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brotherdarrell
12-08-2012, 10:04 PM
This is a pic of an impact slug from my new to me Rem 30-s in 7x57.
55570
I have already reformed 20 pcs. of -06 and trimmed to what the books say is max. cart. oal, which is 2.235". I made the impact slug with a shorter oal case just so I could see where the chamber ends. The best measurements I come up with seem to show that I could go as high as 2.255" and still be just short of the end of the chamber.

How would you guys go about coming up with an appropriate case oal? I would appreciate any and all suggestions. Thank you.

brotherdarrell

Larry Gibson
12-08-2012, 10:20 PM
The measured 2.255 is what I would trim to and then double check that they chabr freely. The oal will probably shorten slightly with fire forming.

Larry Gibson

fatnhappy
12-08-2012, 10:23 PM
Use a micrometer and get a very accurate measurement of that throat diameter in two places, just north of the case mouth step down and at the lead edge of the rifling. Take multiple measurements at different angles. That's the diameter you need to size to. Fill that throat as completely as possible with your chosen boolit.

brotherdarrell
12-08-2012, 11:26 PM
Larry - good to know about possible case shortening.

fatnhappy - Immediately in front of the chamber the throat measures .289" and tapers to .287" within the first .050". It then tapers to .286" to where the rifling first starts. My new NOE hunter mold looks like it is going to drop between .287" - .288" with a perfectly sized nose. I have high hopes for it. My Lee soupcan drops .287"/.289". I will have to have Buckshot make me a sizer for my Lyman sizer. I can't wait.

brotherdarrell

geargnasher
12-08-2012, 11:41 PM
Yup, make them as long as you possibly can without pinching the boolit when chambering and touch them all up just for uniformity's sake with the trimmer after firing. Sometimes they shrink, sometimes not, it depends on how hard the brass is, how well the cases formed to the die, and how hot your forming loads are. I make 7mm-08 and .260 Remington out of .30-'06 brass to have enough metal in the necks to work out a very snug fit, and the added benefit is I can make them reach the end of the chamber. Usually they don't shrink during forming, probably because I don't anneal the necks at all, and the neck/shoulder area being formed from the un-annealed body of the parent case, tend to be very hard.

Gear

.22-10-45
12-09-2012, 12:32 AM
Hello, brotherdarrell. I find long chambers even in custom rifles. I think the reamer grinders do this as a built in safety measure..at any rate..it's not too good for cast bullets.
I chuckle when some of the new guys are sweating .001" on their trim lengths..if they only knew they are already way too short!

brotherdarrell
12-09-2012, 01:36 AM
.22-10-45 - I understand where you are coming from. I have a Contender in 7tcu that is not only chambered crooked but would need brass trimmed to 1.785" to fit the chamber. Trim length is given as 1.74".

Well, I went high tech. I trimmed one of the re-formed pieces of -06 brass to 2.26". I wanted to see if I could feel any resistance. I thought I could feel maybe a little but could not tell with the micrometer. So I pulled out the Sharpie and marked the end of the case. I chambered again feeling no resistance nor were there any marks on the end of the case. I think I may trim it back about .003" and give it a try. I have to start somewhere. The original 20 pieces I formed and trimmed will be relegated to j-words, not that I will be shooting many.

brotherdarrell

noylj
12-09-2012, 03:54 AM
For bottleneck cases, I trim for consistency. I want the bullet close or touching the rifling/lede, depending on rifle, but case length is of no concern as long as it is consistent for all the cases and below max.

blackthorn
12-09-2012, 11:59 AM
Quote "I have a Contender in 7tcu that is not only chambered crooked but would need brass trimmed to 1.785" to fit the chamber. Trim length is given as 1.74"."

My experience is that most Manuals give a "trim-to" length that is 0.010" shorter than book "maximum", so what you quote is cosistent with that. If we trim so that we are on the ragged edge of "too tight" there is no room for the case to safely "grow" and we will have to check, and trim if necesary, after each firing to ensure that we remain safe.

tonyjones
12-09-2012, 04:42 PM
sinclairintl.com sells a chamber length gauge that measures from bolt face to end of chamber neck. Their part # for .30 caliber is G-308. Cost is about $7 and they are reusable.

Regards,

Tony

plainsman456
12-09-2012, 08:17 PM
Before you trim them any shorter,you should shooy 1 or3 to see what the final length is.
Once you take it off you can't put it back on.

brotherdarrell
12-09-2012, 09:47 PM
Thanks for all the suggestions. I have plenty of brass so I can afford to sacrifice a few to work this out. Going to the range in the morning to shoot some j-words. I will be able to see what the brass is going to do as far as size and get an idea of 'potential' accuracy. Once I get the sizing die I will be able to start working on boolits. Still not exactly sure as to the size to make it, leaning toward .287".

Thanks again

brotherdarrell

brotherdarrell
12-10-2012, 04:49 PM
Well, it appears trim length may be the least of my issues.
556725567355674

Inside diameter of case mouth is .289". Outside diameter immediately above shoulder is .002" less than main part of case neck and goes back up to full diam. within a couple thou. FWIW the load was 38 gr. imr 4895, Win LRP and 139 gr. Horn btsp. Cases formed from -06 brass. Necks necks were not turned or annealed.

