Home | Ezine | Forums | Links | Contact
NitroExpress.com: 1903 groove diameter

View recent messages : 24 hours | 48 hours | 7 days | 14 days | 30 days | 60 days | More Smilies


*** Enjoy NitroExpress.com? Participate and join in. ***
You are not logged in. [Login] Main Index · Search · Active Topics
New user · Who's Online · FAQ · Calendar

Shooting & Reloading - Mausers, Big Bores and others >> Mannlicher Discussion forum & Archive
Previous topic Previous   View all topics Index   Next topic Next   Threaded Mode Threaded  

Pages: 1
clatrans
.224 member


Reged: 21/07/12
Posts: 7
Loc: Texas
1903 groove diameter
      #213133 - 21/07/12 06:05 AM

I just bought a 1903 carbine in 6.5x54. I slugged the bore and measured groove diameter to the best of my ability at .2694. I therefore plan to use the Carcano Hornady 160 gr. bullet which measures about .2673 (don't have my notes in front of me). Do these numbers fit the experience of the Mannlicher experts? Many thanks.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Kiwi_bloke
.333 member


Reged: 03/09/09
Posts: 256
Loc: New Zealand
Re: 1903 groove diameter [Re: clatrans]
      #213146 - 21/07/12 10:42 AM

Here's my notes:

Bore slugged by Christian Neubauer, gunsmith 03/10/11. He reports:

Mannlicher:
.2564 .2565 .2564 across three different locations on the lands
.2681 .2680 .2678 “ groove
All measurements done in thousandths of an inch with a 0—0001” reduced anvil micrometer. Note, reduced anvil means small anvil, about 1mm.

Ray Ordorica discusses bore sizes in Handloader's Digest 15th edition. In essence, groove diameter of pre-1945 6,5x54 M.Sch. rifles is typically .2666 to .268”. Greener, quoted by Ordorica, says lands .256” and grooves .268”. Bingo ! So 4 thou over bullet size is normal for pre-1945.

Just keep in mind that, the oversize Carcano bullet you refer to is not very tapered, and will jam in the lands (and create real pressure issues), if set to a normal C.O.L. found in reloading manuals for 6,5x54 M-S. To establish the correct C.O.L. for your rifle with this bullet you'll need a special tool that was made by Stoney Point but which is now retailed by Hornady.

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: Kiwi_bloke]
      #213148 - 21/07/12 11:04 AM

Just as Kiwi block indicates - All bullets, regardless of that any manual says is the overall length, must be seated to THAT bullets PROPER and REAL bullet overall length so that it isn't jammed into the lands.

In comparrison to the Hornady 160gr.RN 6.5mm bullet, the Sierra 160gr. had very long full diameter sides and must be seated VERY deeply in comparrison.

To properly handload your own ammo, you MUST know how to find the proper OAL for YOUR rifle.

Another bullet with very long straight sides (short ogive), it the .375" 300gr. Norma RN. it must be seated very deeply inside the case.

If I had a 6.5 that measured .268" groove to groove, I'd have no problem quickly deciding to use the Hornady Carcano bullet.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
MikeRowe
.333 member


Reged: 23/11/11
Posts: 478
Loc: Arkansas, USA
Re: 1903 groove diameter [Re: DarylS]
      #213167 - 21/07/12 01:05 PM

I have had some of the Carcano bullets, and of two lots they were .2675" and .2680". So there's a little variation. However, with a .2685" groove diameter, they do fine. I have slugged Dutch Steyrs as large as .2690".

I think the original 6.5mm Dutch Mannlicher round used a .262" or .263" bullet in those oversized bores.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Paul
.400 member


Reged: 28/08/07
Posts: 1031
Loc: Melbourne, Victoria, Australia
Re: 1903 groove diameter [Re: MikeRowe]
      #213178 - 21/07/12 05:45 PM

Could there be a difference in the design of the MS rifling that upsets .263" bullets into the larger groove diameter to give obturation?

