45/70 Case Length Question

Discussion of BPCR loading techniques, SAFETY, Case Cleaning and Prep, Indexing, BP Choice, Primers, Wads, Compression, Drop Tubes, Vibration, Load Testing, etc.
shooter37
PostsCOLON 78
JoinedCOLON Mon Nov 21, 2005 8:51 am

45/70 Case Length Question

Post by shooter37 » Thu Apr 29, 2010 8:25 am

What is the optimum case length for 45/70 brass shooting grease groove bullets?
I understand SAAMI data to be case length of 2.10 (-.005).
Do most shooters trim back to 2.o95 or ??
I have experienced some leading recently and I suspect case length to be the issue.
Shooting PJ 45001 1/20 with SPG lube. Load is 65-68 Swiss 1 1/2 with overprimer paper wad and
fiber over powder wad. Compression is .215.
Thanks for your input
Al

DRCook
PostsCOLON 472
JoinedCOLON Sun Nov 27, 2005 3:25 pm

Re: 45/70 Case Length Question

Post by DRCook » Thu Apr 29, 2010 10:10 am

I hate to use the oft repeated mantra about getting a chamber cast, but do so. Some people are actually stretching their cases beyond 2.1 to match their chambers.

Unless a reamer has been erroneously ground, the chamber will always be longer than 2.100 to provide clearance. So you can figure that 2.100 will be a good length to start with.

I would not cut your cases to 2.095, as that just provides more room for the lead to slug up into.

AND, if you fireform your cases and do not FL resize after each usage, you will be surprised at how much they actually shorten when fired

DC
drcook = david r, not dr. but thanks for the compliment :)

User avatar
Ranch 13
PostsCOLON 1584
JoinedCOLON Mon Nov 21, 2005 9:41 am
LocationCOLON Eastern Wy
CONTACTCOLON

Re: 45/70 Case Length Question

Post by Ranch 13 » Thu Apr 29, 2010 12:05 pm

Unless your chamber is really long, the case length probably isn't the culprit for the leading. Go back to what you were using before the leading started and look at one thing at a time that you changed.
There's always the possibility that a bullet got buggered during the loading process , left lead, and until you get the barrel clean right down to bare steel will continue to collect lead.
Plenty of things to look at before jackin around with your cases.

User avatar
montana_charlie
PostsCOLON 1413
JoinedCOLON Sun Nov 20, 2005 8:35 pm
LocationCOLON West of Great Falls, Montana

Re: 45/70 Case Length Question

Post by montana_charlie » Thu Apr 29, 2010 6:14 pm

When you seat the bullets in your 'leading problem' load...
Do you use full length resized cases?
Does the bullet contact the lands?
Are any grease grooves exposed?
(Don't try to read anything into the questions, just answer 'yes' or 'no' to each.)

Also, at your earliest opportunity make a Cerrosafe cast of your chamber...or use some other controllable method to measure the depth of your chamber.

Accurate information from you, and clear answers to the questions, will help to determine if you are likely to have a case length problem.

CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

shooter37
PostsCOLON 78
JoinedCOLON Mon Nov 21, 2005 8:51 am

Re: 45/70 Case Length Question

Post by shooter37 » Thu Apr 29, 2010 9:10 pm

First, thanks for thr replies. All good points.
As to the questions... the rifle(s) are Shilohs, factory chambers.
I FL resize
Bullets just touch the lands.
One grease groove is exposed.

What I realy question is what is the optimum case length?

John Boy

Re: 45/70 Case Length Question

Post by John Boy » Thu Apr 29, 2010 9:26 pm

What I really question is what is the optimum case length?
Shooter, it is the length of the chamber cut for the case. A chamber cast will tell you what that length is. If you don't want to do a cast, try this:
* Drip some candle wax on the back end of the ogive and some at the end of the case mouth. Insert the round and then gently remove the round. You will see from the wax where the end of the case seats in the chamber if your case is too short. Measure the length. Do it couple of times to verify your measurement

And remember that one doesn't want gas leakage from the round in your chamber. Anneal your cases at 650 F (straw to green/blue color)

User avatar
montana_charlie
PostsCOLON 1413
JoinedCOLON Sun Nov 20, 2005 8:35 pm
LocationCOLON West of Great Falls, Montana

Re: 45/70 Case Length Question

Post by montana_charlie » Thu Apr 29, 2010 10:14 pm

shooter37 wroteCOLONFirst, thanks for thr replies. All good points.
As to the questions... the rifle(s) are Shilohs, factory chambers.
I FL resize
Bullets just touch the lands.
One grease groove is exposed.

