Affect of a hot barrel?

jesheba

Is there a predictable affect on a bullet's flight as a barrel gets hotter? Will it tend to drift in a constant direction? I'm talking long range rifle shooting.How many shots on average will it take to start making a difference in a group? How long should one wait between these cycles?(On a summer day-85 degrees)Why does this happen?Is the powder in he cartrige affected by the heat in the chamber as well as the barrel dynamics?

Randy Summers

rsnyder55

When and how much depends on the barrel. In my experience with my 300WM, the drift is not consistant. I experience drift after three shots, but it being for hunting, this is acceptable.

It is my understanding the part of the effect is due to the expansion of the metal of the barrel as it heats. This causes a physical change in the barrel as well as affect the barrel whip harmonics ala BOSS by Browning.

I am sure this will start a long thread of other responses and you will get your answers.

leeblackman

I'd think that metal expands when it gets hotter, so will your groups. Just predict the circle of your group getting bigger and bigger. That makes for an interesting test though.

Borrow someones multimeter with a thermometer on it.

Using the same ammo, measure your group size as temperature increases. See if its consistant.



If I'm wrong please correct me, I won't be offended.

The sound of a 12 gauge pump clears a house fatser than Rosie O eats a Big Mac !

Rocklobster

Makes sense. The metal expands, the bore diameter increases, the bullet rattles around more as it travels down the barrel...

rsnyder55

Another factor in barrel expansion is a freefloating barrel making contact with the stock. If the barrel is already touching the stock, then there would be increasing pressure against the barrel at this point. This pressure against the barrel would cause a torquing effect between the contact point and the action and shift its point of aim.

E.Williams

I dont know but I would think that on rifles wih alot of powder in the cartridge that the rifling would begin to accumualte unburned powder and residue lessening the contact with the bullet.If Im way off tell me cause I know more about handguns than rifles.But coupled with the heat this could play a role in drifting rounds.Maybe?

Eric S. Williams

ranahan

I have looked into this subject a bit though I'm no expert.What I have learned so far is this. The movement of the rifles' zero as the barrel heats is not due to expansion of the bore but to inconsistancies in the molecular composition of the steel which cause the barrels' harmonic vibrations to change as it heats up. The lighter the barrel and the more inconsistant the steel, the greater the change from heat. This is why all target barrels are heavy and the best barrels or those owned by those who insist on the best,whether for target or hunting will be cryogenically stress relieved. This is a computer controled process that takes the steel down to -300 degrees F and then slowly up to +300 degrees F and then back down to normal. this takes about 40 hours I'm told and it rearranges the molecular structure of the steel so that it becomes even and consistent throughout, giving the barrel the same harmonics throughout a wide temperature range and usually reducing group size by 50%.
First thing to do though is to have a good gunsmith (or you can learn this) bed the action into the stock real good, freefloat the barrel and then "tune" or blue print the action (definitly gunsmith's work). That stuff should bring any good rifle down to 1" groups if you've got a good trigger. THEN if you gotta have 1/2" groups or less, cryo the barrel(or barrel and action together). Actually, cryo treating a rifle or barrel isn't that expensive. If you're doing all that other stuff at once, it won't add that much to the cost and it does make a lot of difference. For a complete discussion of this and other accuracy matters look at . It's the best gunsmith's site I've seen on the web and he cryo treats guns. I haven't yet found a gunsmith in Arizona that can do it.

ranahan

ranahan

Well, they deleted the URL of the gunsmth's site I mentioned so if you're interested in that you can e-mail me Randy at rtaylor3@flash.net and I'll give it to you.

ranahan

11echo

I hate to dis-agree with Mr. ranahan But I've read the that "cryo" dip doesn't NOT effect accuracy. I got this form the Shilen Rifle Barrel Company...
"If you have heard that the cryogenic treatment stress relieves steel, this is false. We have measured the residual stress in 4140 and 416 steel with a process called x-ray diffraction. After much R&D, we have not been able to measure any changes in molecular stress after cryo treatment. For this reason we do not endorse the cryogenic process, but we can safely say that it is not detrimental to the barrel either."
I have heard on certain weapons heat causes problems with accuracy ...mini 14 etc. But I thing this is a function of how the barrel is mounted in the stock. My 2 cents, Good Luck! ...Mark


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