Temperature and Peak Accuracy

[skipper]

I took a small thermometer to the range today to see what temperature my barrel was running. I noticed that if I kept it about 90 degrees my groups were smaller and more consistent. The outside temperature was in the low seventies while I was shooting. I was measuring the temperature just in front of the receiver. Has anyone else done any experimenting with barrel temps and accuracy with the 204?

[Hawkeye Joe]

I have noticed the same thing. Never measured the temp though. My I mean "our" Benchmark load does NOT like the outside temp above 85 degrees.When above 85, my groups open up considerably because I can't control or keep the barrel heat constant.Even with my little fan,No dice. On a 70 degree day I shoot 5 rounds one after another, Then one every 4-5 minutes after the initial heating. I'll bet it puts my barrel at about 90 degrees . I don't think there's room for a thermometer on my range cart. Yesterday, I broke a weld on the handle . I guess a 17lb gun in a 22lb case was too much .

[skipper]

Yesterday I was really trying to find out why my groups have opened up. I seem to be having some kind of problem. I can’t hold them in a tight (one hole) group for some reason. The thermometer was just so I would know if it was a temperature related thing or not.

I was, again, testing VV N-133 and Benchmark. It's amazing how similar the loads were considering the charge weight difference. I was running 24.3 gr of VV versus 26.8 gr. of Benchmark. Both loads were running right at 3900 fps. What was real funny was that the ES was smaller with VV but the groups were smaller with Benchmark. It's hard to argue with group size even though the numbers tell a different story. What's a guy to believe? Anyhow, it was also interesting to watch the groups open up once the barrel temp started to reach 100 degrees. Both loads reacted the same to the temperature. I'll be taking the thermometer from now on. I wonder if there is some way to permanently mount it to the gun.

Towards the end of my range time I found that have started to restrict the recoil of my rifle with my thumb. I had noticed that I wasn't having to push the rifle forward after each shot. At first, I thought I was just doing it subconsciously after firing since I do it so often. But I soon realized that I was holding the rifle from recoiling with my thumb. That was making the rifle jump since it couldn't recoil to the rear. Now I just place the tip of my trigger finger on the trigger and pull without pinching. Problem solved. It's amazing the bad habits I pick up even though I know better. Now that the rifle can recoil without restriction the groups tightened up again. With a one ounce trigger I don't really need my thumb to help pull the trigger anyhow.

I know what you are talking about with the broken cart. Now that Jaxon is trying to become a benchrest shooter, I have twice the gear to haul around. He has run out of loaded ammo so he has to reload for the first time this week. This ought to be interesting.

[jo191145]

With the tiny size of groups you two guys are shooting you might want to utilize a tip from the BR world. Adjust your powder charge to the outside temperature.
Mike, you'll have to wait a while but the next time the outside temp goes over 85 try loading .1gn less Benchmark. Skipper as the Houston winter turns from scorching to comfortable you might need to bump up a touch.
As for Benchmark have either of you gents ever fired an Audette ladder at 200 yds with it. (Very enlightening stuff) I cannot remember my old results with the 35 Bergs but using 40 Bergs the super accurate node is only .2gns wide. If I had not fired a 5 shot test group at that charge I probably would have overlooked it on the Audette (2 shots in the same hole at 200 in .2gn increments) Average 25.3gns for the 40 Berg. I'm quite willing to bet Mikes load falls into that same small node for the 35's. Skippers gun is a whole different entity and theres no way I could guess on that.

With WS2 coated 35's in another tube I found pinpoint accuracy at 27.1gns. Without cleaning the barrel that node dropped down to 26.9 gns as the barrel fouled. No Audette ladder at that time as I was only shooting at 100yds. Just chasing the group over the course of a few weeks. Skipper that combo produced at least one zero for me with an ES over 120. At 100yds ES does not seem to matter with the 204. Consistent bore condition and consistent and correct neck tension. With your bullet jamming Panda the neck tension thing should be less critical. Amount of jam will be a factor.

I shot quite a few Audette ladders the few weeks prior to the Postal Shoot. Why? I was slightly changing neck tension through various means to see the change. That small node never disappeared but the charge weight did flucuate slightly as did the overall Audette test size. Always two shots at least touching at two hundred.
There are other nodes of course and larger nodes but not quite as accurate.
The reason I botched the Postal is I cleaned the barrel (I think thats why) I had not cleaned it for all my testing with BM and I shoot fast and dirty. I try to develop my loads hot and dirty so they'll work hot and dirty.
I've never seen a correlation between barrel heat and poor groups. That does'nt mean it does not exist just that my loads are not consistent enough to tell. The pros say it does. But they clean/cool every 6 or 7 shots. Not my style I guess

[rayfromtx]

I shoot Comp. BR. When the temp or humidity goes up I load hotter. It seems to need more powder when the air is less dense.

