case length vs chamber length

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  • Last Post 11 December 2012
R. Dupraz posted this 09 December 2012

Yesterday, I slugged the throat in my old Rem 722 .257 Roberts. Not wanting to ruin a good .257 case, I dug around in my brass junk box and found a couple of '06 cases and ran them up into a .257 FL sizer. Then trimed to the length of a once fired Rem. .257 R case. Filled them full of lead. turned a slug from a st. sided 540grn. Paper Patch .45 bullet that I use in a 45 x 2.4 Sharps. Veral's old trick of chamber the case, slug down the muzzle and tap, tap with a steel rod.

Bolt opened, case out and when I pushed the slug out into the action, I saw a very noticable band around the slug at the mouth of the case. “What the".  Now, I have seen this before when slugging other rifles but not to this exent. Near as I can measure, this band is about .058” in width. AHA !!This reasoning mind ascertained that the band was caused by the space betweed the front of the case and the front of the chamber, This probablly is not good for cast bullets, I say.

So, today I take the other “06” case do the forming in the .257 die again and make another slug. Only this time when trimming the “06” case back, I trim and try until it just chambers in the rifle. Slug the Rem. again and find a very thin wafer of lead at the base of the slug. when it is pushed out of the chamber. Both slugs measure .258” around the throat by the way.

Seems to me that the gap in this rifle is borderline excessive as compared to the others that I have. And when shooting cast bullets would not be conducive to making those gnat size groups that we all like to bragg about. .

What effect on cast bullet accuracy does this cartridge chamber gap have? Has anyone done any experimenting.What do you-all think.

First snow of the season last nite. Wind blowing, Pretty dang chilly in Dakota this morn. Single digit temps predicted. The cabin fever begins!!!!!!!!!!,,,,,,,,,,,,, 

Merry Christmas

RD

 

 

 

 

 

 

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RicinYakima posted this 09 December 2012

RD,

I have done some work on this in 1903 Springfields. It appears to be a fuction of the reamer maker, and not use of the tool.

This can cause a problem with some rifles, but you can work around it somewhat. In my Issue Class Remington 03A3 I only use linotype alloy, as my normal WW + 2% tin has unexplained flyers. Second, I only “clean” the bore once a year, the rest of the time I push one loose fitting patch down the bore at the end of the day. (Here in the desert, there is no rust issue.) This allows hardened lube, fouling to build up in front of the chamber neck. Another way is to wet patch some Lee Liquid Alox into the bore, let it dry and then push a couple of dry patches down the bore. This tends to fill the space.

Back when I was fanatical about cleaning the bores of '03's, I would get lead flakes on my patches. Once I stopped scrubbing the bores, the lead flakes went away. My guess is that they can from the edge of the neck and throat inter-face.

FWIW, Ric

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joeb33050 posted this 09 December 2012

6.2.4 CASE LENGTH VS. ACCURACY

Download attached pdf.

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R. Dupraz posted this 09 December 2012

Very interesting Joe:

After pondering this gap and thinking of some possible solutions, thought of doing the same thing that you write about. I do have a fair supply of 25-06 brass and thought of making some long .257's out of some of them. Then shooting both lengths and comparing the results.

But all is dependent on what this rifle does with cast to start with. May not. Maybe in the spring. Thanks for the information.

RD

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72coupe posted this 10 December 2012

Sinclair sells a device that is a 2 diameter plug that has a large diameter of the outside of the case mouth and the small diameter is the inside of the case. A case is shortened for use with this plug and inserted into the chamber. The the maximum case length can be measured with a caliper.

 Here they are. http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/sinclair-chamber-length-gage-prod32925.aspx>http://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/sinclair-chamber-length-gage-prod32925.aspx

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RicinYakima posted this 10 December 2012

Great idea! Measuring lead plugs gets IFFY sometimes with a heavy finger on the mic. Ric

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pat i. posted this 10 December 2012

And they call it of all things a Chamber Length Gauge. Who Da Thunk? If you full length size a case and then after shortening the neck split it with a cut off wheel in a Dremel it makes it much easier to get the guage back out of the neck. Split the neck down into the shoulder area and it acts like a spring.

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RicinYakima posted this 10 December 2012

Pat, I've tried that and always get a bad reading from pushing the “plug” back into the case from a heavy hand on the calipers. With the other idea, you can measure with a micrometer and a fixed base datum line. Ric

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R. Dupraz posted this 10 December 2012

Ric:

In your first post regarding the Springfield and describing your “fix” for the chamber gap, did the flyers go away and the groups improve?

Might just get one of those Sinclair chamber length gages. For $5.00-$6.00 It would be worth it if they work just for my own curiosity if nothing else.

