Home Forums Reloading Big Game Rifles Strange phenomenon with 338 RCM brass

I recently chambered for the 338 RCM and am having case stretching issues.

I have had a running dialog with Lonnie at Hornady and Dave Kiff. The reamer specs are identical to Hornady's. Chamber was headspaced with Pacific tool and gauge go/no go gauges.


All 200 pcs of brass are 2.010" long as supplied. After firing the most mild loads the brass stretches an amazing .017" and with upper end loads up to .035"!!!

The end of the chamber is 2.025" I measured it and the spec sheet reads that length which is identical with Hornady's specs.

If anyone does some figuring from the above numbers, THE BRASS IS STRETCHING PAST THE END OF THE CHAMBER! I didn't know that was even possible! Extracting the brass is easy and there is no stepped area near the case mouth. Is the chamber expanding and allowing the brass to move into leade area? It is a #2 lilja SS barrel. (Dave Kiff suggested that the chamber is expanding. He sited early tests with Rick Jamison and the WSM and similar results)

Stretching occurs with Varget, RL-17, and H4350.

If the brass is fired again after trimming to approx. 2.007" and partial FL sizing in Redding die it has incipient case separation due to stretching again.

All indicators point to very soft brass but I cannot prove it.
Can't find any more brass anywhere to try as a control. Can't find any loaded ammo either.

I am going to do some very mild loading with Win 760 which Lonnie recommended today and if I it stretches past the end of the chamber then Hornady will be getting some brass for testing.

I would sure like to hear from any 338 RCM shooters. How much does your brass stretch after first firing before resizing? Where is the end of the chamber on a Ruger rifle?

Thanks

WOW, I do not load for the .338 RCM, however, your post is an intriguing reloader's mystery.

Typically, a .007 -.008 case stretch implies a headspace problem and/or a sloppy chamber in most rifles...and you are WAY beyond that, yet, the go/no go gauge discounts headspace as the problem.

I have never heard of a chamber "stretching" but I am NOT a ballistics engineer either. From your post, super-soft i.e. way too soft, brass sounds like it may be the only answer.

For me, the issue of a blown case would be on my mind every time I pulled the trigger, thus, my accuracy with that rifle would definitely be poor with that as an issue.

Ross is the shoulder moving forward a like amount? If it is, try your headspace gauge in the chamber. Can't believe the shoulder would be cut like that for a non-belted case. If the barrel is stretching that much it will come apart before many rounds are fired. Did Dave Kiff offer an answer as to how the problem was solved with the WSM?Rick.

Measure the case head to shoulder length on a before fired and after fired case.

An easy way to do this is to use an empty .45 ACP or .40 case and put it over the case mouth of the .338 and measure with a caliper. This will not be the distance to the datum line, but it will do for a comparison.

I find it difficult to believe that the chamber dimensions, brass, and head space gauges are all in spec. and this is happening. Brass just does not stretch larger than the hole it is in.

If it is the case mouth stretching, there should be a step or crimp at the end of the fired cases mouth where the cartridge neck stretched past the chamber neck.

The first thing I would check would be the headspace gages. Next would be the chamber length. It sounds to me that the chamber is too deep and the no go gage is hitting somewhere on the body of the case instead of the shoulder.

I appreciate the ideas gentlemen. Howdy Rick.

I just grabbed a 45 ACP case and did some shoulder length comparisons of the fired brass vs sized brass AND the go/ no go gauges. HOLY smokes the shoulder is being set WAY back by the sizing die. Dave Kiff also said that he is getting feedback that some dies were not sizing the brass correctly. Won't mention any brands here.

The light finally came on! It is beginning to point to the sizing die rather than the chamber/reamer/go no go gauges. The die must be moving the shoulder back early in the FL sizing and only far deeper settings of the die reduce the taper on the base area. Sounds like a small base die might be in order. To my knowledge they are not made yet. It would be a custom order but could be worth a try.