I've long thought there was something strange and deep-looking about the 1903's rifling, beyond the fast pitch. And no wonder - with a bore of .256, a groove of .268 would be about 50% deeper than used in most American rifles/calibres. Maybe something has to give.

BTW, the 30-year-old 6.5x54 RWS factory loads I have here show a diameter of only .2615" just ahead of the cannelure and case mouth. Though other calibres miked at that point sometimes showed half a thou reduction, these 159-grainers are pretty straight for a fair way. My guess is they do not have a .267" body dia.

Edited by Paul (21/07/12 05:53 PM)

Post Extras: Print Post   Remind Me!   Notify Moderator  
malco
.275 member


Reged: 11/02/09
Posts: 76
Loc: montana, usa
Re: 1903 groove diameter [Re: Paul]
      #213205 - 22/07/12 12:40 AM

This topic pops up whenever somebody first encounters an early Mannlicher--check out this older thread, particularly kuduae's post, as it makes a lot of practical sense.

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=152549&an=0&page=1#Post152549

Best,
Malcolm

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: Paul]
      #213213 - 22/07/12 01:41 AM

Quote:

Could there be a difference in the design of the MS rifling that upsets .263" bullets into the larger groove diameter to give obturation?

I've long thought there was something strange and deep-looking about the 1903's rifling, beyond the fast pitch. And no wonder - with a bore of .256, a groove of .268 would be about 50% deeper than used in most American rifles/calibres. Maybe something has to give.



.006" per side in older rifles is common for some Euro rifles. My 9.3x57 has .0065" rifling per side. It has a .370" groove diameter instead of .366", coupled with it's .357" bore, giving .013" difference instead of modern idea of .008" difference.

The reason I mention this, is that it shoots .365" and .366" jacketed bullets sub 1" at 100 meters. Yes, the blowby, whatever is there, is not good for the grooves, but it isn't a varmint rifle that goes through thousands of rounds a year. It will last me until I die and so will that 6.5 last you, shooting .264's IF they are accurate. If the rifle's chamber will allow the larger bullet to be seated in the case neck, then use the .268's. If not, use .264's. There's only .002" per side difference.

Some time ago, I bought picked up some bulk 6.5's that had huge lead round noses and measured .262". I gave them to a friend with a .266" 6.5x55 M38 to try - they shot quite well in it too, - enough to harvest a moose.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
clatrans
.224 member


Reged: 21/07/12
Posts: 7
Loc: Texas
Re: 1903 groove diameter [Re: DarylS]
      #213352 - 24/07/12 05:28 AM

I thought I posted a reply earlier today, but I do not see it. Apologies if I have served up a duplicate.
First, thank you all for your helpful replies. I had read the thread referenced by malco, but wanted to see if anybody had any new ideas.
I went back and slugged my barrel again and again got a .2694/.2695 max groove diameter. I also re-read Ray Ordorica's article in Handloaders Digest 15 and saw that when he slugged his bore he found, "that it is .269-inch at its tightest groove diameter."
I shot three three shot groups at 100 yards with a bolt peep and some old Norma 156 gr. soft point ammunition the previous owner of the rifle was kind enough to sell me. Groups were 2.875", .915" and 4.25" The front sight bead was larger than the 8" black bull, so I had to hold at 6 o'clock. The groups were around 20" high with the Lyman screwed down all the way, so I will have to put in a higher front sight. Function was perfect, but all the fired cases seemed to have a stretch mark about one half inch up from the head. I cleaned the cases in a sonic cleaner and used a piece of coathanger with a 90 degree bend and a sharpened tip to check for a seam inside the case at the stretch mark. It was definitely there so I will not be re-using these cases.
I had already received some new Norma cases, which were about 5 grains each heavier than the old ones, so hopefully they will tolerate the large chamber somewhat better. A problem with the new cases, however is that the primer pocket is either too shallow or tapers toward the bottom. I had to use two primer pocket uniformers, one .206 dia. and one .208 diameter to open them up enough to seat the Fed. 210 Match primers. I have used them for years in other large rifle cases without a hint of trouble. I am going shopping at my reloading supplier with my micrometer in my pocket. Anybody have a suggestion for a large rifle primer that will fit the new Norma cases?
As Kiwi bloke pointed out, the Carcano bullets definitely will have to be seated quite deep in my rifle. I measured at least one third inch push back when a Carcano bullet was loosely seated in a fired Norma case and chambered.
I will next try loads using IMR 4350 and H4831 and the Lapua Mega 155 in the new Norma cases. At OAL of 3.010 or less they feed and chamber perfectly. Looking for Hornady .264 160 gr. round nose to try after that. If nothing else works I guess I could have the throat opened up to use the Carcano bullets.
Not a normal load development process. But fun!

