Help diagnose accuracy problem Heym sr21

Mungo

Well-Known Member
I would be very grateful for opionions on this and suggestions for possible cures:

Rifle is a wood stocked Heym SR21 in .308. Not threaded. About 6 years old, lightly used - about 30 rounds at most per year. Well looked after and cleaned regularly. Rifle came with recoil lug and first 2 inches of barrel glass bedded from factory.

Until this week, shot very accurately, though with a caveat: Cold bore shots grouped with over-lapping holes. Then Showed about an inch of shift in PoI when shot with a hot bore, but hot bore groups still around an inch, below and slightly to right of cold bore group.

This week, it started shooting very erratically: groups opened up to over 6 inches, with no consistent pattern or stringing. Shotgunning.

Tried everything: switched to a known good scope. Tried 4 different types of ammo. Stripped gun to components, cleaned everything, reassembled and tighted everything. Deep cleaned bore. Got someone else to shoot it. Shot off bipod and bags. Shot with cold bore or hot bore. All the same- large, unpredictable groups.

The only thing I found that might explain this is the front action screw: it looks like it had been cross threaded at some point. It still tightens, and everything seems firm once the screws are done up. So: is a slightly damaged action screw a likely explanation for what I'm seeing?

I'd be very grateful for help: this is a very beautiful gun, and one that was capable of superb accuracy, so it really irritates me that it isn't shooting right.
 

Mungo

Well-Known Member
About the only thing you've not mentioned is having the crown checked.
Good point. Eyeballing it, I don't see any new dings. It is a touch scruffy, and I was thinking about getting it re-crowned.

Thank you.
 

monarman

Well-Known Member
If it was shooting fine and suddenly went off.. unless you've damaged the crown since it was shooting well I'd look at the barrel bedding. If the damaged action screw is cross threaded it may be pulling the action to the stock inconsistently and in turn may be altering the pressure of the barrel on the bedding.

It wouldn't harm the rifle getting it re crowned. .... it will eliminate that particular variable for sure.

Try 'shimming' the barrel with thin strips of plastic at the point at the very tip of the forend. ....basically creating a pressure bedding point..... then try the most accurate rounds in the rifle and see if it is still erratic. This eliminates inconsistent barrel movement and will tell you if there is a bedding problem elsewhere.
 

Muir

Well-Known Member
A dinged crown won't toss 6" groups. It's something else. I can't imagine what if the action bedding is still intact. (?) Generally speaking, guns don't go from being very accurate to shooting shotgun patterns by sitting it the cabinet. The only time I've seen this is when either the wrong ammo is fed into the rifle, or the tang supporting surfaces split on the first shot of a rifle that was over oiled and the wood got soaked.~Muir
 

Mungo

Well-Known Member
A dinged crown won't toss 6" groups. It's something else. I can't imagine what if the action bedding is still intact. (?) Generally speaking, guns don't go from being very accurate to shooting shotgun patterns by sitting it the cabinet. The only time I've seen this is when either the wrong ammo is fed into the rifle, or the tang supporting surfaces split on the first shot of a rifle that was over oiled and the wood got soaked.~Muir
Thanks for that. Just clarify: are you suggesting the bedding might be damaged?
 

Middlebridge

Well-Known Member
Maybe you're a bit wary of tightening the cross threaded screw sufficiently. Might be worth cleaning up with a tap and die.
Other than that I'd look at scope mount and go back to known good ammo.
 

Ronin

Distinguished Member
Loose action screws

Loose scope mounts

Loose rings

Loose bipod stud

Scope damage (internal)

Start looking there.
 

Mungo

Well-Known Member
Loose action screws

Loose scope mounts

Loose rings

Loose bipod stud

Scope damage (internal)

Start looking there.
Checked all of the above. Only likely culprit so far is slight damage to front action screw.

Anyone know now where I can get replacement Heym action screws??
 

VSS

Well-Known Member
The action screw wouldn't have suddenly become cross threaded on its own! Either it was like that all along, even when the rifle was shooting well, or you've damaged it recently by removing it and then screwing it in wonky. However, it appears from what you've said that you didn't strip the rifle down (and remove screw) until after it started misbehaving. Therefore it stands to reason that the screw has always been like that, with no ill effect.
 

triggersqueezer

Well-Known Member
with the sudden impact shift and that degree of accuracy loss it has to be something moving or though you say the barrel is clean if copper or carbon has built up as soon as accuracy goes of it will get worse n worse.if your using a bronze brush with good copper remover and cleaning right back to the chamber and you sure there is no carbon build up then that front action bolt must be it.
 

keith rippin

Well-Known Member
I had a problem with my Heym SR21 in 308 in that it did not like heavier ammo - up to 150 grains it was very accurate but at 175 grains and above the groups became ever larger - I part exchanged that Heym for a Heym SR30 straight pull in 7 x 57 which is extremely accurate throughout from 140 grains up to 180 grains (and perhaps above although I have not tried heavier loads than that). I never did find out whether the barrel on the 308 was too slim or whether the twist rate was insufficient to stabilize the heavier ammo. I am afraid my comments will probably not assist in solving your problem but I do wonder if you find any worsening in groups with the heavier loads.