RD

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John Alexander posted this 10 December 2012

I asked this same question in a Fouling Shot article (#214 Nov./Dec. 2011) . I asked for evidence that this gap degraded accuracy but (typically) received no answer until Joe confessed above that he had indeed checked it out with a well designed test and failed to find that accuracy is any better with cases that reduce the gap. Thanks for reporting your work Joe.

Several years ago I made a large batch of 223 cases out of 222mag cases (.002 -.004” clearance) and have used them for all my practice and match shooting every since -- all without knowing if they were any better. If these cases every wear out (now at about 35 reloads) I won't go to that trouble again unless I see evidence that it makes a difference.

Joe's report may inspire me to do some comparison shooting this winter to help confirm or refute Joe's findings for a smaller caliber.

I have used both the Sinclair chamber length gage and measuring the expanded part of slugs and find that if I do both carefully they agree and the actual gap with new factory cases is usually over .040 inches.

John

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cityboy posted this 10 December 2012

I used the Sinclair gages and the worked fine. They should be part ov every loaders tool box. Jim

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R. Dupraz posted this 10 December 2012

Interesting stuff, Actuall results trump theory any day of the week. Part of the reason why I hang around this outfit.

The cartridge chamber gap has been a topic of discussion among the BPCR boys in time past as well. But mostly opinions. Also, I remember once reading about this gap coming into play when the jacketed benchresters fit a case to a chamber.

What is a safe cartridge/chamber gap to have?  Might try a little experimenting with the Rem. .257 Roberts.

 

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John Alexander posted this 11 December 2012

One thing is clear. The guys specifying the length of chamber reamers for the gun manufacturers and the ones specifying the trim length for new cases are both conservative (not in the political sense) and interested in CYA. “Let's order the chambers with the longest necks allowed by SAAMI and play it safe” and Let's order the minimum trim length SAAMi allows and play it safe."

That's how we get gaps of .040--.060. But then Joe's work implies that it doesn't make a difference so we probably have better things to worry about until someone finds that the gap does affect accuracy or hair loss.

I am personally skeptical about the danger posed by a cast bullet (or even a jacketed bullet with a soft lead core) that is ” pinched” by a too long case mouth. The conventional wisdom is that it will cause a pressure spike that will spread death and destruction in all directions. But doubting that likelihood is just my contrarian and untested opinion until it is tested.

I have gotten as far as buying a relative modern 98 Mauser that has been “sporterized” by the famous gunsmith Bubba to test this theory. I have a friend that I think I can get to glue a strain gage on it and measure pressures relative to factory ammo. If I don't blow the thing up with this fun test, I also plan to test the old chessnut that oversized primer flash holes also cause dangerous pressures which has never seemed credible to me and I have never seen a test to actually confirm.

Unfortunately this project slipped down on my to-do list --maybe next summer. John

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Tom Acheson posted this 11 December 2012

A different experience here. For my .40-70 SS BPCR I use 405 Winch. Hornady cases. They are too long for my chamber and that's a good thing. They are supposed to be 2.583” but mine ran 2.570” to 2.575". The .40-70 Sharps Straight is supposed to use 2.500” long cases. If I remember right I removed about 0.055” to 0.060” to get them close to what the Sharps chamber needed. I did what the magazine article from 2001 said to without having seen the article. Trim slowly in small cuts until an empty case just fits and allows the action to close (Sharps model 74). Then take no more than 0.003"-0.005” off. They end-up being approx. 2.512” long. I'm glad I didn't trim them to the nominal 2.500” right from the start.

Using black powder is different in this detailed study than smokeless. Suggest anyone that is really interested in the article read the entire article.

Tom

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joeb33050 posted this 11 December 2012

I should note, and am, that some BP shooters steadfastly and loudly maintain that the gap causes accuracy problems. No data, but a popular stance.

Also, during the exciting “case length during firing and sizing” experiment I found that fl sized cases get shorter as they are fired. Thus, if fl sized cases are as long as the chamber, there's no danger of “jamming” because the cases shrink. Thank God for that!

joe b. Dipping rules!!

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bushranch posted this 11 December 2012

Always found the 30-30 cases were short for the chamber. Over the years I made a few longer cases out of old Winchester 38-55 brass. They were long enough but the crimp ring came out on the shoulder and the necks had to be turned as there was always extra brass on one side. Later used new Winchester 38-55's , they were a lot shorter to begin with and again the neck had considerable thickness on one side. Now use 32-40 cases and they are the answer for the 30-30. Easy to make and when first fired have to be left extra long for the length loss when they fire form . I centre the end of the case over the front bullet lube groove and force seat it with a crimp. No sign of pressure and they actually shoot pretty good. You can then trim the case to the exact length required. Problem again is to prove any difference in the actual shooting. I am still working on this. Does make a nice looking long neck 30-30 case Rus

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