Delta L problem or "One size doesn't fit all"

[Edward Horton]

Many times I have said something was wrong with our American .303 British cases now even the European CIP seems to agree.
("practical incompatibility with ammunition made for the corresponding chambering")

Delta L problem
The delta L problem (ΔL problem) is a condition that occurs regarding certain firearms chambers and their practical incompatibility with ammunition made for the corresponding chambering. The ΔL refers to a Commission Internationale Permanente (C.I.P.) geometric dimensioning and tolerancing definition for firearms cartridge cases which are longer than the chamber they have to fit in.

Conflicting industry standards
The main cause for the ΔL is that the two main civilian ammunition and firearms industry standards organizations C.I.P. and SAAMI have assigned different standards for the same cartridges. This leads to officially sanctioned conflicting differences between European and American ammunition dimensions and chamber dimensions. Since C.I.P. and SAAMI do not rule nor control civilian ammunition standards worldwide other causes for conflicting standards leading to ΔL issues are also possible.

Firearm cartridges with otherwise problematic headspace
There are also some firearm calibers with problematic headspace listed by C.I.P.[2]
The headspace defined by:
Depth of rim recess
.303 British
.38 Sp AMU
6.35 Browning
7.65 Browning
9 mm Browning long

Delta L problem - Wikipedia, the free encyclopedia

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[Edward Horton]

Honestly, Mr Horton... In my opinion, .004" at the bolthead is going to do precious little to save your American brass when the chamber is nearly 1/8" (.125") longer than the case at to the neck.... The biggest problem with the brass is probably the wall thickness and the wrong "happy medium" between ductility and elasticity of the metal.

Son

The most important thing to me is that people don't blame the Enfield Rifle and understand what the real problem is. Even the European CIP states that commercial .303 cases have a Delta L problem.

With these problematic type cases and the standards they are made under you have two choices, tighten up your headspace or use the rubber o-ring method to fire form your cases. Chamber pressure also plays a big part with these problematic cases but too many people think a weak action with rear locking lugs is the problem when the real problem is cartridge case manufacturing methods.

And Son not everyone has Greek HXP cases to reload that don't stretch like some American cartridges cases do. The one thing we both agree on is there is a problem with these commercial cases with wall thickness and the ductility and elasticity of the brass.

What pains me Son is the fact I can reload Winchester cases for my .243 without any problems that have a chamber pressure of 50,000 CUP or 60,000 PSI and Winchester cases for the British .303 fall apart at pressures above 43,000 CUP.

It also pains me the Serbians can make .303 Prvi Partizan cartridge cases that are .010 thicker and larger in base diameter that do not fall apart.

Son, in my Enfield at a headspace setting of .067 factory loaded Winchester ammunition stretched .009, and at a headspace setting of .064 the same cases stretched .001.

Houston we have a problem...............

[ireload2]

>>>Even the European CIP states that commercial .303 cases have a Delta L problem.<<<
Where?
There is long list of Δ L rounds that does not include the .303.
The .303 rather has the opposite problem in which the maximum cartridge per design is much smaller than the chamber.

[ireload2]

The description of the Δ L problem was related to certain action types that would not close on a maximum material cartridge with a minimum material chamber.
The .303 was mentioned not as a ΔL problem but one of problematical headspace.

CIP has a problem when it tries to force cartridge drawings to fit the CIP drawing dimensioning scheme. You will note on the drawing of the .30/06 that no where do they mention the head to cone datum length that form the basis for the US designs. Per the old fashioned CIP drawing the head to cone dimension is affected by the diameter of the each end of the shoulder and the location of each end of the shoulder. The US drawings simple treats the head to cone as a basic function dimension and gauges that dimension.

[Edward Horton]

The only military grade .303 cases still being made today are Prvi Partizan, they would be comparable to “Lake City” military .303 cases “IF” we made them here in the U.S. American SAAMI commercial cases were NEVER designed to shoot in a military British .303 Enfield.

My 30-30 Winchester has .004 head gap clearance and with an .303 Enfield at the maximum headspace of .074 you can have .016 head gap clearance with commercial cases. (More head gap clearance-headspace than these cases were designed for.

Even CIP the European counterpart to the American SAAMI states the .303 British has a problematic head space condition with commercial ammunition.

Delta L problem

The delta L problem (ΔL problem) is a condition that occurs regarding certain firearms chambers and their practical incompatibility with ammunition made for the corresponding chambering.

Conflicting industry standards

The main cause for the ΔL is that the two main civilian ammunition and firearms industry standards organizations C.I.P. and SAAMI have assigned different standards for the same cartridges. This leads to officially sanctioned conflicting differences between European and American ammunition dimensions and chamber dimensions. Since C.I.P. and SAAMI do not rule nor control civilian ammunition standards worldwide other causes for conflicting standards leading to ΔL issues are also possible.

Firearm cartridges with otherwise problematic headspace

There are also some firearm calibers with problematic headspace listed by C.I.P.
The headspace defined by:
Depth of rim recess
• .303 British
• .38 Sp AMU
• 6.35 Browning
• 7.65 Browning
• 9 mm Browning long

Delta L problem - Wikipedia, the free encyclopedia