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ETA- I am not sure how you could be getting a bullet/boolit that deep into a case without it catching your eye, but my answer(s) here in this post are going on what ya posted in the OP as info. Going on as if you are actually seating to that COL/OAL of 2.10" or 2.075" & not that you made some mistake in what ya posted for COL/OAL. The rest of my post below here, is based on your NOT making a mistake in your info ya posted in your OP.
IF it was just a mistake, just ignore what is below.
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Hodgdon Load data says Varget on a 405gr. (close enough to 410 to give the min./max. comparison) is 40gr. Min. to 50gr. Max. , giving 1392fps@15600cCUP at that Min. to 1718fps@29600CUP.
The COL/OAL being 2.540". Test case parameters was, Case: Winchester, Twist: 1:20", Primer: CCI 200, Large Rifle, Barrel Length: 24"
Trim Length: 2.100"
Source:
http://www.hodgdonreloading.com/data/rifle
Appears to me from your OP ( I bolded it in the quote) that you are using the "trim to" length as your COL/OAL, meaning you are quite a bit further into the case with 2.10" COL/OAL or 2.075" COL/OAL than ya would be with 2.540" COL/OAL. .344" to 369" difference deeper. More than a 1/4 inch(.250") but less than 3/8 inch(.375") deeper. That certainly is going to UP the pressures on that firearm, IMO. And then when ya add the powder above Max. ( 50gr. +) suggested, you are likely "pushing the envelope".
I do not own a 45-70 Govt., but I would like to own one... So I read up on what ther folks are doing & your post caught my eye today.
The reason I replied here, is that I do a bit of reloading & load development myself on other firearms, although mostly with reduced loads, but the basics are the same, and I reckon a person has to watch for signs of issues & also at least double check( I triple check) the load data that one can find for comparison to what is going to get tested. Otherwise there can be some issues & sometimes ones that no one would want to have happen to them or their firearm. Of course I could be wrong, but I fear you may be treading where you may not want to be, with load descriptions like ya mentioned in the OP.
I am not sticking my nose into your business, but you asked about the "donkey kick" & what might be done to help out. Even though I don't own one of those 45-70s, as a fellow caster/reloader, I just wanted to let ya know that either you made some sort of mixup on your info in the OP, or you may be creating a bad situation for yourself with those loads in that firearm. I would hate to hear that someone had an issue that ruined a firearm, or even worse, ruined ones life..
Generically, I would suggest ya stepping back & going over the load data once again & it is certainly up to you, but I would pull those loads that are 2.100" or 2.075" COL/OAL, and start over. Your choice....
To specifically answer your underlined question(s) in the quote above, I would suggest you don't do either, but re-think your load data & what ya want to start with, paying real close attention to the COL/OAL, in particular..
BTW, here is another load data workup where you can see the load data for a 405gr LFP using Varget is Maxed at 50gr. & in this data sheet they suggest 45gr. as a Suggested start point ( but not Min.). As well the barrel is there at 24" and the COL remains at 2.540".
Source:
http://www.handloads.com/loaddata/de...=Powder&Source
G'luck! & realize that I am not trying to cause issue with ya & how ya are doing things, but only to try to help.