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Cause of Continual Fliers in Bedded Sako 85 Finnlight?

25 Jun 2015
@ 10:29 am (GMT)

Bush Chook

Hi All,

I've recently fore-end stabilized and bedded my Dad's Sako 85 Finnlight in .260 Rem. This significantly reduced group sizes overall - which was good -but hasn't fixed its flier problem - instead it appears more pronounced. However, this apparent worsening of the problem could be an illusion due to the fact that overall group size has reduced.

The Symptoms:

While this has been an ongoing issue, todays result was quite the best example of this problem.
I was doing a graduated load test of three shot groups about 1.5 grains over the maximum recommended, increasing in 0.1 grain increments (just being cautious) per group. Of this string, virtually every single group consisted of two shots touching and one flier. As the rifle neared a good load, this “flier” worked its way down to the other two (forming a nice triangle group) and then on the other side of the good load, it worked its way out again. Over about 0.7 grains of powder charge it came in and out twice – forming two good loads, and several also-rans. Group sizes ranged from about 1 – 0.5 MOA so the results aren't that shocking but even in the good load the flier started becoming noticeable at 200 yards. The flier shot was usually the first or third shot, but was sometimes the second.

A sweet spot that I investigated further down the powder charge scale also exhibited the same issue – two good shots and one lonely, unwanted little bullet hole than wandered in and out again.

Possible Causes Investigated:

One of the reasons for doing the bedding job in the first place was to eradicate these nomads so I was particularly careful to relieve all parallel wall metal and the front, bottom and sides of the Boss. (To those who are familiar with the 85 bedding system, the boss fits into a floating alloy lug which, in this case, had been thoroughly glued in by a somewhat-wanting gunsmith. I ground out the front, bottom and sides of the Boss recess. I also ground a triangular shaped piece of material from the lower rear of the Boss recess forming a “trap” for bedding compound behind the boss. The result of this was better than expected, with a thin line of alloy-on-Boss contact at the top rear of the Boss trapping a strong layer of compound against the Boss further down. This seems to have held up well as after 50 shots no signs of cracking have appeared.) I relieved virtually everywhere else with a layer of tape – the only areas with flush contact were the two beveled sides of the base of the action, the back of the boss, the flats and the knox. Maybe this single tape layer is insufficient at high risk areas like the back of the tang and the sides and front of the Boss? The action fits into and out of the stock very smoothly and doesn't need to be walked or wiggled out. I went over the fit of the action after my last round of fliers and found it was pinching in a few areas which I duly relieved. In my very limited experience it now feels spot on. Its also lightly greased except around the Boss. Are there any problem areas with the 85 action that need extra relieving?

The bore looks all good. I have been through it several times with a bore scope, most recently after cleaning after today's shots and apart from a little crazing at the throat and the odd scratch on the lands, I couldn't see anything untoward. However, I am no expert, so it's possible. The crown also looks sharp and undamaged. The barrel had been completely copper-de-fouled before today's shots so it wasn't copper buildup.

The extreme spreads of today's loads were mostly all under 20 so it wasn't wildly varying velocities.

It could be my shooting technique. Are there any habits which cause fliers? I'm fairly sure I wasn't flinching or jerking the trigger (most of the time) but it may have been some other subconscious habit.

Final Musings:

I was wondering if maybe this wasn't in fact a flier problem but just the result of the barrel harmonics of this particular rifle coming down to and going away from a good load. Looking at the groups of the good loads at 100 yards today, one wouldn't say there were fliers in the group. It was just on either side where the walkers appeared. However, as usual nothing in rifles is simple and at 200 yards the fliers appeared with the 2 good shots close together. It just strikes me as very curious that apart from the good loads virtually all groups had a flier.

So what do you guys think? Bedding problem and relieving required? Shooting technique issue? Natural barrel harmonics? Something else?

Thanks very much!!


25 Jun 2015
@ 09:38 pm (GMT)

Nathan Foster

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Hi Chook, really sorry but this post cannot be answered properly without the rifle in hand. The L shaped lug should have been removed from the stock using heat to pull it, and then mated to the action (or cut down and then mated to the action) prior to bedding. Shoulda woulda coulda- all very well in hind sight huh. You may very well have a good system in place but I am unable to tell without having the rifle here. Nevertheless, from what you describe, you know what you are looking for as far as points of contact and points of relief go.

You say that the overall group sizes have come down quite a lot- so this should make all of my comments above moot, regardless of how I would do things. Sorry, the glued lug must have put you in a difficult position.

It is common for these barrels to produce fliers, the fluting is a major problem. To isolate if the barrel is a problem, you'll need to let the barrel fully cool to ambient between shots, this can take a few minutes. If all three shots stay tight, it will be a barrel stress problem. A relatively fast 4 shot group will probably show as a clean double group.

