walking group

[BB1]

300 wby mag
Swarovski 3-18
180 grain barnes ttsx
78 grains RL19
Clean rifle
2 fouling shots
First two 3 shot groups approx 2" at 200 yds
Then pattern went to 4-6 inches and shots started to walk up and right-left progresivly getting worse...
Fell on my ass pretty hard the other day but?.....
Ideas please

[mete]

After checking scope mounting -screws tight etc the next thing is to check bedding .You might just have it bedded that's always a good idea.

[Bud Helms]

Let's go to Rifles.

[hornetguy]

Sounds like a classic case of a "high" point in the bedding. As the barrel heats up, it puts more (or less) pressure on the bedding point, and the groups start walking away from the original point.
Either free float the barrel completely, or bed it solidly at the front of the forearm. Free floating is the easiest first try.

[Bart B.]

hornetguy, if the barrel gets hot, it expands in diameter. That'll put more pressure on any point it's bedded at. So why bed the barrel at the fore end tip where any pressure on the fore end from how the rifle's held will change the pressure on the barrel at that point? No competition shooter winning matches and setting records wants their barrels to touch anything; totally free floated forward of the receiver ensures the barrel's expanding from heat won't change its pressure against anything that'll make it bounce off of.

Barrels walking point of impact as they heat up is typically caused by the barrel is fit to the receiver with uneven pressure around where its flat part is against the receiver. If the receiver face is not square with the chamber axis, there'll be one point where the barrel is hardest against the receiver. As the barrel heats up and expands, a stress line at that point makes the barrel whip more and more in one direction as it gets hotter. Which is why, after letting the barrel cool down, it shoots back to point of aim where it started. This cause is easy to fix; face off the receiver and shim the barrel so it clocks into the same place keeping headspace correct.

If a barrel's not properly stress relieved, they also will bend a bit as they heat up. Replacing it is the only solution.

[hoghunting]

No competition shooter winning matches and setting records wants their barrels to touch anything; totally free floated forward of the receiver ensures the barrel's expanding from heat won't change its pressure against anything that'll make it bounce off of.

Guess many bench rest shooters are doing it wrong then as many have the action and barrel fully bedded or epoxied to the stock.

[Picher]

Be sure that your barrel isn't being fouled by the Barnes bullets. My fully free-floated barrel fouled and walked shots as pressures and velocity increased and the bolt became difficult to open.

The Barnes literature said that the barrel must be free of gilding metal traces before using Barnes bullets. Mine may not have been and yours may not either, should that have had any effect.

[coyota1]

if the barrel gets hot, it expands in diameter. That'll put more pressure on any point it's bedded at. So why bed the barrel at the fore end tip

Bart, more often than not full bedding has corrected this problem with my experience. I have not always had good luck free floating barrels. A similar thing happened to a friend's Ruger varmint/target which had a medium barrel. We put a piece of flat rubber just before the the forend, and it settled down and printed impressive groups.

[hooligan1]

You might of "popped" something loose when you fell on yer ass real hard the other day....

[Bart B.]

hoghunting, I've never heard of having the action and barrel fully bedded or epoxied to the stock. Who does this, anyway, for example?

Are you thinking of a rail gun where the barrel's clamped in a 6 to 12 inch long metal block bolted to a 3-point free recoiling machine rest sort of thing?

[coyota1]

Hogunting is partially correct Bart. Competitive benchrest shooters glue in the reciever, and free float the barrel. This happened when awhile back a shooter glass bedded the reciever in and forgot to apply the releasing agent, hence the "glue in". It was discovered that the gun maintained optimum accuracy this way. I have fully glass bedded (reciever and barrel) several sporter barreled rifles, and had better more consistent groups this way.

[Bart B.]

coyota1, it's my belief glued in receivers came about after too many folks were gluing them in metal sleeves and got tired of having to go through extra work to take the receiver out. Don't matter who or when it happend, but it was popular with all the round receivers as they tend to shoot loose from conventional epoxy bedding when heavy bullets are shot fast; the barrel torque twisted the receiver a bit out of good fit to the epoxy. That sometimes still happens. Three cheers for flat bottom/side receivers.

And if you have fully glass bedded (reciever and barrel) several sporter barreled rifles, and had better more consistent groups this way, you're the only person I know of who's claimed good results. I know of three or four others who tried it; none worked with their standard Rem. 700 and Win. 70 standard sporting rifles. Even helped one guy rout out Devcon from the stock's fore end and wow, what a difference we saw; almost 3 MOA at 100 before, under 1 MOA after.

[coyota1]

Well Bart, I don't know what to say. I have an old very seasoned gunsmith do my bedding work for me. I really don't want to attempt it as long as I have him around. To paraphrase him, he said some guns respond to free foating, some to complete bedding. I have 3 rifles that are this way, and they tack drive. I had a 700 VLS that I ended up bedding barrel and all. It came factory with a part of the channel designed to press against the barrel a couple inches from the forend. I removed this to completely float, and I still wasn't happy with group size, so I had Stan (my gunsmith) glass the barrel channel, and It tightened the group size nicely. He may have a technique he isn't telling me about, and this is typical if him. He doesn't like to give up secrets. Go figure.

