Short cases

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John Carlson posted this 17 November 2018

One of my pet peeves is that I can never find cases for my 03 Springfields that are long enough to trim to the recommended OAL let alone long enough to need trimming for any of my chambers.  

The last Remington brass I processed ended up with some batches as short as 2.470.  In my Remington, this leaves a gap of .080 between the case mouth and the throat.  Seems like this could be a place for powder residue to collect.  Might even produce results similar to lube purging!

My question is:  Does anyone know of a brand of brass that comes out of the box long enough to actually need trimming?

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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RicinYakima posted this 17 November 2018

I'm sorry, John, but I never found any. I had this idea that if I could get the end of the case "just" into the throat, it would help. Tried every 270, 280, 7MM express, etc. etc. in every brand I could find. None were close to max length when resized to 30-06. Hope you have better luck! Ric

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Ross Smith posted this 17 November 2018

Maybe a long shot. When I bought new winchester 30-30 brass they came with with a warning that the brass would be long and the neck out of round. They were right. Had to size and trim them. Maybe '06 wold be the same???????????????

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joeb33050 posted this 17 November 2018

 

6.2.4 Case length vs. accuracy

 

 

 

In the Nov./Dec. 2001 ASSRA Journal article: “The Importance of Case Length in Cast Bullet Accuracy”, the author stated that short cases yield less accuracy than cases close to maximum length with cast bullets. The mechanism proposed is that the unsupported bullet in the gap between case end and chamber end will be expanded by the firing pressure, then the expanded section will be swaged down as the bullet moves through the throat-and the expansion/swaging will be uneven and cause inaccuracy. This article opened up a potential accuracy-improving easy and inexpensive shortcut. The article did not include any supporting data, so I imagined that what was put forth was a hypothesis.

 

            To test this hypothesis I needed a rifle that shot fixed ammunition at high enough pressures, with sufficient accuracy, and for which extra long cases could be made or found.

 

The only rifle available to me that met these criteria was a Savage Tactical rifle with synthetic stock in 300 Winchester Magnum, fitted with a Weaver 3-9X telescopic sight. I owned this rifle for about four years, and it was reasonably accurate with cast lead bullets at slower velocities, 1200-1500 fps.

 

(We are told, and I believe, that cases that are too long will jam bullet and case neck into the throat of the rifle and cause very high pressures on firing.)

 

Pressure must be sufficient to expand the bullet into the space left by the short case. Expansion of the bullet under the gas pressure on firing is sometimes called "obturation".

 

            In a private communication with the author, he said “… obturation of lead-alloy bullets occurs at about 1500 psi times each Brinell hardness point, e.g., a Brinell hardness 10 bullet requires about 15,000 psi peak chamber pressure to achieve sufficient obturation to essentially fully seal the bore”

 

            With wheel weights reported at 9-12 BHN, the pressure required to obturate would be 13,500 to 18,000 psi. 

 

A pressure of greater than 18,000 psi was required. The Lyman Cast Bullet Handbook, third edition, shows a 187 grain 311334 bullet in the 300 WM with 17.5 grains of Unique at 1605 FPS and 26,400 psi. The load given below of a 208-grain bullet and 17 grains of Unique should produce at least this pressure, which exceeds the obturation threshold.

 

After several weeks of experimentation I found a load that shot accurately at higher velocity:  The 311299 bullet was cast of newly melted wheel weights, weighing 208.5 +/-.5 grains, sized in a .314” die, lubed with the NRA alox-beeswax formula and gas checked (Hornady).

 

This bullet has three bands and two lube grooves along with the gas check shank. As loaded, the first band is out of the case with none/little of the first lube groove exposed.

 

17 grains of Unique was used with no filler, Remington L.P. #2 1/2 primers, LOA = 3.455”.

 

I loaded one case at the range, sizing the neck in a Lee sizer, expanding the neck in a Lyman “M” die and seating the bullet with the Lee loader.

 

I used this load and loading method for all groups shot in this test.

 

Extra long cases were made from Federal 300 H&H Magnum cases full-length sized in 300 WM dies and trimmed to about 2.660”.

