trim length vs. chamber length

[JonnyV]

While waiting (impatiently) for my Shiloh order to be built, I got a heads up from a shooter I know where there was an 1874 rifle available. It's in very nice shape and I bought it. First things first, I slugged the bore, found the null point, figured my max COAL, and then I measured the chamber length...

Turns out the chamber is 2.110". I did this with the tail end of a micrometer and repeated the exercise a few times to make sure I was getting it right. Basically, I just inserted the thing into the chamber until I could feel the transition, and then backed the mic down onto the chamber mouth. Anyone else done this?

Anyway, this brings up a question...how close do you guys like to run your case mouth to the end of the chamber? Or, in other words, what's the brain trust think the overall trim length should be?

I just ordered 300 new Starline cases for this rifle. Primary use will be silhouette match shooting with Swiss 1.5F, Brooks 540 gr New Postell (1.42" OAL first two bands reduced), MVA mid range sights with magnum Hadley eyecup (ordered, waiting on production). The rifle has an 18" twist.

I did find an old thread on here about this.....

https://www.shilohrifle.com/forums/view ... hp?t=23140

[kenny sd]

In my 40 70 ss, I trim them just short of the 2.5 case length. 2.497. I set the case cutter to that length and occasionally measure. any over 2.5 even slightly, I trim back. over length cases take the chance of a split case sticking in the chamber. Never happened so I may be chasing a NON problem.

Many more here with much more experience than me. so listen to them...Distant Thunder for one....Ken

[desert deuce]

Well JohnnyV, I am looking at two chamber casts that Dan T had me take on two different rifles for the purpose of him designing a proper fitting money bullet for each individual rifle.

He had me use cerrosafe and perform the cast two inches into the rifling.

Based on that request I did chamber casts on two additional rifles. NONE OF THE FOUR HAD NOMINAL LENGTH CHAMBERS ALL EXCEEDED NOMINAL LENGTH. One Kreiger Barrel, One Badger, One Douglas and One Green Mountain.

One 40-65 Chamber measured 2.117. All were over the nominal length stamped on the barrels. In this rifle I have been shooting Annealed 2.105 length fireformed and stretched Remington 45-70 cases that new in the box measured in the 2.08 category. In that rifle they work just fine at 2.105 and frankly did OK at 2.08. But OCD kicked in and I stretched, fireformed and trimmed to 2.105 (Most Starline Cases are close to or at nominal length that I have measured as they come from the factory. (Measured 50 NEW unfired starline 45-90 cases yesterday all were 2.40" +/- .002" which is close enough to start with.)

When I would full length size a stretched and fireformed case it would be shorter than when fireformed and the difference was inconsistent which is why I fireform new fireformed and stretched cases with cornmeal rather than bullets.

Therefore, consider cerrosafe casts for your rifle chambers and if you go into the rifling you get a very nice imprint of the transition and only trim fireformed cases to the desired length, not full length sized cases.

Hint, take a fireformed case and deburr the inside mouth of the case. Take a ready to load bullet and slide it base first into the case. If the bullet won't go, is difficult to sticky to slide into the case (needs to slide freely) you "will likely" have a problem with separated cases and stretched cases down the road whether you use unsized or sized cases as the bullet will tend to pull the mouth of the case with it as it leaves the chamber. Which implies potential vertical inconsistency at the target.



I am only responsible for what I say, not what anybody else may assume I said.

[kwilliams]

New Starline 45-90 brass barely measures 2.4" and after the 1st firing always comes up short. I have the reamer and chamber casts but the actual length needs to be 2.411 in this rifle to eliminate paper rings. So spent a week nibbing/stretching the cases I had...yah a big pain and takes a lathe. Easier route would have been trimming 2.6 cases. Breech, frame, rim thickness tolerance, spring back and a bit of headspace adds .002-.003" to what you get by measuring the cast or reamer. Fire an empty case and measure the primer back out. I believe correct case length can also minimize the lead flakes you see shooting grease grooves also. Different chamber lead angles also affect the optimum length.
kw

[JonnyV]

I have some 45-90 brass on hand and some more inbound so if cutting down to length is easier, then I guess that's what I'll be doing. I do have some Cerrosafe around on the bench somewhere too, that's a good idea!

I don't have a lathe so no case stretching for me....

[jackrabbit]

I don't paper patch, so I have no knowledge there, but I can tell you that cases that are a little short don't matter with grease groove. When I started I fretted about case length, but don't worry about it much now. I have shot some super groups with brass that measures 2.09 and change out of a rifles with chambers that measured 2.1+ and could not detect any change in accuracy. If I were you, I would just load up 45-70 brass that has been annealed and trimmed to all the same length and let 'er fly.
Take care, Cody

[bobw]

Wouldn't t trim any case till they are fireformed. Period bobw

[JonnyV]

I think I'll measure up the new 45-70 cases when they show up and if only a couple thousandths short, probably won't worry much. However, if it gets beyond a few thousandths then I might look at cutting down 45-90 brass. I don't want to have any way of bullets obturating before they make it to the bore. I would think that a smooth transition from brass to bore would make for the best possible results.

As suggested above, all the brass would be annealed prior to fire forming as well...

[charlie young]

I just got done bore scoping quite a few rifles. One 38-55 roller with a Douglas Barrel, one Cody Built Highwall MVA action with Green Mountain barrel. And several Shilohs all if various 45 caliber. Not one rifle had lead or any sort of fouling in the throat area, all as slick as a whistle. I make sure the brass is not to long in all of these and like Cody said load 'em and shoot 'em if you are shooting grease groove. Paper Patch is a horse of a different color. As BobW said "Wouldn't t trim any case till they are fireformed. Period"

[MikeT]

Shooting gg bullets, you may get by just fine with brass that is up to 0.050" short. I have a 40-65 that always has a grease extension on the mouth of the fired case that is about 0.050" high. Once the grease fills the space ahead of the case, the bullets will not expand into that space.

I only shoot pp bullets now, so I want the brass to fill the chamber a fully as possible.

Keep on hav'n fun!
MikeT

[JonnyV]

I always get that grease lip on the ends of my fired brass and I didn’t put two and two together…now I know.

So when the new brass gets here, the first step will be annealing, then loading and fire forming? There clearly won’t be any trimming involved…

[jackrabbit]

I always full length size everything, so fireforming doesn't seem real important. If you are slip fitting or only neck sizing, it is obviously important. I also believe that consistency is key so I like my brass all the same length even if they are a little short.

[TexasMac]

Before he left us I had many discussions with Dan Theodore on case length vs. chamber length. After extensive testing he said that accuracy starts to degrade a bit as the difference exceeds 0.010" or so. So I either stretch or trim longer brass to closely match the chamber & headspace length.

And due to the lead alloy softness of BPCR bullets, which will generally obturate prior to moving forward, it's a good idea to have a grease groove exposed just in front of the case lip. The grease will extrude into the gap rather than lead, preventing lead stripping.

Wayne

[JonnyV]

So today 500 brand new rounds of brass showed up. Everything so far mic’s within .002 of 2.1”…

Resize? I ran one piece through and it grew .004”

I will anneal for sure

No trim needed.

[kenny sd]

I agree with trimming after fire forming...and....I check the trim every once in a while on my 40 70 ss. any even slightly over 2.5 get cut to 2.497.
also, I never thought about leaving one grease groove open at the top of the loaded case.
I have been doing this for years.
65 1F and one 060 veggie wad with 1/16 comp and hand seated 390 grain RN GG expose the top groove.
I have never had a leading problem...so maybe I had the cure for a problem I didn't think I had...

interesting....Ken