Vmax has left the county !!

[Alycidon]

Yesterday afternoon Vermincinerator and I went to play with loads for the 20BR.

 

Having played around with 50s we came to some 40gr Vmax I had loaded under a light charge of H322. The first two three shot groups felt nice but were 3 inches right at 200 yards from the 50gr impact point.

 

The last was at a dot 4 inches in and 4 inches down a sheet of paper, nothing on the paper at all!!. Not even any possable hits on the backer although we could not be sure about that.

 

 

Why would a rifle that shoots one bullet very well shoot another so wildly. I suspect that as I used the same die seating setting as the 50gr the bullet was only a couple of mm into the case, so another 10 thou may straighten it out. Velocity was about 3600 so they should not be breaking up in the air, should they?, twist is 1 in 9 , according to this;

 

http://accurateshooter.wordpress.com/2008/...s-and-stability

 

The rotational speed is 288,000 rpm.

 

http://accurateshooter.net/Blog/millerformula.xls

 

This also looks ok at about 1.87.

 

Anybody any thoughts?

 

 

A

[grahamfarmer]

hi alycidon,

 

have a similar problem with my 243. now a sierra blitz king 70 grain seated over 40 grains of varget will group sub .5" at 100 yds yet change the bullet to a sierra 70 grain hollow point match bullet and everything else is unchanged you could shoot a cullender with it go to 41.2 grains of varget and it groups as good as the starting load but change to a blitz king and that now shoots cullenders you would of thought the two bullets would swap.

 

now move up to a 87 grain v max using 37 grains of varget same sub .5" performance swap to a 90 grain nosler and its down the same holes then i tried a few 90 lapau secmars and it still shoots the same holes swapped a few 90grain hornady soft points to try and we are shooting cullenders again .

 

cant explain whats going on but it evidently backs up what we already know in that some guns will shoot any fodder you feed it and others are very fussy even with in the same make and caliber ,but there must be a element of some bullets prehaps behave better at certain velocities it is noticeable that when loading for the 308 win the geneal theme seems to be around the 44 grain mark of your prefered powder will perform better than trying to push the velocity for accuracy.

 

so prehaps its what we already do as home loaders ie ladder test and meticulous attention to detail that allows us to find the holy grail for each of our precioucs guns.

 

would love to know if some one had a one hole load for a gun and then rebarreled it did that same load work in the new barrel our was it back to basics and find the load again.

 

 

graham.

[1967spud]

i spose the bullet co-efficents make the difference graham but i am not 100% sure of that, just an observation

[Redfox]

The 243 is known to be fussy anyway, but each bullet, powder and primer has to be developed into a working load combination, which is part of the fun/challenge of reloading.

My 243 has 3-4 loads that work in it , for instance 48grs H4831, CCI BR primer, Rem cases, Speer 75gr holow point ( not the TNT ) and .040" off the rifling gives better than .7 at 250yds, I had it rebarreled by Sako and the same load ( and the others) works perfectly in it just like the original barrel, except the lead is back .020" which is where the original barrel was when new. So if you keep things the same it will still work, but change barrel profile, rate of twist etc, or bullet make, type etc and all the bets are off.

It will shoot speer 85gr spt boat tails like they were made for it, but Sierra 87gr spt boat tails are nowhere near as good even tweaking the powder load ( H 4350) doesnt get it better. The general wisdom is that whatever the sweet spot jump distance is for the rifle it will hold good for pretty near all bullets and I have found it so with my rifles.

Redfox

[Alycidon]

I suspect that the 26.0 H322 load did a group with all 3 touching but as they landed in the N160/Berger 50 group then its hard to tell for sure. Got a few to pull so I will take them down to 26.0 and seat them deeper.

 

The 50s shoot very well, I was just lookimg for a bit more explosive expansion on crows etc.

 

A

[menial 1]

As Foxhunter said, 85grn Speer sp bt work brilliantly in most .243's but are not always available, when I changed to 85grn Sierra varminter sp flat base I thought I would have to start from scratch with the loads, but fortunately they shot well with the same powder load (43.5grn vv160) and the same jump at 40thou out, I have stuck with them for general deer/fox work and shoot 70grn Blitzkings over 47grns vv160 for crows, rabbits and general fun shooting.

I used to try and work everything seated into the lands at one time, but now start at 20thou out and work my way ot till I'm happy when I'm working up a load for a bullet I haven't used before. Sometimes I think we tinker too much and expect more than either we or the rifle can achieve.

Pete.