 

The chamber would accept a case of 2.648”, .028” longer than the published case length and .033” longer than the trim-to length.

 

Being chicken, I trimmed the cases to 2.643”. After extensive firing, the cases measured 2.621" to 2.630”. What happened was that the tapered 300 H&H case had blown out to fill the chamber and shortened during firing.

 

 

 

The first test with short cases.

 

On March 13, 2002, using the load noted above and one R-P case measuring 2.605” long, I shot five 5 shot 100-yard groups that averaged 1.132":

 

 

 

The test with a long case made from a 300 H&H Magnum case

 

On March 21, 2002, using a case 2.630” long made from a 300 H&H Magnum case and the load noted above, I shot five 5 shot groups averaging 1.468".

 

After shooting, the 2.630” case was 2.626”/2.628” long, it had blown out and shortened.

 

 The problem was that the 300 H&H cases were tapered, and a 300WM case formed from them and trimmed to just fit in the chamber, shortened after firing. I needed longer cases.

 

 

 

The test with a long case made from a 375 H&H Magnum case

 

I went to the Internet and asked for samples of 375 H&H Magnum cases, which don’t have the taper of the 300 H&H. Alston Jennings was kind enough to send some. I formed three of the cases to 300 Winchester Magnum, leaving the necks long.

 

 

 

On March 27, 2002, with one case formed to 300WM 2.642" long and the same load, I shot five 5 shot groups averaging 1.438"

 

After these 25 shots the case length was 2.646”.

 

 

 

The test with the long 375 H&H Magnum case trimmed short

 

I then trimmed the case to 2.605” and shot five 5 shot groups averaging 1.036", same load as above. 

 

After these 25 shots the case was 2.608” long vs. 2.605” before the shooting.

 

 

 

Lengths of 300 WM cases

 

"Book" case length                             2.620”

 

"Book" trim to                                    2.610”

 

My rifle chamber length:                    2.648"

 

            Formed from 300 H&H, case length: 2.630"             after firing, 2.626"/2.628"

 

            Formed from 375 H&H, case length: 2.642"             after firing, 2.648"

 

            Formed from 375 H&H, case length: 2.605"              after firing, 2.608"     

 

 

 

Table of group sizes fired with 300 WM cases of different lengths, inches.

 

 

 

Date

13-Mar-02

21-Mar-02

27-Mar-02

27-Mar-02

Case Length

2.605"

2.630"

2.642"

2.605"

First

1.378

1.117

0.978

0.880

Second

0.821

1.073

1.497

1.627

Third

1.111

2.224

1.099

1.106

Fourth

0.986

1.653

1.399

0.785

Fifth

1.364

1.271

1.438

0.784

Average

1.132

1.468

1.282

1.036

 

 

 

 

 

All these groups were shot at a pace determined by the time required for reloading the one case. No wind flags were used, the rangemaster stopped the shooting after each 15 minutes of “hot line” for target change. The gun was cleaned once at the end of the day.

 

Comments and Conclusions

 

I don’t like to use cases that are close to the maximum possible length. If the case lengthens slightly, then excessively high-pressures may be experienced, as the bullet and case neck are jammed into the leade/throat/ball seat.

 

The average group size for the 20 groups was 1.23”. Six of 20 were under an inch.

 

Pressure was high enough, bullet hardness was low enough (new wheel weights) and the bullet had an exposed section outside the case about 1/8” long ready to expand or obturate.        There were no called flyers in 100 record shots from the bench. There was one stranger in the third group shot on 3/21/02.

 

I see no accuracy improvement using longer cases. The hypothesis failed this test.

 

One test doesn’t establish the fact, but I have seen no data supporting the hypothesis that longer cases improve accuracy in soft cast bullet shooting. If longer cases do produce better accuracy, I want to know it. I would welcome any other data on either side of the issue.

 

            I have worked with a Savage 12BVSS in 223, forming brass from 222 Magnum cases because the chamber/brass on hand combination resulted in a gap between the end of the case and the end of the chamber. I was not able to detect an improvement in accuracy.

 

            I've been working with my Martini bench rifle and a M54 Winchester rifle, both in 30/30, both with "long" chambers. Using Buffalo Arms "long" 38/55 brass, I've formed 30/30 brass about right for the chamber.

