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> Wildcatting the .303 Brit
Wildcatting the .303 Brit
@ 10:08 pm (GMT) |
Andrew MurrayHi all,I'm wondering if anyone can provide advice on creating wildcats versions of existing cartridges? I'm considering if it's possible to neck-down a .303 to accept 30 cal projectiles while keep the rest of the dimensions the same? In the same vein doing it with a7.62x54R? I've got a 303 that needs a new barrel and am wondering if there's any worth in jumping down a size to take advantage of the wider selection of projectiles? Cheers |
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@ 08:06 am (GMT) |
Nathan FosterRe: Wildcatting the .303 BritHi Andrew, lets see if we can help a bit..303 Brit. The minimum spec for the .303 neck diameter is .345". The leade is .313" diameter and goes into an immediate taper at .4 degrees (basically a Brenneke style throat with no parallel free bore). Noting that Highland / NNY / Prvi is the most common .303 ammo / brass now, a measurement of the loaded neck yields .335" (with .311" projectiles) and .336" when hand loaded with a .312" projectile. A measurement of the case, necked down and seated with a .308 projectile yields a neck diameter of .332" .308 Win. The minimum spec for the .308 neck diameter is .344". The leade is .309" diameter and has some parallel before transitioning to 1.75 degrees. Loaded ammo ranges from .333 to .340" at the neck depending on the brand of brass used. About .336 to .338" would be the most common numbers. Results will vary depending on the type of reamer you want to use. If you use a .303 reamer which has a min neck diameter of .345 (or possibly .347 if max diameter), the necked down ammo (at .332") will have quite a bit of wiggle room (potential bullet yaw during ignition) within the chamber. After expanding to .345 to .347", the case neck will also require some work (potential work hardening) to get it back down to .308. In addition to this, the leade just ahead of the case mouth is quite wide at .313 rather than .309, but does taper in gentle fashion. So, the issues are 1. loose tolerance at the chamber neck which may interfere with accuracy, 2, a degree of work hardening at the necks and 3, loose specs at the leade. In layman's terms, it is not the ideal scenario for optimum accuracy in a rifle that is already potentially finnicky to tune. If going this route, neck sizing is the key including partial neck sizing, leaving the bottom of the neck at its fire formed diameter. The .308-303 using the standard .303 reamer is not a new concept and has been done more than a few times. If you want to try it - then try it. I am not trying to warn you off but am instead simply relaying potential outcomes for the sake of realistic expectations. The other option is to have your own reamer constructed with a neck diameter .006" larger than the .332" loaded case neck - i.e. .338", followed by a .309" FB and 1.5 degree leade. Though potentially accurate, the problem with this approach is that if anyone accidentally chambers and fires .303 Brit ammo in the rifle, the results may be disastrous. The neck will only have .002" clearance which is very tight and can drive up pressures but is secondary to the fact that the .309" bascially means no freebore (with a .311 or .312" projectile) for gas expansion. Going the other way (though not recommended for reasons of safety), it is less dangerous to fire .303 ammo in a chamber reamed with a standard reamer but with a .308" bore. The same basic principles apply to the 7.62x54R. Loaded (.311") case neck is .335" to .336". Minimum chamber neck diameter .339" (max = +.003" note that the Russians generally work to or above max specs). Leade angle .5 degrees (no parallel). Hope that helps a bit. All the best. |
@ 05:03 pm (GMT) |
Steve WilsonRe: Wildcatting the .303 BritHi Andy,Some years ago I had a Lithgow SMLE barreled with a .30 cal barrel and a 303 chamber. In fact I see the rifle is now for sale on Trademe here in NZ. Anyway I found the accuracy to be only adequate from this particular rifle with 308 projectiles, somewhere in the 1.5" group size on average. I suspect that as Nathan has commented, the oversize neck for the 308 projectiles allowed enough wiggle to perhaps cause the less than stellar accuracy. Obviously much depends on what kind of accuracy you are after and what kind of ranges you want to shoot to. In contrast my No 4 T replica will shoot sub 0.5" groups from a .311 bore and standard 303 chamber. I have been contemplating whether 30 40 Krag would be the solution to using a .30 cal barrel on a Lee Enfield. The only issues being brass and a reamer. A quick search online shows that 30 40 brass can be made from 303 if you can't find any in Oz and Manson Precision Reamers make a 30 40 reamer. Dies are available from Lee, although they don't do a neck sizeing die. Cheers |
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