Cold bore accuracy?

[Todd_ID]

Can anybody explain how to get a cold bore and a hot bore to shoot the same?  I'm an engineer, so I can handle the technical stuff, but I just don't know it.  I've been reloading for .223 and .50 Beowulf trying to find the right load.  I can get .25" to .38" at 100 with the .223, but the cold bore on the same round is maybe 1/4" from the rest of the group.  I've got a M-77 Ruger in .30-06 that I can hit a gnat on the first shot, but the next will be 2" off at 200: WHY?!

Is there such a thing as a load that will shoot the same from a cold bore and a hot bore?

[Bofire]

I do not think there is. metal heating/cooling over the length of a barrel is not something that can be controled or duplicated. I am surprised an Engineer would ask this.
Carl

[norsepeak]

The short answer is no.  But you can minimize it by making sure your action is bedded (preferably pillar), and your barrel is free floated.

[GregMcFadden]

It is not just the heating of the barrel that affects the first shot impact point compared to follow on.  You can change it by changing your cleaning procedure or just the difference between a barrel with a few rounds through it from the last time at the range and a clean barrel.  you just need to experiment and make sure you know where the first shot hits versus the second.

You may find that certain loads are better than others, but there is no way to know other than to shoot a lot and record how your rifle responds

[Todd_ID]

I am surprised an Engineer would ask this.

An engineer that admits he doesn't know everything should be the surprising part.  All along I thought that was the sign of genius when you knew what you didn't know.

I guess I can accept that the first shot will never hit the same as the second or tenth.  I'm surprised that someone hasn't figured this problem out, though.  I'd guess it's a common theme in shooting.

[Bob33]

Todd, the problem is neither unique nor easily diagnosed.  Some rifles shoot some ammunition to the same point of impact with cold and warm barrels, and some don't.  Rather than spending lots of time and ammunition trying to find a barrel/load that doesn't, you could just accept it.  If the first shot from a hunting rifle always goes to the same point of impact, that's what matters most.  (If a hunter hasn't hit an animal on the first shot, or worse yet the second, what makes him think he can hit it with a third when the animal is fully alert and probably in motion?)

Many years ago a hunter told me that the most important three shot group is measured this way: take a target to the range, and shot one shot.  Take the target home. Come back another day, put the target up, and shoot a second shot.  Do it a third time.  That group will probably be more meaningful than shooting three in a row.

Also, make sure the factor isn't "clean barrel syndrome"; that's an easy one to fix: hunt with a fouled barrel.

[BOWHUNTER45]

Todd, the problem is neither unique nor easily diagnosed.  Some rifles shoot some ammunition to the same point of impact with cold and warm barrels, and some don't.  Rather than spending lots of time and ammunition trying to find a barrel/load that doesn't, you could just accept it.  If the first shot from a hunting rifle always goes to the same point of impact, that's what matters most.  (If a hunter hasn't hit an animal on the first shot, or worse yet the second, what makes him think he can hit it with a third when the animal is fully alert and probably in motion?)

Many years ago a hunter told me that the most important three shot group is measured this way: take a target to the range, and shot one shot.  Take the target home. Come back another day, put the target up, and shoot a second shot.  Do it a third time.  That group will probably be more meaningful than shooting three in a row.

Also, make sure the factor isn't "clean barrel syndrome"; that's an easy one to fix: hunt with a fouled barrel.

yeah I agree , their is so many factors that come into play when it comes to grouping bullets .. barrel length - barrel twist - and the shooter and most importantly how thick the barrel is .. the thicker barrel will of course out perform the thinner barrels like those found on rifles like the remington mt. rifle..

[jaymark6655]

I think it has to do something with the way the grain of the metal is oriented with respect to the barrel.  That is what makes a match barrel so special, the bore runs exactly parallel to the grain.  I think it is pure luck to get a perfect bore like this and that is why such a barrel cost so much.  When the metal heats up, it shifts just enough and there is no way to fix it.  Thicker barrels help, but they suck for hunting and hiking long distances.