As to the barrel getting warm and opening up the groups, that's nothing new. It happens to me all the time. I sure am enjoying this cooler weather.

[skipper]

jo191145

I did bump the Benchmark up a little. I went from 26.5 to 26.8 gr. I bumped the N-133 down a little though because back during a ladder test I noticed a node down around 24.3 gr. I was shooting 25.1 gr. of N-133 for the Postal Shoot. And yes, I will be headed to the 200 yard line next weekend. I have decided to stick with Benchmark. I should have stayed with it for the shoot. The N-133 advice had me going for a while. It just isn't working out even though the difference has to be measured with a micrometer.

My shooting is kinda like my golf swing. I pick up bad habits sometimes and have to go back to square one and figure things out. Now that I know what I was doing wrong, I should be back on track. I'll keep the thermometer handy.

[jo191145]

rayfromtx
Always lookin to learn. Is that the general consensus among BR shooters? Temp rises powder charge does also. I quess I always assumed it would be the opposite. Ya know the temp sensitivity thing where heat creates more velocity.

Skipper
I know what your saying about the Viht. N-135 has given me a zero or two at 100 and a .140 something at 200. I had a bunch of rds left over from the first egg shoot I used 135 in. At home I was shooting group after group hot and fast at .25 moa at 200 yds. I was hooked.
Been a strange rollercoaster ride ever since with my results getting steadily worse with an occasional ray of hope. Not to mention the brass woes. In reality its not that bad but its easy to get spoiled. One unexplained flyer and I'm disappointed.
I switched back over to H-4895 then BM myself for the last half of the season.
The thing I do not like about BM is the low velocity I'm getting with the 40 Bergs. I really noticed it at the last egg shoot. The wind was gusting and switching all day. I was getting great groups on the sighter but the POI was changing all day with the wind.

Now that the season is over I'll try the N-135 again but I'm not gonna beat myself up with it. I can always shoot BM when the weathers calling for calm and H-4895 or higher node BM if its gonna be windy. Lots of other powders too.
Trying different combos is what I do for fun. Pretty wierd huh.

[Hawkeye Joe]

I have the same issues with the 204's fluctuating ES's. It doesn't seem to dictate group size though so I ignore it. I keep the 35's around 3820-3850 FPS. Now my 6.5/284 will have single digit ES's and still shoot like crap .Maybe it's the full case helping . I picked up a range data log book from Sinclair to help keep track of what's going on. My target file was a fire hazard! A while back I had a flexable thermometer strip on my aquarium glass. I think it went up past 90.

[jo191145]

Mike
I havent shot my 6.5 since the last shoot except for brass retrieval of the rejected match loads which I knew were gonna shoot bad. (and they did) It sure was shootin good at the match though. If it were'nt for the one botched shot by the idiot operator it would have made it to the custom class shootoff. Been takin a little vacation from the shooting stuff.
The 6.5 was getting blown about by the wind too. Similar to the 204 I developed a mild (2650fps) load for it the day before the match with Win 760 ES's can get pretty high with just a half case of powder.
I've found that if my case necks are clean with that super thick Lapua brass it will not shoot well due to excessive seating pressure. If I leave just a little lube inside the neck it groups real tight. I'm just using a standard FL die so I cannot change neck tension easily. I do plan on giving the brass a slight neck turn which may help just a bit but most likely not.
Gonna be fun trying the sexy stuff and warp speed!!

[rayfromtx]

Jo-
The consensus seems to run contrary to what I do. Over on benchrest.com they have a thread going right now about this issue and are in agreement not only to load cooler in the heat but how much cooler per 5 degree increment. I'm always trying to learn too. I've only been at this for a short while and have had some beginners luck. I still have a real hard time figuring out how the density of the air in the barrel can affect the tune of the rifle so much. Just 10 degrees hotter and things can change a great deal. Let me cram another half a grain into this case and I'll let you know what happens.

[jo191145]

Ray
Yes I was reading that post last night and scratching my head pretty hard
The way I read post 5 and 8 they're actually not in consensus.
It could very easily just be me though. Very often the light goes out and I require a large hammer to turn it back on.

Just another test to try when the mercury disappears.