Paper Patching Problems with 303 Brit

[303Guy]

This with a specific rifle. My BSA & M 1896 Lee Enfield 'target' carbine.

This is it.

Now here's the problem I've been having.



These are the first patch wraps all in one piece! Ain't gonna work!

Then I cranked up the pressure.

Almost!

These bits were still attached to the base of the boolit! (The boolit was turned inside out). They're not completely separated.

The boolit. (It's a bit inside-out).

So, I took the next step of annealing the boolit nose and tried again.

Success! The patch fragments on the left are the biggest pieces I could find.



The L/H boolit is the one that did the deed. A curious aside is the difference in shape between it an the one that was un-annealed (centre) and 'almost' cut the patch but held on to it just the same.

[303Guy]

Well, a little more testing and finally this.

Total patch fragmentation.


Chamber presure was high - too high.

[no34570]

303Guy
Jeez mate,I like your bullets,well done.
Do you have a template for wrapping the .303?would you like to share?
Where do you get a mould for them Boolits???
Cheers

[303Guy]

Thanks. I do indeed have a template to share. Several templates actually. These are for individual boolits I am trying in different chambers. This one is large to fit a large and well worn throat and initial rifling. I have a formula for creating a printer template based on actual boolit measurements. That's to get the curve right and the ends to meet with minimal gap. I'll draw up a diagram showing where the measurements I need are and PM them to you and then I'll design the patch template and post that for you.

The boolits are from my own molds I make. One day I shall be able to make some for others consumption. I have the principle sorted but am still to make it into a simple mold unit.

Oh ... The patch disintegration problem is unique to this one rifle due to the very rounded nature of the rifling. The last test load I fired with less powder did not release the patch fragments early enough and got trapped on the 'inverted' boolit in the sand trap.

Here is the 'inverted' boolit with patch tail still attached.

You need to look real carefully.

The sand trap is very close to the muzzle. I got the 'tail' real symmetrical.

[303Guy]

Here's the patch template I am using. It's printed on A4 notepad paper.



The resolution is too low to show that the horizontal lines are actually curved arc segments.

[303Guy]

Further tsting reveals the correct alloy hardness and velocity and produces total disintegration (pulping, actually) of the patch. Use of Dacron filler seems to prevent patch bits from adhering to the boolit.



Soft sand as I am using expands the boolit a lot more than wet rags (which seems to be a lot closer to flesh) but the hold together is rather astounding! (183gr from a 208gr boolit - 88%!)

Close-up of the boolit - 204gr of it!
Close-up of the pulp. Patch bits are visible in it.

Recovery of the 'pulp' is only possible by virtue of the pulp being draw into the sand trap by the vortex created behind the boolit as it enters the sand. (That pulp was sucked in through a dry bundled rag and no doubt most of it is actually rag).

[303Guy]

Well, I finally got the patch to disintegrate fully at lower chamber pressure. I switched from bulky shotgun powder to AR2205/H4227 and doubled the charge. I also added a waxy-lube smear to the patch. Velocity seemed to go up with the lube. Not sure but bullet deformation increased, even at a lower powder charge. The bore now stays clean and shiny.

So now I'm ready to load up a batch of ammo for range testing!

[no34570]

Great stuff mate
The template is small or is it supposed to be?
Would be good to get one of those moulds when you start to make them.

[303Guy]

That template does look small and so does the boolit but it weighs 208gr and the patch fits.

Something I am wondering about is the optimum boolit length for a given powder type, i.e shotgun powder builds up to max pressure very quickly so the nose of a long boolit will not be able to obturate before chamber pressure falls so maybe a shorter boolit would be best and so on.

[Zeek]

That template does look small and so does the boolit but it weighs 208gr and the patch fits.

Something I am wondering about is the optimum boolit length for a given powder type, i.e shotgun powder builds up to max pressure very quickly so the nose of a long boolit will not be able to obturate before chamber pressure falls so maybe a shorter boolit would be best and so on.