You may just have to make piece with this as being a one shot wonder.

If you get the urge to take this to its final conclusion, you may need to look for a heat treatment outfit. Strip the rifle, take in the barreled action, then ask them if they can heat to 525C, hold, then slow cool. The outer will need to be re-blasted afterwards and the bore given a brief re-polish. Then hope like heck that it helps and was worth the dozen beer and trouble stripping the action.

Make sure you shoot over sand bags, no bipods during this stage of testing. Shooting technique is covered in great detail in the final book, but yet to publish sorry.

Thanks Beretta- another customer left scratching their heads.

New Zealand readers please note, there are currently deep fluted Tikka T3 Lite rifles on the gun racks at some gun stores. Stay the hell away from these rifles.
26 Jun 2015
@ 04:04 am (GMT)

Bush Chook

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Thanks very much Nathan for your prompt reply.

When bedding I did think long and hard about what to do about the lug. I read your updated "How to" on bedding the 85 but the lug seemed so well stuck in I was afraid that I might end up wrecking the stock trying to get it out. When I was grinding the lug down keying into it, the lug got so hot that it started melting the plastic stock around it. However the titanium bedding compound that was holding the lug showed no sign of moving. The main thing I was afraid of when leaving the lug in was ending up with a super thin shim of bedding material between the boss and the lug which would eventually crack and fall out. So I ground a large "cave" recess in behind the boss to take a thick layer of compound but left a small overlap at the top to go against the boss and trap the compound in. It seems to have worked pretty well. I've actually got another tampered with 85 to bed pretty soon so I might take a chance on destroying the stock and try to dig the lug out and bed it your way. This should provide a good comparison enabling me to see if this bedding method stacks up against your recommended method.

Thats very interesting what you say about this problem probably being caused by barrel temperature affecting the fluting. This could well explain one of the more confusing aspect of yesterday's results. This was that when we tried a good load at 200 yards, it suddenly went walkabout. The first shot of the first two groups were a good four inches away from the others. But then the first shot of the third group came down to about an inch away from the others. Throughout this shooting session the ambient temperature was hovering around -2 degrees and before the first 200 yard group the barrel would have had plenty of time to cool right down while we set the target up and mucked around. Once we were established, the turnaround time between groups was pretty rapid. It could be that by the third group the barrel hadn't cooled off as much as it had before the first shot of the first and maybe second groups.

The plan now is to do as you suggest and fire several groups allowing the barrel to cool down completely between shots and then fire a few rapid four shot groups and then analyze the results..

I'm interested in the heat treatment option. If this is done, does it change the properties of the steel so much that the barrel needs to be proof tested again?

I have been using a gun sled (with forearm hold) when doing these loads to try to reduce the human error element. I've been somewhat of two minds about using it but, for the sake of consistency, I didn't want to dump it halfway through. Maybe I should though... I can't wait for your shooting techniques book to be released, you've got a guaranteed customer here!

I will report the results of the barrel heat test when done.

Thanks once again.

26 Jun 2015
@ 07:36 am (GMT)


Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Thanks for the heads up on the fluted tikka Nathan. (A mate was asking about a Tikka the other day)
I feel a bit sorry for guy who can't carry a t3 lite without flutes.
26 Jun 2015
@ 09:31 pm (GMT)

Nathan Foster

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Hi Bush Chook, the heat treatment I am talking about is only for stress relief without enough heat to completely change the structure of this particular steel. Nevertheless, load work would have to be redone.

Just keep in mind that there is only so much that can be done with a barrel like this.
27 Jun 2015
@ 04:27 am (GMT)

Bryan Webster

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
I would recommend doing away with the sled. Use a good sand bag for the rear of the stock and the front as well. I have in fact watched while people used led sleds and observed few could obtain decent groups from otherwise accurate rifles.

My eldest son had the reticle of a Vortex Viper scope fall apart while shooting a 300WSM T3 Tikka in a Led Sled. He now uses a Zeiss scope and only bags front and rear.
27 Jun 2015
@ 09:38 pm (GMT)

Nathan Foster

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Very good advice Bryan. Sorry Bush Chook, I neglected to comment on this earlier.

Regarding optics, I would not want to put a short eye relief Ziess on a lightweight high recoiler. Nevertheless, it sounds as though your son is doing well with the rig.
02 Jul 2015
@ 11:41 am (GMT)

Bush Chook

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Hi Nathan and Bryan, thanks for your earlier comments.

The results from the barrel heat test were interesting but didn't quite run to the script. This seems to always be the case when mucking about with rifles – you never seem to quite get the result that you were looking for.

