I think I've got the answer! we had a similar problem i.e. large lambs that all had to be pulled. this is our third year at lambing and this year so far we haven't had to pull a single one and have'nt lost any nither. We started with 6 lowland commercial ewes with three ewe lambs they had a mix of texel, charollais and lleyn in them and for the first two years we borrowed tups including a texel, charollais and suffolk for free from the farmer we bought the ewes from. 90% had to be pulled and there were several dead on delivery. We were understocked and thus had loads of grass over the wintern in the first two years and we cautiously over fed them with concentrate in our ignorance so the singletons in particular were massive. We have kept ewe lambs every year and are now up to 21 ewes and grass is very scarce but the lambs, nearly all twins come out themselves. The key bit is the tup we now use - a soay! We were "donated" two soay ewes by a neighbour and when crossed with a texel or charollais tup, we were so impressed by the lambs and the milkyness and mothering qualities of the soays, we bought a pedigree registered soay ram lamb for £50. Last autumn we put him to the whole flock and hey presto the results are now to be seen - all twins, all self-delivered outside and tough as nails in this horrible weather. Although initially small and will not make the 40kg, they'll be a reasonable size by next autumn. For us the benefits of easy lambing far outweighs the final size. We've also kept some of the soay cross ewe lambs and crossed them back to a soay tup to get a three quarters soay lamb. They look and taste like a soay but are bigger meatier and mature faster - the best of both worlds - perhaps I should breed these pure and market them as a new easycare breed! sorry that's already been done once here on Anglesey!!