Gunsmithing Cold/Warm Bore POI Shift Issue

[TxShooter63]

Guns are like women, when you start to think you have them figured out, they humble you. I recently built a .260 Remington using a Broughton M24 barrel 25 1/4" in length, .900 at muzzle, Stiller Action, and AICS stock. We used a Manson reamer with no throating and then throated the barrel specifically for 140 Amax's and Lapua Scenar 139's. (By that I mean both were capable of going .000" to the lands without exceeding AW magazine length. I have put over 200 rounds through the rifle using both H4350 and H4831. I have found numerous accurate loads at varying velocities with both.(2750-2950fps)
The issue is that on my cold dirty bore shot, my first shot is about 1" high then the next 4 shots are .250"-.375", one hole. I let the barrel cool enough that I can lay my hand on it at the receiver (still warm just not "hot"), I fire the first shot and it is 1" high, next 4 in one hole. Every time I let the rifle sit for more than 5 minutes, the first shot POI moves at least 1/2"-1" straight up at 12 o'clock. I have tried changing jump on both bullets and it seems to help some but have not corrected the problem by any stretch. I checked chassis bolts for tightness and torque (55 inch lbs). In all humility, it isn't the shooter. I am in the process of skim bedding the rifle but any other suggestion are appreciated. It isn't the scope and it isn't me. If it didn't one hole the next 4 shots after the "warm" bore shot it would be a little easier to understand!
Thanks for any help in advance.

 

[cooleyjc]

Re: Cold/Warm Bore POI Shift Issue

Any chance the barrel is making contact with the barrel channel when its cold and not when its hot?

 

[Quigley77]

Re: Cold/Warm Bore POI Shift Issue

If you shoot one round, and let it cool for three min, shoot the second round and cool, and so forth, do all the rounds group with the first shot?

 

[Graham]

Re: Cold/Warm Bore POI Shift Issue

Re-torque your barrel and see if it still does it.

 

[Gene Poole]

Re: Cold/Warm Bore POI Shift Issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">Re-torque your barrel and see if it still does it. </div></div>

Barrel?

 

[Graham]

Re: Cold/Warm Bore POI Shift Issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gene Poole</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">Re-torque your barrel and see if it still does it. </div></div>Barrel? </div></div>Yes. If he's built it correctly there should be one on the rifle.

 

[LRI]

Re: Cold/Warm Bore POI Shift Issue

If I were a betting man I'd lay a dollar that something is going on with your receiver/stock fit.

The hot/cold thing is something I don't buy. Not with an M24 contour stick.

If we could go sit at Camp Perry and watch the match rifle guys you'd see back to back 10 shot rapid fire strings being fired. These are both done in a time limit of 60 seconds.

The zeros hold and good shooters can clean the course of fire with little trouble. The point in sharing this is the barrel temp during the 2nd string is elevated. No- it's hot! Yet the guns still shoot very well. Cartridges used by these guys cover the full gamut. 22, 6, 6.5, 7, and 30.

Hope this helps.

 

[x ring accuracy]

Re: Cold/Warm Bore POI Shift Issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gene Poole</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">Re-torque your barrel and see if it still does it. </div></div>Barrel? </div></div>Yes. If he's built it correctly there should be one on the rifle.

</div></div>
LOL

 

[oldfatguy]

Re: Cold/Warm Bore POI Shift Issue

This is another part of the ever-popular "cold bore - cold shooter" debate. It probably is not the shooter in this case, but has the OP tried dry firing before the first live round from the cold (cooled) barrel?

OFG

 

[9H_Cracka]

Re: Cold/Warm Bore POI Shift Issue

Lawton 223 barrel at 400 yards. Would move 1 1/4 MOA up and 1/2 MOA right from cold.

Same barrel, same distance, warm, shot right after the first 4 on the next target over:

It got screwed off, returned, and 9 months and several phone calls later, I got my $$ back. Still out the $200 gunsmithing to thread/chamber/crown.

Yes it CAN be the barrel, but have another accomplished shooter shoot the rifle before deciding it is the barrel.

I had 4-5 range trips with this one before I did the test above. Seemed like I had to re-zero it every time I shot it. Not normal for me. So, I set up the test above at a bud's ranch. Cleaned it. Shot it/verified zero as best I could the day prior so it was cold and dirty. Came out in the AM with no wind and did the test.

