Bullet Selection

[Barry Davies]

It has been stated many times and again in this topic by Alan " Some barrels don't like particular projectiles "
My Question to the knowledgable is " how does one determine that a barrel prefers one projectile over another"?
A load I can understand --but a projectile!!
Just because a rifle does not perform with a certain projectile at a certain load does not mean the barrel hates that projectile --or does it?
Could it be that the reloader has not investigated ALL the possible loads, powders and seating depths combinations before making such a statement.
Could somebody tell me in layman terms what is it about any projectile that a particular barrel may dislike.
I could well say that my barrel does not like any of the five projectiles that are currently approved for the 308 --simply because I have not put in the effort to fully test --so where does this leave me? Do I push for more projectiles to be approved or do I purchase a new barrel in the hope that a love affair will develop?
Alan this is an interesting subject and although not directly relevent to the current topic probably deserves a topic of it's own --I leave it to your discretion.

To support what I say my good wife Jenny who is an excellent FS shooter shoots a particular barrel with two projectiles equally well BUT there is over two grains difference in the powder load. The two projectiles are HBC's and the new Sierra --different as chalk and cheese.
Nothing special about the barrel - off the shelf Maddco with an M 852 chamber AND I have other barrels that do the same .

Barry

[AlanF]

Barry,

Over the last several years I've dropped in quite often to the benchrest.com forums. This is no slight on the likes of yourself and other very capable rifle/ammo tuning experts in Australia, but there is a greater general level of expertise in that field at the top level of BR in the US. I've heard it said there on many occasions that the likes of .257 and .270 calibres are scarce in BR for one primary reason which is a narrow choice of target grade projectiles. The same was being said of 7mm until about a year or two ago.

I can think of several possible reasons why one projectile can succeed in a particular barrel where another won't. BTW for this discussion I'm including the throat characteristics as being part of the barrel.

1. Projectile diameter.
2. Bearing surface profile (inc. sealing ring).
3. Ogive shape (at lands).
4. Jacket metallurgical properties.

I haven't detailed exactly why each of those properties would affect performance - because at my level of knowledge about internal ballistics, it would involve mostly guesswork.

I remember once reading a post on benchrest.com by Dave Tooley (whose record speaks for itself) on his load tuning steps, and it basically went get your powder charge about right, fine tune with seating depth, and if still not good enough, forget that projectile and try another. No-one disagreed with that, and there were some very accomplished people in on the discussion.

Alan

[IanP]

There is one very definite reason why one barrel may not perform as well as another with a certain projectile. I am sure Alan and Barry are aware of bullet stability.

Long bullets need faster twist rates to stabalise than shorter bullets, hence a fast twist barrel may work well with a long, heavy VLD but the same calibre barrel with a slow twist rate wont.

I am assuming you guys are talking about same calibre, length and twist rate barrels. Then the chamber comes into play and a particular chamber is normally made by a reamer designed for one bullet type and weight e.g. VLD. Two barrels that are exactly the same but have different chambers will shoot bullets differently.

If you have taken chambers into account as well as barrels being identical in every way then F_Nose why they dont shoot the same.

Ian

[saum2]

I agree with Ian, twist rate is very important with projectile selection, just take the .223 barrels. this info is from a past post on the Amax .223.
I have a .223 barrel 1-8 twist (but measures1-8.25) shoots the Sierra quite well but not the Amax. I've tried every powder load, jump whatever over a number of weeks and could not achieve a group smaller than 250mm at 300 yds with the Amax. Sierras group about 12mm using similar loads etc.
Put in a new barrel with 1-7.5 twist, hey presto, the Amax is perfect.

just my 2 bobs worth.

Geoff

[M12LRPV]

I agree with Ian, twist rate is very important with projectile selection, just take the .223 barrels. this info is from a past post on the Amax .223.
I have a .223 barrel 1-8 twist (but measures1-8.25) shoots the Sierra quite well but not the Amax. I've tried every powder load, jump whatever over a number of weeks and could not achieve a group smaller than 250mm at 300 yds with the Amax. Sierras group about 12mm using similar loads etc.
Put in a new barrel with 1-7.5 twist, hey presto, the Amax is perfect.

just my 2 bobs worth.

Geoff

I've found seating depth to be a bigger issue with the amax's. They're just too long and too many 223 rifles are being chambered incorrectly for the long stuff.

Which brings me to what I think is the issue of why one projectile works and others don't and that is the chamber dimensions and more specifically the neck and throat.

[Barry Davies]

Krakey ( Geoff )

How did the Sierras handle the 7.5 twist barrel ?

Barry

[Quinny]

I have found that my Tikka doesn't seem to be that fussy with powder loads or seating depth - nothing I have played around with has really made that much difference - hell, it shot 3/4" groups consistently with factory Remingtons.

However, one thing I have noticed made a difference was the projectiles. My rifle seems to prefer the Dyers 155gn HBC projectiles over the Sierra 155gn (2155 & 2156). A fortnight ago I took a couple of mates out to the range and basically used every projectile I had left - some Dyers, some Sierras. All 3 of us got better and more consistent results with the Dyers. I don't know how that works, but that is my experience. This is a factory rifle, and I have only been shooting less than 12 months, so I was never going to expect miracles. I don't have the skill to shoot sub 0.5" all day, even though I am fairly sure that the rifle probably could in the hands of a more experienced shooter. But I did notice a significant difference mostly in consistency with the Dyers, hence I will only be buying Dyers now.

[saum2]

Barry,
The Sierras shot similar groups to the Amax .223 in the 1-7.5 twist barrel.
The older 1-8 barrel only had 1000 rnds thru it so it wasn't worn out. It came down to price of the Amax compared to Sierra.
Geoff