So far as I am aware (now THERE's a limitation!), the obturation is strictly a function of the accelleration, and all portions of the PPCBoo core that have enough mass ahead of them (at that degree of acceleration) to obturate WILL obturate at the same time. If the acceleration is less than optimal, then the rear portions of the PPCBoo core will obturate (because they are pushing more mass than the forward portions are), but the forward portions will not. Once the max pressure of the load bleeds off significantly, the acceleration is present but is small (compared to the at-the-start and at-near-max-pressure acceleration), so only the rear portion of the core TRIES to obturate. By then, though, that portion of the core has already crushed the PPatch against the bore-and-grooves, so this attempt at obturation results, instead, in jamming the crushed PPatch against the inside of the barrel, thereby providing sealing. At least, that is my mental model on the issue.
Zeek

[longbow]

You have it right ZEEK.

The powder gases exert a force on the base of the boolit proportional to the pressure behind the boolit and the area of the boolit.

That force pushes the base of the boolit but inertia gets in the way so the boolit doesn't want to accelerate. If (mostly when) the force produces a stress greater than the yield stress of the lead, it... yields. The highest stress is at the base of the boolit since it has mass ahead of it. The stress will decrease towards the nose. Since the lead has nowhere to go it "obturates" to fill the bore. In extreme cases, lube grooves will collapse.

For the most part, chamber pressures and the forces on the boolit base far exceed the yield strength of the lead. For example, the strongest heat treated lead/antimony alloy has a yield strength of 12,350 PSI. Most of our cast boolit loads have chamber pressures well above that.

So for the most part, the very base of the boolit should be yielding and obturating at least some but just how far that yiedling goes up the shank of the boolit depends on the stress along the boolit shank.

Longbow

[303Guy]

Mmmm ... I'm just trying to clear my head .... I have the notion that obturation is a function of pressure and time. (I use the term 'obturation' because I am thinking not of a boolit 'upsetting' to take the bore form but rather a boolit exerting crushing pressure against the patch in the bore, i.e. small upset). I'm thinking that the alloy will undergo plastic deformation at a rate proportional to the pressure or stress it is subject to so that the lower the stress the more time that stress needs to be exerted to get the deformation required to 'crush' the patch. There was a time in history when mines were timed by a piece of lead under a spring loaded 'shear'. The longer time required, the thicker the lead piece. This is why a hardness test must be done in the correct time.

Somethine one does not want is for the deformation stress to be high enough while the boolit is still sitting between the case mouth and the throat to upset into the gap between the case mouth and throat entry chamfer. I have had this happening with the very fast powder.

So, ideally, one wants the boolit to undergo mild deformation as it transits into the throat where an increasing pressure obturates it completely so it can then be swaged down into the tighter bore.

I have had it when a PPCBoo nose section is a 'touch fi't in the bore but on firing the nose section takes on a healther rifling impression and crushes the patch nicely. That is with a long barrel and a 'rifle velocity' slow powder charge.

Methinks this game can be made as simple or complex as one desires!

(I wonder whether anyone else tries to 'restore' an otherwise scrap bore to useful life? It's more fun than taking a good bore and loading up for it!)

[longbow]

303Guy:

True enough, lead does "creep" (deforms) over time at room temperature and pure lead has a poorly defined yield strength becasue of the tendency to creep.

However, what happens in a gun barrel all takes place in milliseconds so no time to creep. The boolit material will only yield if the stress exceed it's yield strength. Obviously, the stress along the boolit from base to nose diminishes as there is less and less mass to push in front.

Of course the whole boolti is subject to rotational stresses too but we are not talking about those with respect to obturation.

I have had soft alloy Lyman 429421 boolits collapse enough to almost obliterate the lube groove. To do that, the stress in the reduced diameter at the lube groove was beyond the yield strength of the lead.

