L8 and Sterling/Charnwood 7.62 conversions- Harmonics and Mathematics

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.

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.

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Originally Posted by 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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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.

What is the twist-rate in this specimen?

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

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.

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

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Originally Posted by tbonesmith

I think you might do better to tune the bedding

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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.

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.

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Originally Posted by Peter Laidler

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

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

Have you looked at "The ladder method" of load development. Fast and effective. Google it.

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Originally Posted by 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

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Me? My Charnwood No. 5 in .308 (in the right hands ... certainly not mine) is very accurate indeed. Although (I´m shamed to admit) it´s been Acraglassed. But like my other No. 5 in .303, it seems to be a lot better at 300 metres that at 100.

I have owned two No4 .308 conversions,
The first rifle is a Savage with the Sterling .308 conversion and what I believe to be a standard profile barrel.
The second rifle is a Longbranch with a Lithgow .308 conversion and a heavy barrel.
I am not an expert on the different bedding techniques, however both these rifles appear to be floating for at least the front half of the barrel.
Both these rifles shoot very mediocre with mild loads.
I wish this wasn't the case however as the load gets to the point where it's hot both of these rifles shoot with much greater accuracy.
Cheers

Re the Sterling barrel, an example I checked some years ago (about 40!) had bore diameter 0.298" and groove diameter .3092 to .3095" by slugging (a bit on the high side). 6 groove rifling with a 1 in 12" twist.
I believe that some research was carried out at the Royal Military College of Science, Shrivenham 40 years or so ago on barrel vibrations and people would certainly have looked at improving the accuracy of the Sterling/L8 barrels by adjusting the bedding: it is a matter of tracking down the trial reports.

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Originally Posted by tbonesmith

Have you looked at "The ladder method" of load development. Fast and effective. Google it.

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I have done a search and understand the principle.. have you used it? If it really works as easy as it sounds it will save heaps of time and ammo to my usual method of taking heaps of rounds to decide if a powder/projectile combo is any good or not.

Perhaps this is just the engineer in me, but given that there's a mathematical formula for determining barrel harmonics, is there a comparable formula for round harmonics?

The one I had was a twist rate of about 1:10.5, and it would not shoot M80 ball equivalent worth a damn. Only with reloads with a 180/190gn bullet did the groups shrink dramatically. This was with Fulton's 'New Zealand' bedding, as I recall.

The thing I learned about bullets and the associated harmonics is that whatever happens thereafter to the bullet, it's first exposure to the outside world (or life outside the case), even before it hits the atmosphere, is travelling up the vibrating bore of the rifle, accellerating (and not even at a steady or constant rate either.....) as it does so. That barrel, what it does and the way it moves dictates everything the bullet does. Not an scienmtifically EXACT statement I agree, but one at the forefront of how Armourers, as opposed to ballisticians think

Question here. Why were the DCRA barrels so accurate then? were they a different profile from the 303 barrels? my DCRa without any special bedding is very accurate and to all intents and pruposes looks identical to a 303 apart from the lack of bayonet lugs.

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Originally Posted by newcastle

Question here. Why were the DCRA barrels so accurate then? were they a different profile from the 303 barrels? my DCRa without any special bedding is very accurate and to all intents and pruposes looks identical to a 303 apart from the lack of bayonet lugs.

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Isn't your DCRA centre-bedded or free-floated?

It is not any different that I can see to any of the 303 No.4's I have. it's certainly not free floated, but would center bedding look different?

I'm even more curious now.
How often do these rifles, especially DCRA and Sterling, come up for sale in the UK?. I've only seen a few for sale here in the last year or so.

There were only about 2000 DCRA 'official ' (ie numbered 1 - 2000 or so by the DCRA) conversions done. I would be surprised if many of these were in the UK at all

Just out of interest, Sterling Ltd's blurb...
Attachment 24750

My Charnwood 7.62 converted LE No. 5 used a No. 4 action. The barrel was free floating from the knox form forward.