.30 cal tight barrels

[wilson85]

Hello everyone,

I know its been discussed plenty of times before, but is there any benefits to using a .3065/.298 or .307/298 barrels vs standard .308/.300 barrels? I will be using Optimus HBC 155g projectiles.

Cheers

[Brad Y]

You can save money reducing your powder charge a whisker

[johnk]

The best barrel I ever shot .308 (TR & FS) with was an orphan bought in to the QRA for a 300 meter shooter who didn't want it. It was a .300/.308 Kreiger & I pulled it out at 5500 rounds to travel to Bendigo for the inaugural FS teams shoot. I still keep it clean & will slip it back in one day.

It shot within 10 fps of all the barrels I'd had to date with the load of AR 2206 that I favoured for the Dyers.

[Frank Green]

If shooting match type bullets there is no practical difference in terms of accuracy and or barrel life for the most part.

If your building a .300 win. mag type gun I recommend against the tight bore .30cal. barrels. Why? Carbon fouling is going to build up quicker and this will drive up your pressures even faster. Your burning more powder in a .300wm type round then a .308win.

Also even with a .308win. it will drive up pressures just with the tighter bore and groove. Changing the groove size has the biggest impact on pressure/velocities then the bore does but anytime you start changing the total surface area of the bore of a barrel you can effect pressures and velocities.

I don't remember the name of the barrel maker that started the tight bore .30cal. barrel. It was back in the early 70's here in the U.S if I remember correctly. It came about for the palma shooters. If you made your country's palma team and went to the International Palma Championships you are not allowed to bring your own ammo/team ammo etc...the host country would issue you the ammo. In a lot of cases even up into the late 90's or early 2000 the host country was issuing 7.62nato ball ammo. Those bullets can run as small as .3065" diameter. The tight bore and tight groove would bite/drive those under size bullets better. Also being typically a bullet under a 156gr. and the ammo having run out issues etc...the twist was slowed down. All of this helped the accuracy of that type of ammo. Remember the lands in the rifling do the driving on the bullet.

I've shot tight bore/tight groove barrels, tight bore/standard groove and standard bore/groove barrels in .30cal. and with match type bullets I see no practical gain anywhere. My opinion.

I have shot tight bore barrels in the 6mm and don't anymore. Bullet failure is higher in the smaller calibers. The tighter bore will also cut into the bullet jacket more and not help anything in this case.

If I'm wrong on any of it please correct me.

Later, Frank
Bartlein Barrels

[wilson85]

Thanks for all the replies gents. Have had conversations with people and some claim they longer barrel life out of them. The replies from JohnK and Frank Green are good enough for me!

[KHGS]

Thanks for all the replies gents. Have had conversations with people and some claim they longer barrel life out of them. The replies from JohnK and Frank Green are good enough for me!

For what it is worth I agree with both of these learned gentlemen. However If you are shooting short bearing surface .30 155 grn bullets I do favour a .3075" groove dia barrel.
Keith H.

[Frank Green]

Thanks for all the replies gents. Have had conversations with people and some claim they longer barrel life out of them. The replies from JohnK and Frank Green are good enough for me!

You would think it would as your giving the land more meat for wear but I cannot prove it does and or have any proof that it does.

Later, Frank

[Frank Green]

Thanks for all the replies gents. Have had conversations with people and some claim they longer barrel life out of them. The replies from JohnK and Frank Green are good enough for me!

For what it is worth I agree with both of these learned gentlemen. However If you are shooting short bearing surface .30 155 grn bullets I do favour a .3075" groove dia barrel.
Keith H.

Hey Keith, I have two go to bullets I shoot in my .308win. type guns. A 155 Lapua and the 175 SMK. Both shoot extremely well and again I see no difference.

Later, Frank

[AlanF]

Frank,

Regarding tightness of Bartlein barrels, I have both a 5R and 4 groove in 7mm. If I didn't specify anything, what would be the bore and groove diameters of these?

Thanks
Alan

[williada]

It is my understanding it was Boots Obermeyer who first explored the suitability of tight bores in relation to the issued 7.62 ammo and first explored canted lands. I believe also that Krieger and Border Barrel owners worked for Obermeyer early in their careers. Correct me if I am wrong please. Those three names have greatly influenced the barrels used by Australian fullbore shooters. Today, quality Bartlein barrels are the yardstick in precision manufacturing.

