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James 1

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Natural consequence of increasing the combustion capacity of the cartridge and so lowering pressure.

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Depends on your mv, range expectations etc etc....but if you are happy with current grouping and the range that you are achieving then why force pressures?

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Your choices (within normal safe reloading bounds and calibre limitations) are therefore to increase powder load watching out for pressure signs and / or to reduce COL keeping in mind both calibre COL book min / max recommendations .....also knowing what your chamber can accomodate having measured it with a Hornady lock and load tool or similar to keep your bullet off of the rifling which could elevate pressures.

 

Would help if you state all components , lengths and loads etc.

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As Mike / M99 says we need calibre and your actual load and COL to advise further.

 

Eg....If you are loading for , say, a 260 Rem then 46g of N560 will be fairly 'hot' even at extended COL.

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You are about at realistic limits with that load....perhaps another grain headroom depending on your rifle/ chamber / freebore.... but beware pressures created by being on / close to the lands at 2.9 col.

 

Unless you have a very short barrel you should be sniffing around 2800fps?

 

What is your mv?

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Agreed sounds low....I will tinker with Quickload tomorrow and think on it.

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Just checking here....Are you confident on your Chrono figures?

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2750 fps is about the median velocity for SAAMI 260 commercial ammo.None is over 2800,and some is 2700.

Those velocities of course do not mean good grouping,but do mean acceptable pressures and barrel life-though less fps generally means more barrel life.

 

There are some options for your rather low reported velocities of 2625,down about 100 fps on above.

Have you checked your powder measure is actually dispensing the weight of powder the book data say gives your desired velocity?

Have you checked your velocity with a valid and reliable chrono-magnetospeed/lad radar? Screen ones can be chronic,not chrono.

 

What performance do you need for your uses? 100 fps may not be a big deal-eg for target shooting to 600y,better accuracy than velocity.Will 25 ft lb more put pressure on your freezer?

 

As you say,there may be advantages in brass life too,with a reduction in velocity (of little consequence).

 

As your own question-is adequate with accuracy better than velocity without validity? Or even velocity with equal groups?

 

If you are shooting at 1000y,you might want a bit more velocity-actually you need quite a bit more ,really,in another cartridge if at all serious (start with 6.5x84...better yet, just 284....or.... :-)

 

gbal

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this is one of those things that could really wind you up but in reality if you run it though an app you will see small difference from 100 fps on wind call ,which will probably be the reason for missing. if you could get past it and enjoy shooting it with good accuracy life is so much easier .chasing that extra 100-150 fps will probably get expensive .

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James,SAAMI data given is for 24" test barrel. DEpendig on cartridge/velocity range/etc shortenng a barrel will reduce MV 20/25 fps per inch shortened,innthe 'normal' range normal range velocities and barrels (26"-20"

 

 

Accuracy etc maywell be just as limiting for 600y plus distances,but here is an idea of what fps translates as:

 

Nosler Part125g BC .45 MV 2950/2875 200 zero drop at. 600y 71/75. 800y 163/173. 1000y 316/335 drift is 1,2,3 inch more

 

Rem 140g core lokt UB/PSP BC.457/.436 @2750 drop 60082/84. 800 189/196. 1000 367/382. Drift is 2,4,15 more for lower BC

 

(Wind is 10 mph,and actual drigts at 800 are 57" for hi BC 125,and 62" for hi BC 140g)

 

NOte small effects of 75 fps velocity increase,and .2 BC improvement (these are hunting bullets,not best BC target bullets,but the differntials make the point-thee really isn't a lot in it...precision/accuracy may be just as important,and gowith the less zippy loads-or not,of course. But ballistics don't make much of a case for losing sleep if casual/club level plinking! S0...just enjoy,see how it goes.

 

Whatever the load,it won't get competitive...but so what- you didn't buy a (hot) 7mm......:-)

 

gbal

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James,I meant to be more positive-if you have an accurate load,you won't gain much by another 150 fps-unless you are doing something with the cartridge,on the edge of it's design potential (and therfore has to give best to bigger cartridges anyhow). WAY better an xbull than a super fast bullet zipping through the 9 ring....and likewise all down the line. As you will be dialling in anyhow,two more clicks for your velocity will not have any discernible effect on scores. Enjoy it.

(Another 200fps would just mean you are less behind the good 7s anyhow.....plus ca change,plus ces't la meme chose...not all good 7s are created equal either.... :-)

 

g

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Quickload projects 2650 fps out of 24" barrel, 44.8g N560 and col 2.9 but also shows barely 90% powder charge burnt and pressure barely 45k psi.

 

Its only a projection but you appear to have a bullet which creates lowish pressure...I dont have a diagram to check if it has a short bearing surface.....and a barrel which is too short to properly / efficiently use the slow burning N560.

 

You could up the powder charge but would need to go over 46g to reach 2700+ and may hit pressures.

 

Dropping the col to 2.8 as well as 46g N560 sees about 2772fps....same caveats.

 

Alternatively N550 at around 42g shows 2761fps and near 100% burn....so better powder choice if pressures dont appear.......normally I would only use N550 with 123 / 130g class bullets but in this short barrel case it might be worth a go.

 

Also consider 123g Scenar or SMK......EASILY A 1000 YARD choice with N550.

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I thought I would of been ok with a 24” barrel I am getting some eld-x bullets wen they come in the post, does it show any better with them daveT, if not I will at the n550 the Viht site and data is abit poor not as Gud as quickload.

 

Cheers James

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