Post Extras: Print Post   Remind Me!   Notify Moderator  
MikeRowe
.333 member


Reged: 23/11/11
Posts: 478
Loc: Arkansas, USA
Re: 1903 groove diameter [Re: clatrans]
      #213413 - 25/07/12 03:14 AM

Check your headspace, sounds like this is your case problem. Early Mannlichers are notorius for extra headspace - don't ask me how I know this.

You can adapt by handloading, or by setting the barrel back and rechambering, or a different bolt head.

Post Extras: Print Post   Remind Me!   Notify Moderator  
clatrans
.224 member


Reged: 21/07/12
Posts: 7
Loc: Texas
Re: 1903 groove diameter [Re: MikeRowe]
      #213420 - 25/07/12 05:22 AM

Mr. Rowe, I agree there is a lot of headspace, but I cannot work on that by handloading unless I have a fired case that is safe to at least neck size. I thought I would fire a few of the new Norma cases and see if they develop an interior ring. If they do I think you are right about a different bolt head, which I had not thought about, or setting the barrel back and rechambering. My first thought, if the headspace problem turns out to be incurable is to rebarrel with a genuine .264 bore and a minimum chamber. My bore is somewhat dark and sewer-pipe looking, but I wanted to try it a little bit first. Can you recommend a gunsmith to do any of this work? I really like the little rifle and am willing to spend some money to get it right, as it has no scope holes bored in it and the wood and metal are in good shape. Thanks for your interest.

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: clatrans]
      #213421 - 25/07/12 06:35 AM

clatrans - I would take a new, unfired case and neck it up to .308 calibre on an '06 or .308 die, or any other die in that calibre, ie: .300 mag. whatever. You only have to open it up with the expander button, not FL size it.

Then, in your 6.5 dies, size the neck down only until the case will chamber with 'feel' on the bolt, ie: what is called a crush fit. You should see a slight false shoulder on that case before it's chambered, that is, if it has excessive headspace. That is what is meant by making them fit via handloading.

Another way of seeing if it has excessive headspace, is firing an empty case with a live primer in it. The pin will shove the case forward to engage the shoulder, then the primer will back out against the bolt. The amount (thousandths of in inch) it remains backed out, will "roughly" show the headspace.

If the case is properly fitted before fireing it will not stretch lengthwise at the web when it is fireformed. It will simply move the whole shoulder foreward to where it should be. That is, if the chamber has excessive headspace.

Overly large diameter expansion at the web is caused by an oversized chamber, not by excessive pressure nor excessive headspace. You must find out first, what the problem is - oversize chamber at the head, or a bonified headspace problem.

