I have a question for the DR shooters. Has anyone experienced an increase in impact spread from their double rifle when the bores become hot vs. cold bore shots. ...With my Rigby .450 NE, my cold bore shots are perfect (less than a 2" spread for cold bore). As the bore heats up, by my 4th shot, the spread increases to about 4".
Any winning long range or bench rest shooter will tell you that each and every barrel is unique in how it acts. Boots Obermeyer was a premier barrel maker for 1000 yard match and bench rest rifles. He used the 5R cut rifling. Even with Obermeyer barrels which 99.9% were very accurate, some were more accurate than others. Those rifled from the same maker's barrel blanks could have differences at the molecular level.
This commercial outfit seems to know a lot about this,
https://tacomhq.com/structured-barrel-science/
I can tell you that the above business if NOT the Army’s Tank and Automotive Command (TACOM),
https://tacom.army.mil/
I don’t care for businesses that re-use government organization names, but the commercial TACOM HQ dot com does have significant capabilities.
Cryogenics is a process that deep freezes metals during which the molecular structure may realign to relieve stress. This may de-stress barrels that act differently when they heat up.
https://dsiac.dtic.mil/technical-inquiries/notable/cryogenic-barrel-treatments/
An excerpt from the above US Government (.mil) site,
“2.0 Summary and Conclusions
The topic of cryogenic treatments for firearm barrels (regardless of the type) is contentious. There are several vendors and operators that claim that this treatment is 1) exceedingly useful to increase barrel life; 2) makes the barrel easier to clean; 3) potentially increases muzzle velocity; and 4) increases accuracy (as the treatment decreases shot dispersion on a target). However, a large group of manufacturers, scientists, and operators’ claims that cryogenic treatment does not provide any substantial benefit to firearm barrels, but they note that it will not necessarily harm the barrel and may make machining easier. It may also impart wear and corrosion resistance.
Although there is ongoing research in the material science and processes behind cryogenic treatments for a wide range of steels, specific research into cryogenically treating firearm barrels (specifically sniper barrels) does not appear to be ongoing.
Section 2.1 provides a list of barrel fabricators/operators [15–19]. The cost of cryogenically treating firearm barrels is affordable, usually less than $100 per barrel, although the cost does vary depending on the vendor [20–22]. Section 2.2 lists cryogenic treatment operators.”
If one of my doubles acted like yours does when the barrels heat up, I would consider having the barrels cryogenic treated. That stated, I spent a half hour reading reports of the effects of cryogenic treating of solder. You will need to research this yourself because there are a lot of variables to consider. The solder’s tensile strength may be increased but the solder’s ductility (Ability of a material to be drawn out longitudinally to a reduced section without
fracture under the action of a
tensile force) may be decreased. One report stated the degree of sub-zero temperature affected the solder ductility.
Before cryogenic treating a set of double rifle barrels, I would confirm with those more knowable than myself on how cryo treated solder acts.
