K31 accuracy and poi problems

[andrew375]

I've had my k31 for well over a decade and shoot it a lot, about 200 jacketed and maybe 600+ 150gr and 200gr cast.

From the beginning it had the odd trait of shooting to the right with cast bullets. I was going to knock the front sight over but then I found it shot perfectly to the sights with jacketed bullets and service loads. I'm talking about 3 and a half inches for 150gr and 5 inches with 200gr bullets, this is at 50 metres. This is consistent no matter the load or how I'm shooting; prone with, or without, a sling or using a rest. I don't get this from any other rifle. It cannot be due to the recoil moving the point of impact sideways as I am left handed so I would expect the shots to go left if that was the case, also I would expect to see some horizontal stringing but that's not evident. The stock was putting some sideways (left side) pressure on the barrel at the fore end tip, but relieving that has made no difference.

It is now started stringing shots vertically, like 3 inches vertically whilst horizontal is just 3/4". It doing this with several different loads, including ones that I've used many times before that gave tight, round groups, just several inches to the right!

I've already checked out the Swiss rifles site and various other bulletin boards and going by posts about bedding the k31 I've tried shiming the front barrel block up and down, no difference. Shimed under the barrel at the fore end tip to apply upwards tension, no differance. Fully floating the barrel, groups opened right up. Removing the top hand guard so there is no pressure there, groups became more like a random scatter! The recoil abutment looks good, solid, even contact.

So any ideas before I move on to devcon ?

I did notice accuracy seemed to have dropped off when I last shot it with jacketed bullets. That was in May and I found afterwards the action screws had decided to wind themselves out - again!

[Der Gebirgsjager]

A bit of locktite on the screws might help-- but I wonder if you have accumulated some leading in the bore.

DG

[HWooldridge]

I have a K31 but only shoot GP11 and Prvi Partisan JSP. Outstanding accuracy and fun to shoot…I hope you figure out the grouping problem with your rifle.

[725]

Yep. I'd start with the basics. Clean the bore like crazy. Remove all traces of lead & coper. Check to see that the crown isn't damaged. Tehn review your shooting from bench/bags technique. Consistency is king. also, those K-31's were never designed to shoot with a sling hold like our service rifles were. Pressure from the sling adversely affects accuracy. They just used the sling to carry. ----- As far as I know. Good luck.

[beemer]

I no longer own a K31 but owned two several years ago, I bought them when they first hit the market. I shot them a good bit and accuracy was outstanding with both rifles. Both rifles shot to the right with cast loads. I did a bit of playing around with both cast and jacketed. I found that lighter loads with both shot to the right and increasing the load moved the poi back left. Your guess is as good as mine but I thought maybe light loads stressed the action differently.

I have no idea about the vertical stringing unless you fouled the bedding or something is loose. I never could improve on the original bedding or accuracy of the GP11 ammo and I tried. That stuff would shoot moa at 100 yds, I could see a bit better then. Personally I would leave the bedding original or at least do nothing that can't be reversed.

[Dan Cash]

Most of your problems have been answered but I offer the following regarding vertical stringing: Fix bayonet. Your string will probably string horizontally. 3 inches at 100, don't sweat it.

[andrew375]

Barrel is absolutely clean. Multiple passes with eds red on a brush, followed by sweets 7.62 until I get no reaction. Bore is checked thoroughly with a borescope. Bore is worn but well defined rifling. Groove diameter is. 3094" end to end. I'm using the Lee 200gr and 150gr bullets sized .310".

You're right about the sling, absolutely hopeless! I just put it in to show I've at least tried it. With the vertical dispersion, it is clearly not the random dispersion of poor bullet fit , if the vertical dispersion matched the horizontal then it would be a less than 2 moa group, this is firing prone, unsupported with battle sights and 64 year old eyes.

I've put spring washers under the action screws, which seems to be working.

I'll put the aperture sights back on just to rule out bad front sight alignment due to eyesight.

The fact that it shoots to the right is no big deal, so long as it groups well. I use 50 metre, twin bull, small bore targets. Shoot at the left target to put shots on the right, then simply turn the card upside down to use the other target. Like I said I don't get this with any of my other rifles. With my mosins and mausers the only change in point of impact between light and heavy loads is vertical.

[guzma393]

Following, I've also ran into the weird issue where my k31 is shooting to the right with cast bullets even when the front sight was lined up for J-words. I'm left handed too. I seldom run my k31 on J-words, so I decide to drift the front sight to cater to cast loads. The original configuration has been marked/pinned, so I can always reverse it later on with J-words. I haven't noticed any stringing though.

It's probably k31 specific, its older cousin, the k11 i own, shoots fine, windage wise when transitioning from J-words to casts; just have to adjust the elevation.

[HWooldridge]

IIRC, both K-11 and K-31 barrels are nominally 1/10.63" RH twist rate, so there should be no major differences between the two models. Call me crazy but I wonder if the cast pills are affected by rotational drift and behave like a fast-pitch curveball. GP11 bullets are very pointed and I suspect most of the lead designs people typically use are more blunt. Just a thought...

[Herb in Pa]

The K31 that I owned shot really well with the RCBS 165 SIL sized to .309

[uscra112]

Ya got me. Mine shot to the same scope settings as the Swiss milsurp ammo, and darn near cloverleafed at that, with a 165 Eagan GC bullet cast very hard and loaded to something well over 2000 fps. Never tried it with anything milder. Been years since I had it out, more's the pity.

[Rich/WIS]

Not unique to the K31, both my Garand and 03A3 shot to the right with madium power cast bullet loads (1600 fps). Not an issue with sights readily adjusted for windage but inconvenient if you have to drift the sights for different loads.

[Tedly]

+1 on what Rich/WIS says. I marked my sight for GP11 ball and then drifted the blade to track for cast , shift 6"@100yds. was.04" and the blade nearly out of the dovetail to the right , but , it shot

[Eddie1971]

The K31 has a super tight throat compared to the other Swiss rifles. The IG11, 96/11 and K11 we're able to shoot the older GP90 and GP90/23 whereas the K31 won't chamber them. My IG11 doesn't seem to throw cast any different than jacketed. Never tried cast in my K31.

[Black Beard]

I shoot cast in my K31 (180 grn Lee RN with 25 grn of 5744) and I had to push the foresight right the way over to. It seems pretty accurate with them.

[Schreck5]

Your boolits sized to .310" sound about perfect, but you might try bumping them up to .311". But then I am certainly not as experienced as a lot of others on here so I may be way of base. Bruce