Could it possibly be a 6.5x55?.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
clatrans
.224 member


Reged: 21/07/12
Posts: 7
Loc: Texas
Re: 1903 groove diameter [Re: DarylS]
      #213423 - 25/07/12 07:05 AM

Daryl, thanks for the suggestions. I am pretty sure it is not a 6.5x55 because the 54 cartridges fit the magazine perfectly and appear to fit the bolt head perfectly. There is also only a normal, small, amount of resistance felt when the bolt is closed on a cartridge. The fired cases are not visibly the wrong shape, they are just stretched more than they should be. My understanding of what happens when a case is fired in a chamber that is slightly too large at the rear and also too long is that the firing pin whacks the case forward against the shoulder of the chamber, the powder ignites, gas pressure develops and expands the case to hold it forward and the rear of the case then expands/stretches back to the bolt face, thus creating the stretch marks a short distance ahead of the stronger web. If I understand the above process correctly, which I may not, then it appears to me that I have both a too large chamber and too much headspace.

I will try the idea of necking up and then down. I am also going to take the rifle to an old bench rest and Scheutzen gunsmith out at New Braunfels, Howard Dietz, and see if he has any ideas.

I have emailed Norma to ask them what gives with the too small/primer pockets. No answer yet.

Many thanks again for the suggestions.

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: clatrans]
      #213428 - 25/07/12 10:56 AM

Welcome - your idea of what happens when firing is correct.

Necking up then down to create a new shoulder is the best way to handle a bit of excess headspace.

What do the cases measure around the web - about 3/8" up from the rim?

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
Paul
.400 member


Reged: 28/08/07
Posts: 1031
Loc: Melbourne, Victoria, Australia
Re: 1903 groove diameter [Re: DarylS]
      #213432 - 25/07/12 01:48 PM

Quote:

This topic pops up whenever somebody first encounters an early Mannlicher--check out this older thread, particularly kuduae's post, as it makes a lot of practical sense.

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=152549&an=0&page=1#Post152549

Best,
Malcolm



Thanks Malco,
sorry but I haven't thought to look in on this thread for a few days, being otherwise engaged

So, yes, the old guys expected the bullet to 'slug up'. Some of the other posts show better accuracy with larger bullets but I notice the discussion moving on to headspace and excessive web expansion.

Could it be that the bigger bullets, while shooting better and suppressing 'Young gas', might bring higher pressures by having to engrave so much deeper?

On the matter of measuring headspace, is the old method of putting little discs of feeler gauge behind the cartridge until the bolt won't close too obvious to mention?

Daryl, when you mentioned the web starting 3/8" up from the rim, I thought that sounded a long way, but you a right; the 6.5x54 seems to have a longer solid head than any other rimless calibre we have here.

As you know, I reload so intermittently that my grip on the craft is a bit dodgy - but fragments of info from my youth haunt me from time to time. Isn't expansion ahead of the web more an indication of an oversized chamber (except where there's excess headspace and an incipient separation) than the definitive pressure warning? My understanding was that minute expansion (in 10,000s) of the solid head was the real deal - and that even that was expansion after the large movement caused by the initial firing of factory ammo.

Maybe I've been unlucky but the few front-locking rifles we've got all give more expansion of both web and solid head from factory fodder than I'd like - and, yes, I do clean the barrels before shooting. Maybe that's why I don't reload more. A chemical engineer I know who used to work for ICI won't touch reloading with a barge poll for safety reasons, though he has quite a few rifles and used to shoot pistols. He does use his knowledge to make great wine and vodka, however.

Edited by Paul (25/07/12 02:23 PM)

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: Paul]
      #213444 - 25/07/12 11:49 PM

The web, ie: thinning of the case where expansion to seal the chamber starts, is usally around 3/8" up the case in all cases, rimmed, belted and rimless, not just the 6.5x54. This location is easily seen by merely looking at a fired case or measuring it with a mic or calipers. A micrometer will give more accurate measurements than calipers will provide.

I allow NO expansion of the solid head of the case. I have read that up to .001" expansion is OK, however I prefer '0' expansion of that part of the case. Any expansion there, loosens the primer pocket. This 'loosness' is immediately felt when repriming the case and sometimes when poking out the old primer, depending on your method of that.

