So my first post here will be asking for advice, not the best way to start out I know but since I'm new to Long Range shooting and there are many people with more knowledge than me I decided to ask.
So here is the question. I'm shooting a custom sporter weight barrel out of 300 RUM. I have great accuracy with a few loads I've worked up IF I let it sit for 45 min. between shots. I've shot all types of combination of loads and without fail, the first two shots are good and the rest are all over the place mainly 2-3 inches high at 300 yards. I let it cool a few hours don't clean it or anything and the next shot is back on track. My velocity is consistant etc.. The only thing I can think of is that for some reason when it gets hot it may be pushing on the stock or something, but there is plenty of space between the stock and barrel, so I'm not sure if it is just taking more time to cool than normal.
Any help or helpful hints appreciated, thanks,
Definitely sounds like a stress issue. How good is the bedding? Is the bottom of the recoil lug free ? (it should have some clearance). How much space is between the stock and barrel? Can 2 business cards freely slide all the way back to recoil lug?
If some is good and more is better, then too much is just right.
My mind is a raging torrent, flooded with rivulets of thought, cascading into a waterfall of creative alternatives
So what's wrong with asking for advice? From your description of the problem, I can think of a couple things that could be an issue here. AJ's spot-on about the stress issue, but it doesn't necessarily mean that there's only a problem if the barrel warps enough to be making contact with the stock. That, I'd call a huge problem. Your barrel can have stresses within it that simply show themselves once the temps start gettin up there a bit. The barrel is moving as it "un-stresses" itself, causing a shift in the POI downrange. Once you let it cool, and the barrel re-establishes it's normal state, it comes back into zero. repeat the process, and it'll move again. Light barrels are somewhat more subject to this than heavier barrels, but none are immune to this sort of behavior.
The heat itself can also be an issue, entirely aside from the stress question of the barrel itself. Even a very good quality, stress-free (as possible) barrel will show accuracy degradation when it gets hot. Near and dear to my heart, as I spent the earlier part of the week watching some initial firings in a new test range. The rifles were all top quality, fired from a RTB machine rest, using excellent quality factory Match (sniper) ammo, and being shot in an indoor 300 meter tunnel. In otherwords, no real outside influences to muddy up the works. We were monitoring temps with an IR thermometer, both at the muzzle and over the chamber areas throughout the test. Without fail, the larger groups showed themselves once the muzzle became too hot to comfortably grasp for a few seconds (around 135-140 degrees). The groups were still passing spec, but there was a definate, and repeatable correlation between larger groups and a hotter barrel. These were dedicated heavy barreled sniper rifles. A lighter sporter would most likely show this sort of tendency a bit faster, and possibly in a more pronounced fashion.
As AJ had suggested, make sure the gun is sound; no bedding issues, proper floating of the barrel, etc.. Beyond that, I'd suggest that you just take a bit more time on the range, and don't rush a warm barrel. If in doubt, go talk to another shooter for a few, and let it cool down a bit more. Avoid long strings of fire for a hunting rifle, since you'll never need them anyway (not always the case for competitive shooter; we're usually stuck with 20+ shot strings, like it or not). Remeber, especially for a hunting rifle, the first shot from a cold bore is probably the only one that'll matter. The only other (possible) solution here would be a new barrel, which would be a waste since it sounds like this one is shooting well when it's not hot. Strictly a last resort there, and I wouldn't rush into it lightly.
Hope this helps, or at least gives you a few things to consider,
I appreciate everything so far.. It is a pretty new barrel 2 months but I've put over 300 rounds through it, with never more than 3 quick shots, 90% of my shots are at least 7 min. apart. Usually more like 15. I checked the spacing on the barrel and it has plenty of room until the last 2 inches before the recoil lug, then it gets a touch tight but I can still pass 1 business card through all the way. I am ecstatic about every cold shot hitting in the same place, because it will be for hunting, but I know it will shoot better, longer. I will recheck all the work, my gunsmith did an awesome job, very reputable, so I don't expect anything major, hopefully something small.
Here is an example. I shot 2 shots before work yesterday that were touching at 300 yards 15 minutes apart... I waited another 15 min. shot my third 3 inches high, waited 15 min shot my 4th 2 inches high. Went to work, did nothing with the rifle, after work went out shot two more shots within 1/2 inch of the original two.. Waited 15 min. next couple 3 inches high, that has happened multiple times with various loads and bullets. .. AGAIN I'm not complaining tooo much, it shoots good but I figured something must be a little wrong. It is a schneider barrel with a Hi tech specialties stock with muzzle brake, could the brake have an effect possibly?
Location: The rifle range, or archery range or behind the computer in Alaska
Re: I need advice
Another vote for potential stess.
It could also simply be the load or loading tequniques.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.