Another issue that may well come into play too is that the base of the boolit is trying to catch the nose (that pesky inertia thing again) while the nose is being engraved so friction may slow the nose a little while the base is pushing through the throat.

Think of what happens during explosive forming operations. Metals can be made to do amazing things when deformed at high pressures and velocities.

Also, think of an extrusion process. You need enough extrusion pressure to cause the material to be extruded plus enough to account for internal and external friction as well.

This may well be why the recommendation for a chamber pressure of approximately 3 to 4 times the yield strength of the lead for optimum results.

A little food for thought.

Longbow

[303Guy]

A little food for thought.

Yup. Thanks for that. (I suppose that's the difference between hoping - i.e. wishful thinking - and reality! )

Well, having 'developed a load with AS30 (shotgun powder) for my pig gun that seemed to shred the patch and finding that same load not working at all in the carbine (difference in bore condition) then finding a AR2205/H4227 that works perfectly at lower pressure in the carbine and now having just tried that load in the pig gun, and finding (or not finding) the patch has totally 'dissappeared'! Pressure was still lower than with AS30 (chambers are similar) but muzzle blast has just got to be greater.

Something with both these chambers is that the prepped case neck is a tight fit and the patched boolit is a snug fit in the neck. What happens is the chamber tightens the neck onto the boolit allowing for a fair bore-ride impression without leaving the boolit in the throat on extracting an unfired cartridge. This raises the pressure of the AS30 and no doubt for AR2205 too but that powder is slow enough in that largish case for pressure to remain moderate but still extract substancial energy from the charge.

[Naphtali]

. . . Well, having 'developed a load with AS30 (shotgun powder) for my pig gun that seemed to shred the patch and finding that same load not working at all in the carbine (difference in bore condition) then finding a AR2205/H4227 that works perfectly at lower pressure in the carbine and now having just tried that load in the pig gun, and finding (or not finding) the patch has totally 'dissappeared'! Pressure was still lower than with AS30 (chambers are similar) but muzzle blast has just got to be greater. . . .

This is great stuff, a real help during my quest?? to create satisfactory paper-patched-bulleted hunting ammunition for my Savage 99. Have you developed any 200+ grain 303 British loads with muzzle velocities exceeding 2200 fps, whose accuracy is better than 4 MOA? If I can achieve this result from a lightly alloyed 200+ grain .308-inch bullet - yielding much slower expansion than your bullets appear to have - I have precisely what I want.

[303Guy]

- yielding much slower expansion than your bullets appear to have -

Aah! I should hasten to mention that my catch medium is soft, fine sand. That produces an expansion equivalent to a much higher velocity in wet rags that seems to closely resemble flesh. I use the sand for its ease - I just pour the sand through a seive to recover the boolit and any patch fragments. Quick and easy. It does give some idea of the difference between hard and soft alloys and flat tip and hollow point boolits.

I made two attemps at higher velocity - one with my two groove 303 using 180gr conventional G/C boolits and vellum patch and that did not work. OK up to about 50yds. The other was with my five-groove 303 and heavier boolits - 225gr, patched with cig paper. These were lubed and I suppose the patch did not come off properly and so accuracy was poor. One loading gave promising results at 50yds but at 180yds was a joke but the boolits made perfectly round holes.

Something always manages to stop me getting out and doing some range testing! Soon, I hope. (I am aiming for 1 MOA at all ranges - or better).

According to JBM Calculations, a 1-in-14 twist 30cal will stabilize a 245gr torpedo.

[303Guy]

I finally got to take the carbine on its maiden voyage! The loads I had test tube developed for it performed superbly and even with its horrid open sights it gave me 1½ MOA at 110yds. And I bloodied the gun with three turkeys! I just couldn't quite hit a magpie at 100yds but hell it was close! (I could see the strike in the earth bank behind it). This gun is ready for a scope!

I pushed a cotton wool wad through the bore and it came out with very little dirt.

First and second cleaning wads.