To properly measure case head expansion, one needs to mark the case prior to firing it - and measure those marks - fire the ctg. then re-measure on those marks. That is the ONLY way of discerning an accurate measurement. When a mere thousandth is the maximum allowed, calipers are NOT the tool to use. You must use a mic that is capable of measuring and being read to the 1/10,000".

I already noted that overpansion of the web area is indicative of an overly large chamber, NOT an indication of pressure.

From a post above.

"Overly large diameter expansion at the web is caused by an oversized chamber, not by excessive pressure nor excessive headspace. You must find out first, what the problem is - oversize chamber at the head, or a bonified headspace problem."

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
Paul
.400 member


Reged: 28/08/07
Posts: 1031
Loc: Melbourne, Victoria, Australia
Re: 1903 groove diameter [Re: DarylS]
      #213539 - 27/07/12 10:16 PM

Thanks Daryl,
the visible pressure line at the web on .30/06 and 270WSM cases here seemed to start about 1/4" from the back of the rim but the 6.5x54's was 3/8".

Your zero-expansion allowance on the solid head in front of the extraction cannelure makes sense to me according to the ancient advice I was given BUT I find it often in fired factory cases (including the belts of magnums) and even 2 thou on the 270WSM, hence my resolve about reloading them. Is it possible because of less-brittle brass that factories are loading to higher pressures than they use to? I noticed tables on the opposition website where some maximum loads nudged 64,000psi. As I noted there, when I was young that would have been a British proof load, though they may have been CUP figures 50 years ago.

Sorry, I must have read too quick and missed your already saying that 'overpansion' of the web area indicated a large chamber.

- Paul

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: Paul]
      #213542 - 27/07/12 11:50 PM

Years ago, copper units of pressure was used and many writers interchanged the words CUP and PSI when talking about pressure.
Today, pezio measuring systems give us actual pounds per square inch - thus, the numbers sound high.

Yes - many rounds today list seemingly high numbers, but when you compare those high PSI numbers with the CUP numbers on the same loads, you see the difference.

Here's a chart, showing SAAMI pezio PSI and CIP pezio PSI numbers, as well as the SAAMI and CIP 'crusher' #'s.

Note how some are listed as maximum pressure of 65,000 under the PSI row, and 54,000 under the CUP row, or 62,000 under the PSI and 50,000 under the CUP.

Note the .22 Hornet at the top of the link's list - 46,000CUP, but 53,000PSI!

Note also how some ctgs. on a particular case, ie: .30/06 case is listed so much lower than another round on the same case, ie; the .338/06 - or 35 Whelen vs, .270 Win, or .280- all on the same case, all with different maximums. There is no obvious reasoning, except perhaps WHEN the various rounds were run through testing and when they achieved the ballistics desired, they stopped.

Note the 8mm Rem Mag - CIP max of CIP 67,000PSI! That's the highest, I think, for a factory load.

Now, if your handloads are giving you higher speeds than factory ammo, I have to wonder what your loads actually are producing for pressure?

http://kwk.us/pressures.html

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
clatrans
.224 member


Reged: 21/07/12
Posts: 7
Loc: Texas
Re: 1903 groove diameter [Re: DarylS]
      #213544 - 28/07/12 12:46 AM

On Wednesday afternoon I had a little time and went out and shot three rounds loaded with 35 grains IMR 4350 and three rounds loaded with 37 grains H4831, both using the 156 gr. Lapua Mega soft nose, Federal 210 Match primers, at an OAL of 3.005, not crimped.
Velocities with the 4350 load were 1969, 1983 and 1934. The H4831 loads were 1881, 1852 and 1866.
I measured the base diameter of the cartridges before firing, new Norma cases, by putting the edge of the micrometer spindle (?) at the top of the extractor groove, so the measuring point was one half of the diameter of a Starret mic spindle up from the extractor groove.
In all cases the primers were pushed back by firing by an easily visible amount which I have not measured yet....more or less 20 to 50 thou.
The before and after head measurements for the 4350 loads were: .4430 and .4497, .4433 and .4497 and .4432 and .4494. I did not measure the 4831 loads but assume they would have been similar.
Opening the bolt and the extraction process was easy and smooth...no resistance. Accuracy at 100 yards was about 7 inches for the 4350 loads (very old powder but still smells OK) and about 3 inches for the H4831 loads.
About .006 case head expansion and way too much headspace makes me wonder if re-barreling is not the best course to follow.
As a 6.5x55 was mentioned above I looked up the head diameter of a 6.5x55 and found it to be .4803 on the 6mmBR website.
I would be very interested in your thoughts on this.

