What's Overbore; or Underbore For That Matter?

[Bart B]

Scot E,

What crazy numbers does the boys at GAP get for barrel life with that 6.5 SAUM 4S?

What powder, charge weight, actual peak pressure (measured psi) and criteria for end of life for the barrels do they use?

Without the data, I cannot compare their barrel life numbers to what my formula has produced for 26 caliber cartridges. Neither can anyone else.

 

[Scot E]

I'll try to find the thread on snipers hide. They covered most of what you mentioned.

 

[Rich Coyle]

I'm interested too.







Time check3:03

 

[Rich Coyle]

Here are a couple I found on BING.

1. Garage built with Skeeter, surgeon 591, Bartlien Med Palma 8.5 twist,27", New GAP neck turn reamer by PTG,Bushnell DMR G2, AIAX hybrid chassis by P.Jones of TTGC, Timney Calvin elite,Cerakoted by yours truly
2. H1000 60.4g RCBS Chargemasterredface
3. Federal215m
4. Once fired CCCC loaded Remington brass,.291 neck bushing, Re-turned to 15thou. and chamfered, will trim when all cases are re-fired.
5. Berger 140g VLD target, Lot 4636





1. Built by Robert Gradous of Gradous Rifles / Surgeon 591R action / Jewell trigger / 25 7/8" Krieger MTU contour 1:8.5 twist 5R / Cerakoted Flat Dark Earth / Badger Ordnace FTE muzzle brake / KMW Sentinel stock GAP camo / Nightforce .885" UL rings / Nightforce NXS 5.5-22x50 MOAR / Atlas Bipod / PTG GAP 6.5 SAUM 4S .2962 NK .081 FB Reamer

2. 62.5 gr. of H-1000 (Mixed lots)

3. Tula Large Rifle Magnum primer

4. Remington 7mm SAUM brass self processed with Redding FL 7 SAUM dies .295 & .291 bushings. Neck turned with a K&M neck turing kit to .015" & trimmed to 2.019". Camfered in side / out & annealed.

5. Berger 140 gr. Hybrid Lot # 6047

6. Seated 2.206" @ Ogive (.010" out of lands)

7. 3212 fps. per Magneto Speed V3 chronograph (average of 5 shots)

 

[Bart B]

For me to use my barrel life formula, the only useful data given is the 62.5 grain powder charge. Bore capacity using my formula is 33 grains; barrel life a little over 800 rounds. That assumes a psi pressure in the low 60K range and a 50% reduction in accuracy after starting out at 1/4 MOA at short range. About the same as the 6.5x.284.

If GAP uses different criteria, then, of course, their numbers will be different.

I'd like to see Quickload's psi number for that load.

 

[Mikecr]

GAPs extreme barrel life claims are merchandised similar to those of the 6mm Competition Match -vs- 6XC. Both declaring H1000, which is the coolest of slow powders, and in a large enough case to get away with H1000 lower pressure loads, as key to the 'genius' behind their cartridge design.
This helps.

GAP rifles are also accurate enough that they can demonstrate their guns shooting well enough with many many shots down the barrels. I can't even imagine one so gone that it shoots worse than 1/2moa with a good load.
This helps a lot.

That's how they arrive at barrel life numbers that are less than credible otherwise.
So we should recognize the good and bad in it as a special circumstance.

 

[Scot E]

Scot E,

What crazy numbers does the boys at GAP get for barrel life with that 6.5 SAUM 4S?

What powder, charge weight, actual peak pressure (measured psi) and criteria for end of life for the barrels do they use?

Without the data, I cannot compare their barrel life numbers to what my formula has produced for 26 caliber cartridges. Neither can anyone else.

Looking through over 100 pages of posts isn't exactly easy but here are some basics I found.

The most popular load for the 140 grain Berger hybrid is 61.5 grains of H1000 going about 3100 fps. I read of at least 4 of the initial xtreme hunter barrels lasting over 3000 rounds. Two were over 3500 rounds.

I never could find where they ended up numbers wise before re-barreling. I know for at least 2 or 3 of these they were still shooting around .3 MOA even after passing the 3k mark. I haven't heard of any that shot over .5 MOA.

I don't know about pressures. I know GAP had a pressure barrel done and tested the loads. I read it a couple times but can't find it now. Under 60k was their goal and GAP thought they beat that goal by a few 1000 psi. I do know that copper creek loads their 6.5 4S ammo to 3100 FPS with H1000 and they tested their loads at 58k.

I'll post again when I find the pressure tested numbers from Hornady and GAP. I am sure I have read them somewhere in the 1000's of posts!

 

[Scot E]

GAPs extreme barrel life claims are merchandised similar to those of the 6mm Competition Match -vs- 6XC. Both declaring H1000, which is the coolest of slow powders, and in a large enough case to get away with H1000 lower pressure loads, as key to the 'genius' behind their cartridge design.
This helps.

GAP rifles are also accurate enough that they can demonstrate their guns shooting well enough with many many shots down the barrels. I can't even imagine one so gone that it shoots worse than 1/2moa with a good load.
This helps a lot.

That's how they arrive at barrel life numbers that are less than credible otherwise.
So we should recognize the good and bad in it as a special circumstance.

I agree with this for the most part. Special circumstance however seems better explained as being smart by adapting the newest technology of powders and using the newest and best designs available in making accurate guns and barrels to change existing performance and concepts on performance.

These technologies are changing the way we do everything in long range. I just had a great conversation with a 30'06 enthusiast that is able to get great numbers from 215 grain bergers and these new slow, cool burning powders. Excellent performance, excellent barrel life, excellent case life.

I talked to another gent that added a special throat and increased freebore on his '06 and is biting at the heels of typical 300 win mag velocities with these new powders. Just a few years ago this was simply impossible.

I just say all of that to make the point that these could all be considered special circumstances. But this is the direction everything is moving. Taking the best of products and technology and using it to change our game, especially some of the old standards of thinking that many of us grew up under.