40 rounds at a time

 

[Stammster]

How about wind?
10 mph from the left previously and 10 mph to the right this time could explain 1.5" POI shift at 100 yds, but not shooting higher.

I think you were on the right track with temp effects. Load up some 20 fps less (I.e. 0.3 - 0.4 gr less) and see how they shoot.

Inch and a half and it wasn't always the third shot. Sometimes the 1st and 2nd too. POI shift was high and right

 

[LongWalker]

Wind was maybe 5mph blowing straight in

 

[BrentM]

That is the issue I have found with upper node loads developed in cooler temps. It seems everytime I create a hot load that works in the winter or spring I have issues in the hot temps. Usually its a combo of chamber temps and atmosphere. For example 1-2 rounds are ok, then a flyer etc. For a hunter, temp increase per degree is generally identifiable and correctable, if the load is accurate. If it is not, back off .5 and test back up in .2 or just drop .2 and see how it goes.

 

[Mikecr]

This is where cold bore development comes in. You don't need to group shoot at animals.
So where is the cold bore shot hitting w/resp to POA (accuracy)?

 

[Sheldon Root]

Hi there. A Canuck buck here. I know there are claims of stable powder not being temp sensitive. I am not disputing that but something is going on, when a bullet is lit up, when the temp. is in the 40's or in the 80-90 range. As example: A friend and I were at a 600 yd. range on different occasions. First time was in Nov., weather was hovering around 42 Fr. I managed to get 2 1/4"group at the 600 yd. Then come May of the following year was there again with the temp. just over 85. At this temp. I could not get a group that was under 10". I am running a 338/378 and had the same load each time. Load is .5 gr over max with no signs of pressure on VV N570 powder, es of 5. The only difference was time of year and temp. So from this you can make up your own mind on what is going on. I can only suggest you work up a load for Spring to early fall/winter load and one for cold weather hunting or use. Best of luck.

 

[LongWalker]

Good point. I cleaned it so I was fouling it first and then hoped just to reconfirm zero and drops at 200 & 300 which would be my longest potential shot.

As my usual fouling routine I shoot two factory rounds then 3 handloads with the V3 chrono on. Since that impacts POI (which I've fixed for every rifle but this one) and then check for zero. I saw the first 3 velocities were all at least 10fps over average. I did let the rifle cool for almost 15 minutes after that string.

First after that was high and left almost 2" for both. Corrected for that and the next shot was good horizontal but about an inch low. Figured that could be anything so fired another round with no adjustment and it was an inch high and almost 2 right. That's when I got frustrated and probably should have quit and come back but I checked scope, rings, action screws then fired another round that was like the very first I corrected for high and left.

That's when I put the chrono back on and saw the temps were up quite a bit. Tired a few more round just to see they were grouping and they weren't so I finally hung it up

 

[BrentM]

Good point. I cleaned it so I was fouling it first and then hoped just to reconfirm zero and drops at 200 & 300 which would be my longest potential shot.

As my usual fouling routine I shoot two factory rounds then 3 handloads with the V3 chrono on. Since that impacts POI (which I've fixed for every rifle but this one) and then check for zero. I saw the first 3 velocities were all at least 10fps over average. I did let the rifle cool for almost 15 minutes after that string.

First after that was high and left almost 2" for both. Corrected for that and the next shot was good horizontal but about an inch low. Figured that could be anything so fired another round with no adjustment and it was an inch high and almost 2 right. That's when I got frustrated and probably should have quit and come back but I checked scope, rings, action screws then fired another round that was like the very first I corrected for high and left.

That's when I put the chrono back on and saw the temps were up quite a bit. Tired a few more round just to see they were grouping and they weren't so I finally hung it up

Curious was it new reloads or old? Like they have been sitting for a bit.