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: clatrans]
      #213561 - 28/07/12 09:32 AM

Quote:

In all cases the primers were pushed back by firing by an easily visible amount which I have not measured yet....more or less 20 to 50 thou.




Your rifle has excessive headspace. Allowable headspace is .006" to .007" only by SAAMI and CIP standards. The primer cannot backout more than that amount in a factory rifle. Perhaps your bolt or action lugs are set back?

The heads should not have expanded with such light pressure loads. I cannot fathom that, except that perhaps your measurements are catching the web expansion, not just the solid portion of the case head.

When measuring head expansion, it's best to mark the rim in two spots (felt pen) and measure that on a new case, before and after firing. That is the case head expansion measurement we're looking for, not on the case with a round anvil, ahead of the groove. If your mic, had blades instead of anvils, it could more accurately measure actual head expansion, in the grooves or just at the top edge of the groove. It's just easier to measure the rim- but mark it. The spot of measuring must be marked so the measurement can be taken at exactly the same spot each time.

Because the primers backed out, shows your actual pressure was less than around 35,000CUP- probalby WAYY under due to the horrid velocities noted. Primers back out only due to headspace, not excess pressure. At about 38,000CUP, the case will lose it's ability to withstand the building pressure exerted against the walls of the chamber and the case will slide back in the chamber to be stopped by the bolt face. This sliding back will re-seat the primer to flush with the case rim. That is normal and what happens to most factory ammo today - expect for the VERY lightly loaded ones, like the 9.3x57Norma which runs aorund 40,000PSI. The same rifle is chambered for the 6.5x55 which generates 55,000PSI & the 9.3x62 which generates 57,000PSI.

Not sure why I thought 6.5x55 brass might work.

What is the ac tual measurement on the expanded case web?

The 6.5 X 54 MS is rated at 53,000PSI or 46,000CUP. The 6.5x54 Mauser is rated lower, at 39,000CUP or 44,000PSI - all CIP (European law) measurements. I surmise that is why factory ammo delivers some 2,200 to 2,330fps or so, with 156gr. bullets.

I would think 2,200fps would be a worthwile goal, IF the rifle didn't have excessive headspace.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
Paul
.400 member


Reged: 28/08/07
Posts: 1031
Loc: Melbourne, Victoria, Australia
Re: 1903 groove diameter [Re: DarylS]
      #213566 - 28/07/12 01:57 PM

Quote:


... Yes - many rounds today list seemingly high numbers, but when you compare those high PSI numbers with the CUP numbers on the same loads, you see the difference. ...

Here's a chart, showing SAAMI pezio PSI and CIP pezio PSI numbers, as well as the SAAMI and CIP 'crusher' #'s.
...
Now, if your handloads are giving you higher speeds than factory ammo, I have to wonder what your loads actually are producing for pressure?

http://kwk.us/pressures.html





Thanks for that info and the table, Daryl,
Most of the new, fat cartridges, which often lack CUP figures, seem to be right up there, pressure-wise. Maybe the increased base area* helps spread the back thrust, though years ago I read the situation was better with a smaller head (eg: rebarrelling a SMLE to .30/30). I noted with some disquiet that the back-locked .375 Win pushes 64,000psi - but maybe the large rim area helps there, too.

That calibre at the top of the list, I think, is the 17 Hornet, which could screw the nozzle up a bit.

