Warm barrel changing point of impact ?

[jethro75]

I have a Winchester M70 CS in 7mm STW (wood stock). I have been working up loads for it and was at the range today. I ve been getting between 1 1/2 and 2 inch 3 shot groups with it. The thing is I noticed that the first two shots are usually touching or real close and then one flys off(usually to left) and opens the group. I would let the barrle cool before the next group. I then tried not letting the barrel cool down as much but still warm. The first shot hit normal but then the second two hit to the left but where touching, and the barrel was a bit warmer then the usual 3rd shot. I looked at were the forend and barrel meet and could not put a dollar between which I can when cool. What would be the best thing to do in this situation?

 

[dakotasin]

free-float would be first. glass bed the action/lug second.

even better: look at this in context. you have a hunting rifle, and you can get two shots that are very close together. in a hunting situation, are you likely to ever need a rapid 3rd shot? i say no. 2 quick shots i can see, but usually a 3rd rapid succession shot is uncalled for. hunters should've practiced and zeroed prior to the season, not on game during the season.

if you just want to minimize your groups for your own entertainment and amusement (and i do), float, bed, re-visit load development, in that order.

 

[Bartholomew Roberts]

Most hunting rifles are like that... my 7mm Mag will do 3-5 shots at most (and that is pushing it) before it will start throwing rounds.

 

[beerslurpy]

On my thin barrel tikka, I have much better accuracy letting it cool between shots.

 

[jethro75]

Thanks for all the help I am really considering on free floating. Like was said, for hunting I probally dont need to worry about it, but I would like to be able to go to the range and shoot at least 3 shot before it starts to stray. If I free float the barrle, I assume it shouldnt change the barrels accuracy, but just keep the barrel from touching the forend correct? what is the easyest way to free float?

 

[Geno]

The Factories Straighten the Barrels, Then--

The factories that forge their barrels usually have to resort the straightening them too.

Conversely, companies like Shaw barrels, Douglas Barrel, etc. do NOT straighten their barrels. They ARE straight. Then, they air-gauge them to assure that they are less than .0001 variance tip-to-tip. That is why they can guarantee their accuracy, and why you can shoot them all day, hot or cold, and get NO change in zero.

Lose the factory barrel and ship it to Shaw or Douglas. They will give you a real barrel. By the way, the fact of a light barrel V varmint barrel is not the critical factor. The critical factory is straight-drilled, and air-gauged to verify straightness.

Doc2005

 

[dakotasin]

free-floating won't affect the barrel's accuracy. it will change its harmonics, so you may have to re-do load development (sometimes, not always).

free-floating takes all pressure off the barrel, not just the tip. from the muzzle to the recoil lug nothing touches the barrel.

take a dollar bill, fold it in half, and try to slide it between the stock and barrel. this is what i consider minimal clearance.

best way to free float is to buy the barrel bedding tools from brownells. next best way is some 80-grit sandpaper and a deep well socket. just remove wood from contact points. work slowly and check frequently to make sure you are removing just enough wood from the right spot.

 

[Bartholomew Roberts]

Actually, you've got two possible issues:

1) If when the barrel heats up, it expands and contacts something then it will vibrate differently and shots go to a different point of impact. Free-floating will solve this.

2) When the barrel heats up, basic imperfections in the manufacture of the barrel become more apparent. Free-floating will not solve that.

 

[jlmurphy]

Bed the action first, then float the barrel, leaving plenty of space since a light barrel moves a lot when fired. Whether the pattern will open up when hot you won't know until you test it. A really good barrel, properly stress relieved ( by the manufacturer) that has enough ventilation to prevent one side from heating more than the other, will not open up when hot. I have two Hart barrels that shoot great hot or cold, no shift. Most barrels will change point of impact to some degree when hot. If it was me, I would bed, free float, work up a decent load and call it good. I have shot thousands of rounds downrange trying to make the groups a little bit smaller, there is a point of diminishing returns.

 

[MCgunner]

It's the first shot that counts. My M7 and its soda straw barrel shoots 1" groups for three rounds, then the groups begin to grow.

I read an article once that made sense though I never did it. It said to keep one target, each trip to the range from a cold gun, fire one shot on that target same POA. Then measure the group. The bad thing about that is, it needs to be windless each time you fire and finding a windless day around here is impossible...:banghead: