Gunsmithing I Know I'm Gonna Get Hammered ;-)

[Turd in the Pool]

This is more for conversation than a miracle cure. Just thought I'd throw it up and see what sticks. I've only heard of one other rifle that did this but I didn't shoot to verify.

Scraps I put together,

Pre '64 70 in 375 H&H #3 Douglas XX walnut stock acraglas bedded from tang to fe tip. 2nd hand 1.5-5 Leup on their QR b&r.

Usually when I've seen stock or bbl stress issues, bullets tend to go up or up rt/lf.

This stupid thing shoots the 1st x. Second goes 1" to 2" straight down @ 100. Maybe a little wind but it is very consistent. WTF????


I've about convinced myself that the stock/bedding is acting like a heat sink allowing the top of the bbl to expand more throwing the 2nd down. #3 with a big hole is pretty flimsy.

Bottom line is I really don't want to cut the glass out and float the bbl if that won't fix it. I'm going to put a shim behind the recoil lug to "float" the bbl for the next test as well as trying a diff scope.

Anyone else experienced this?

 

[JGilesEastTx]

But it might only be a baby ruth? I wouldn't imagine the problem would be so macro as to warp the barrel. And the shim under the recoil lug might "stress" your action haha. Play with the action screw torque.

 

[1SMALLJOHNSON]

You say it's bedded to the rear tang. Is it possible that the glass...hmmm...how do I say this? OK, you certainly have a vertical wall of glass, just behind the recoil lug. Do you have ANOTHER vertical wall of glass, just behind the rear tang? If so, grind this vertical wall of glass behind the tang out. Relieve this area. If you have any other vertical walls, that are not the recoil lug wall, then relieve them as well.

Next, stand the rifle vertically. Loosen both (or all 3?) action screws. Now, tighten the rear screw only. Place your thumb or finger at the junction of the barrel and bottom of the fore-end barrel channel. Here, you'll be able to feel any movement. Slowly tighten the front screw. Tighten it to your desired torque. NOW, loosen that front screw again, keeping your finger/thumb at the fore-end barrel channel junction. Did you feel any significant movement? If so, you've likely got internal stressors built into that bedding job. If true, then that COULD be a culprit.

You could check several areas. First, "smoke" the action and barrel with a burning styrofoam cup (but don't hurt the environment!), and soot it up really well. Carefully set the barreled action down into the bedding and tighten everything up. CAREFULLY remove it again, and look for spots where the soot was transferred to the bedding. Does this provide you any clues?

Next, and this one ain't easy to do: Do you see any indication that the barrel threaded onto the action is not as tight as it should be? Do you see (under magnification) any evidence that the mating surface between action and barrel is not square?

Finally, it could just be that that barrel isn't stress relieved. If so, I'd guess that it's possible that as you heat it up, it might just curl up like a pretzel. Doubt it.

 

[wareagle700]

How long does it take for the POI to come back up? Is it possible its the shooter? Does it happen every single time or just after you take down and reassemble the rifle?

 

[Turd in the Pool]

JG; When I shim it, the screws will only be tight enough to hold it in the stock. Just want some air between the bbl and bedding. I'm well aware of stressing the action when bedding.

SJ; I haven't pulled it to verify but I normally relieve everything vert. behind the lug. including the curves behind the mag well. I can assure you the bbl is tight and the face of the action is square. Faced on a solid mandrel with no tapered bushings (in case you caught my thread about that ;-).

war; Never shot it more than 3 before letting it cool. Only 16 thru it so far. I thought it was the shooter (tho he shot 5 with his swift that you could cover with a nickel) I finally told him to let me shoot it and 2 were touching. After several more of his attempts, I shot 2 and 2 with cooling and they did the same thing so I guess my 1st 2 were a fluke or the shooter.

I find it interesting that no one seems to think it unusual for the impact to drop. Have y'all seen this often?

Got BS to do today but I will update bedding vert relief etc when I can.

 

[wareagle700]

Most of the time when I have seen someone thinking they have POI shift it's due to them shooting 3 shots. Naturally, one will be further away from the other two. Try shooting multiple 3 shot groups at the same target. Once you have several groups in top of each other it will be easier to see where you stand.

 

[Beef_Supreme]

So... the barrel is making contact with the barrel channel bedding material 100%?

 

[Turd in the Pool]

So... the barrel is making contact with the barrel channel bedding material 100%?

Yep.


Got in late so it will have to wait 'til tomorrow. I'll try to post pics of the bedding and target. Owner has the target and is threatening a shrimpfest tomorrow night so it may be another day before I can post pics.

Kinda bummed that Chad, Dave and 300sniper are silent. Surely someone else has seen this.

 

[Turd in the Pool]

Most of the time when I have seen someone thinking they have POI shift it's due to them shooting 3 shots. Naturally, one will be further away from the other two. Try shooting multiple 3 shot groups at the same target. Once you have several groups in top of each other it will be easier to see where you stand.

Couldn't see the sense in shooting 3 since the 2nd wasn't acceptable. I have another guy telling me the same or shoot 4 or 5. I can't live with a 2" drop so if I can't fix it with a float or pressure point it's getting a new tube.

 

[Rprecision]

375 H&H + 2nd hand 1.5-5 Leup on their QR b/r

With that kind of caliber I would ALWAYS be skeptical of mounts and optics.

 

[Turd in the Pool]

With that kind of caliber I would ALWAYS be skeptical of mounts and optics.

I agree but my experience is mounts and optics failure tends to spray 'em. This thing is consistent. Granted we were havin' some beers after the 1st 10 or so rnds so my recollection of wind may be off a little but it's not much more than an inch in most cases.

 

[wareagle700]

Couldn't see the sense in shooting 3 since the 2nd wasn't acceptable. I have another guy telling me the same or shoot 4 or 5. I can't live with a 2" drop so if I can't fix it with a float or pressure point it's getting a new tube.

My point being; it may not be a shift in zero, it may just be poor accuracy. You will never know unless you put more rounds into the group. Shoot 3, let the barrel cool, shoot 3, etc... Just shoot them all to the same POA. This will give you a bigger sample size to critique.

 

[msalm]

Just try a small shim between the barrel and the forearm tip to see if that changes something. A business card type thickness or a matchbook. Usually your better off with two small strips (1/8th or so wide) @ 45 degrees in the barrel channel.

 

[Turd in the Pool]

Ok, hammer away if you want. I looked at it yesterday and the front screw was loose Totally. It's been 7 or 8 mo since I handed it off to him. I know it was at least snug then. I am guilty of wanting the slots to line up with the bore but I wouldn't leave it loose. I'm guessing the stock may have shrunk some. it's just skim bedded with no pillars. Looks like I need to fix that.

Anyway, I decided to shoot it with just the screws tight 1st. Bore naked. 1st 3 (I know 3 shots have no count on here but this is just preliminary) had no vert but 3" of wind. Next 2 groups shot the 1st 2 about 3/4" and the 3rd went up an inch. More like what I'd expect.

Put the shim behind the recoil lug and the results were about the same. I think the stock is trying to warp because it still touches the bbl on the rt side. I will take a lot of the blame because the crosshairs cover a 2" spot and I shoot like a rock thrower.

Pulled a 6.5-20 off one of one of my ars for the last group and the 1st 2 touched and the 3rd went up about 1/2". You can cover them with a quarter.

Going to ditch the shim, add pillars and float it and see how that goes.