You got a deal!! That is about what those cost when they came into the country in the mid 90's. The MKII were the best built of the No 4's and it shows in the lack of tool marks and tight fitting. Of the No 4 MK1's, the Long Branch show the best fit and finish, and yet, their chambers look like they were cut with wood rasps. The MKII's have nice clear cut rifling, a nice smooth tapered throat. Simply the best of the bunch.
I shot mine, I did not conduct extensive load development , and what loads did work, I used WC852 powder, which is a surplus powder. I think IMR 4064 or equivalent is the best powder to start, Varget if you have it. The 303 Brit was not a high pressure round by today's standards, the pressure was kept in the low 40 K psia range. I think the upper limit was 45,000 psia, but with this action, lower is better than higher. While the action is relatively weak, I would not say that about the round. Any round pushing a 174 grain bullet 2500-2550 fps is a powerful round. The 303 Brit has wacked everything on the earth, every mammal specie, and every race of human. Lot of unsatisfied customers.
The World War One sniper, Herbert McBride made comments on the ability of the round to put round holes in square heads. Compared to modern service rounds, like the 7.62 X 39, 5.56 Nato, the 303 Brit is a cannon. I shot Greek ball through my MkII and this are the velocities I got:
No. 4 MkII mfgr 12/53
174 Greek Ball ammo mfgr 1970
9-May-92 T ≈ 70 °F
Ave Vel =2488
Std Dev = 12
ES = 27
Low = 2473
High = 2500
N = 5
174 grain Greek Ball HXP 70
8 Feb 2012 T = 50 °F
Ave Vel =2423
Std Dev = 14
ES = 53
High = 2456
Low = 2403
N = 14
180 grain Winchester Silvertip Factory Ammunition
8 Feb 2012 T = 50 °F
Ave Vel =2297
Std Dev = 14
ES = 46
High = 2319
Low = 2273
N = 10
That Winchester factory ammunition is positively anemic, but then, they are selling ammunition to the world. The US does not have proof laws such as the European countries. I know for Germany and Britain, and probably all the others, you have to submit the rifle to a proof house prior to a private sale. If the rifle does not pass inspection, gaging, and final proof testing, you can't sell it. Final proof testing is conducted with a lubricated case and a proof round about 20-30% over standard pressures. The lube is there to ensure the locking mechanism is fully loaded, which makes the proof test technically valid. If the case was dry and the chamber was dry, then the case will take load, reducing the load on the bolt, but stretching the case. Incidentally, according to pre 1968 German proof law, the proof house destroyed the whole gun if it failed proof compliance. Then the law was changed, no doubt to the regret of the Proof House workers who probably had fun destroying expensive rifles, after a buttplate screw fell out!. Now, only the defective part is made inoperable. But, the point is, European ammunition manufacturers know that the weapons in European civilian hands are 100% up to snuff, and they can produce ammunition that would blow the relics in American hands, to pieces.
Which explains why Winchester produces such anemic ammunition, Americans have a lot of rusted out, worn out, out of spec, military weapons in their hands.
Case stretch is a continual issue with Lee Enfields as rear locking actions stretch much more than front locking action. Basically, lets say steel compresses about 0.001" per inch (SWAG). And the locking lugs are four inches behind the bolt head, then that four inch spread will compress the bolt 0.004" when the rifle is fired. That distance, plus the headspace in the rifle, means that rear locking mechanisms are hell on the case. The case gets stretched 0.004" just due to bolt compression alone. Dry cases in dry chambers will be stretched so much in Lee Enfields that cases will separate in as little as two to three reloads. Some people have tried to compensate for the headspace, that is remove the headspace, by adding O rings ahead of the rim. I think that was a poor solution. The best solution is what Parashooter did in his Lee Enfield, lubing the cases:
Cases and Enfields and lube - Oh my!
http://www.milsurps.com/showthread.php?t=11182
As long as cartridge pressures are less than or equal to service requirements, the action won't be damaged. Over pressure loads are easy to figure out in the Lee Enfield, the bolt gets very hard to open, because it bows. Load down to the point where bolt lift is effortless and everything will be fine, your cartridges will last forever, and the mechanism will be fine.
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