L8 and Sterling/Charnwood 7.62 conversions- Harmonics and Mathematics

[jss]

I have a Sterling 7.62 conversion which has been reported as shooting 2-5 moa depending on ammo and have also read here that the L8 suffered from similar accuracy problems caused by incorrect barrel harmonics. Also here somewhere is a thread stating that an algorithm or formula existed for the development of a cartridge for experimental rifles, and I have seen a web site (although modern, probably "bench rest") proposing a method for reloading to tune out resonance I think and thus improve harmonics.
If the mathematics existed to model and tune barrel/cartridge harmonics, then why did the L8 project even begin as they must have known that a 303 barrel was not compatible with 7.62 NATO ammo, or was this algorithm/formula just a starting point?.

Also, has anyone else tried reloading to tune out the inaccuracy of one of these conversions?.
I know it can be done by DCRA type bedding but I'm just curious to know if a simple reload wold make the difference.

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[Peter Laidler]

Put it this way........ a bog standard, off the shelf No4 rifle used as a control sample out performed EVERY 7.62mm L8 converted rifle on the trial, even the telescoped L8T's.

There might be an answer - somewhere, but the barrel standard barrel configuration didn't fit in with what a) they wanted and b) what was available and c) the cheap option of availability. The best that emerged was the big, heavy, long barrel. Enter, stage right, the L42............. As a matter of interest, during the first year or so after its introduction, when the sniper courses were running both the L42 and L96, the old L42 could match the L96 except when the bipod was employed.

[Thunderbox]

I have a Sterling 7.62 conversion which has been reported as shooting 2-5 moa depending on ammo and have also read here that the L8 suffered from similar accuracy problems caused by incorrect barrel harmonics. Also here somewhere is a thread stating that an algorithm or formula existed for the development of a cartridge for experimental rifles, and I have seen a web site (although modern, probably "bench rest") proposing a method for reloading to tune out resonance I think and thus improve harmonics.
If the mathematics existed to model and tune barrel/cartridge harmonics, then why did the L8 project even begin as they must have known that a 303 barrel was not compatible with 7.62 NATO ammo, or was this algorithm/formula just a starting point?.

Also, has anyone else tried reloading to tune out the inaccuracy of one of these conversions?.
I know it can be done by DCRA type bedding but I'm just curious to know if a simple reload wold make the difference.

The L8/Sterling programme was simply intended to convert hundreds of thousands of rifles as easily as possible and at the cheapest possible price. Keeping the same barrel profile clearly meant that it was a simple screw-in conversion with no woodworking required - hence saving time and money.

A point to consider is whether the L8/Sterlings are actually outside of the presumed accuracy specification? Lets not forget that most .303 No4s easily exceeded the accuracy specification so, even if 7.62mm appear slightly less accurate by comparison, they were probably mostly still inside the acceptance criteria. Certainly all of the Sterlings/Charnwoods/anon conversions I've tested have shot 3 or 4 moa - so good enough for what was intended.

[Mk VII]

What is the twist-rate in this specimen?

[Peter Laidler]

Also worth remembering is that the Sterling conversions were never a military option and never trialled at any stage either, As for the Charnwood conversions, well................................... The least said the better but somewhere in the world there might be one with a happy owner

[tbonesmith]

I think you might do better to tune the bedding. Plenty of No4 7.62 conversions shoot very well with Lithgow Heavy and standard profile barrels. Centre bedding is the norm. Mine has a standard profile No4 7.62 Lithgow barrel and shoots superbly, it is centre bedded as per the Canadian instructions on this site, no glass.

[Peter Laidler]

That's interesting TBone but I suspect that there must be a lot more to it than that. I'm not a ballistician but my understanding of the trial paperwork was that the harmonics of the 7.62mm NATO round (as was then.....) was such that the disasterous accuracy might be solved if the barrels were muzzle bound. This would alleviate the problem which was that the muzzle vibrations would whip vbiolently and it was this whip that sent the bullets, well......, anywhere really. Centre beding would just exaggerate the condition..........yes? Modern barrel steels might be the Lithgow answer.

What say you ENSCI? Any ideas

[jss]

I think you might do better to tune the bedding

Thanks, yes I've had a look at the Canadian Instructions. Not sure whether it would "spoil" the rifle, althought they don't seem to be deemed collectable.
When your new to this Enfield stuff it's unclear as to what you can or should change and what not. Perhaps I'll get another and compare bedding with reloading; except that I've just changed my two remaining slots to 303's. Theres just something about the 7.62's!. Still, can't have them all.

[tbonesmith]

All the Lithgow barrels were made decades ago ('60s)May have made some later, but most ones that float around were made around that time.

[jss]

This would alleviate the problem which was that the muzzle vibrations would whip vbiolently and it was this whip that sent the bullets, well......, anywhere really

Simplistic I know but I was thinking that a fast burning powder with a light projectile might reduce that effect, pressures permitting of course!.