You seem to have checked all the usual suspects (bedding, loose scope action screws, muzzle crown etc) and although it seems pretty unlikely is it possible that the barrel/action joint may be coming loose?

Good luck with a solution - please divulge if you find the answer.
 

NigelM

Well-Known Member
At 6" groups either something has to be moving or the stock is erratically touching the barrel or both. No minor change in ammunition is going to throw 6" groups - or never that I have experienced. Has the problem with the bedding screw resulted in an alignment issue that has the barrel touching the stock inconsistently? Do you have a moderator fitted? Is there a problem developed with that? Try it without the mod and see if the problem is still present. Many years ago I had a mod with a bur on it that threw bullets all over the place.

I wonder if it's got something to do with the 1" high cold bore shot you have had a problem with?

Keep us informed. Would love to know the answer.
 

bbrc

Well-Known Member
Is the damage to the front action screw definitely from cross threading? or could it be that the stock has compressed up and is allowing the screw to bottom out in the hole and get damaged that way?
I have seen this happen, Trying a washer between the head of the screw and the bottom metal ( depending on if it is countersunk or counterbored etc) can allow the screw to tighten up on the stock and clamp up tight rather than the screw bottoming out and leaving the stock loose to the action
 

Mungo

Well-Known Member
The action screw wouldn't have suddenly become cross threaded on its own! Either it was like that all along, even when the rifle was shooting well, or you've damaged it recently by removing it and then screwing it in wonky. However, it appears from what you've said that you didn't strip the rifle down (and remove screw) until after it started misbehaving. Therefore it stands to reason that the screw has always been like that, with no ill effect.
I agree that it can't have spontaneously become damaged.

I only removed it from the stock once before (about 18 months ago), and it could have happened then. Thinking back on it, I did have a number of poor shots that were hard to explain in the time since then - though I can't be sure these weren't due to my own errors or things like wind. I noticed the cold bore flyer about a year ago, and again can't be entirely sure that it wasn't there before - I very seldom shot groups once the rifle was zeroed.

If the damaged stock screw is to blame, then my theory to explain the sudden worsening is that it was being held by a relatively small bearing surface that was worn away by recoil. One observation seems to support this to some extent: when I first started to diagnose the problem, the first thing I did was tighten everything up as hard as I could by hand. The first 9 shots after that were consistent (with the cold bore flyer), and then it fell apart again.
 

Mungo

Well-Known Member
Is the damage to the front action screw definitely from cross threading? or could it be that the stock has compressed up and is allowing the screw to bottom out in the hole and get damaged that way?
I have seen this happen, Trying a washer between the head of the screw and the bottom metal ( depending on if it is countersunk or counterbored etc) can allow the screw to tighten up on the stock and clamp up tight rather than the screw bottoming out and leaving the stock loose to the action
I don't think the stock can have compressed - it comes with pillars from the factory.

Having said that, the screw does seem a bit short, and the amount that appears to actually engage with the action can't be more than 3mm, at most.
 

bullet chucker

Well-Known Member
Is your first shot accurate to your last outing? or is there a new point of impact. I found an issue with a 6.5 Heym that was great after a spell of target/zeroing then when I had issues in the field it turned out the first shots POI was nothing like what I had set at the range,but subsequent shots were back on the money.

BC...
 

Mungo

Well-Known Member
Is your first shot accurate to your last outing? or is there a new point of impact. I found an issue with a 6.5 Heym that was great after a spell of target/zeroing then when I had issues in the field it turned out the first shots POI was nothing like what I had set at the range,but subsequent shots were back on the money.

BC...
So prior to this episode of very erratic grouping, I had a situation similar to what you describe, though perhaps not as extreme. Cold bore shots grouped high and left of warm birevshits, by about an inch, maybe a bit more at times.

But that consistency is now gone, and cold bore shots are just as erratic as any other.

Did you solve your problem?
 

Edinburgh Rifles

Well-Known Member
Rifles dont go from touching hole groups to 6"+ groups without a significant change in the physical interference between stock and barrel IMO

Scopes can die, but thats not the rifle.

scruffy bores can open up groups when deep cleaned but will settle down again with fouling

Crowns can be shagged to within an inch of their lives and still shoot better than some DSC1 candidates

Bores can be minus inches of rifling and still shoot sub MOA (I had a cracking .222 that had about 2-3" of rifling missing on one entire side of the bore about 4-6" down from the muzzle, bloody thing shot anything!!)

I had a similar issue with a BSA .270
3 shots with factory ammo inside an inch suddenly became 6-12"

anyone have first hand experience of having a barrel bore scoped by a gunsmith

Watch the barrel channel gap with slight torsion through the grip



Ditched the non swivel bipod on the light stock, barrel interference went, groups shrank to 1-1.5" with factory and then sub inch with homeloads


Recently tested a client Steyr Mannlicher 6.5x57 that was not doing what it previously did.
Turned out to be variable pressure on barrel through a cracked stock.
Raised the pressure point of the front action screw in the same cracked stock and shot 3 inside an inch with factory ammo with no pause for cooling.
 

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