what shoots better a 308 or .3065 dia barrel??????

[lee_enfield223]

'Hi All
I have been experimenting with shooting the same rifle with two 30 cal barrels of different bore diameters. from Maddco. Here are my results,,,both barrels were chambered with the same reamer and loads were worked up and bullet runout was kept below 2 thou for all testing at 100m with a leupold MK4 6.5 to 20 power scope. the rifle was a rem700 short action in a heavy fclass type stock with an alloy bedding block.
Both barrels were brand new and made by the same person at the same time and all groups were 10 shot groups fired off a concrete bench. and the shooting conditions were close to the same.

1) the .3065" (this is a tight barrel) barrel no matter what load was used shooting sierras bergers and other 155gr projectiles would only group into .700 at 100m and over 200 rounds were fired using different loads

The barrel was unscrewed and the brand new Maddco 308 barrel was installed and the entire process carried out again,I also played with seating depth during the testing of both barrels.
the 308 dia barrel shot into sub .4 groups once a good load was found and I have always found that true 308cal barrels seem to shoot slightly better, I know projectile damage is linked poor accuracy and I and thinking that the tighter barrel deforms the projectile too much and leads to poor accuracy....
If you people have some solid info or tests of your own I would love to hear of your results.

[Longranger]

If there is any slight ovality in the projectiles then I suspect the pressure variations might be more pronounced in the 0.3065" barrel.

I have seen 0.3065" barrels that shot brilliantly though...

Very hard to do a meaningful comparison with all the other variables to contend with. It may be that with more development time the tighter barrel could well be a better performer.

[shooter mcreid]

I'm under the impression that there is a "window" of what size projectile works with a given barrel, where half a thou or so difference between the two seems to work well. let me give an example, In my standard Barts (0.284") the Bergers shoot well. I used a quality micrometer and measured them at 0.2844" to 0.28445", which is in the window. I'm not sure how far the window extends but there must be a point at which the barrel is too tight.
On a related point I have heard of people not getting the best results from the new sierra 183s but when i measured the batch that i have they are very consistent but measure slightly under at 0.28365".
OP, can you or have you measured a few of your projectiles?

[Razer]

Somewhere, buried in the archives is an article on tight barrels.
From memory, there was no advantage to be gained using modern projectiles and one of the disadvantages was projectile deformation?
Here is part of an article posted by David (willianda) in 2014.

Let me say after considerable experiment with bore size and land depth. Tighter bores are slower than bigger bores despite an initial higher peak pressure. The bullet is quickly swaged to bore size and it travels the length of the barrel in its new dimensions forged at the throat unless you have a tapered bore. Some are purposely lapped that way. I believe Obermyer led the rash of .3065 bores for English ammo because it was less than .308 for 144 grn bullets. I believe new bullets increased to .308 and Shultz and Larson who went with .3074 had great success. However some carried the tradition on of the tight barrel, even when the diameter went to .308. It still worked for the new English round and I have tested brown box and blue box (now you can use reloads). Why I wondered? Now if something is squashed down it can only get longer. If it gets longer does this increase its BC in a 1-12 barrel commonly used? We know jacket hardness can be a factor and old military jackets were harder and required deeper lands. Was the land depth right for this new form? Or was the frictional timing right due to swaging and bore finish (porosity)? In this sense if you use Plasticene on glass it will stick and foul because it is too smooth but used on a rougher surface it will not. The bore surface has consequences for fouling. Matches are won at long range, assuming you can read the conditions with better gear.

Using the Australian .308W around 2002, its jacket was thin and soft. The bullet must maintain the velocity above the transonic range to remain stable at 1000 yards otherwise you have to increase twist rate. You must realise the speed of sound changes with temperature and so does the transonic zone. Subsequent testing of bore sizes for the older Sierra ranging in .0005” graduations from .3065 to .308 were tested in pairs with varying twist rates and land depth throat length and leed angle with British and Palma chambers in Krieger barrels which all shot well. Another brand name barrel was hopeless but its mate was ok and my Border was superb. The best and consistent results came from 1-13’s, .3075 x .298 Kreigers from the machine rest at 1000 yards in summer conditions. The length to beat the transonic zone was 31 inches. They consistently grouped 10 shots well under 1 minute of angle with factory ammo. But remember this dimension was for that particular bullet If you were running bullets with a longer bearing surface there would be nothing wrong with .308 X .300.

I have not tested other calibres to this extent, but I imagine the results would be interesting.

As a note, land sizes can be lead lapped down to size by tapping up the lap with a copper rod. The rounded edges of the lands have to be removed by a copper lap. The resulting belling of the muzzle has to be cut off with the crown placed at the minimum diameter. That’s all folks, I can get carried away.


Last edited by williada on Wed Jun 11, 2014 1:02 am, edited 1 time in total.

[johnk]

The three best shooting .30 barrels I've owned were all relaxed bores (around .300/.308) & all three had an encouragingly long accurate life. It wasn't a brand issue - they were Border, Kreiger & Maddco. Two were TR/FS barrels & one a MR barrel.

It isn't surprising that the MR barrel was an open bore. All of them I've used for this discipline have been no tighter than .3075 & most .308.

[lee_enfield223]

Thanks Guys for all the information and your ideas they are eye opening !!!!!! It seems to me that every barrel is really unique and should be tried out ,,,,, well I have shot out about a dozen barrels over the years so if I am around for a few years I guess I will try out a few more
I am building up another rifle on a rem700 clone (Nimrod) but it's much thicker and has a small ejection port and ill post the accuracy results late in Febuary.

[KHGS]

'Hi All
I have been experimenting with shooting the same rifle with two 30 cal barrels of different bore diameters. from Maddco. Here are my results,,,both barrels were chambered with the same reamer and loads were worked up and bullet runout was kept below 2 thou for all testing at 100m with a leupold MK4 6.5 to 20 power scope. the rifle was a rem700 short action in a heavy fclass type stock with an alloy bedding block.
Both barrels were brand new and made by the same person at the same time and all groups were 10 shot groups fired off a concrete bench. and the shooting conditions were close to the same.

1) the .3065" (this is a tight barrel) barrel no matter what load was used shooting sierras bergers and other 155gr projectiles would only group into .700 at 100m and over 200 rounds were fired using different loads

The barrel was unscrewed and the brand new Maddco 308 barrel was installed and the entire process carried out again,I also played with seating depth during the testing of both barrels.
the 308 dia barrel shot into sub .4 groups once a good load was found and I have always found that true 308cal barrels seem to shoot slightly better, I know projectile damage is linked poor accuracy and I and thinking that the tighter barrel deforms the projectile too much and leads to poor accuracy....
If you people have some solid info or tests of your own I would love to hear of your results.

Well, I would think you just might have answered your own question, given the small test sample which only tells you which is the better of these two barrels! You would need to do this test over 10 barrels of each size to get an indication! However over 35 years of barrel fitting the indications I see is that .3075" t0 .3078" are as close to ideal as you will get for short bearing surface bullets.
Keith H.

[lee_enfield223]

Thanks Keith for your reply. yes I think you are correct