Case captivity vs.pressure

[Yooper003]

Didn,t know where to put this guestion, but I see Larry Gibson usually monitors this site & I know he will have an answer. Loading 45/70 ,I have quite a few Hornady cases & loading them with same boolits to same LOA. How much am I raiseing pressure? The factory FTX load according to my measurements is jumping over .110 to rifling in my gun it shoots real well. Same bullet my reloads in star line brass only about .020 jump, shoots about the same, maybe not quite as good.conversely some of my reloads with cast boolits, loaded in shorter Hornady, to same LOA as in longer cases look better. I guess if I move boolits out to same LOA, I am not decreasing capacity. If I seat boolits to groove, how much am I raiseing pressure? I have read where people said to beware of the shorter cases but I have been loading both & seen no signs of trouble.

[mdi]

Reloading with FTX brass (shorter) with bullet seated to the cannalure/groove, giving a shorter OAL than with standard length 45-70 brass?

[rsrocket1]

Are you stuffing these with 70g Black Powder? If you are using smokeless powder, you are probably filling the case with 50-75%, maybe even less. With modern rifle cartridges, the bullet seat depth has little effect on the peak pressure when moving forward or back by small distances. With a big old BP case like 45-70, its the same thing. A quick estimate with Quickload shows that a change of 0.1" increases or decreased peak pressure by about 2,000 psi with 45/70 loaded with a 340g bullet. It's not linear except for small differences so don't just assume a 6k psi difference with a 0.3" change in OAL.

This is in contrast to a small high pressure cartridge like 9mm where a 0.1" change in OAL can mean the difference of close to 12,000 psi in peak pressure.

[Yooper003]

I have been loading Hornady 325 FTX. To cannalure with both cases, see no difference, due to the ogive on some of my castthey actually work better in the short cases. Some of these boolits loaded to groove in reg cases make action hard to close as boolit is Jammed into rifling.




Thank

[Tackleberry41]

Seating depth has a big effect. Books tend to say '180gr bullet' like the Lee manual. But what 180gr? I recently loaded some 450bushmaster, straight from the hodgdon site. I did not have the specific barnes 300gr listed in the data, used a hornady XTP 300gr. My mid range loads came out below the min specs. Factored in barrel length, still way less than the data on velocity. I dug around the Barnes 300gr is .840 long, the Hornady XTP is .815 long. So the base of the bullet is .025 shallower in the case. Once I shortened the the OAL so the base of the XTP was same as the Barnes, then the velocity was the same.

Or some 7.5 swiss I have been messing with. I pushed the bullets out to fit the deeper throat of a 1911 vs K31. 2.090 is whats listed in the Lee manual, mine are 3.050. With the resulting velocity loss. They are 3gr past max loads in the manual, to come close to the listed velocity. The cases are barely even warm, no sticking or flattened primers. And I know when I try to use up a box of different 180gr bullets in the rifle, the data will have to be adjusted, as they were when I messed with some 178gr Amax. Actually longer than the 180gr boat tail spitzer am currently loading. So set to mag length the base will be much deeper in the case than the heavier 180gr.

[fredj338]

In a 45-70, nor real pressure issues loading short. With any rifle round, loading short most often reduce pressures, you are further away from the rifling. Not like handgun ammo at all. A lot more case capacity & much slower powders.

[Petrol & Powder]

I'm not sure if holding the casing in captivity has any effect on pressure but case Capacity might :-)

Maybe you should pick up those "free range" casings that other shooters leave on the ground. :groner:

[Yooper003]

Yes the captivity might be affected, see spellcheck changed it and didn't pay attention. Sorry about that. Haven't found any free- ranging 45/70 cases ,think most 45/70 shooters reload

[Tackleberry41]

Yea its rare to find someone shooting 45-70 who does not reload them. Knew a guy who worked at a range, gave me buckets of brass. Not one 45-70 over the course of 2 years. Think found 5 45 colts. Pistol it was 9, 40 and 45. Rifles 223, steel cases, and the occasional box of 270. Was always 270, guess few who hunt with it reload for it. .

[Larry Gibson]

Given the larger the case volume along with the smaller the expansion ratio of the 45-70 case the less any appreciable increase in psi will be found between standard length cases and the Hornady FTX length cases. As several have mentioned they've found no difference. Unless one is pushing top end level IV pressures with jacketed bullets I wouldn't get concerned over the difference.