What I realy question is what is the optimum case length?
To answer your question, the optimum length is one that matches your chamber depth.
You can't know what that is unless you measure the chamber...and every rifle needs it's own measurement.

Since you FL resize, your cases are as long as they will ever be...unlike fireformed ones.
Since you seat bullets to touch the lands, you can't make your ammo any longer. But, since you do have at least one grease groove exposed, you can seat a little deeper...just for this test.

Let's start off under the assumption that your case mouth lies right on a driving band.
When fired, the driving band bumps up to fill the tiny space between the end for the case and the end of the chamber (occurs when a case is too short). We'll say this is a load that causes leading.
If the description doesn't match your situation, you'll have to tell me that.

Make sure you have all of the lead cleaned out of your barrel.

Adjust your bullet seating depth so that the mouth of the case covers half of the exposed grease groove.

Make sure that half exposed groove is full of lube, and go fire four or five loads.

Check your chamber end...and the beginning of the bore...for accumulated lead.

If you get no leading when there is a grease groove at the end of the case...but you do when there is a driving band at the end of the case...that indicates the leading is caused by 'short brass'.

Sure, you can adjust the bullet seating to get a grease groove in the right spot, but that might not get the accuracy that comes from having the bullet touch the lands.
It's up to you to decide which works best.

If you think you suffer from 'short brass' you really need to measure the chamber so you know what length is actually needed to correct the situation.
If it seems you can be helped by a case stretcher (and we don't actually know that, yet), I know where to get them.

If this little test seems to have cured the leading problem, your next assignment is to beg, borrow, or steal a 45/90 case which has been full length resized.

CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

TexasMac
PostsCOLON 1035
JoinedCOLON Sun Nov 20, 2005 6:08 pm
LocationCOLON Central Texas
CONTACTCOLON

Re: 45/70 Case Length Question

Post by TexasMac » Mon May 03, 2010 9:16 pm

shooter37,

You've been offered some great advice. By the way, what rifle are you shooting? If you mentioned it I missed it. If it's a Browning BPCR with an unmodified chamber the fireformed brass should be 2.114" long, which allows approximately 0.005" for length expansion during firing.

Wayne
NRA Life (President's Council) Member, TSRA Life Member, NSSF Member
Click on http://www.texas-mac.com/index.html to my home page containing information on my Browning/Winchester BPCR book & associated articles.

HpGuy420
PostsCOLON 325
JoinedCOLON Mon Aug 14, 2006 5:57 pm

Re: 45/70 Case Length Question

Post by HpGuy420 » Tue May 04, 2010 12:10 am

Τίποτα για το τίποτα
Last edited by 1 on HpGuy420, edited 0 times in total.

shooter37
PostsCOLON 78
JoinedCOLON Mon Nov 21, 2005 8:51 am

Re: 45/70 Case Length Question

Post by shooter37 » Tue May 04, 2010 9:30 am

Again Thanks to all who responded.
I did find some significant leading beyond the throat after shooting this weekend.
Using these suggestions I will do some testing and see what variations seem to work.
Since I have been shooting this rifle (Shiloh) for some 5000+ rounds with good results I suspected case length as
the problem.
I have culled all cases below 2.0975 and trimmed any long cases to 2.10. I will play with bullet seating and try and let you know the results.
Thanks again
Al

User avatar
montana_charlie
PostsCOLON 1413
JoinedCOLON Sun Nov 20, 2005 8:35 pm
LocationCOLON West of Great Falls, Montana

Re: 45/70 Case Length Question

Post by montana_charlie » Tue May 04, 2010 9:37 am

HpGuy420 wroteCOLONOK,

I've actually done the testing to say something that none of you can. I ditch any case that is 0.01" shorter than it's chamber.
If they are Winchester cases, I would agree with Dan. But, if they have some meat in the wall, they can be stretched .020" - .030", or more.

CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

checker
PostsCOLON 103
JoinedCOLON Sun Nov 08, 2009 7:49 pm
LocationCOLON Utica, MS
CONTACTCOLON

Re: 45/70 Case Length Question

Post by checker » Fri May 28, 2010 12:29 pm

What is the optimum gap between the end of the chamber on a 45-70, and the end of the case mouth? .001, .005, ? After some initial shooting with a new 45-70 I was getting very thin rings of lead shavings at the end of the chamber, but I suspect most of that was caused by a common beginners mistake (me) of trimming my brass before fire forming. The bullet was a Brooks 545 gr. Creedmore that engraves the rifling. Measuring new untrimmed brass, the gap will still be .010 to .012"+.
Shooting a Brooks 520 New Postel, I am able to seat the bullet out further to engrave the rifling, and it has a grease groove exposed at the case mouth. No lead rings, but the accuracy of the 545 gr. is slightly better than the 520 gr. New Postel. I own the PT&G custom 45-70 reamer, and after Raton, I am thinking of sending it back to Dave Kiff, and ask him to trim back the reamer's cutting face at the end of the chamber by about .020", and then set back the shoulder of the barrel, and recut the new chamber. New brass will be trimmed to that dimension. Hence the first question.
Casting 20:1 lead. Neck sizing fire formed brass. Thanks, Tim
"There is nothing simple about a simple point pattern"

User avatar
montana_charlie
PostsCOLON 1413
JoinedCOLON Sun Nov 20, 2005 8:35 pm
LocationCOLON West of Great Falls, Montana

Re: 45/70 Case Length Question

Post by montana_charlie » Fri May 28, 2010 12:56 pm

checker wroteCOLONWhat is the optimum gap between the end of the chamber on a 45-70, and the end of the case mouth? .001, .005, ?
If your question is directed at me, I would say that 'optimum' is 'zero'...but it's hard to get.
If you trim a case that is quite near 'fireformed' dimension, you can take it down to exact chamber depth. But, it might lose a couple of thousandths when fattened up to actual fireformed dimension.
If you can leave that case a few thousandths 'long' until after it's fired, you have an easier time of getting it exactly right.
Using packed cream of wheat, instead of a bullet, is supposed to make that workable...but I haven't tried it.

I have been shooting some stretched cases which shortened to .003" under (when fired) and they still appear to be acceptable.
If any had reached .005" under, I would re-stretch them.

I was shooting some PP rounds the other day. Somehow, a case that was .007" under got included in the batch. I got a paper ring when that one fired.

CM
Retired...twice. Now, just raisin' cows and livin' on borrowed time.

checker
PostsCOLON 103
JoinedCOLON Sun Nov 08, 2009 7:49 pm
LocationCOLON Utica, MS
CONTACTCOLON

Re: 45/70 Case Length Question

Post by checker » Fri May 28, 2010 4:28 pm

Thank You Charlie. My question was directed to anyone who had an experienced answer, and I respect your opinion as experienced. By measuring the length of the PT&G reamer, it appears that the cutting length will have to be shortened, so I will do the barrel lathe work after the BPCR-S Nationals in July. I'll just have to shoot the 520 gr. Postell at Raton and fine tune it to get acceptable accuracy until then, but that will also give me a chance to fire form new brass. BTW, my oldest son is a Sgt. at the Malmstrom AF base near you. He's been there 10 yrs. and it looks like he'll be there another 4 to 5. He just re-enlisted. Looks like he will be a "lifer", and get in his 20 there. Thanks again, Tim
"There is nothing simple about a simple point pattern"

shooter37
PostsCOLON 78
JoinedCOLON Mon Nov 21, 2005 8:51 am

Re: 45/70 Case Length Question

Post by shooter37 » Tue Jun 01, 2010 7:07 am

OK, here's a follow up.
I purchased a batch of new Starline 45/70 cases: all fell into a range of 2.995 to 2.10. Cases were annealed, neck sized, expanded to .457 and deburred. Primer pockets were also uniformed.
Shooting with a 540 gr. Jones Creedmore bullet, 65 gr. Swiss 1 1/2 with .030 Walters wad and BR2 primers there was NO leading and the load held up to 500 meters. Fired cases extracted just fine and show nothing remarkable.
The chamber in my rifle still hasn't been checked with cerrosafe so I can't make a call about length.
Bottom line appears to be as Dan T. and others stated, cull the short cases.
Thanks to all who responded... BPCR remain 1/2 skill and 1/2 witchcraft

BUTTON_POST_REPLY