Still cannot figure out how the brass can be longer than the chamber's end with no stepped marks near end of neck. Extraction is easy even with some cases that are 2.035" long in a chamber that ends at 2.025".

I guess I'll continue the conversation with Lonnie at Hornady and send him some fired cases. I have heard good things about the dies he custom makes. They use a comparitor and CNC equipment with a boring bar so costs are far less.

I appreciate the help.

I would not spring for a small base die just yet, sounds like the regular dies are not set to the chamber.Rick.

My loads do fit the chamber better since I switched from Hornady dies to RCBS dies...

Dennis

Dennis,
My understanding is that custom RCBS are now being made by Hornady. Either way ... dies are designed differently and will work slightly differently. A mate and I have 2 rifles chambered with the same reamer on the same day for identical chambers. Yet if I set up my custom Hornady dies like his custom CH/4D dies, I wont be sizing. Screw his die onto the shellholder like I can with my Hornady dies, and cases wont fire due to excessive headspace.
Cheers...
Con

I understand Rick. A custom die not a SB die is the solution. Not to worry no one makes a SB die yet.

I guess I was not working on all cylinders when I resized this brass. For 30 yrs I have never had an issue with the dies not properly partial FL sizing. Apparently the die dimensions do not match the fired brass dimensions.

I will send several fired cases to Hornady and have Lonnie evaluate and make me a die if necessary. Perhaps all I need is the Hornady die.

Con,



A buddy and I had the same problem. We had 7MM-.300 Wea made up. Even used the same brand of barrels. Yet his chamber was ever so slightly larger than mine.

My RCBS dies aren't customs...just ordinary order-from-anyone dies that I bought (I think) from Midway. Not, by several, the only set of Hornady dies I've replaced with someone else's because they weren't working right for me.

Dennis

let me ask a foolish question. "If" you had some factory ammunition and you fired it in your rifle. Then you put a stick in the press and screwed the die down until it stopped on the shoulder of the fired case, would this solve the problem? I am probably showing my ignorance. For all my rifles and again I am showing my ignorance I screw out the reloading die to produce a snug fit for the cartridge case. In a 270 win made up in a weatherby mark 5, at this setting I am only neck sizing for sure.

Do you think that would help? Or am I just off the page somehow??

Jimmy, it would be hard to tell when you reached the shoulder since you would be sizing the sides of the case as you screwed the die down. Don't know what you mean by putting a stick in the press. A much better way would be to measure off the datum line on the shoulder.Rick.

"A buddy and I had the same problem. We had 7MM-.300 Wea made up. Even used the same brand of barrels. Yet his chamber was ever so slightly larger than mine."

That is not unheard of. A reamer wants to cut oversize in the best of conditions, and depending on alignment and chatter, two chambers cut by the same reamer can be different.

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Thanks for your professional courtesy.

so my point and perhaps incorrectly stated was that I have a tight fit when I close the bolt on a re-sized case. The bolt is a bit snug to close. I screw the die down to touch the shell plate on an extended ram, then back it up a turn and a half, size a stick of brass. Then chamber it in my rifle, it will not chamber, so I screw the die down an 1/8-1/4 turn and try it again until I just get the bolt to close.

Jimmy,

You are doing things correctly. I have been doing that method for 30 years and finally got caught. All the dies I have ever used managed to push the shoulder back as well as some body taper without causing excessive headspace.

This particular 338 RCM chamber done with a sammi spec reamer is not compatable with the FL die I used. To get the proper bolt closure with little or no effort the die was moved down to the point it reduced the base/body diameter for the right fit but moved the shoulder to the point where it created excessive headspace.

I will now include datum line measurements in my FL/partial FL sizing. It is interesting that this is the first time in 30 yrs of reloading this has happened. I have loaded for at least 50 different chamberings. Guess I have been lucky.

Just another lesson learned about the handloading game...NEVER ASSUME anything with a new set-up.

I have a multiple of dies, mostly RCBS, cause thats what I like, that do not size my brass as they "should". I`ve had to mechanicaly tweek them...most all because of head space.