303 Pressure sign?

[Jimbo69]

Hi,

Here's the setup

Rifle: .303 Brit no1 mk3 exc condition matching parts
Ammo: Factory Rem 174gr FMJ
Problem: Primers are moving slightly back 0.010 inch once fired.

Brass looks OK no splits and roughly 2.226 inch.

Primer is not flattened and no bulge around firing pin. Just a little exit.

Is that a dangerous pressure sign?

 

[Johnn Peterson]

Experienced similar problems with a couple of Jungle Carbines I had. It may be a chamber / headspace problem. There seems to be a lot of 'give' in this action that shows up sometimes with primers backing out a little or changes in the brass overall length because of stretching. Something to try, I believe there are three different sized bolt heads 'available', numbered 1 - 3. Check the number on yours & try one with a different #.

 

[Jimbo69]

I believe there are three different sized bolt heads 'available', numbered 1 - 3. Check the number on yours & try one with a different #.

Not sure, but i think No1 have not the bolt interchangability like others Lee Enfields.

Here's what i found:

Heavy load: severely flattened primers and some cratering.
Normal load: slightly flattened primers.
Somewhat less than normal: primers popped out, no flattening at all.
Reduced load: no flattening, no popping.


Interresting, It looks like a not enough pressure problem. A visit to my nearest gunsmith is probably a good idea

THanks!

 

[p-17]

These sound like classic problems of headspace on the long side. Try neck sizing the brass only and see what happens to the primers after a reload.

Better option: Pick up a new boltface with tighter headspace. I have a No. 1 which had a bit of headspace gap and a new bolt face did the trick.

 

[tiriaq]

You'll have to experiment with different boltheads and a set of gauges to try to reduce headspace in a No. 1 Mk. III.
If the primer is left standing proud, headspace is likely generous. If you are going to reload for a Lee enfield check your brass for incipient separations.

 

[grouch]

If it's a serious headspace problem, you can get some idea like this.
- Tear a piece of typewriter paper to about the size of the case head.
- Chamber a sized case with the paper on the case head. If it compresses into the head stamp, headspace is good. The No 1 Mk 3 that I used to have didn't compress cereal box cardboard, but would work with neck sized cases. In hindsight,using that rifle was probably not a good idea.

 

[Jimbo69]

Thanks for replies.

I'll try partially sized brass with the smallest load of W748 written in my book.

If primer pop out again, i'll go right away to the gunsmith.

 

[tiriaq]

If a rifle has excess headspace, you can work around it by disregarding the rim for headspacing, and treating the cartridges as if they were rimless, headspacing off the fireformed shoulder. Size just enough for rounds to chamber, don't push the shoulder back. Necksizing accomplishes this. Once the brass is fireformed and necksized, and has been checked for incipient separations, it should be OK to use normal loads. What you want to do is prepare custom ammunition for the one rifle.