However, the quality work of Keith Hills had for many decades has been sought after by many successful Australian team members and he was the go to person by the NRAA for the examination of catastrophic failure. There is a body of experience here and in Britain that have explored the very subtle gains to be made by matching bore size to the issued ammunition over the years when the only thing that could be altered was the barrel and I am sure Keith’s customer’s also told him what worked and what didn’t and confirmed his extensive knowledge. The Brits didn’t dismiss tight bores but followed advice from a Pressure Trial Consortium that led to the introduction of the 150 rule that all competitors have to pass in a gauge of their .308 chambers having explored the safety aspects. Larger throats relieved dangerous pressures. It is valid if new shooters who reload without sound knowledge increase the risk of catastrophic failure and potential harm to those around them.

With regard to accuracy, a different study initiated and largely resourced by the NRAA was that Project Penumbra, where paired barrels ranging from large to tight fit were empirically explored from a machine rest at distances out to 1000 yards which supports Keith’s advice.

In the past, fine armourers may have carefully prepared a barrel internally as well as fitting it to the action. The quality of blanks has improved today although manufactures are at the mercy of the steel suppliers. Fine barrel manufacturers such as Frank’s company are literally at the cutting edge of manufacture together with their knowledge of their product and CNC equipment that can deliver fine tolerances. They offer a custom service to make anything you want and I am sure like Keith the customer feedback will in time refine what they offer because competition on the mound will be the final arbitrator.

[pjifl]

Everything said by others agrees with my own experiences and again I believe the tight barrel was a response to poorer military ammunition. Bisley issued stuff at one time was of lower quality than Australian military and US 308s. So the Brits learned to 'squeeze' the most out of it and this was one reason they were very hard to beat on their own turf where one had to use as issued ammo. But the tight bore has become a fad carried on for too long. And many forget that the bore size (usually measured on the lands) is only one factor. For example, a two groove barrel which shoots well has a different land/groove area ratio and needs a 'bore' size that is different to achieve best results. Some two groove barrels were wartime emergency items. Many moons ago I shot a two groove barrel in TR that was competitive for the times.

These days I seem to get the best results from a standard or very slightly oversize 'bore' but cannot say I have enough samples to conclude anything definitely.

I did have some experience with an extremely tight 6.5 barrel once.
No one could figure out why the owner has massive problems and many many exploding bullets not making the target. This with very conservative loads and measured velocities that were not even up with others. The problem was solved when the bore was measured and found to be very very undersized. That maker shall remain nameless but it was dangerous. Eventually this barrel was turned into dies and other turned items - about all it was good for !

Peter Smith

[williada]

Just to add to what Peter has said, and I have mentioned this before, it is the bore volume that counts i.e. the displacement metal that the groove sizing and depression of the lands make. When working with a local manufacturer in the 1980’s we tested this and I won a regional champion of champions with a barrel having a land height of .0015”.

We were also searching for the minimum land height that would not strip. The other thing we were testing was PO Ackley’s contention you did not need to new lap barrels, the bullets will do the lapping. Yes, they do but over time and other factors with regard to accuracy come into play in modern times and the practice is not valid.

The thing most people forget is the top shooter usually goes into a National Championship with less than 500 rounds through the bore and will discard barrels that do not shape up very early, while running in and with load development. The leed angle and seating depth have not worn sufficiently, nor has the throat developed pit marks through gas erosion to be significant. Better barrels are slugged and lapped to dimension the whole length of the barrel sorting out high and low spots. This reduces fouling. Of course modern manufactures usually only have to take the whiskers off because of better cutting fluids or lubrication fluids, QA of steel and CNC equipment make the job so much easier. These barrels have to jump right out of the box in a target rifle.

While the prime purpose of the land is to turn the bullet there are other factors that affect accuracy. Dennis Tobler, another Australian manufacturer, adopted 5 groove barrels with a view to balance the core of the projectile and handle light skinned jackets which were different to the thicker military pills. This links to some of the aforementioned thinking with regard tight bores by the British but in an opposite context.

The diameter of some of the issued 7.62 was smaller, but they had thicker, harder jackets that could be fired through very hot machine guns. To this end a deeper land was beneficial for accuracy and so it went, with the tight bores. This added to high pressure with modern projectiles as discovered by the British trials consortium on pressure. It is a carryover as Peter suggests and is not ideal.

Furthermore, project Penumbra discovered that the increased pressure did not lead to higher velocity and expected gains were swallowed up in swaging of the projectile down in the throat in tight bores and so efficiencies were lost. It’s not surprising the British went for the 150 rule with regard to throat size.

