Vertical stringing cause?

When I purchased this 1899 carbine a decade or so ago, it would group about 36" at 25 yards! And, those were keyholed! It also looked like about as well as it shot. I've done a lot of work on her, tailored some cast loads, and I am now keeping it within 6" at 100 yards. However, as you can see, it appears to be stringing vertically as the barrel warms. The first two rounds, touch, then it goes upward. I'm guessing I have some kind of stock issue. This is not the stock that came with the weapon. Instead, it is a cut-down rifle stock, but one that was very well done back in the day. Definitely not a bubba job. After I shot this group, I checked the action screws. They were snug, but not tight. I got about five more degrees of twist into them simply using a screwdriver in my hand. I'm going to try again soon, to see if those slightly loose screws are the problem. If not, where should I look?Attachment 127256

Assuming the bedding is solid and even under the receiver flat, and in the recoil area (behind the magazine), the next key area is the barrel band. It should fit snug so that it it won't slip off without light force...like a light tap with a wooden dowel, but not so tight that it binds. binding as the barrel heats up will cause problems. Full disclosure, I've never touched a carbine, but the bands on the krag rifle are very touchy indeed when fitting on new wood. The rear has more effect then the upper band, and it is the more difficult too, so I would assume the same principles apply to your carbine. A loose band will cause issues too - common in old tired original stocks. Easy to fix with a piece of felt between wood and band (on the underside, not against the barrel).

Check that your action screws are not contacting the sides of their holes. Looks like you have an original stock, so this likely isn't an issue.

Often, if the old wood is tired enough, the action screws might bottom out in their holes. Pretty easy to check by measuring. My first krag suffered from this affliction on the front screw, and filing off 1 thread was enough to make it shoot like a dream. Similarly the wood under the tang may be shrunk. cut some pieces of notecard to see if it helps.

Check your screw torque. I would say the krag likes no more than 30 inch*lbs, and maybe slightly less (28ish) on the tang screw.

Another guess... minor slop in rear sight. Sometimes they are just barely noticeably loose in the base. A brass drift and a very light, loving, tap will tighten it up. it doesn't take much so be super careful. A tap on the front edge, pushing toward the rear, will tighten up any minor slop in the windage, and a couple taps straight down on the rear part will tighten any minor slop there.

Lastly...shooter inconsistency. I don't mean to question you're ability, but it's a common enough problem for many when using barrel mounted rear sights with tiny peeps and narrow blades. On one of my krags, I can easily shoot 5 shots in <1in groups with 220gr round nose...the problem is it takes 10 rounds and I get 2 such groups!...one a few inches above the other! Depending on the weather, sunshine, or indoor lighting conditions, using a 6 o'clock hold with a "sliver of white" cleans it up, and makes a refrigerator worthy target after range day.

EDIT: a little non-permanent (blue) loctite on the band screw(s) may be a good idea. Sometimes the old threads are worn, and they back out when shooting unless you really tighten them...see first paragraph for possible affects.

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Originally Posted by ssgross

Lastly...shooter inconsistency.

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You didn't tell us whether you're shooting off a sandbag or your elbows. If you want to accurately group, take away as much of the human factor as you can. I shoot off sandbags now because I ain't gettin' younger and steadier. When we coached in the army, vertical groups were breathing. A diagonal group was a change in position like elbow shift. Bag it and try again.

Quote:

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Originally Posted by ssgross

Assuming the bedding is solid and even under the receiver flat, and in the recoil area (behind the magazine), the next key area is the barrel band. It should fit snug so that it it won't slip off without light force...like a light tap with a wooden dowel, but not so tight that it binds. binding as the barrel heats up will cause problems. Full disclosure, I've never touched a carbine, but the bands on the krag rifle are very touchy indeed when fitting on new wood. The rear has more effect then the upper band, and it is the more difficult too, so I would assume the same principles apply to your carbine. A loose band will cause issues too - common in old tired original stocks. Easy to fix with a piece of felt between wood and band (on the underside, not against the barrel).

Check that your action screws are not contacting the sides of their holes. Looks like you have an original stock, so this likely isn't an issue.

