Why do some rifles apparently dislike certain cartridges

[Gazza]

I normally reload for my .243 T3 and the rifle is accurate.

Recently just for convience I bought some Winchester 100gr soft point and they are totally inconsistant. All the mounts, screws etc are secure and the barrel is not touching the stock. The rifle is fairly new and has fired less than 500 rounds.

I regularly hear the phrase that a rifle does not like a certain round. Is this possible and why?

 

[devilishdave]

When you fire a rifle a shock wave moves down the barrel in 3 dimensions. If you imagine it exagerated it is like when you get a steel rule 10 inches over the bench and flick it and it vibrates and reverberates. efectively the muzzle is moving in the shape of a sign wave. if the bullet exits the barrel 1/2 way up the slope of the sign wave then small inconsistancies in velocity will mean a bigger differance in accuracy due to the ammount the barrel is moving. If the bullet exits the end of the barrel when it is at the top or the bottom of the sign wave any slight inconsistancys wont cause as much differance and hence will be more accurate. the more or less powder you use will change the pulse and effect where on the sign wave the projectile will leave the barrel.

Dave

 

[Gazza]

Dave, From your reply I take it that you are suggesting that if the powder content of these particular cartridges is inconsistant the end result on the target is the same. If this be the case surely this would then apply to any rifle these cartridges were fired from. I cannot see this being the case but I accept that what you are saying has basis.

 

[Gazza]

Dave, From your reply I take it that you are suggesting that if the powder content of these particular cartridges is inconsistant the end result on the target is the same. If this be the case surely this would then apply to any rifle these cartridges were fired from. I cannot see this being the case but I accept that what you are saying has basis.

 

[Dalua]

I've always assumed that my rifles do that deliberately to irritate me and make my life difficult.

I get my own back by finding a load they like and sticking to that, which is fine until the makers discontinue that particular load.

Apart from the various rifle-based factors as mentioned by Dave, I guess that some cartridges are loaded such that their dimensions (e.g. bullet distance off the lands) suit a particular rifle well.

Apart from that, presuambly tolerances in terms of bullet and powder weight and quality, seating depth, consitency of priming and so on may very between makers.

The whole thing is a mystery to me, and when I add myself into the equation, the whole business seems almost beyond comprehension.

 

[devilishdave]

Dave, From your reply I take it that you are suggesting that if the powder content of these particular cartridges is inconsistant the end result on the target is the same. If this be the case surely this would then apply to any rifle these cartridges were fired from. I cannot see this being the case but I accept that what you are saying has basis.

No becase a longer barrel from a gun other wise identical would cause the projectile to leave the muzzle at a differant part of the sign wave. Even a gun the same model and cal as yours may shoot differently due to tallerances in the chambre for example with a slightly bigger chambre you will get different pressure, defferent velocity and again the projectile will leave the barrel at a different part of the wave.

An example of this is a mate of mine and I have rem 700s in .243. His reloads will go in my rifle no problem but my reloads wont go in his rifle.

Dave

 

[manc-munsters]

Everything everyone else has said plus other factors too!

The bearing surface on the bullet may be different brand to brand. This causes different pressures and effects accuracy.
Some ammo is so powerful that the bullet actually strips for the first few millimetres after entering the barrel, in effect this reduces the length of the barrel (ie the bullet only grips the rifling part way up the barrel).
IMX Chamber length and OAL of the ammo is one of the biggest factors in finding the right factory ammo for a particular rifle.

This really is a minefield. Even the top ballisticians will tell you that ballistics is not a constant.

 

[Heym SR20]

My .243 is the same - one hole groups with RWS 100gn, 1 inch groups with Norma 100 gn - to the same point of impact, but tried some Winchester's once - struggle to keep them on 1 sheet of A4 paper.

It is all to do with barrel harmonics etc and most rifles will have one load they like and others they don't. It also seems that the higher the pressure of the cartridge the more fussy they become. Thus high velocity high pressure cartridges such as the .243 tend to be quite fussy, whereas the old .303, 7x57 will shoot most cartordges reasonably well.

Craig Boddington's Accurate Rifles is worth getting hold of and he discusses all of this with a view to making a hunting rifle shoot accurately and more importantly consistently - more important in his view than pin point accuracy, is to have good accuracy with the right type of bullet that will give good terminal performance.

He is also a strong advocate of pressure bedding - whereby there is a pad in the tip of the forend (typically a couple of business cards) puts a positive upward pressure on the barrel, rather than the barrel being fully free floated. He suggests that for particularly light barreled sporters this provides much more consistency and particularly in the field the rifle is much less susceptible to throwing shots due to different pressures on the forend due to how the rifle is held, or crap getting into the barrel channel etc. Often free floating is used by rifel makers as a quick and easy way of getting good accuracy, but if you touch a free floating barrel whilst shot is being fired the bullet will go off.

 

[Gazza]

Interesting stuff. I also reload for my sako 75 22-250 and I know that it is spot on but I had tried a box of Federal. Again no consistancy but my mate tried the same cartridges in his Sako 75 and they were bang on.

Serves me right for being a bit lazy with the reloading.

 

[Mauser66]

Why do some rifles apparently dislike certain cartridges?

I reload almost all my ammunition and avoid factory rounds as they are expensive and quite often give average to poor groups.

In the past when I was given factory ammuntion for culling work I would knock out the bullets with a kinetic puller, get rid of the factory powder and recharge with an exact charge of my own preferred powder.

Here's a couple of examples:
.308Win Norma 150gr Ballistic Tips
at 100yds from my Riflecraft LSR (usually sub 0.5MOA) the best I could get were 2" groups. I emptied my remaining 80+ rds and recharged with 46gr Varget and those rounds now do the usual 1/2" and under groups for that rifle.

.270Win Norma 130gr SP
From my old bedded, free-floated and recrowned Ruger M77, which was admittedly still choosy about fodder all I could get were 2-3" groups. Just awful and I had 100s of rounds of Norma 130gr to use up. So I recharged them with Reloder 22 and, surprise surprise, they consistently slipped into 3/4" - certainly under an inch.

.243Win Winchester 100gr SP
From my old, but bedded and set up, .243 BSA I just could get anything approaching a group with those rounds. 3" maybe, but fliers all over the paper. Federal 80gr would print sub 1" groups and my reloads would go under that so the rifle was fine. I recharged some of the Winchesters with Re22 and they came in to just over an inch - certainly under 1.5".
Oh and when I recharged the Fed Classic 80gr they would come in under 1/2" at 100yds.

I fire off good sandbags and always free recoil for grouping purposes.

So, question is, what on earth are we paying for in factory ammunition? Of course there are exceptions, but this whole argument about factory ammo being made for the 'average' rifle I think is just rubbish. The ammunition I make at the reloading bench is less 'hot', and far better quality.

I haven't weighed any of the charges I emptied out. Just didn't have time. Maybe there are big variations. But that doesn't make sense either... have tested my LSR with small powder weight differences of and at 100yds the difference in MPI is very small indeed. Maybe breaking the crimp on factory rounds helps precision?

Oh and I've even recharged Hornady Match 168gr AMax ammo with Varget and even they print smaller groups.

Rolling your own is the way forward I think.

 

[techman]

Gazza, Like mauser66 I found the winchester rounds erratic. I could fire five rounds at the target and get a 3" group at 100yds, no better. A friend offered me his Chrono and I found a difference of 80fps between the five shots I fired through it. I took up reloading.
This was some years ago and I have not tried winchester since, so they may have improved.