Comments? Observations?

brotherdarrell

plainsman456
12-10-2012, 08:23 PM
I would anneal some of those cases and try again.
They look like some 308 cases that I had,almost all of them spit when fired.
They had not been fired for at least 20 years.When they were annealed the rest of them worked like a charm.
I also had some 06 cases that I made into 6MM and after trying one for length,it split.So i annealed they others and they all formed the way they were supposed to.

geargnasher
12-10-2012, 10:56 PM
You didn't finish the brass prep job before shooting. You have to be careful shooting jacketed stuff with the cases being too long, they get very unfriendly to "pinch". My post previously assumed you would be shooting cast, not fireforming with jacketed.

When you reform brass from '06 you will have a thickness variation along the length of the neck, since it was formed partly from the shoulder of the parent brass. This needs to be reamed out with a case mouth reamer, either in a bench lathe tool or in a reaming die. I see that the fired neck diameter is ~.325", that gives .0205" clearance around a .284" jacketed bullet, which with unturned brass is tight at the thick part near the base of the neck. Based on the fired neck OD dimension you wouldn't even come close to chambering a cast boolit at .288" or so unless your case necks were in the .019" thick ballbark or less.

The thing to do is decide whether you're going to shoot jacketed or cast, and stick with one or the other, and make your brass fit your choice using your very nice looking impact cast as a guide. A half-thousandth to a thousandth total loaded chamber neck clearance is pretty much a requirement for sub-moa accuracy at any sort of decent velocity with cast boolits, so you don't want to trim too much off the neck, but also keep in mind that thickness variation (either from mouth to base of neck, or from one side of the neck to the other) is no good either, so you'll need to ream and probably outside turn the necks to true them up for best results on target.

I have yet to need to anneal newly-formed 7mm brass, but I run very tight clearances with cast (albiet ENOUGH clearance!), so tight that neck sizing is not required for reloadings after the forming operation. Obviously your necks demonstrate being overworked and brittleness, a LIGHT anneal may be in order, and may have been needed before setting back the shoulder in the first place with your particular cases.

Gear

brotherdarrell
12-11-2012, 12:36 AM
Gear - I am going to ask you to be patient with me on this one. Sometimes I can be a little thick headed and can't see the forest for the trees. What I think you are saying and what I think I am seeing are complete opposites. Here are a few numbers.

.280" - inside diameter of neck of formed brass w/o boolit or bullet. measured w/ caliper
.315" - max outside diameter of neck of formed brass w/o boolit or bullet. measured w/micrometer.
.316" - max outside diameter of neck w/bullet seated(max diameter .2837")

.325" - outside diameter of fired case mouth.
.289" - inside diameter of fired case mouth.

.018" - thickness of brass in neck area

Seems like plenty of room for boolit up to .287"?

I cut off approx. .010" from end of fired case:

.297" - inside diameter at case mouth
.332" - max outside diameter of fired case
1.88" - approx. length from base of case to base of neck on un-fired formed brass(chambers easily)
1.86" - approx. length from base of case to base of neck of fired brass.

2.235" - OAL of un-fired formed brass
2.233" - OAL of fired brass

What I think I am seeing is a chamber with grossly oversized neck area. My numbers show minimum clearance around neck of loaded round w/bullet to be .00875" not counting area at case mouth. This seems absolutely huge. .3325" - .316" = .0175"/2=.00875". Notice oal before and after changed .002" while approx length to base of neck changed by approx. .020". This, to me, could only be explained by grossly oversized neck area in chamber.

A couple of notes:

I did plan to shoot boolits but, as noted in previous post, I have no sizer die of appropriate size. I do have a .285" die but based on chamber cast it is way too small.

I shot j-word for two reasons:
I wanted to see what a fired case looked like.
My first post shows a case loaded with a Lee soupcan. It was sized @ .285". It chambered easily. I had also seated an as-dropped soupcan boolit that was .287"/289" into a case w/oal of 2.235" and it chambered easily. This case mouth was expanded with an expander sized .287" for a case mouth of .285". I felt a j-word of .2835" would be cause no problem, and still do(fired case has mouth of .289").

Now, as I stated at the start of the post, I can be a little thick skulled sometimes. My interpretation of your post was that I had too much brass in the neck area, and thus too little clearance. This is based on saying j-words don't like pinch and mentioning turning necks after forming. The measurements above, to me, don't back this up. I had also measured neck thickness in many places and never found any measurement over .019". If I did not understood your post properly my feeble mind could use some clarification. Again, what I think I am seeing is a chamber with a grossly oversized neck portion.

Thank you for your time and patience.

brotherdarrell

popper
12-11-2012, 11:22 AM
I'm with plainsman456. And I'd wait and shoot cast. I had problems with 30-30 & 308 doing that with J-word. Annealed and shot cast - problem went away. Burn-outs like that can't be good for the throat.

geargnasher
12-11-2012, 09:32 PM
BD, you never posted your pound cast neck dimensions, that's the whole thing you should be going off of. I assumed that your mic reading in the pics of .325" was close to your neck dimension, not .332", so I thought they might have been pinching. If your loaded neck outside dimension is .316" and fired is .332", yes, that's GROSS chamber neck slop, even with unturned necks, and explains the splits very well.

Personally, I'd throw in the towel on it and either trade it or rebarrel, not much you can do unless you can figure out a way to add .008" to the case necks.

Gear

brotherdarrell
12-11-2012, 10:04 PM
Gear - actually post #4 has dimensions for the pound cast. I do agree that it is likely a lost cause, but I am a little bullheaded and have a little unguided optimism. I annealed 5 cases today and am going to give it one more shot next week. If it is an obvious no-go (which I assume it will be) I will be putting this rifle on the market for a 'collector'. If I had the money I would love to have it re-bored to a 7.62 x 57.

Thanks for all suggestions

brotherdarrell