For this test we only used a single, moderately-powered load of 43.0 grains of AR2209 driving a 140 grain Amax at an average velocity of 2640 fps. This load had previously given good, warm-barrel, three-shot results of approximately 0.5 MOA on several occasions but had inexplicably thrown fliers on the first shot of a cool (but fouled) barrel as explained previously.

In order to attempt to isolate the problem, I only changed one variable at a time. Thus I used the gunsled for the first few groups, then changed to front and rear sandbags thereafter. Before beginning this test the barrel was sparkling clean, copper free, the throat polished and all oil residues had been removed with brake cleaner.

Having fired three fouling shots which were used to get the rifle on paper at 100 yards, I fired three shots off the gunsled allowing the barrel to cool between shots till it felt cold to the touch - allowing approximately 10 minutes or so between shots. The result of this was a 1.25 inch long diagonal string on the five past seven line, each shot higher than the last but nothing that could be called a flier. The next group was another slow, “cooled”, three-shot group of 1.58 MOA. The first shot was high and to the right, the other two shots were about 0.5 inch apart about 1.5 inches to the lower left of the first shot. The POI of the first shot of this second group was about 2.5 inches above and to the right of the POI of the first shot of the first group. The final gunsled group was a fast four shot group fired soon after the last shot of the previous group – the barrel was just warm to the touch on the first shot. The result of this was a very clear double-group, the first two shots nearly touching, the next two shots also nearly touching about 1.4 inches to the left of the first two.

The final four groups were fired using a front and rear sandbag. The first of these was another “cold” four-shot group – maybe not quite completely cold as the 4°C ambient temperature and the sandflies did try one's patience a little but the barrel was allowed to cool between shots until it was mostly cold to the touch. The result of this was a wide, roughly triangular group about 1.2 inches apart in the horizontal plane and 1.5 inches in the vertical plane. The POI worked its way around in a random fashion, the first shot was, once again, in the top right, the next the lower left, the third shot was to the bottom right and the final one was in the top left, nearly touching the second shot. Soon after the last shot of this group I fired a four-shot group in quick succession, This group was about 1.2 inches square with no fliers or apparent double grouping. The first two shots were at the top of the group and the final two were at the bottom of the group. As this group is somewhat of an anomaly when compared with the previous and subsequent rapid-fire groups, there is a very good chance that it is the result of poor shooting resulting from my reaquaintance with the recoil of a gunsled-free rifle. Following this fast group, I fired another two, four-shot groups in reasonably quick succession. However, at no time did the barrel temperature rise above being comfortably warm to the touch. These two groups were both a rectangular shape, each showing a distinct double group. In the first group, I didn't see the order of shots but two shots were touching and the other two were very close together, the pairs being about 0.5 inches horizontally apart. I did see the order of the second group. In this group the first and second shots were close with the third and fourth shots touching. In this case the pairs were about 0.7 inches apart vertically.

What we were hoping to find from these hot/cold barrel tests was what you said would definitively indicate a barrel stress issue – that with a cold barrel the rifle would group nicely and as the barrel warmed up, it would start to throw double groups. However, these results seem to indicate that there is a bit more going on. In my opinion they suggest that a cool barrel throws unpredictable shots and when the barrel is maintained at a constant warm temperature and is firing a load that it likes, it shoots reasonably tight, but at the same time, double, groups – each pair moving incrementally as the temperature of the barrel increases. Supporting evidence for this theory is the fact that most of the fliers we had in previous loads were on the first shot of a group, as after a group, we have been letting the barrel cool down until it is just warm. However, several fliers also occurred on the third and one on the second shot. Maybe the barrel is quite sensitive to small temperature variations and in these cases it wasn't as cool when we started and because we were firing a load it didn't like the POI moved further than it would have for a good load? What would be your overall interpretation of these results?

If you still think this problem is caused by barrel stress, we are considering whether we should undertake the heat treatment option or just re-barrel straight away. If we do try heat treatment, is it a requirement or only beneficial to treat the action as well? If it is a requirement, will this affect the action at all (other than cosmetically) with regard to re-barreling? Or can it not do any harm?

Thanks for taking the time to wade through this treatise!
02 Jul 2015
@ 09:04 pm (GMT)

Nathan Foster

Re: Cause of Continual Fliers in Bedded Sako 85 Finnlight?
Hmm. So the barrel is generally inaccurate when cool and then shows heat stress when warm and double groups. Its got you coming and going.

Still, I am hesitant to rush into a rebarrel recomendation just yet. The rifle is not wildly inaccurate.

There are factors I am unaware of such as your hand loading procedures or your shooting methods with or without the sled. You may need to give me a call at some stage but please call during day hours. Trying to help with this particular problem via forum posts is fraught with difficulties. Even a phone call has limits as I cannot see the rifle. But it does at least get me closer to the coal face and I might be able to help a bit better.



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