I know that some of the older calibres are loaded lower for fear they'll be fired in unsafe rifles but the new-calibre pressures still surprise me. This uneasiness is compounded by my own experience with the Tikka 270WSM using factory ammo. One day after the barrel was run in and well-cleaned, I fired about 15 shots, slowly, to find the bolt hard to open on the last shot or two. Supposedly, the industry knows what it's doing but, in an age of plastic bolt shrouds, it doesn't impress me.

As to my own reloads, I never go anywhere near maximum with the 338 as my bush shooting doesn't need taught trajectories. I've only ever chronographed a couple of shots, which registered where expected.

On the opposition forum's tables, though, I noticed some maximum loads for the .30/06 going way over the old 180gr at 2700fps, into 300H&H territory and high pressures. These loads were two grains more than the max in my book from 40 years ago. Unless you're too poor to buy another rifle, why not just get a magnum of some kind for increased power?


*though I notice WSM rims seem to be rebated a bit.

Post Extras: Print Post   Remind Me!   Notify Moderator  
DarylS
.700 member


Reged: 10/08/05
Posts: 27000
Loc: Beautiful British Columbia, Ca...
Re: 1903 groove diameter [Re: Paul]
      #213599 - 29/07/12 02:08 AM

The larger the rim, the greater the pounds per square inch against the bolt face, with a normal tapered round. The .30/30 has a rim size of .506" while the .303 has a .540" rim. As the Brit has much greater capacity, it will therefore develope much better ballistics.

Many of the newer fat ctgs. are quite straight sided with sharper shoulders and are loaded to what is now considered normal max pressure of 65,000PSI. The older standard tapered magnums like the 8mm Rem mag. and say, 7mm Rem, .300 Winchester mag, with a .532" rim have similar SAAMI maximums as the .338/06 and .270 Winchester which have even more taper and a much smaller .469" rim.

Suffice to say, the magnums have less taper and therefore the chamber area takes up more of the pressure, ie: less bolt thrust due to the case sticking in the chamber better- than the more tapered round. The '06 sized rounds have smaller rims which offsets their greater taper. Ballistics are for the most part, a juggling act of characteristics.

The more taper on the case walls, the greater the bolt thrust.

The larger the rim, the greater the potential for more bolt thrust in pounds per square inch.

How much bolt thrust is increased depends entirely on the case taper and chamber condition, just as it does with any other case.

A very straight sided case with a huge rim, can have literally no bolt thrust at 55,000psi, like a .577 IMP, or if heavily or excessively tapered like a NE case, produce excessive bolt or breech thrust at only 45,000psi.

A very small diameter rim of an improved type case, say .218AckBee can have a maximum of, say, 62,000psi due to it's .408" rim adding immense strength to what is a very small diameter case, but taper that round excessively like a factory .218Bee and it might produce excessive bolt thrust at 50,000psi - higher than the bigger NE case, due to the PSI against the breech being less due to it's smaller diameter.

--------------------
Daryl


"a gun without hammers is like a Spaniel without ears" King George V

Post Extras: Print Post   Remind Me!   Notify Moderator  
Paul
.400 member


Reged: 28/08/07
Posts: 1031
Loc: Melbourne, Victoria, Australia
Re: 1903 groove diameter [Re: DarylS]
      #213629 - 29/07/12 11:24 AM

Thanks Daryl,
so I take it you think there's nothing surprising about my 270WSM being hard to open, considering the straight case walls and the fouling from 12-15 shots?

- Paul

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Previous topic Previous   View all topics Index   Next topic Next   Threaded Mode Threaded  

Extra information
1 registered and 33 anonymous users are browsing this forum.

Moderator:  CptCurl 

Print Topic

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled

Rating:
Topic views: 11394

Rate this topic

Jump to

Contact Us NitroExpress.com

Powered by UBB.threads™ 6.5.5


Home | Ezine | Forums | Links | Contact


Copyright 2003 to 2011 - all rights reserved