No.4 Mk1 Lee Enfield: How strong - CUP

Pathfinder

Pathfinder

CGN Ultra frequent flyer
Rating - 100%
124   0   0
Location
Northeast Ontario
Just wondering how much this action can handle ? I know .303 British runs around 47k-48k CUP but then again where they not also made or rebarrelled in .308 win? which runs around 65k CUP or is it actually a different receiver ?????
 
Pathfinder said:
Just wondering how much this action can handle ? I know .303 British runs around 47k-48k CUP but then again where they not also made or rebarrelled in .308 win? which runs around 65k CUP or is it actually a different receiver ?????
Click to expand...
This is strictly from memory, so you better search to confirm what my aging brain is dredging up from the past.

The "normal" operating pressure (not proof pressure) of the Mk4 action is 45,000 psi, with a maximum operating pressure of 48,000 psi. I think the Mk VII ammunition generated 47,000 psi. Once again, confirm my memories from a printed source, don't take them as gospel.

The 7.62 NATO is not exactly the same as the .308 Winchester, and discussions of this and what those differences are abound on this website and elsewhere. However, people who have tested many batches of military 7.62 ball as part of their employment with governments say it is not uncommon for some lots of military ball to hit 60,000 psi, whatever SAAMI may or may not say regarding pressure differences between the two.

DCRA conversions were built on these rifles, and a search on the subject will come up with quite an assortment of stories, personal anecdotes, and opinions.

Anecdotal evidence I have heard regarding the No 4 action is that it is amazingly strong, even when abused. Bill Leeper and I were having a chat in his shop one day and he told me of his efforts one time in an attempt to blow up a bubba'd old Lee Enfield. This conversation took place probably ten years ago, but as I remember it, he worked at it pretty hard without getting any pleasing visual effects. Bill does check this forum from time to time, so you might ask him to relate the story - I found it fairly intriguing.

I wouldn't abuse any of my No. 4's by pushing pressure limits - they aren't making Long Branch Lee Enfields any more. Then again, I wouldn't lose any sleep worrying about how strong they are, either.

If I was musing about rechambering a No. 4 to another NATO cartridge, it would have to be a bubba'd rifle to start with, and I would probably look to the 5.56 rather than the 7.62 when I trotted off to have a word with my gunsmith.
 
A goodly number of #4s were indeed converted to 7.62 and it seemed to work. Not a handloader's dream however because the action tends to stretch brass a bit.
I load my 30/40 #4 much heavier than I would load a Krag. These loads are not shot often , however, and brass life is relatively short.
In general, I can't recommend hot rodding a #4 too much. There are actions much better suited to this. The #4s ( and the SMLE for that matter) don't blow up when they fail; they just stretch out. The head comes off the brass and the gases escape doing less damage than one might expect. A wrecked Lee Enfield looks OK from across the room but is wrecked nonetheless! Regards, Bill.
 
Leeper said:
The #4s ( and the SMLE for that matter) don't blow up when they fail; they just stretch out. The head comes off the brass and the gases escape doing less damage than one might expect. A wrecked Lee Enfield looks OK from across the room but is wrecked nonetheless! Regards, Bill.
Click to expand...
Hi Bill:

I was hoping you'd relate the experiment again to refresh my memory.

Anyways, your comments remind me that I probably didn't choose my words properly. I shouldn't have said that Lee Enfields are "amazingly strong" - what I should have said is from what I have told they don't let go with a lot of drama when taken past their structural limits. I think of that as "strong" in that I would much rather they just stretched out and let gas go here and there than have a pipe bomb fragment beside my face and eyes.

However, God willing, I will never be dumb enough or negligent enough to overload any rifle that I'm holding in my hands when I pull the trigger.
 
Those are long tons, so the pressure doesn't convert to 37 000, its higher.
I have no idea which measuring system was used to establish the /sq. in. Psi and CUP are not directly comparable. Different numbers will result with different systems if the same loads are used.
The proof was for ammuntion developing 18.5 Tons/sq. in. Pressure level of proof loads was higher.
 
Let me clarify the situation, If I want to reload a No.4 Mk1 (chambered in 45-70) and I follow a reloading manual, I have 3 choices:

- Trap door springfield loads
- Marlin Lever Gun loads
- Ruger No.1/No.3 loads

Im pretty sure the No.4 is stronger that the marlin and weaker that the ruger so where does one stop without scientic data ?

I think the ruger top loads in Lyman's 48th handloading manual are listed aroud 50k cup (correct me if Im wrong). I know the ruger is stronger than the enfield but Is 50k too much for an enfield ??
 
Pathfinder said:
Im pretty sure the No.4 is stronger that the marlin and weaker that the ruger so where does one stop without scientic data ?

I think the ruger top loads in Lyman's 48th handloading manual are listed aroud 50k cup (correct me if Im wrong). I know the ruger is stronger than the enfield but Is 50k too much for an enfield ??
Click to expand...
In my opinion, yes, it's too high. Will a No. 4 action in good condition handle it? Yes, but it is over the working pressure the action was designed for.

I would keep my 45/70 loads to those not exceeding 45,000 psi, and certainly not over 47,000. I don't think that will cost you a tremendous amount of velocity, and it will give you some fudge factor as well if something unexpected crops up.

There's two ways off the top of my head to ensure you're staying below pressure limits, whatever that limit happens to be. One is to stick with load data that comes with pressure figures, which should give you a reasonably close idea of the pressures your loads are creating. The second is to invest in Quickload, and use it to calculate pressures for your loads - or find somebody with Quickload and ask them nicely to do it for you.

QuickLoad
 
ipscgraz said:
I'm sure you saw that the barrel is marked "18.5 Tons/sq inch"

37,000 pounds per square inch proof test at the time of manufacture.
Click to expand...
I'm sure you're aware that the British system didn't use the 2000 lb ton for the iron and steel industry, which is apparently what you're using to do your math.

They may have used the long ton (2240 lbs) which would give you 41,440 psi. Given the pressure of the standard Mk VII load as I recall it, that is pretty unlikely. The more likely possibility is that the longweight ton used by the iron and steel industry was used - 2400 lbs. This would give you 44,400 psi - which is closer to the operating pressures of .303 Ball ammunition, but certainly unlikely to be the proof pressure for these firearms.

I'm away from home right now so I don't have access to my little library. However, I think it is a safe bet that operating pressures for military .303 ball around the 45,000 - 48,000 psi range. The proof loads will obviously be something higher than that. Somebody out there somewhere must have the real figures handy from SAAMi or whoever.
 
Path finder, glad you finally got your 45-70 no.4, congratualtions.

You may find that the pressure limit for the rifle will be your shoulder and ocular lenses!

Let us know how it goes.
 
You must log in or register to reply here.
Back
Top Bottom