 

 I was not able to detect an improvement in accuracy with longer cases in either of these guns. I'm still trying.

 

At high pressure and velocity I have been able to shoot cast bullets and have a ring of lead left in the chamber. It looks like the bullet expanded into the gap between the case neck and the step at the end of the chamber, and then the resulting ring was sheared off.

 

 

 

Opposing viewpoints:

 

 

 

Jeff Bowles mentioned (on the CBA Forum) that he makes (from 30/06) 308 Win cases that are .0015" from the end of the chamber and that this enhances accuracy.

 

Frank Marshall, in "Neck Length and Accuracy In Cast Loads", TFS March-April 2005, page 174-9, mentions seeing substantial accuracy improvements when using cases with "long" necks-not to exceed the chamber case length of course.

 

            Black powder cartridge rifle shooters claim that short cases reduce accuracy, and go to great lengths to make cases longer.

 

 

 

 Bill McGraw:

 

We have a compromise in dealing with case length in a chamber that appears to be too long. From what I did with making 308 Win from 30-06 brass, I found the max OAL for my chamber that would lock the bolt on firing yet chambered easily without any constriction of the case neck. From that experience only two things could have occurred: one, that the primer strike drove the neck into the transition and increased PSI or, two, that the cases actually stretch temporarily on firing. If there was any other explanation, I couldn’t find it. As for accuracy, the factor that makes a difference is the condition of the chamber fouling from low PSI loads. An extra long chamber won’t hurt accuracy as long as the extra chamber neck length is kept clear of any fouling that might be deposited.

 

 

 

 

 

Norm Johnson:

 

With cast bullets, it is particularly helpful to keep the trim length within about .010" of your chamber dimension so that when the cartridge is fired, the bullet does not enlarge (obturate) to chamber neck diameter just ahead of the case mouth.

 

Depending on pressure and bullet hardness, the bullet can upset into the chamber neck area just ahead of the case mouth, then the remainder of the bullet will shoot through this ring of lead.  With cast bullets, an indication of this is when a portion of the above mentioned ring of lead sticks to the case mouth and is withdrawn as the case is extracted.  The unwanted obturation damages the bullet's integrity and leaves a varying cylinder condition that, at best, is not conducive to good accuracy.  Under some circumstances, subsequent rounds fired in that chamber could cause increased pressures.

 

The above can happen even to jacketed bullets with short necked cases and/or long cylinder necks. 

 

See the photo of the resulting anomaly where there was a .050" space between the case mouth and the end of the chamber neck.  The jacket expanded, and then sheared as the rest of the bullet passed through it. 

 


God Bless!"

 

 

 

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John Alexander posted this 17 November 2018

Wow! That is an answer. Thanks for doing the experiment and for gathering all the other comments.

I can't add much but to say the last six 223 rifles (4 Savages and two Tikkas) I have checked for length of chamber to end of neck have all been within a few thousandths. But long enough to leave .020" gap with the SAAMI max length cast. No-one seems to be taking any chances that a case will lengthen enough to cause problem with pinching the neck down on a bullet.

In a article in TFS #214 I discusses why the big gap and asked for evidence that it is a problem.  I didn't get an answer like Joe's, in fact none.  I decided the heck with it I would emiminate the possibility and made up a large batch of 223 cases out of 222 mag cases. I trimmed to almost the length of chamber but after firing they shrunk a bit like Joe's even though the 222 Mag case was similar. After many reloads they did stretch a bit.  I check after 10 or 15 reloads and I keep them trimmed a few thousandth less than chamber  length. They now have just over 50 reloads and are still working fine but I still don't know if the very small clearance improved accuracy.

At first after making the cases I decided that it didn't improve things but not with a formal test -- something I should still do.  Maybe next year.

John

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John Carlson posted this 17 November 2018

Thank you all for the information.  One might hope that when a hypothesis is tested by several unrelated scientists, they would all reach the same conclusion.  At least life would be simpler if that were the case.  Looks like I have another issue to ruminate on over the winter.

Holding public office should be viewed as an obligation to serve, not an opportunity to rule.

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