24" 8 twist Rem Varmint contour on a M700 BTW.

 

[Gene Poole]

Re: Cold/Warm Bore POI Shift Issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gene Poole</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Graham</div><div class="ubbcode-body">Re-torque your barrel and see if it still does it. </div></div>Barrel? </div></div>Yes. If he's built it correctly there should be one on the rifle.

</div></div>

I thought maybe you meant action screw torque. Is barrel torque something I'm going to have to add to my checklist now every time I go to the range? What is the consensus on what value to torque it to?

 

[Graham]

Re: Cold/Warm Bore POI Shift Issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gene Poole</div><div class="ubbcode-body">Is barrel torque something I'm going to have to add to my checklist now every time I go to the range? What is the consensus on what value to torque it to? </div></div>No. And there's no consensus. I have seen some barrels unscrew themselves during matches, though.

I have a rifle that does almost the same thing, CB to warm barrel. But with 100in/lbs on the action to an aluminum chassis it wasn't a receiver issue. The best we could come up with was that it probably had something to do with the barrel threads heating-up (from the way they were cut), because the first shot was always .3 Mils low and the next few shots walked ever so slightly up to the zero. The first shot was predictable, and the rifle would be fine after that for the rest of the day. Now, at 3500 rounds through the tube the CB is always .4 Mils low. And it's not me; it's repeatable with everyone else behind the rifle. Go figure!

That's why I told him to torque the barrel and then see if it still does it. It might not be a cure, but it would eliminate another variable.

 

[TxShooter63]

Re: Cold/Warm Bore POI Shift Issue

I bedded the receiver last night so we'll see. I don't clean my barrels much, maybe ever 100-200 rounds and then I don't use a brush. I have no issue with cold bore POI shift. That is normal to some extent. But I have never seen a rifle that had a POI shift going from hot to warm. I will keep you posted on what I figure out. These types of deals are frustrating but they allow you to learn some in the end that you can carry forward so it isn't all bad.

 

[Advokaten]

Re: Cold/Warm Bore POI Shift Issue

How about the chassi/action interface,

being a lazy ass like me would mean that i would shift the action in to a real stock that I know will shoot when paired with a decent action and barrel.

Yet I am put a poor country boy so how would I know.

/Chris

 

[9H_Cracka]

Re: Cold/Warm Bore POI Shift Issue

Typically bedding issues cause "two grouping" - the metal jumping around in the stock in a somewhat repeatable fashion.

Stress on the action from poor bedding/bowed action on straight bedding block in my experience opens up the group in a more random way. Rifle will shoot like it has no zero - just no consistency to POI.

Putting one of my BAs that has a bowed 700 receiver in a stock that was bedded to a fairly straight 700 receiver took my groups from .33 MOA to 1.5 MOA in my 6mm-250.

 

[2156SMK]

Re: Cold/Warm Bore POI Shift Issue

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: _9H_Cracka</div><div class="ubbcode-body">Typically bedding issues cause "two grouping" - the metal jumping around in the stock in a somewhat repeatable fashion.

Stress on the action from poor bedding/bowed action on straight bedding block in my experience opens up the group in a more random way. Rifle will shoot like it has no zero - just no consistency to POI.

Putting one of my BAs that has a bowed 700 receiver in a stock that was bedded to a fairly straight 700 receiver took my groups from .33 MOA to 1.5 MOA in my 6mm-250. </div></div>

Another one to check is for a scope base screw touching the barrel threads or the front action screw touching the bolt lug.

 

[TxShooter63]

Re: Cold/Warm Bore POI Shift Issue

Turned out that the barrel threads were cut slightly undersized. This allowed barrel to act as lever until threads warmed and expanded. Two wraps of Teflon tape and I shot a 4 shot group @ .150"! This was my first build so I am happy. Being a .260 I will have to re-barrel before spring and I learned a good lesson without any real harm.

 

[Rprecision]

Re: Cold/Warm Bore POI Shift Issue

Its always been for me the warm cold POI shift is related to bedding / barrel free float.

I would be highly suspect of your above findings. If properly torqued, even .010 undersize, it would settle to one point as its tighted.

I find it intresting that removing it from the stock was part of this change