On the positive side, the swaging process may have balanced the cores with the jacket and lengthened the bullet to increase (but insignificantly) BC because displaced material has to go somewhere and produced a sound gas seal. On the negative side, dangerous pressures produce high heat and reduce throat life. The Brits were notorious for scrubbing out their tight bores with abrasive compound. Not surprising as tighter bores seem to produce more carbon produced from powder and bituminous sealant that is tougher to remove due to heat produced in the throat. So on balance Dennis’s method of balancing the core was safer than a tighter bore and it handled the soft jackets.

For what it is worth, I found the Berger 156 bullet performs better at higher speeds i.e. in excess of 3000 fps. This bullet can reach higher speeds in a larger bore. Similarly so does the BJD and it matches the Berger with BC. The BJD has a long bearing surface in the body but a steeper transition at the junction of the ogive and body which may not perform as well as the Berger at long range due to increased drag when the bullets are on the downward slope of the trajectory and slowing. The Berger should retain its velocity longer. You should also consider the angle of the boat tail and those with lesser slope tend to produce less parasitic and turbulent drag for long range. (The older Sierras liked about 2975 fps had a short bearing surface). What we do know is bigger bores and grooves in thirty cal are faster barrels. Projectiles with more bearing surface are therefore better suited to larger sizes as there is less friction. There is sufficient slap on the bullet base to enlarge the pill there and gas seal in larger bores, but a general rule of thumb is for the groove to be held in a range of .0004” under of bullet diameter for thirty calibres e.g. If the projectile measures .308 then you want it lapped to a max of .3076". As I have indicated earlier land height is not as critical but needs to consistent and certainly without variable twist (except gain twist). This is also taken into account with lapping by the masters.

With regards to internal concentricity of the core/jacket, the Bergers are superior on my Juenke machine compared to the BJD’s, but my wife shoots BJD’s exclusively because they perform in her barrel. I think that barrel’s internal size is a proper mate with the projectile producing better harmonics in the donut shockwave as well as other factors of tune at play. The Berger’s will not perform in her barrel as well. Of course a barrel with a slower twist rate can suit other brands which have poorer cores and jackets so they don’t perform like a wheel out of balance but they are prone to atmospheric density changes when there is insufficient gyroscopic stability.

With regard to special barrels with canted lands (C or R) etc, they tend to be faster barrels due to less friction and drive the projectile more efficiently on one side of the projectile. Barrel length has been used to add a few feet a second to get the added speed we crave. The other thing I see of benefit of the special barrels is they can be shorter, better for balance and stiffness yet get a margin on velocity and perhaps have less wear for longer barrel life.

If was going to use a BJD projectile exclusively, due to its longer bearing surface, it is well suited to a .300”/.308”. But looking at the Juenke performance, I used a .298”/.3075” in the wife’s TR barrel who in the last pennant shoot at 900 yards had 8 centres on with her 9th shot when the target was pulled due to lightening and rain. The event was cancelled as Alan will recall. We will never know what the tenth shot would have been. The BJD is a great bullet.

[Frank Green]

Frank,

Regarding tightness of Bartlein barrels, I have both a 5R and 4 groove in 7mm. If I didn't specify anything, what would be the bore and groove diameters of these?

Thanks
Alan

We do 7mm's standard with a .277" bore. We are tooled for a tight bore 7mm (.275" bore). The only reason we tooled up for the .275" was at a request from Norma to make some special test barrels so we did but it's not a standard offering or should I say we really don't get any requests for it. If memory serves me correctly the old spec. for 7x57 is a .2755" bore but for all practical purposes we just make the .277" for that as well.

If you wanted one in a .275" bore we could make you one. Groove size would be up to you. If it was me wanting to try one I would go .275" x .277".

Later, Frank

[Frank Green]

Williada, Krieger never worked for Boots. They we're shooting buddies and good friends but that is it. It is a common misconception that Krieger worked for Boots. I asked John the question directly when I worked for him.

It was Creighton Audette (wasn't a barrel maker that's where I was wrong) but a gunsmith/match shooter and if I got the info. correctly he asked Boots to make the first tight bore .30cal. barrels back in the 70's. It bugged me so I had to make a phone call to who would know.

Thanks for the nice comments!

Later, Frank

[williada]

Hi Frank, thanks for clearing that up. The beauty of the forum is, someone will know. We are only as good as the information we get. Have a safe and merry Xmas. David.