Grandson bought an old bubba No4 mkI a while back. His first rifle with his money, he's 13. He has really been fascinated by the rifle, seems to be dealing well with the recoil of HXP milsurp ammo. I'd like to duplicate the military load as well as we can...I have some Grafs/Hornady 174 gr .312 bullets, some new Hornady brass, every flavor of IMR powders and most primer brands. I understand it's a good idea to fireform the new brass with the rim held firmly against the bolt face, either with an o-ring or a secondary shoulder on the neck?
Any tips at all greatly appreciated.

4895 is what I have used fir a very long time.
I never worried about Fireforming, but the majority of my Lee Enfields had very good Chambers, and my hunting rifle, although it is in .303 , is not a Lee Enfield.
Cat

Honestly, there is no need to use o rings or anything like that. I remember years ago, when Lee Enfield boards were still popular, you would read all sorts of "unusual" ideas to make the rifles shoot better or increase brass life. For example, people incorrectly blamed headspace for excessively stretched brass. That was rarely the case. Because the 303 headspaces off the rim, the rifle could be perfectly gauged, but have a long chamber and the brass would stretch. I agree with Cat. either 4895 is appropriate. I would shoot 2 grains less than book max at most.

It was easier and faster to fireform with less than maximum loads. Let the case stretch without the trauma. Two or three grains less than max will move the case without stressing the brass as much. Once it is stretched a bit, you can adjust your FL die to barely move the shoulder and use a collet die for two or three reloads until it does not want to chamber again.

I don't know how old your grandson is, but the iron sights will work ok when firing cartridges up to about 100 fps less than the 2440 fps design max.

Prvi Partizan brass is a bit thicker than US made stuff. The Greek surplus is good as well, so I would reload that.

I was hoping you would respond, sounds like we are overthinking the project a little, mostly worried about brass life.
Some would say I'm nuts turning a kid onto an old battle rifle...but my motive is...it doesn't have a video screen or a battery, and at age 13 that is a good thing. If this all goes well, I have found all the wood and bands to restore it to full military dress. LOL, the kid watched a movie on El Alameine, now he is an Enfield collector. Probably need a bayonet next.

I think what you are doing with him is great. Before you know it, he'll be dragging you around to gun and militaria shows!

We been sharing a vendor table for 4 years, he's my security guy. LOL.

Wonderful. You're making memories!

I killed a wolf today with No4 Mark1 Longbranch.

Mine was marked as having been rated a sniper rifle, shoots tight groups even at 200 yards.
I load 150 and 180 grain bullets, but favor 150 unless hunting moose or such.

Was my first rifle, was a spoterised version from Parker Hale, I ended up putting an ati stock on it, much lighter and slimmer.

Great rifles, my dad gave me one he sporterized himself, a bit before he passed.

It’s one I will not part with.

Just for your info and it's only my experienceI have had the best luck [groups] with IMR 3031 powder and federal 210 primers. A close second was RL15 powder. My most accurate loads with both was 2405 ft per second with 180s very close to the stated velocity. I also used DI 1943 surplus brass. I forget the exact charges as I am 500 miles from home and its been quite a few years since I did this but I remember everything except the charge, they would be different for your gun anyway. Best of luck and I am sure he will get a lot of enjoyment from it. PS I turned into a looney after starting with the 303 British.

Wow...shades of the Big '80s for me here. My first big game rifle was a kitchen counter custom no4 mkI* lend lease Savage. I was a whopping 14 years old when I bought it for farm next door earnings during the summer.It shot 3" at best 100 yd groups regardless of the ammo it was fed, yet dropped a lot of deer. It belongs to a friends daughter these days.

Depending on the chamber , you can triple brass life by creating a false shoulder.

In my case , I neck up to 375 in two step and back down in one step. Anneal and shoot. I shoot the 303 lots so I tend to try and make the brass last as long as possible.

My 2 groove likes the Hornady 200gr elx and a stiff load of imr 4350. Been shooting that for years and accuracy is great for whatever reason. (2 groove)

4350 was a popular powder for the 303 for years.

There have been at least three powders that came along that have added to the cartridge's versatility. Re 15, Varget and Re 17.

You can never have too many choices! 🙃

I like varget for moderate loads. I like 4350 for heavy loads. Regardless of chamber dimensions, if you use heavy loads in a Lee Enfield (180's at 2500, for instance), brass life will be short. GD

Yes, Varget works well for moderate loads and 150 grain bullets too. When I received my 30-303 barrel. I cleaned it and shot these four groups at 100 yards to see how the MGM barrel grouped. They were shot with old fashioned 180 gr Rem CL bullets. I used Re 17 at several Milsurp shoots and did well. Re 17 has the same burn rate as the 4350s, but produces more velocity. And it shoots tighter in the three rifles I tried.

This group of four targets was shot with minimal experimentation, using my "fave four" powders. This picture was from my single shot, but produces the same from a couple of No 4s as well. Re 17 loads are about 75+ fps faster than either H or IMR 4350, but the big thing was the accuracy.