SKS: Is my hot barrel causing accuracy issues?

[lee sherman]

I have an SKS 59/66 A1 rifle. The firearm is in excellent cond. It is quite accurate at 100 yards and has no issues, except one! Last week I shot 60 rounds thru it. The last ten rounds all went way high, say 6 inchs high. This week I shot 40 rounds thru it. The last ten rounds all went high again. Approx. 6 inchs high. Same ammo both times. The barrel is pretty much hot to the touch for the last ten rounds. Is excessive barrel heat the cause for this?. Before the last ten rounds everything is bullseyes, nines or eights. If I give it time to cool, the rifle, and I are happy again. So maybe I answered my own question. Anyone else ever notice this? Ever since I bought the "C" tool and zeroed it, the rifle has been a dream. Siminov did a good job. Anyone have anything to add?? Thank you gentlemen. Lee

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[Patrick Chadwick]

So maybe I answered my own question.

You did! The answer is that if two pieces of metal are firmly bound together, and are heated up at different rates, then the combination has no option but to bend. The same happens if a mass of metal is heated on one side. To prevent (or at least reduce) this effect, one piece must be free to move. A rifle barrel, if free-floating, is usually symmetrical - with the exception of foresight and backsight - and will therefore remain pretty straight when heated. Unless, of course, it binds on the barrel channel, which often reveals itself as a steady drift as the barrel heats up.

If the rifle shoots OK, and then suddenly goes off course, this indicates that something has expanded to the point where it has become jammed by something else. Self-loading rifles have a very asymmetrical construction, because of the gas channel/piston etc. and are very prone to the effects of metallic warpage. Lever-action rifles also show this effect if the magazine tube is not free to move at one end.

In other words, if the POI changes suddenly, then something does not have adequate freedom of movement, and is being constrained to the point of jamming. What and where that is can often only be discovered by a detailed examination of the stripped-down rifle, looking for burrs, rubbing marks and other signs of metallic unhappiness!

[Gun Surfer]

I have similar issues with other milsurp rifles. Thats why I like shooting my milsurp rifles on cold winter days, don't have to wait as much between shot strings (and there's less people at the range too).

[1911crazy]

With the yugo I would slug/mic the bore diameter and the ammo your shooting. The yugo's seem to have larger bore diameters.

Are you sure you got all the cosmoline out of the gas tube and the exhaust ports are wide opened and not clogged up? (heat)

I lube my sks with moly and put a tad of moly on the gas piston/tube too, besides the recoil springs, op rod, bolt carrier/bolt and trigger sear.

[MK Wheelie]

I have the same issue with my CZ 858. After 60 rounds, the bullets start to drift up to between the 10 and 11 o-clock, progressively going higher and higher with every shot. PC brought up an interesting point on the duel metals. My CZ's barrel is chrome lined, so I wonder if that may be a contributing factor to my particular delema.

[Stevo]

Interesting. I've never noticed that with my non-restricted 858s. I really doubt your chrome-lined barrel has anything to do with it.

What sort of mods, if any, does your rifle have?

[MK Wheelie]

Stevo, no mods whatsoever, it's just as I got it out of the box. It was perplexing, as at first, I couldn't see what was happening to my shots. It was at the end of the day at the range, so when I started missing the target, I just chaulked it up to fatigue.

It just so happened, I had my video camera set up to record where I was hitting. When I viewed it at home is when I saw where the errant bullets were going. After that, I took carefull note when I was shooting the CZ. It's pretty consistant. 60 rounds on the nose, and away goes the accuracy.

I have no idea why, or even if I can fix the problem. But like you say, "interesting." I just thought that PC's comment may be a remote possibility as to what is happening.

I'm sure this problem is limited to my rifle, and not to the 858 in general. Another person I shoot with, has the restricted version and has no problems.

Cheers, MK

[Stevo]

How many times have you shot the 60 round strings and noticed the difference? Do you shoot the 60 at the same rate of fire from string to string?

If you're shooting at a consistent pace it probably is heat related somehow. I wonder if the tension on your lower handguard is changing?

[MK Wheelie]

Stevo, I generally shoot the strings the same way. I shoot at swingers at a fairly steady rate, a shot every two or three seconds, stop, pull magazine, reload with five more, start shooting again the same way. I'm fairly consistant with my style. I do the same thing with my SKS, up to 120 rounds, depending on my mood for the day. (thank goodness for surplus ammo. those rifles go through ammo like a fat kid goes through smarties.)

Your hand guard sugestion is quite plausable, something I will look into.

Thankyou, MK

[Stevo]

MK,
Yes, they sure do manage to chew through the ammo at a great rate. I'm glad I've stocked up.

Last question: are you shooting from a rest? If so, is it possible the rifle is moving on the rest over the course of the string, leading to a deflected POI?