Palma barrels...smaller diameter???

[jaredc]

Can someone tell me my Palma barrels have a smaller bore diameter than regular .308 barrels? Is it for extra velocity? Also, are Palma bullets different than regular .308 bullets?

 

[memilanuk]

I think it got started a while back when shooting some of the British issue RG ammo that was a bit on the small side... then it kind of hung on afterwards on the mentality that taller lands lasted longer as far as accurate barrel life. From talking w/ some people who have been on the Palma team in various positions,shooters, coaches, etc.) w/ modern quality bullets like the Sierra, Nosler, Berger, and Lapua pills there isn't really a need for the tight bore dimensions of the past.

YMMV,

Monte

 

[Wild_Bill]

HI there is a definate need for a bore around.307. the projectiles used are restricted to 155gr Sierra's and if you shoot them through .308 barrels the accuracy drops off within 800 rounds because the projectiles are short and dumpy. Also the 155gr Sierra has a verry short baring surface and by reducing the bore diameter it helps with accuracy. In the past you were issued a rifle and ammunition and it was military 7.62x51 and it has a projectile .307 in diameter but some manufactures have made diferent batches with projectiles as small as .306. I have an old barrel and it is .304 if you shoot a Sierra through it you dont get as much velocity as loads have to be reduced and recoil is increased. The seccondary effect to this is slightly higher velocity's with factory ammo and this is a definate advantage at 1000 yards. Over here in Australia we only reccomend barrels less than .3075 for Palma team shooting if you have a .308 barrel you have to replace it as they can just stop shooting with no warning usualy in the middle of an important shoot at 1000 yards. But a .307 is definately the best choice to shoot with 155gr bullets with 14 to 12 twists. If you have a 10 twist .308 you are better shooting a 175gr Sierra or equivelent as they will seal the gasses better and give you better results at the longer ranges.

I hope this helps a lot i actualy am going out to test Palma loads this afternoon for our State team captain

Cheers Bill
Australia

 

[jaredc]

So, there are no Palma bullets out there that are different than other .308 bullets? I was thinking of shooting them in a standard .308 win barrel?

 

[Asa_Yam]

HI there is a definate need for a bore around.307. the projectiles used are restricted to 155gr Sierra's and if you shoot them through .308 barrels the accuracy drops off within 800 rounds because the projectiles are short and dumpy. Also the 155gr Sierra has a verry short baring surface and by reducing the bore diameter it helps with accuracy. In the past you were issued a rifle and ammunition and it was military 7.62x51 and it has a projectile .307 in diameter but some manufactures have made diferent batches with projectiles as small as .306. I have an old barrel and it is .304 if you shoot a Sierra through it you dont get as much velocity as loads have to be reduced and recoil is increased. The seccondary effect to this is slightly higher velocity's with factory ammo and this is a definate advantage at 1000 yards. Over here in Australia we only reccomend barrels less than .3075 for Palma team shooting if you have a .308 barrel you have to replace it as they can just stop shooting with no warning usualy in the middle of an important shoot at 1000 yards. But a .307 is definately the best choice to shoot with 155gr bullets with 14 to 12 twists.

Bill,
When you say a .307" bore, are you talking about groove diameter,groove-groove), or land diameter,land-land)? I'm assuming the former. In the US, common bore diameters are,groove/land diameter):
.3065"/.298",Kreiger barrel)
.307"/.298",Kreiger barrel)
.3075"/.298",Kreiger barrel)
http://www.kriegerbarrels.com/RapidCat/catalog/pagetemplate.cfm?template=/RapidCat/common/viewPage.cfm&PageId=3390&CompanyId=1246

By measuring a 155 grain Sierra,using a dial caliper), I get the following measurements:
Presure ring diameter,maximum diameter, found at body/boattail junction): .308"

Diameter at estimated junction of ogive and body,by eyeball): .307"

Bearing surface length: .350"

Initial analysis: A .3080" groove diameter will just match the projectile. There should be enough bearing surface on the projectile to ensure it remains straight in the barrel on firing.

Most bores for .308 Winchester rifles are smaller than .308" in diameter. Land heights certainly are smaller - the loosest ones I'm aware of are usually .300" in diameter.

 

[Asa_Yam]

From http://www.jarheadtop.com/article_handloading.html,Boots Obermeyer's Notes):

Examples of old wives tales.
...
Groove diameter must be tight and extremely uniform In the early 60's Bob Jablonowski had a late 50's M70 match that he won the state championship with and shot a 250 on a possible 250 course of fire, the old 5V target. After pulling the barrel and air gauging it, I found the barrel was .0015 larger at the muzzle than the breech. Everyone would say it can't shoot but it did. The reason is that in single point rifling, the rifling head rides on the lands. The bore reamer was defective and as it wore in, it cut a funnel type hole which caused the inverse on the grooves. The lands drive the bullet not the grooves and they kept tightening on the bullets as it passed through the bore. Would I suggest making such, of course not but this has remained with me for many years and why I went to deeper rifling and odd number of lands.

 

[Wild_Bill]

Sorry i have been away the measure ment of .307" in the groove to groove diameter most have a land to land diameter of .298 to .300 depending on manufacturer the main reason is the lack of baring surface in boat tail 155gr bullets we are limited to the Sierra nad an Australian made BJD 155gr projectile. You also have to realise that they are shot to 1000 yards and the 308Winchester and a 155gr projectile is marginal at best for the purpose. The tighter bore allows extra velocity and also gives the projectole more baring surface as it squezes it down 1 thou. Major matches have been won with bores from .304 to .3085 but in general a .307 to .3075 barrel will last longer with acceptable accuracy with a limited projectile choice. The Victorian State team has a requirement for a barrel of .307 to .3075 and no other barrels will be allowed in the match for shooters in the team because the .308 barrels can all of the sudden loose their edge and loose a match for you. Now if you were allowde any 155gr projectile there is no issue as the 155gr Lapua shoots verry well in 13 twist .308 barrels as it has more baring surface to seal the bore.

Hope this clears a bit up i have just lapped 6 .307 Palma barrels this last week and they shoot very well from 300 th 1000 yards. With a 30" Palma type .307 barrel 3000fps is achievable with Lapua cases 46.2gr AR2208,Varget) and a Fed 210GM primer with a M852 Reamer being ideal as the 155gr Sierra has the same front end as a 168gr MatchKing so the ogive dimentions with a 2.8" loaded cartrige work very well.
Cheers Bill
Australia