Often, if the old wood is tired enough, the action screws might bottom out in their holes. Pretty easy to check by measuring. My first krag suffered from this affliction on the front screw, and filing off 1 thread was enough to make it shoot like a dream. Similarly the wood under the tang may be shrunk. cut some pieces of notecard to see if it helps.

Check your screw torque. I would say the krag likes no more than 30 inch*lbs, and maybe slightly less (28ish) on the tang screw.

Another guess... minor slop in rear sight. Sometimes they are just barely noticeably loose in the base. A brass drift and a very light, loving, tap will tighten it up. it doesn't take much so be super careful. A tap on the front edge, pushing toward the rear, will tighten up any minor slop in the windage, and a couple taps straight down on the rear part will tighten any minor slop there.

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Good info here. The stock is nice and solid, not spongy. I'm not a great shot, but I can keep some of my other milsurps in a fist-sized group at 100 yards, and with straight vertical stringing, I'm thinking that has to be the rifle. Your info about the barrel band is something I will look at. This is a cut-down rifle stock, so there could be too much/not enough pressure under that barrel band. Carbine bands are held on by springs, so no chance the band screw is loose. I hadn't thought of the simplest things first, and that is the rear sight. I'll check to make sure it is all snug. I've had to do that to some '03 sights. Like I mentioned, I'm just glad to actually get it on paper after how it was when I got it. I'm loading up some more ammo for it, and I will check the things you mentioned soon. Thanks again!

---------- Post added at 07:09 AM ---------- Previous post was at 07:06 AM ----------

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Originally Posted by browningautorifle

You didn't tell us whether you're shooting off a sandbag or your elbows. If you want to accurately group, take away as much of the human factor as you can. I shoot off sandbags now because I ain't gettin' younger and steadier. When we coached in the army, vertical groups were breathing. A diagonal group was a change in position like elbow shift. Bag it and try again.

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I'm shooting off a bag. My shooting is not great, but I can keep most of my other milsurps within a fist-sized group at 100 yards. So, I'm thinking it is something with the rifle. It shoots much better than when I got it. But, now I'm trying to wring out the last bit of accuracy the old girl is capable of.

FWIW - I treat the two guard screws differently, when reassembling a Krag.

With both trigger-guard screws loose and the handguard and (loose) barrel-band on the Krag, I hold the carbine or rifle level and wiggle it a few times, so the action and barrel settle onto the bedding and barrel channel.

I look at the handguard and make sure it has been pushed adequately rearward on the barreled/action, so that the front edge is not quite touching the barrel-band.

I wrap a hand around the action and stock, with a firm grip, and very fully tighten the front guard screw.
The rear guard-screw just gets turned in until snug. (Over-tightening the rear guard-screw can lever the barrel upward off the barrel channel).

If the barrel-band is a rifle band, I then tighten the swivel-screw until it clamps the swivel from freely pivoting.
Krag rear barrel-bands are tapered on the inside. The "U" marking goes on the right-side of the arm.

If the band no longer makes firm contact with the stock, the wood surface can be 'built up' a bit with narrow layers of cured epoxy. (It will be hidden by the barrel-band).

Barrel-bands should not be putting undue pressure on the barrel, which could have an effect on expansion and harmonics.
A dab of silicon grease or graphite between band and barrel could be worth a try.

Just an update: I checked everything mentioned in your replies. I did loosen and then retighten the action screws, bring sure to get the front screw really tight, but the back one just nice and snug. I took it to the range again and tested several different handloads. My best group was no bigger than a fist. So, I know it's accurate. I loaded some more of that handload and looking forward to tweaking that rear-sight and get it centered. Thanks for your help.

P.S. Part of me wonders whether or not my front bag might have been touching the barrel and that caused the stringing. You wouldn't think so, but with a carbine, being in a hurry, sun beating on me, etc., who knows?

I coach a high school rifle team. They only shoot prone and with slings, gloves and peep sights. Stringing up and down is breathing issues, stringing right and left is trigger pull issues. Probably completely unrelated to your issue as you are using bags not the bones in your arm to support the rifle but I figured I'd throw it out there. Kind of automatic when I see that kind of vertical line. Their rifles are capable of putting the pellet through the same hole at 10 meters if it's in a vise.