[hoghunting]

hoghunting, I've never heard of having the action and barrel fully bedded or epoxied to the stock. Who does this, anyway, for example?

Have you ever been to a bench rest match? Many bench rest shooters have the action and barrel fully bedded or epoxied to the stock, and they've done it for quite a few years.

[coyota1]

There are many rifles that have a barrel band, and it's placement is no accident, or guess. That band is where the "wave" of vibration comes closest to the barrel. It helps it settle down. Another similar thing is when you may occasionally see a barrel with an abrupt taper along it. It helps interrupt (deadin) the wave of vibration that is imparted on the barrel when the bullet zings through the barrel. This is similar to what fully glass bedding the barrel channel does.

[Bart B.]

I've no idea how a barrel with an abrupt taper along it helps interrupt (deaden) the wave of vibration that is imparted on the barrel when the bullet zings through the barrel.

Nor why a barrel band is where the "wave" of vibration comes closest to the barrel. How far away from the barrel are vibration waves? Seems to me if the vibration wave is away from the barrel, the barrel won't whip or wiggle at all.

I think there some laws of physics that are left out of this situation.

The above aside, here's a link to some interesting stuff on barrel vibrations:

http://www.varmintal.com/ashot.htm

Check out the following sections:

Esten's Rifle & Tuner
Light Rifle & Tuner
Barrel Harmonic Movie
Barrel Tuner Analysis
6PPC Barrel Dynamics

[coyota1]

Bart, think of a bell. Put your hand on the bell and what happens? It dampens the sound... vibration. Imagine the bell with bands around it, or abrupt angles, instead of smooth. It would sound different. It wouldn't ring (vibrate) as well. A rifle barrel does essentially the same thing. A short thick bull barrel will soak up vibration and not vibrate as nearly as much as a longer slender hunting barrel. Vibration travels in a oscillatiing nature (it's a law of physics)). where the oscillation meets the barrel, that is where the barrel band is placed, or in some older barrels where an abrupt taper is.

[Bart B.]

Where does that oscillation come from and why does it meet the barrel where a band's placed. What prevents the oscillation from meeting the barrel at some other place?

[coyota1]

A barrel vibrates. Vibration by nature oscillates. How and where on the barrel this is determined I don't know. I was taught this years ago by a master gunsmith. It may be old school, and not as affective as once thought, or maybe it is. I was taught that a shorter thick target barrel doesn't change poi with different loads like a slender barrel. The less vibration, the less affect different loads will have on it. I've seen this at the range when a target barrel will be less fussy than a standard field barrel.

[Bart B.]

A barrel vibrates. Vibration by nature oscillates. How and where on the barrel this is determined I don't know.

For an education on how barrels vibrate:

http://www.varmintal.com/ashot.htm

Check out the following section: Barrel Harmonic Movie

I've smaked a hammer on 22 and 24 inch sporter barrels with conventional tapers as well as M1 and M14 barrels with stepped tapers. Both make a nice ringing sound; only their frequency is different.

[coyota1]

That was good stuff. I need to spend more time with this though. I bet barrel bands and step tapering were discontinued due to new info, or better barrel making, and better alloys. Some doctors early on used to suggest to patients to take up smoking to relieve anxiety. Maybe it worked, but with modern knowledge, they know this isn't the way to approach this problem at all. I am skeptical about the barrel doing the vibrating after the bullet has left the end of it. It is a fact that when I had my sporters fully receiver, and barrel bedded they shot better, tighter, and didn't need sighting in again.

[Picher]

I've bedded many rifles over the years and found a few like a forend pressure pad, but most shoot equally as well free-floated. Single stock-screw rifles like 10-22s shoot best with pressure pads in the forend, especially with bull barrels. If I were to fully bed a barrel in a stock, I'd put several pounds of upward pressure on it while the epoxy sets up.

There are several reasons for free-floating hunting rifles. Probably the best is that, with wood-stocked rifles, POI doesn't change with humidity. Another reason is that sling pressure or rest position doesn't affect barrel vibration.

People tend to put way too much emphasis on group size and not enough on POI consistency. The smart hunter would rather have a rifle that shoots 1 1/4 MOA, but never varies it's POI, than a .75 MOA rifle whose POI changes as much as 1.5 MOA depending on humidity, rest position, rest flexiblity, sling, etc.

[coyota1]

I have an old walnut 10 22 carbine that I had glass bedded both barrel channel, and receiver. I have not had to sight it in in years. It groups well, and maintains poi.

[Bart B.]

coyota says:

I bet barrel bands and step tapering were discontinued due to new info

Right. Better testing and ammo showed they hampered, not helped accuracy. Lots of match rifles use to have barrels banded or pressur fitted to stock fore ends. They quit in a few years.

[coyota1]

The step tapering uglies up the gun also. On the other hand, the barrel band on my 10 22 looks alright.