[Jamieb]

The change in impact point between the first few shots from a clean barrel and the fouled barrel I dont think can be helped, after cleaning a rifle I just figure that I'm going to waste a few shots refouling the barrel. Some of my rifles will shoot the first shot from a cold barrel to the same group as the rest of the shots.
Before I ever shoot a new rifle, I bed the action, lighten the trigger, on heavy barrels I float, on light barrels I want neatral pressure in the forarm tip to start and may change it later. Load development is a long prosess for me, some rifles it has taken over a year of messing around to get the load to the point I'm happy. Theres only been two rifles that I gave up on and sold without ever finding a good load for.  For a rifle I want to hunt with, I work up a load to use, load up 100 cartriges to shoot/hunt with but I keep playing with load development. My .223 shooting 50gr molyed V-max's, 26.8gr of Tac. PF sized WW brass, with a COL of 2.295" ( Kissing the lands) will shoot well under 1/2" 10 shot goups at 100yards, even with the cold bore shot in there. This load is only going 3300fps out of a 26" barrel. I worked up to 3500fps but accuracy trumped speed. My 7rem mag always throws the first cold bore shot 1/2" strait up from the rest of the group. My 300RUM will shoot 3 shots touching at 100 yards over and over but the first "cold bore" shot is always 1/4" to 1/2" off. Those two I've stoped working on, I'll live with that and be happy. My 22-250, just like my .223 has a 26" heavy barrel, is bedded and floated the same but I had to lean on the 50ge molyed V-max;s pretty hard to get rid of the cold bore flyer,3950FPS and COL of 3.625" witch has a bit of jump.

[Malottguy]

Also, make sure the factor isn't "clean barrel syndrome"; that's an easy one to fix: hunt with a fouled barrel.

My rifle is that way. It has decent groups with a clean barrel, but once I hit the fifth shot the group tightens up. So before I go hunting I put five rounds through it.

[lokidog]

Lots of good advice here. 

Personally, one of the things I think would make a big difference is your target.  Someone mentioned it previously.  If you try to put a crosshair in the center of a circle, you've got the square peg in a round hole thing and no matter what distance you are, it is very difficult to hold the crosshairs in the exact center.  I do one of two things when working up a load, I will either use a diamond shaped target so I can put the cosshairs on each point, or I draw a + through the middle of the target so i can line the crosshairs up exactly on it.

When I got my Browning A-bolt back in the 80's. I lived in So Cal.  It was 80 + degrees when I tried patterning it and I would wait a full fifteen minutes between shots to let the barrel cool down.  This spring has good temps for faster cooling, fortunately for you....

If I were you, I would 1.  move your target to 50 yards  and 2. draw/use a more accurate target than a dot.

I use 56.5 gr IMR 4350 with a 165 gr jacketed bullet which is what my 30-06 really likes.  I have not tried reloading 180's.

Good luck.

[JackOfAllTrades]

I see a mix of terms in this thread that should not be confused.  Cold bore, is not necessarily the same as a a fouled bore. Some barrels shoot better when fouled as a cold bore. Others generally shoot good groups until the barrel warms up enough for the metal to constrict. No barrel is molecurely identical from chamber to crown. Heat, created by the internal explosion, burn of powder and the friction of the bullet as it glides on the lands will create hot spots where the barrel inner diameter is tight, and less heat where the diameter is loose. No barrel has the exact bore diameter from one end to the other. Realize that what I am saying is an exageration, but the temperature of a barrel is not the same from end to end. Most barrels are tapered. There will certainly be more differences in temperature for light weight barrels. All of this contributes to friction applied to a bullet. That friction can create vibration leading to wobble of the bullet as it leaves the muzzle. A wobbling bullet will have a different point of impact down range. It may be a consistant or inconsistant POI.

I have a rifle that will shoot MOA all day long with one bullet, cold bore, fouled bore, warm, doesn't matter. But I don't shoot that bullet for hunting. I have another rifle that throws the clean/cold bore shot just a tad up/left. Still MOA, but certainly noticeable at 300yds.

-Steve

[demontang]

I seen a lot of info on this and come to find that a dirty bore has more even pressure from shot to shot then a clean one, Ive also see that the more you shoot without cleaning a bore the tighter the groups can get. The guys at sierra have seen this in there test barrels and only cleaned the barrel to clean it, there was no loss in accuratecy at all after shooting hundreds of rounds. They believe this is do to copper and powered residue filling the flaws in the bore making the bore more uniformed there for more accurate. I have not cleaned my barrels that much since reading this and normaly only to oil then so they dont rust and have seen a increase of first shot to 10 shot accuracy. My cold bore shots are almost dead on to the warm bore shots. I can wack a 12x12 plate at 600 yds with a cold bore or warm bore. I do know powders can play a part in this to cause some are more sensitve to heat then others which can make the mv change as the chamber builds heat and warms the powder