Shortening a 303 Brit chamber with a Shoulder Insert

[303Guy]

This is just an idea I have had for some time for a rifle that must never fire full pressure loads. (I know I should just chop up the action body but that's a nudder story). OK, so the idea is to make a neat fitting shoulder insert and secure it with non other than high strength Loctite. Difficulties I foresee would be firstly making the said insert to exactly fit the existing shoulder which can be done. Then there is mating the extended throat with the existing throat. I see that as being tricky without the appropriate reamer. If it is slightly larger that's fine but if there is a gap then there would (or could) be a problem with extraction. However, I have a rust pitted action that fires full power loads without bulging the neck into those pits (large open but shallow pits) so with keeping to the intended low pressure loads that may not be a problem.

The advantages would be a longer neck which could hold a fibre wad. Disadvantage would be a difficult job.

Reality check? Is this a hair brained idea?

Bear in mind that I want a dedicated low pressure Lee Enfield and this one cannot shoot normal bullets due to an oversize bore and chamber and cannot shoot normal pressure loads because only the inner lug bears.

[Bjornb]

So will you first make a prototype case with the longer neck, and then fabricate (on a lathe by using a chamber cast for measuring purposes I presume) the insert?

[PAT303]

Re cut the chamber for a 30/30 aka 32/30,32/40,32 special etc. Pat

[Bjornb]

It sounds like 303 Guy wants to accomplish this without having to resort to excessive gunsmithing (ie. re-cutting the chamber). An insert like he describes, if fabricated by a skilled machinist, should slide into the chamber and be kept in place with chamber pressure and a little Loctite.

[303Guy]

Yes, and to retain the 303 Brit parent case. I can make the insert and forming dies (with considerable effort). I would undoubtedly have to make several attempts to get it right and it does need to be a perfect fit. It won't be easy for me. I would have to make a once off collet and mandrel to hold it in reverse to cut the new shoulder. It could be challenging fun.

The 32-30 idea is a great one but I wouldn't want it capable of firing a full pressure factory round - not that anyone would actually find them anywhere. I'm quite sure there is no danger to life or limb (or eyes) if the inner locking lug gave way but in principle it is a bad idea. Plus it would ruin my gun and shoot.

Just thinking about it, if one were to fire a 30-30 in a 32-30 chamber, would the pressure developed be considerably lower?

[lefty o]

if your talking about a lee/smle type rifle, i'd just hunt down a longer bolt head. they made like 4 different sizes to chase down excessive chambers. if your talking about doing something else, set the barrel back, inserts are and always have been a fairly poor idea.

[EDG]

Why not just cut one or two turns off of the barrel breech and move the barrel shank shoulder forward.
There is even a CIP standard for one turn off called the .303 Sporting used in France.
If you still want the longer neck just bore the chamber neck or ream it with a neck and throating reamer.

[bob208]

yes it can be done. it was done by the navy when they converted their m1's to .308 from .30-06

[lefty o]

and the navy discontinued use of chamber inserts very shortly after it began.

[KCSO]

The problem with the inserts is that the heat and pressure eventually degrade the bonding agent and there is a remote possibility of pulling the insert out with an extracted case. Tis is a serious problem with 30-06/308 as the next 308 in the gun will either jam it or blow gas in your face. With the 303 your insert wil be small enough that even if it comes out you will only be back to the loose chamber you had to start with. Turn you insert carefully on a lathe and use a steel dummy to press it into place. You will have to make sure the neck are is reamed exactly the same as your chamber so you i=will need some carefulle measurments. All in all you would probably be beter off just using 30-40 Krag cases fireformed and necksized for your gun as the front of the chamber is no looser than the base and the Krag case is just enough bigger to take up the slack at he rear.

[303Guy]

So will you first make a prototype case with the longer neck, and then fabricate (on a lathe by using a chamber cast for measuring purposes I presume) the insert?

I was thinking of simply deciding on how much to shorten the case body and make the insert then sizing the cases to suite. I could then set the sizer so the cases just chamber.

The problem with the inserts is that the heat and pressure eventually degrade the bonding agent and there is a remote possibility of pulling the insert out with an extracted case.

The worst that can happen is the cases will then headspace on the rim and the reformed shoulders might blow out to normal. Actually the worst thing will be all that effort wasted!

For now I'm going to just find a boolit that suites the throat and load up some rounds and see how it shoots. I'll also load up a some paper patched boolits.

[JSnover]

and the navy discontinued use of chamber inserts very shortly after it began.

They certainly did. Because the full pressure loads did as KCSO described. in this case it shouldn't be a problem.